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1.
  • Drobyshev, Igor, et al. (författare)
  • Masting behaviour and dendrochronology of European beech (Fagus sylvatica L.) in southern Sweden
  • 2010
  • Ingår i: Forest Ecology and Management. - : Elsevier BV. - 1872-7042 .- 0378-1127. ; 259:11, s. 2160-2171
  • Tidskriftsartikel (refereegranskat)abstract
    • To identify weather controls of beech diameter growth and masting in southern Sweden, we analyze records of monthly weather, regional masting record, and tree-ring chronologies from five beech-dominated stands. The results indicate a strong weather control of temporal pattern of masting events in southern Sweden over the second half of the 20th century. Negative summer temperature anomaly 2 years prior to a mast year, coupled with positive temperature anomaly in the year immediately preceding the same mast year, is a characteristic weather pattern associated with known mast years. Strong dependence of beech masting behavior on temperature explains the high degree of regional synchronization of masting events. Growth of beech in southern Sweden is strongly and negatively correlated with previous year's summer temperature and positively - with previous year's October temperature. The present study does not provide a conclusive answer in identifying a full set of direct and indirect effects of climatic variables controlling tree-ring growth, since the negative effect of previous year's summer temperature may be a result of a temperature-controlled increase in the beech nut production in the current year. Consistent and significant negative departures of ring-width index during mast years support the hypothesis about a trade-off between investment of bioassimilates into production of beech nuts and tree-ring growth. Alternative explanation of growth anomalies in mast years, relating such anomaly to a negative impact of previous year's growing season, was not supported by the data. We found a limited effect of masting on diameter growth in the following years, indicating that decline in the overall wood production, associated with heavy masting, is short term and typically occurs in the year of actual masting. (C) 2010 Elsevier B.V. All rights reserved.
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2.
  • Drobyshev, Igor (författare)
  • 352 years long fire history of a Siberian boreal forest and its primary driving factor
  • 2021
  • Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 207
  • Tidskriftsartikel (refereegranskat)abstract
    • Fire is a major disturbance agent in the boreal forest, affecting the structure, dynamics and biogeochemical cycles in this biome. In the Asian section of boreal forest, the records of long-term fire history are few that limits our understanding of factors forcing regional fire dynamics. We presented an annually-resolved 352 year (1666-2017) fire chronology based on fire scars of Scots pine (Pines sylvestris L.) and Siberian larch (Larix sibirica Ledeb) from the Transbaikal area in the southeastern Siberia. Fire activity showed an increasing trend from 1720 to 1929 (R-2 = 0.80, P < 0.0001), and a significant decreasing trend from 1920 to 2010 (R-2 = 0.62, P < 0.001). We assessed the potential relationships between drought (as represented by the Palmer Drought Severity Index, PDSI, and the Monthly Drought Code, MDC), ocean-atmosphere circulation and forest fire by Superposed epoch analyses, cross-wavelet analysis and Granger causality analysis. Increased fire activity was associated with stronger drought from previous winter to current summer of fire event years and positive Arctic Oscillation (AO) before and during major fire season (February and April to May), as revealed by superposed epoch analysis. Granger causality pointed to the significant role of drought in driving forest fires. Our findings provide insights into the climate drivers of forest fire activity and its prediction in the Transbaikal region.
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3.
  • Drobyshev, Igor, et al. (författare)
  • A 700-year record of large fire years in northern Scandinavia shows large variability and increased frequency during the 1800s
  • 2015
  • Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 30:3, s. 211-221
  • Tidskriftsartikel (refereegranskat)abstract
    • Years with climatically mediated increases in boreal forest fire activity, referred to as large fire years (LFYs), contribute to a disproportionally large portion of the burned area over centuries, and are important drivers of ecosystem processes by affecting forest structure, biodiversity, and carbon balance at regional and continental scales. We analysed changes in LFY return intervals in northern Sweden (the area above 60°N) over 1273-1960 using a network of 29 sites with dendrochronologically reconstructed fires, complemented by documentary records of fires available from forestry statistics. We observed large variability in return intervals of LFYs, an increase in LFY frequency during the 1800s, and consistent associations between LFY occurrence and 500-hPa pressure anomalies over the European sub-continent over 1800xps2#1960. An increase in LFY frequency during the 1800s might be climatically driven, and would thus long precede the period of likely human-induced climatic changes of the 1900s. Long-term variability in climatically driven LFYs may present a challenge in partitioning the effects of human-related and human-independent components of climatic forcing upon forest fire activity. © 2015 John Wiley & Sons, Ltd.
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4.
  • Drobyshev, Igor, et al. (författare)
  • A mixture of human and climatic effects shapes the 250-year long fire history of a semi-natural pine dominated landscape of Northern Latvia
  • 2019
  • Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 441, s. 192-201
  • Tidskriftsartikel (refereegranskat)abstract
    • Fire has been shown to shape successional pathways and dynamics of forest vegetation. However, its role in European hemiboreal forests remains poorly understood. Here we provide the first annually resolved reconstruction of fire history from the Eastern Baltic Sea region, developed in the pine-dominated landscape of Slitere National Park (SNP), northwestern Latvia, over the last 250 years. Our results suggest that forest fires have been a common disturbance factor in the studied landscape. In total, we dated 62 single fire years, with the mean-point scale fire return interval of 46 years and the length of the fire cycle ranging from 45 to 80 years. We identified periods of high (1750-1950) and low (1960-2000) fire activity, with the corresponding lengths of fire cycles being 45-68 and 58-80 years, respectively. Although both long-term (century and decade-long) and annual dynamics of fire activity in SNP was closely linked to socio-political changes in Latvia, fire activity in SNP was also affected by climate, as indicated by the close positive association of years with increased area burned and positive SST anomalies in the Baltic and North Seas. Future management of SNP should make fire an important element of natural forest dynamics and consider using prescribed fires of various spatial extent and severity.
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5.
  • Drobyshev, Igor (författare)
  • An empirical prediction approach for seasonal fire risk in the boreal forests
  • 2020
  • Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 40, s. 2732-2744
  • Tidskriftsartikel (refereegranskat)abstract
    • The ability to predict forest fire risk at monthly, seasonal and above-annual time scales is critical to mitigate its impacts, including fire-driven dynamics of ecosystem and socio-economic services. Fire is the primary driving factor of the ecosystem dynamics in the boreal forest, directly affecting global carbon balance and atmospheric concentrations of the trace gases including carbon dioxide. Resilience of the ocean-atmosphere system provides potential for advanced detection of upcoming fire season intensity. Here, we report on the development of a probabilistic empirical prediction system for forest fire risk on monthly-to-seasonal timescales across the circumboreal region. Quasi-operational ensemble forecasts are generated for monthly drought code (MDC), an established indicator for seasonal fire activity in the Boreal biome based on monthly maximum temperature and precipitation values. Historical MDC forecasts are validated against observations, with good skill found across northern Eurasia and North America. In addition, we show that the MDC forecasts are an excellent indicator for satellite-derived observations of burned area in large parts of the Boreal region. Our discussion considers the relative value of forecast information to a range of stakeholders when disseminated before and during the fire season. We also discuss the wider role of empirical predictions in benchmarking dynamical forecast systems and in conveying forecast information in a simple and digestible manner.
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6.
  • Drobyshev, Igor, et al. (författare)
  • Atlantic SSTs control regime shifts in forest fire activity of Northern Scandinavia
  • 2016
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the drivers of the boreal forest fire activity is challenging due to the complexity of the interactions driving fire regimes. We analyzed drivers of forest fire activity in Northern Scandinavia (above 60 N) by combining modern and proxy data over the Holocene. The results suggest that the cold climate in northern Scandinavia was generally characterized by dry conditions favourable to periods of regionally increased fire activity. We propose that the cold conditions over the northern North Atlantic, associated with low SSTs, expansion of sea ice cover, and the southward shift in the position of the subpolar gyre, redirect southward the precipitation over Scandinavia, associated with the westerlies. This dynamics strengthens high pressure systems over Scandinavia and results in increased regional fire activity. Our study reveals a previously undocumented teleconnection between large scale climate and ocean dynamics over the North Atlantic and regional boreal forest fire activity in Northern Scandinavia. Consistency of the pattern observed annually through millennium scales suggests that a strong link between Atlantic SST and fire activity on multiple temporal scales over the entire Holocene is relevant for understanding future fire activity across the European boreal zone.
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7.
  • Drobyshev, Igor (författare)
  • Attribution of the role of climate change in the forest fires in Sweden 2018
  • 2021
  • Ingår i: Natural Hazards and Earth System Sciences. - : Copernicus GmbH. - 1561-8633 .- 1684-9981. ; 21, s. 2169-2179
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, we analyse the role of climate change in the forest fires that raged through large parts of Sweden in the summer of 2018 from a meteorological perspective. This is done by studying the Canadian Fire Weather Index (FWI) based on sub-daily data, both in reanalysis data sets (ERA-Interim, ERA5, the Japanese 55 year Reanalysis, JRA-55, and Modern-Era Retrospective analysis for Research and Applications version 2, MERRA-2) and three large-ensemble climate models (EC-Earth, weather@home, W@H, and Community Earth System Model, CESM) simulations. The FWI, based on reanalysis, correlates well with the observed burnt area in summer (r = 0.6 to 0.8). We find that the maximum FWI in July 2018 had return times of similar to 24 years (90% CI, confidence interval, > 10 years) for southern and northern Sweden. Furthermore, we find a negative trend of the FWI for southern Sweden over the 1979 to 2017 time period in the reanalyses, yielding a non-significant reduced probability of such an event. However, the short observational record, large uncertainty between the reanalysis products and large natural variability of the FWI give a large confidence interval around this number that easily includes no change, so we cannot draw robust conclusions from reanalysis data.The three large-ensembles with climate models point to a roughly 1.1 (0.9 to 1.4) times increased probability (non-significant) for such events in the current climate relative to preindustrial climate. For a future climate (2 degrees C warming), we find a roughly 2 (1.5 to 3) times increased probability for such events relative to the preindustrial climate. The increased fire weather risk is mainly attributed to the increase in temperature. The other main factor, i.e. precipitation during summer months, is projected to increase for northern Sweden and decrease for southern Sweden. We, however, do not find a clear change in prolonged dry periods in summer months that could explain the increased fire weather risk in the climate models.In summary, we find a (non-significant) reduced probability of such events based on reanalyses, a small (nonsignificant) increased probability due to global warming up to now and a more robust (significant) increase in the risk for such events in the future based on the climate models.
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8.
  • Drobyshev, Igor (författare)
  • Bird communities of reference and altered mixed-pine forests: Implications for restoring fire-dependent forest ecosystems
  • 2014
  • Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 318, s. 183–193-
  • Tidskriftsartikel (refereegranskat)abstract
    • Changes have occurred to disturbance regimes that drive composition, structure, and function in many forest ecosystems. In the northern Lake States, USA land use change has impacted fire-dependent mixed-pine forests of red pine (Pinus resinosa Ait.) and eastern white pine (P. strobus L.). Although restoration is now being conducted on many federal and state forestlands, we currently lack baseline data on wildlife communities. To address the need for such information we sampled 25 reference and 29 altered mixed-pine sites in a wetland-upland landscape mosaic representative of eastern Upper Michigan. We put forward three questions: (1) do bird communities differ between reference sites and altered sites?: (2) what forest compositional and structural attributes are associated with differences in bird communities and how might they be related to fire history?; and (3) how does heterogeneity of natural land cover affect bird communities? Analyses revealed that richness of forest bird species was greater in reference sites (T = -1.93, P = 0.06), even though reference sites exist within 20-ha patches with less forest and more wetlands compared to altered sites. Bird assemblages also differed between reference and altered sites (Multiple Permutation Procedure, T = -5.26, A = 0.02, P <= 0.001). Eight indicator species were associated with reference sites, and four species were found in altered sites. Although correlations among environmental variables were generally low, they suggested the important role fire played in this ecosystem. Our findings support the hypothesis that mixed-pine ecosystem restoration can be an important management tool in restoring bird communities. Published by Elsevier B.V.
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9.
  • Drobyshev, Igor (författare)
  • Chemical changes in thermally modified, acetylated and melamine formaldehyde resin impregnated beech wood
  • 2024
  • Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 78, s. 459-469
  • Tidskriftsartikel (refereegranskat)abstract
    • Wood modification (by thermal or chemical treatment) helps to improve the dimensional stability of wood and enhance its resistance to biological agents. Beech wood is non-durable and exposure in exterior settings dramatically shortens its service life. To determine the full potential of beech wood for advanced applications, a better understanding of the chemical changes induced by modification is needed. Two chemical treatments (acetylation and melamine formaldehyde resin impregnation) and three thermal treatments (heating to 180, 200 and 220 degrees C) were performed on beech wood. The modification effect was examined based on (i) molecular changes in functional groups by Fourier-transform infrared spectroscopy (ATR-FTIR); (ii) extractive content; and (iii) pH changes. Moreover, the explanation of these changes was supported by the FTIR-analysis of isolated main wood components (cellulose, holocellulose and lignin) from the modified wood. The high temperatures applied to samples during thermal modification promoted the deacetylation and degradation of hemicelluloses. Hemicelluloses were targeted also by acetic anhydride and melamine resin, the bonding of which was confirmed by FTIR analysis. The formation of fewer methylene bridges affected the properties of the melamine network. This observation suggests the need to determine optimal curing conditions in future research, to reduce melamine-wood hydrophilicity.
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10.
  • Drobyshev, Igor (författare)
  • Climate forcing of regional fire years in the upper Great Lakes Region, USA
  • 2023
  • Ingår i: International Journal of Wildland Fire. - 1049-8001 .- 1448-5516. ; 32, s. 796-813
  • Tidskriftsartikel (refereegranskat)abstract
    • Background. Drivers of fire regimes vary among spatial scales, and fire history reconstructions are often limited to stand scales, making it difficult to partition effects of regional climate forcing versus individual site histories. Aims. To evaluate regional-scale historical fire regimes over 350 years, we analysed an extensive fire-scar network, spanning 240 km across the upper Great Lakes Region in North America. Methods. We estimated fire frequency, identified regionally widespread fire years (based on the fraction of fire-scarred tree samples, fire extent index (FEI), and synchronicity of fire years), and evaluated fire seasonality and climate-fire relationships. Key results. Historically, fire frequency and seasonality were variable within and among Great Lakes' ecoregions. Climate forcing at regional scales resulted in synchronised fires, primarily during the late growing season, which were ubiquitous across the upper Great Lakes Region. Regionally significant fire years included 1689, 1752, 1754, 1791, and 1891. Conclusions. We found significant climate forcing of region-wide fire regimes in the upper Great Lakes Region. Implications. Historically, reoccurring fires in the upper Great Lakes Region were instrumental for shaping and maintaining forest resilience. The climate conditions that helped promote widespread fire years historically may be consistent with anticipated climate-fire interactions due to climate change.
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11.
  • Drobyshev, Igor (författare)
  • Climatically controlled reproduction drives interannual growth variability in a temperate tree species
  • 2018
  • Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 21, s. 1833-1844
  • Tidskriftsartikel (refereegranskat)abstract
    • Climatically controlled allocation to reproduction is a key mechanism by which climate influences tree growth and may explain lagged correlations between climate and growth. We used continent-wide datasets of tree-ring chronologies and annual reproductive effort in Fagus sylvatica from 1901 to 2015 to characterise relationships between climate, reproduction and growth. Results highlight that variable allocation to reproduction is a key factor for growth in this species, and that high reproductive effort ('mast years') is associated with stem growth reduction. Additionally, high reproductive effort is associated with previous summer temperature, creating lagged climate effects on growth. Consequently, understanding growth variability in forest ecosystems requires the incorporation of reproduction, which can be highly variable. Our results suggest that future response of growth dynamics to climate change in this species will be strongly influenced by the response of reproduction.
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12.
  • Drobyshev, Igor (författare)
  • Contrasting Growth Response of Jack Pine and Trembling Aspen to Climate Warming in Quebec Mixedwoods Forests of Eastern Canada Since the Early Twentieth Century
  • 2021
  • Ingår i: Journal of Geophysical Research: Biogeosciences. - 2169-8953 .- 2169-8961. ; 126
  • Tidskriftsartikel (refereegranskat)abstract
    • Forest monitoring studies show contrasting trends in tree growth rates since the mid-twentieth century. However, due to their focus on annual and decadal dynamics, they provide limited insight into the effects of long-term climatic variability on tree growth. Here, we relied on a large tree-ring dataset (similar to 2,700 trees) of two common North American shade-intolerant tree species, trembling aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lambert), to assess their lifespan-long growth dynamics in the mixedwood forests of Quebec. We also determined how the environmental conditions of the stands influenced tree growth. We observed a significant increase in the radial growth rate of trembling aspen during the study period, while the jack pine decline was not significant. Over the whole study region, the trees growing in sites with lower competition, and those at the lower sections of the terrain slope experienced more of the positive effects of temperature on growth rates. Our study suggests that the tree growth response to climate warming may be species-specific and will vary across the boreal mixedwoods.
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13.
  • Drobyshev, Igor (författare)
  • Contrasting Root System Structure and Belowground Interactions between Black Spruce (Picea mariana (Mill.) BSP) and Trembling Aspen (Populus tremuloides Michx) in Boreal Mixedwoods of Eastern Canada
  • 2020
  • Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 11
  • Tidskriftsartikel (refereegranskat)abstract
    • This study explored the underground interactions between black spruce and trembling aspen in pure and mixed stands to understand how their soil resource use help these species coexist in the boreal mixedwoods of Western Quebec. We analyzed species-specific fine root foraging strategies (root biomass and root tissue density) along three soil layers (organic, top 0-15 cm, and bottom 15-30 cm mineral soil), using 180 soil cores. We collected cores in three sites, each containing three 20 x 50 m(2) plots of pure spruce, pure aspen, and mixed spruce and aspen stands. Spruce had a shallow rooting, whereas aspen had a deep rooting in both types of stands. Compared to pure spruce stands, spruce had a lower fine root biomass (FRB) and a higher root tissue density (RTD) in the organic layer of mixed stands. Both patterns were indicative of spruce's more intensive resource use strategy and competitive advantage over aspen in that layer. Aspen FRB in the organic soil did not differ significantly between pure and mixed stands, but increased in the mineral soil of mixed stands. Since we did not observe a significant difference in the nutrient content of the mineral soil layer between pure aspen and mixed stands, we concluded that aspen may experience competitive exclusion in the organic layer by spruce. Aspen exhibited an extensive nutrient uptake strategy in the organic layer of mixed stands: higher FRB and lower RTD than spruce. In mixed stands, the differences in aspen rooting patterns between the organic and mineral layers suggested the use of contrasting nutrient uptake strategies along the soil profile. We speculate that the stronger spatial separation of the roots of spruce and aspen in mixed stands likely contribute to a higher partitioning of their nutrient uptake along the soil profile. These results indicate the competitive exclusion of aspen by spruce in boreal mixedwoods, which likely occurs in the soil organic layer.
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14.
  • Drobyshev, Igor (författare)
  • Contrasting structure of root mycorrhizal communities of black spruce and trembling aspen in different layers of the soil profile in the boreal mixedwoods of eastern Canada
  • 2022
  • Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 479, s. 85-105
  • Tidskriftsartikel (refereegranskat)abstract
    • Purpose Mycorrhizal fungi are critical for the growth and survival of trees although the knowledge on the extent of their association with different tree species in the boreal forest remains limited.Methods We examined the vertical distribution and composition of the root mycorrhizal communities of black spruce (Picea mariana (Mill.) B.S.P) and trembling aspen (Populus tremuloides Michx) along three soil layers (organic, minerals top 0-15 cm and bottom 15-30 cm) in pure and mixed stands, using next generation sequencing.Results We found that spruce and aspen differ in the composition of their mycorrhizal communities in respective pure stands. The difference was present also in mixed stands, despite a shift in the composition of species-specific mycorrhizal communities between pure and mixed stands. In mixed stands, the relative abundance of spruce-specialist mycorrhizae in the organic layer was higher than that of aspenspecialists. The opposite pattern was observed in the mineral soil. The mixed stands exhibited lower richness and abundance of generalist mycorrhizae in the organic and in the mineral soil layers.Conclusion The results suggest that it is the soil chemistry that structure species-specific mycorrhizal communities between pure stands and along different soil depth within stands. However, in mixed stands, it is the identity of tree species that determines the structure of mycorrhizae communities within soil layers. We speculate that the differences in the richness and abundance of individual mycorrhizal communities of spruce and aspen along the soil profile would likely contribute to stronger partitioning of tree nutrient uptake between these two species in mixed stands.
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15.
  • Drobyshev, Igor, et al. (författare)
  • Contrasting tree-ring data with fire record in a pine-dominated landscape in the Komi republic (Eastern European Russia): Recovering a common climate signal
  • 2004
  • Ingår i: Silva Fennica. - 2242-4075. ; 38:1, s. 43-53
  • Tidskriftsartikel (refereegranskat)abstract
    • For the period 1420-1960 we contrasted fire events reconstructed at 14 sites distributed over a 50 km x 50 km area in the central part of the Komi Republic (European Russia) with a set of tree-ring width chronologies of Scots pine (Pinus sylvestris L.), developed for the same area. Our aim was to infer common climatic information contained in treering variables and independently dated fire events with the help of a superposed epoch analysis. The strongest weather-growth link was shown for the latewood width, which was positively correlated with the temperature in April-May and July-August of the current growth season and with previous year precipitation in July-August. Earlywood width was positively affected by previous year precipitation in May and November. The relationship between yearly ring variables and multiple-site fire events was dependent on the seasonal timing of fire events as recorded in the scars. In years with early-season fires (which made up 37% of all fires dated with seasonal resolution) total ring width was significantly narrower. In years with late-season fires (63%) total ring width, earlywood, and latewood width were significantly wider. Years with late-season fires tended to be associated with local highs of the latewood width chronologies over 1400-1960, which implied a link between decadal-scale climate variation and fire regime of the area.
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16.
  • Drobyshev, Igor (författare)
  • Converging and diverging burn rates in North American boreal forests from the Little Ice Age to the present
  • 2022
  • Ingår i: International Journal of Wildland Fire. - 1049-8001 .- 1448-5516. ; 31, s. 1184-1193
  • Tidskriftsartikel (refereegranskat)abstract
    • Warning. This article contains terms, descriptions, and opinions used for historical context that may be culturally sensitive for some readers. Background. Understanding drivers of boreal forest dynamics supports adaptation strategies in the context of climate change. Aims. We aimed to understand how burn rates varied since the early 1700s in North American boreal forests. Methods. We used 16 fire-history study sites distributed across such forests and investigated variation in burn rates for the historical period spanning 1700-1990. These were benchmarked against recent burn rates estimated for the modern period spanning 1980-2020 using various data sources. Key results. Burn rates during the historical period for most sites showed a declining trend, particularly during the early to mid 1900s. Compared to the historical period, the modern period showed less variable and lower burn rates across sites. Mean burn rates during the modern period presented divergent trends among eastern versus northwestern sites, with increasing trends in mean burn rates in most northwestern North American sites. Conclusions. The synchronicity of trends suggests that large spatial patterns of atmospheric conditions drove burn rates in addition to regional changes in land use like fire exclusion and suppression. Implications. Low burn rates in eastern Canadian boreal forests may continue unless climate change overrides the capacity to suppress fire.
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17.
  • Drobyshev, Igor (författare)
  • Decline in the strength of genetic controls on aspen environmental responses from seasonal to century-long phenomena
  • 2019
  • Ingår i: Ecosphere. - : Wiley. - 2150-8925. ; 10
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding intra-specific variation in climate sensitivity could improve the prediction of tree responses to climate change. We attempted to identify the degree of genetic control of tree phenology and growth of trembling aspen (Populus tremuloides Mchx.) in a natural stand of this species in northwestern Quebec. We mapped and genotyped 556 aspen trees growing within the plot, using seven nuclear microsatellite loci for clone identification. We selected 13 clones (n of trees per clone >5, in total 350 trees) and evaluated the explanatory power of clone identity in (a) variability of spring leaf phenology and (b) short- and long-term growth responses. The clone's identity explained 43% of the variability in spring leaf phenology, between 18% and 20% of variability in response to monthly climate variables significantly affecting growth, between 8% and 26% of growth response to insect outbreaks, and 12% in the long-term growth rates. Strong clonal control of aspen phenology and moderate control of growth responses to monthly weather do not result in an equally large impact on long-term growth rates. The result suggests an important role of environmental extremes and within community interactions as factors averaging aspen growth performance at the stand level.
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18.
  • Drobyshev, Igor (författare)
  • Detecting changes in climate forcing on the fire regime of a North American mixed-pine forest: A case study of Seney National Wildlife Refuge, Upper Michigan
  • 2012
  • Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865. ; 30, s. 137-145
  • Tidskriftsartikel (refereegranskat)abstract
    • The study of forests dominated by red pine (Pinus resinosa Alt.), one of the few fire-resistant tree species of eastern North America, provides an opportunity to reconstruct long-term fire histories and examine the temporal dynamics of climate forcing upon forest fire regimes. We used a 300-year long spatially explicit dendrochronological reconstruction of the fire regime for Seney National Wildlife Refuge (SNWR, 38,531 ha), eastern Upper Michigan to: (1) identify fire size thresholds with strong vs. weak climate controls, (2) evaluate effect of landform type (outwash channel vs. sand ridges) in modifying climate-fire associations, and (3) check for the presence of temporal changes in the climate control of large fire events over the time period 1700-1983. We used a summer drought sensitive red pine chronology (ITRDB code can037) as a proxy of past fire-related climate variability. Results indicated that fires >60 ha in sand-ridge-dominated portions of SNWR and >100 ha in outwash channels were likely climatically driven events. Climate-fire associations varied over time with significant climate-fire linkages observed for the periods 1700-1800 (pre-EuroAmerican), 1800-1900 (EuroAmerican settlement) and 1900-1983 (modern era). Although an increase in fire activity at the turn of 20th century is commonly associated with human sources of ignitions, our results suggest that such an increase was also likely a climatically driven episode. (C) 2012 Istituto Italiano di Dendrocronologia. Published by Elsevier GmbH. All rights reserved.
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19.
  • Drobyshev, Igor, et al. (författare)
  • Did forest fires maintain mixed oak forests in southern Scandinavia? A dendrochronological speculation
  • 2021
  • Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 482
  • Tidskriftsartikel (refereegranskat)abstract
    • In northern Europe, a long history of human exploitation effectively eliminated legacies of natural disturbances in mixed oak forests and we currently lack understanding of the role of natural disturbance factors in affecting oak regeneration into the forest canopies. We compiled dendrochronological, observational and paleochronological data from Southern Sweden to discuss the role of forest fires in oak (Quercus spp.) dynamics. We analyzed oak age structure and its growth dynamics in six southern Swedish forests, which experienced fires between 42 and 158 years prior to our sampling. Extending our analysis over longer time frames, we studied the relationship between sediment charcoal and oak pollen in an area of south-eastern Sweden, where oak has been a common canopy species. In three of the study sites, forest fires resulted in increased oak regeneration. Although fires were generally not associated with a wave of growth releases in surviving trees, the mean basal area growth rate of oaks increased by a range of 108% to 176%, following the fires. The overall pattern indicated that historical fires in oak-dominated forests were of low severity, did not kill canopy oaks, and yet provided a window of regeneration opportunities for that species. Post-fire sprouting of oak and an increase in oak seedling densities following modern prescribed fires are consistent with this explanation. Consistent with this conclusion were significant positive correlations between charcoal concentration and the oak pollen percentage in a site in southeastern Sweden. We discuss the co-occurrence of oak and pine in the historical southern Swedish landscape, as a possible analogy to eastern North American oak-pine forests. Modern conservation policies aimed at the preservation of oak in the southern Swedish landscape should consider the use of low severity fires to maintain natural oak regeneration.
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20.
  • Drobyshev, Igor (författare)
  • Did long-term fire control the coniferous boreal forest composition of the northern Ural region (Komi Republic, Russia)?
  • 2020
  • Ingår i: Journal of Biogeography. - : Wiley. - 0305-0270 .- 1365-2699. ; 47, s. 2426-2441
  • Tidskriftsartikel (refereegranskat)abstract
    • Aim Documenting past vegetation dynamics and fire-vegetation relationships at a regional scale is necessary to understand the mechanisms that control the functioning of the boreal forest, which is particularly sensitive to climate change. The objective of this study is to document these interactions in the Komi Republic during the Holocene. Location Yaksha, Vychegda river basin, Republic of Komi, Russia. Taxon Plantae, gymnosperms, angiosperms. Methods Two palaeoecological approaches are combined, based (1) on pollen (this study) and charcoal analysis (recomputed from our previous analysis) applied to cores from two peatlands and (2) on a REVEALS model (a part of the Landscape Reconstruction Algorithm "LRA") applied to six regional pollen cores in order to obtain a regional estimate of vegetation cover during the Holocene. Results The pollen diagram produced locally from Yaksha was compared with the regional vegetation cover determined by REVEALS. Taxa such asAbiessp. andPinusspp. showed differences between the two approaches, but vegetation signals remain qualitatively consistent. From 10,000 to 6,000 cal. yr BP, the forest was mainly a light taiga (composed ofPinus sylvestrisandBetulaspp.) and low fire activity was recorded. From 6,000 to 3,500 cal. yr BP, a dark taiga (composed ofPiceaspp.,Abies sibiricaandPinus sibirica) was established due to favourable climatic conditions, despite higher fire activity. From 3,500 cal. yr BP onwards, the continuous increase in fire activity allowed for a gradual return of light taiga,Betulaspp., likely reinforced by human activities. The dynamics ofPiceaspp. andAbies sp. were asynchronous between the sites. ForPiceaspp., the hypothesis of local inter-site expansion distributed along stream corridors is supported by the data. ForAbiessp., a bias in REVEALS, and in climate cooling may explain disparities between sites. Main conclusions We found evidence that in the early and mid-Holocene, vegetation dynamics were probably more influenced by climate, as fire activity was low. During the late Holocene, fire activity and geomorphology, eventually augmented by human activities, increased in influence on vegetation dynamics and led to the predominance of the light taiga forest up to the present.
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21.
  • Drobyshev, Igor (författare)
  • Disturbance and regeneration dynamics of a mixed Korean pine dominated forest on Changbai Mountain, North-Eastern China
  • 2014
  • Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865. ; 32, s. 21-31
  • Tidskriftsartikel (refereegranskat)abstract
    • We used dendrochronological methods to study disturbance history of a mixed Korean pine (Pious koraiensis Siebold et Zuccarini) dominated forest on the northern slope of Changbai Mountain, North Eastern China, over 1770-2000. Frequent small-scale canopy gaps and infrequent medium-scale canopy disturbances dominated natural disturbance regime in the forest, which did not experience stand-replacing disturbances over the studied period. Percentages of growth releases in subcanopy trees were below 6% in most decades, suggesting that disturbances initiating these releases were of low intensity. Strong winds were likely cause of moderate disturbance events. Two episodes with increased disturbance rates (19% and 13%) were dated to the 1920s and 1980s, timing of the 1980s event was consistent with a hurricane occurred in 1986 on the western slope of the Changbai Mountain. Age structure and growth release analyses revealed species-specific regeneration strategies of canopy dominants. Shade-intolerant Olga bay larch (Larix olgensis Henry) recruited mainly before the 1860s. Recruitment of moderately shade-tolerant P. koraiensis occurred as several regeneration waves (1820s, 1850s, 1870-1880s, 1930s, and 1990-2000s) of moderate intensity. Shade-tolerant Jezo spruce (Picea jezoensis Carr. var. komarovii (V. Vassil.) Cheng et L.K.Fu) and Manchurian fir (Abies nephrolepis (Trautv.) Maxim.) regenerated continuously over the last 220 and 130 years, respectively. Enhanced recruitment of P. koraiensis, P. jezoensis, and A. nephrolepis was observed during the 1930s and 1990s, coinciding with increased growth release frequency in the 1920s and 1980s, and suggesting disturbance events of moderate intensity. Our results indicate that the current disturbance regime of the mixed Korean pine dominated forest maintains coexistence of lightdemanding and shade-tolerant species and that change in wind climate may be particularly important for future forest composition. (C) 2013 Elsevier GmbH. All rights reserved.
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22.
  • Drobyshev, Igor (författare)
  • Do partial cross sections from live trees for fire history analysis result in higher mortality 2 years after sampling?
  • 2011
  • Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 262, s. 940-946
  • Tidskriftsartikel (refereegranskat)abstract
    • Although partial cross sections from live trees have been utilized in the development of fire history studies, few efforts have been made to examine the effects of this method on the individual trees that were sampled. We examined 115 red pine (Pinus resinosa Ait.), eastern white pine (Pinus strobus L.), and jack pine (Pinus banksiana Lamb.) trees from which partial cross sections had been removed 2 years earlier. and 209 similarly sized neighboring red pine and eastern white pine trees. Two years following the removal of partial cross sections, 22 sampled trees (19%) had died. When compared with neighboring trees, removing a partial cross section did not appear to increase the mortality rate for a given tree (t-test; P = 0.150). However, when we compared the characteristics of the trees with partial cross sections removed, we did observe some trends; i.e., those trees that died were primarily killed by wind-induced breakage at the level of the partial cross section. Almost all stems where partial cross sections were collected from a catface edge or had >30% of the total area removed were more susceptible to stem breakage and experienced an increased likelihood of mortality. While these results suggest that the collection of partial cross sections from live trees may be an effective method for fire-history sampling, the negative impacts of the sampling on individual trees may be reduced by ensuring that samples are collected from the center, rather than the catface edge, and <25% of the total stem area is removed. (C) 2011 Elsevier B.V. All rights reserved.
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23.
  • Drobyshev, Igor (författare)
  • Does soil organic layer thickness affect climate-growth relationships in the black spruce boreal ecosystem?
  • 2010
  • Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 13, s. 556-574
  • Tidskriftsartikel (refereegranskat)abstract
    • The observed long-term decrease in the regional fire activity of Eastern Canada results in excessive accumulation of organic layer on the forest floor of coniferous forests, which may affect climate–growth relationships in canopy trees. To test this hypothesis, we related tree-ring chronologies of black spruce (Picea mariana (Mill.) B.S.P.) to soil organic layer (SOL) depth at the stand scale in the lowland forests of Quebec’s Clay Belt. Late-winter and early-spring temperatures and temperature at the end of the previous year’s growing season were the major monthly level environmental controls of spruce growth. The effect of SOL on climate–growth relationships was moderate and reversed the association between tree growth and summer aridity from a negative to a positive relationship: trees growing on thin organic layers were thus negatively affected by drought, whereas it was the opposite for sites with deep (>20–30 cm) organic layers. This indicates the development of wetter conditions on sites with thicker SOL. Deep SOL were also associated with an increased frequency of negative growth anomalies (pointer years) in tree-ring chronologies. Our results emphasize the presence of nonlinear growth responses to SOL accumulation, suggesting 20–30 cm as a provisional threshold with respect to the effects of SOL on the climate–growth relationship. Given the current climatic conditions characterized by generally low-fire activity and a trend toward accumulation of SOL, the importance of SOL effects in the black spruce ecosystem is expected to increase in the future
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24.
  • Drobyshev, Igor (författare)
  • Environmental controls of the northern distribution limit of yellow birch in eastern Canada
  • 2014
  • Ingår i: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 44, s. 720-731
  • Tidskriftsartikel (refereegranskat)abstract
    • To evaluate environmental controls of yellow birch (Betula alleghaniensis Britton) distribution at its northern distribution limit in eastern Canada, we analyzed abundance, age structure, biomass accumulation rate, and growth sensitivity to climate of this species at 14 sites along a 200 km latitudinal gradient spanning three bioclimatic domains and reaching frontier populations of this species in western Quebec. We observed a large variability in seedling density across domains and presence of sites with abundant yellow birch regeneration within all three bioclimatic domains. Seedling density was positively correlated to mean age and abundance of yellow birch trees in the canopy, while sapling density was positively associated with dryer habitats. Growth patterns of canopy trees showed no effect of declining temperatures along the south-north gradient. Environmental controls of birch distribution at its northern limit were realized through factors affecting birch regeneration and not growth of canopy trees. At the stand scale, regeneration density was strongly controlled by local site conditions and not by differences in climate among sites. At the regional scale, climate variability could be an indirect driver of yellow birch distribution, affecting disturbance rates and, subsequently, availability of suitable sites for regeneration.
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25.
  • Drobyshev, Igor (författare)
  • Evaluation of CMIP6 model performances in simulating fire weather spatiotemporal variability on global and regional scales
  • 2023
  • Ingår i: Geoscientific Model Development. - 1991-959X .- 1991-9603. ; 16, s. 3103-3122
  • Tidskriftsartikel (refereegranskat)abstract
    • Weather and climate play an important role in shaping globalwildfire regimes and geographical distributions of burnable area. Asprojected by the Sixth Assessment Report of the Intergovernmental Panel onClimate Change (IPCC-AR6), in the near future, fire danger is likely toincrease in many regions due to warmer temperatures and drier conditions.General circulation models (GCMs) are an important resource in understandinghow fire danger will evolve in a changing climate, but, to date, thedevelopment of fire risk scenarios has not fully accounted for systematicGCM errors and biases. This study presents a comprehensive global evaluationof the spatiotemporal representation of fire weather indicators from theCanadian Forest Fire Weather Index System simulated by 16 GCMs from thesixth Coupled Model Intercomparison Project (CMIP6). While at the globalscale, the ensemble mean is able to represent variability, magnitude andspatial extent of different fire weather indicators reasonably well whencompared to the latest global fire reanalysis, there is considerableregional and seasonal dependence in the performance of each GCM. To supportthe GCM selection and application for impact studies, the evaluation resultsare combined to generate global and regional rankings of individual GCMperformance. The findings highlight the value of GCM evaluation andselection in developing more reliable projections of future climate-drivenfire danger, thereby enabling decision makers and forest managers to taketargeted action and respond to future fire events.
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26.
  • Drobyshev, Igor (författare)
  • Fire history, fuels, and overstory effects on the regeneration-layer dynamics of mixed-pine forest ecosystems of eastern Upper Michigan, USA
  • 2014
  • Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 322, s. 37–47-
  • Tidskriftsartikel (refereegranskat)abstract
    • Mixed-pine forest ecosystems of the northern Lake States were historically dominated by red pine (Pinus resinosa Ait.) and eastern white pine (Pinus strobus L.). The late 18th and early 19th century logging activities, followed by significant changes in the characteristics of the fire regime altered the structure and composition of these forests. Prior to making decisions about restoration treatments aimed at promoting natural regeneration of red pine and eastern white pine, there is a need to develop a better understanding of the influence of fire history and current stand conditions on the regeneration-layer. To this end, we quantified the seedling and sapling densities of tree species in altered second-growth and reference old-growth stands at Seney National Wildlife Refuge in eastern Upper Michigan. We then related these densities to descriptors of fire history, fuel loadings, and overstory characteristics. Our results indicate lower densities of red pine and eastern white pine seedlings compared to saplings in second-growth stands. Red pine and eastern white pine seedling densities were positively associated with number of fires in the last 142 years, and negatively associated with time since last fire. Time since last fire also influenced red pine and eastern white pine regeneration indirectly through positive correlations with organic matter depth and negative correlations with importance values for these species in the overstory. jack pine (Pinus banksiana Lamb.) seedling density was also positively associated with the number of fires in the last 142 years. Red pine and eastern white pine seedling and sapling densities exhibited negative relationships with most of the descriptors of fuel loadings. Compared to the second-growth stands, the overstory was found to be a stronger driver of regeneration-layer dynamics in the old-growth stands. Our findings suggest that regeneration of red pine and eastern white pine in the second-growth stands is limited due to unfavorable seedbed conditions, abundance of competing species, and an insufficient seed source. The long-term management objective should be to reintroduce fire with characteristics that resemble those of the historical fire regime. In the short-term, however, managers need to explore management options focused on creating favorable conditions for regeneration of red pine and eastern white pine, and on reducing jack pine. Our findings indicate that opportunities exist for restoration treatments that can manipulate successional dynamics to favor red pine and eastern white pine dominance in these stands. (C) 2014 Elsevier B.V. All rights reserved.
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27.
  • Drobyshev, Igor, et al. (författare)
  • Forest fire activity in Sweden: Climatic controls and geographical patterns in 20th century
  • 2012
  • Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923 .- 1873-2240. ; 154-155, s. 174-186
  • Tidskriftsartikel (refereegranskat)abstract
    • We used Swedish county-scale forest fire statistics to quantify modern fire activity, identify its main temporal and geographical patterns, and evaluate statistical performance of six fire-related weather indices as proxy of fire activity in Sweden over 1942–1975 and 1996–2008, the periods with available countyscale fire statistics. The analyzed indices were monthly precipitation, SPI, MDC, PDSI, calibrated PDSI, and DI, a Drought Index calculated as a ratio between actual and equilibrium evapotranspiration. The modern fire cycle (FC) in the northern part of Sweden varies between 2 × 103 and 3 × 104 years, whereas in southern Sweden the FC is somewhat shorter (103–2 × 104 years). No temporal trend in average FC was evident at the country scale between the two periods. Significant and negative values of a Mantel test, obtained on county data for both periods (r = −0.494, p = 0.001 for 1942–1975 and r = −0.281 and p = 0.015 for 1996–2008) indicated the presence of a geographical pattern in annual forest fire activity. Over 1942–1975, PCA revealed that the central and northern counties formed one group with synchronized fire activity, and the southern and south–western counties formed another group. This pattern became less evident during the more recent period (1996–2008). Over 1996–2008, the analysis showed little synchronicity in annual fire activity across different parts of the country. The geographical position of a county had a clear effect on seasonal pattern of forest fires. In southern Sweden, the peak in the number of fires and the burnt area was in April–May, during a relatively short dry period immediately following the snowmelt. In northern Sweden, fires in the second half of fire season dominated the total annual area burnt. Analyzed indices differed considerably in their predictive power in respect to counties’ records of annual area burnt. Calibrated PDSI was a superior proxy of fire activity for the southern region (R2 = 60.8% in regression against total annual area burnt for respective provinces), and DIlate (Drought Index for the first half of the growing season) was superior for the northern counties (R2 = 73.3%). Predictive power of the indices was much higher for the recent period (1996–2002), with R2 values staying within 81.2 and 97.8%. Even if modern levels of forest fire activity in Sweden are very low from historical perspective, there is a strong spatiotemporal association between fire activity and climatic variability at regional scales, which provides a basis for modeling of the future fire hazard.
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28.
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29.
  • Drobyshev, Igor (författare)
  • Gradually increasing forest fire activity during the Holocene in the northern Ural region (Komi Republic, Russia)
  • 2019
  • Ingår i: Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 29, s. 1906-1920
  • Tidskriftsartikel (refereegranskat)abstract
    • In many boreal regions of Russia the past natural variability of forest fire activity remains largely undocumented, preventing accurate assessment of the impact of current climate warming on forest ecosystem dynamics. This study aims to reconstruct the Holocene fire history of the northern Ural mountain foothills, in the Komi Republic, based on analyses of charcoal particles from peatland deposits and coupled with dendrochronological investigations. The results show that there was a gradual increase in forest fire activity during the past 11,000 years. Between 11,000 and 5100 cal. yr BP, the mean fire return interval (FRI) oscillated between 600 and 200 years. During this period, regional data showed that cold temperature, humid climatic conditions, combined with steppe vegetation between 11,000-9000 cal. BP, and then the development of spruce-dominated forest between 9300 and 4600 cal. yr BP, were less conducive to fires. After 5100 cal. yr BP, a gradual increase in drought conditions through reduced precipitations, associated with the establishment of a Scots pine forest favored fire frequency, with a mean FRI under 200 years (range, 200-40 years). Nowadays (since CE 1500), human activity induces an unprecedented fire activity with a mean FRI below 100 years (range, 100-40 years).
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30.
  • Drobyshev, Igor (författare)
  • Growth-climate response of Jack pine on clay soils in northeastern Canada
  • 2012
  • Ingår i: Dendrochronologia. - : Elsevier BV. - 1125-7865. ; 30, s. 127-136
  • Tidskriftsartikel (refereegranskat)abstract
    • We used tree-ring data from a major North American boreal tree species. Jack pine (Pinus banksiana Lamb.), to decipher spatial and temporal tree-growth responses to climate variability within the area of northwestern Quebec and northeastern Ontario. Fifteen sites with clay soils were selected and grouped into North and South sub-regions at approximately 49 degrees N and 50 degrees N, respectively. Tree-ring chronologies were analyzed through a response function for the years 1951-2000 to identify growth-limiting climate factors. Increased precipitation in June in the previous year and a warm month of April this year favored radial growth whereas higher temperature in September and increased precipitation in October, both of the previous year, and current June precipitation were negatively related to growth. There was a clear difference in climatic response between the southern and northern sub-regions: southern sites were more responsive to temperature dynamics while on northern sites Jack pine growth appeared negatively influenced by an excess of precipitation. Soil conditions, with larger areas covered by less water permeable clay deposits in the northern sub-region, explain this result. If recently observed trends towards warmer springs continue. Jack pine may increase its radial growth in the study area. However, increases in fall precipitation, also predicted under the future climate, may offset the positive effect of previous years weather on clay sites. (C) 2012 Istituto Italian di Dendrocronologia. Published by Elsevier GmbH. All rights reserved.
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31.
  • Drobyshev, Igor, et al. (författare)
  • Growth response of spruce saplings in relation to climatic conditions along a gradient of gap size
  • 2000
  • Ingår i: Canadian Journal of Forest Research. - 1208-6037. ; 30:6, s. 930-938
  • Tidskriftsartikel (refereegranskat)abstract
    • To evaluate the relative importance of climatic factors and the level of natural canopy disturbance on sapling growth rates, terminal shoot increment of Norway spruce (Picea abies (L.) Karst.) saplings was analyzed in old-growth Sphagnum-Myrtillus forests of the European southern boreal zone (Tver Region, Russia). For a 5-year period, terminal increments were retrospectively measured in 225 saplings in a range of naturally created canopy gaps. Climatic variability was estimated by Seljaninov hydrothermal coefficient. Variation in the growth rate was partitioned as (i) annual variation observed within a particular sapling over a 5-year period ("within-stem variation," WSV) and (ii) variation of 5-year cumulative height increments within a particular location ("within-location variation," WLV). Sapling growth was positively related to gap size and, except when under canopy location, with the height of the saplings. For the growth, differences in sapling location along a gradient of gap sizes were more important than annual dynamics of water availability. Impact of the annual climatic variability was less pronounced in large gap, compared with other locations. Absolute values of WSV and WLV were similar under an intact canopy. WSV had a tendency to decrease in greater gaps, whereas WLV variation increased.
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32.
  • Drobyshev, Igor, et al. (författare)
  • How old are the largest Southern Swedish oaks: a dendrochronological analysis
  • 2010
  • Ingår i: Broadleaved Forests in Southern Sweden: Management for Multiple Goals. - 9781405188869 ; 53:53, s. 155-163
  • Bokkapitel (refereegranskat)abstract
    • In the southern Scandinavian landscape, large oaks Quercus robur provide habitat for a wide range of species, including a large number species on the national Red list and the EU habitat directive. Since most of these trees are hollow and have likely been growing in conditions different from the ones of an “average” oak in today’s more forested landscape, direct inference of their age from diameter may be biased. To provide support for the management of these trees, we estimate their age by combining inventory data on diameter distribution of the largest oaks (n = 236) in the Swedish province of Scania and ring width distribution for large (> 1 m in stem diameter) oaks collected in seven oak-dominated stands (both woodland-type and denser closed-canopy forests) in southern Sweden (ntrees = 69, nrings = 12399). The mode of ring-width distribution was 1.26 mm /year. The central 90% of ring width distribution was within 0.54 and 3.38 mm, demonstrating the high growth plasticity of the species. Both ring width distribution in large oaks, divided into 16 width classes, and cumulative 20-yr diameter increments (19 classes) were well approximated by the log-normal function. The largest oaks in Scania are unlikely to exceed 1000 yr, the most probable age estimates of the majority of the inventoried oaks were centered around 500-700 yr. The age distribution of 18 large (69.4 - 178 cm dbh) non-hollow oaks suggesting the maximum age being around 400-600 yr. Conservation-oriented management of oak populations should address the need for preservation of such old trees
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33.
  • Drobyshev, Igor, et al. (författare)
  • Influence of annual weather on growth of pedunculate oak in southern Sweden
  • 2008
  • Ingår i: Annals of Forest Science. - : INRA, EDP Sciences. - 1286-4560 .- 1297-966X. ; 65:5, s. 512-512
  • Tidskriftsartikel (refereegranskat)abstract
    • A network of oak (Quercus robur L.) chronologies containing 49 sites and 635 single trees was analysed to identify weather variables affecting annual tree-ring increment dynamics in southern Sweden during 1860-2000. We analysed (1) the growth response of oak to non-extreme weather, and (2) the temporal and spatial patterns of regional growth anomalies (pointer years) and associated climatic extremes resolved on a monthly scale. Growth was controlled by precipitation in the current (June-July) and the previous growing season (August) in 48% and 22% of all sites, respectively. Temperature during July of the current year and August of the previous year was negatively correlated with growth in 29% and 43% of the sites, respectively. Growth was positively correlated with temperature in October of the previous season in 72% of the sites. The most extensive growth anomaly occured in 1965 and was probably caused by intrusion of cold Artic air masses into the region at the end of March that year. During the climatically non-extreme years, oak growth is driven mostly by the dynamics of summer precipitation. Many of the negative growth anomalies, however, were associated with temperature extremes. Southern Swedish oak pointer years tend not to coincide with the pan-European pointer years.
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34.
  • Drobyshev, Igor (författare)
  • Insect defoliation modulates influence of climate on the growth of tree species in the boreal mixed forests of eastern Canada
  • 2022
  • Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 12
  • Tidskriftsartikel (refereegranskat)abstract
    • Increasing air temperatures and changing precipitation patterns due to climate change can affect tree growth in boreal forests. Periodic insect outbreaks affect the growth trajectory of trees, making it difficult to quantify the climate signal in growth dynamics at scales longer than a year. We studied climate-driven growth trends and the influence of spruce budworm (Choristoneura fumiferana Clem.) outbreaks on these trends by analyzing the basal area increment (BAI) of 2058 trees of Abies balsamea (L.) Mill., Picea glauca (Moench) Voss, Thuja occidentalis L., Populus tremuloides Michx., and Betula papyrifera Marsh, which co-occurs in the boreal mixedwood forests of western Quebec. We used a generalized additive mixed model (GAMM) to analyze species-specific trends in BAI dynamics from 1967 to 1991. The model relied on tree size, cambial age, degree of spruce budworm defoliation, and seasonal climatic variables. Overall, we observed a decreasing growth rate of the spruce budworm host species, A. balsamea and P. glauca between 1967 and 1991, and an increasing growth rate for the non-host, P. tremuloides, B. papyrifera, and T. occidentalis. Our results suggest that insect outbreaks may offset growth increases resulting from a warmer climate. The observation warrants the inclusion of the spruce budworm defoliation into models predicting future forest productivity.
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35.
  • Drobyshev, Igor (författare)
  • Inter-annual and decadal changes in teleconnections drive continental-scale synchronization of tree reproduction
  • 2017
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate teleconnections drive highly variable and synchronous seed production (masting) over large scales. Disentangling the effect of high-frequency (inter-annual variation) from low-frequency (decadal trends) components of climate oscillations will improve our understanding of masting as an ecosystem process. Using century-long observations on masting (the MASTREE database) and data on the Northern Atlantic Oscillation (NAO), we show that in the last 60 years both high-frequency summer and spring NAO, and low-frequency winter NAO components are highly correlated to continent-wide masting in European beech and Norway spruce. Relationships are weaker (non-stationary) in the early twentieth century. This finding improves our understanding on how climate variation affects large-scale synchronization of tree masting. Moreover, it supports the connection between proximate and ultimate causes of masting: indeed, large-scale features of atmospheric circulation coherently drive cues and resources for masting, as well as its evolutionary drivers, such as pollination efficiency, abundance of seed dispersers, and natural disturbance regimes.
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36.
  • Drobyshev, Igor (författare)
  • Interactions among trees: A key element in the stabilising effect of species diversity on forest growth
  • 2019
  • Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 33, s. 360-367
  • Tidskriftsartikel (refereegranskat)abstract
    • There is mounting evidence that species diversity increases the temporal stability of forest growth. This stabilising effect of diversity has mainly been attributed to species differences in their response to fluctuating environmental conditions. Interactions among individuals could also contribute to the stabilising effect of diversity by increasing the mean and reducing the variance of tree growth, however, this has never been directly demonstrated.We used tree-ring width chronologies from temperate and boreal mixed stands of Eastern Canada to identify the role of interactions among individuals in the stabilising effect of diversity on forest growth. Using neighbourhood competition index and a mixed model, we compared the effect of interspecific and intraspecific interactions on the mean and the variance of tree growth.We found that interspecific interactions are less detrimental to tree growth than intraspecific interactions. We also found that interspecific interactions buffer tree response to drought and thereby reduce the variance of tree growth.Our results indicate diversity may increase the mean and reduce the variance of tree growth through interactions among individuals. Thus, we demonstrate interactions among individuals play a role in the stabilising effect of diversity on forest growth, and in doing so, we bring to light other mechanisms of the insurance hypothesis.
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37.
  • Drobyshev, Igor (författare)
  • Interactions between climate, natural disturbances, and regeneration in boreal and hemi-boreal forests
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Natural disturbance is an important driving force of community dynamics in many forest types around the globe. Understanding spatial and temporal properties of disturbance events in the present and in the past is important in formulating the nature conservation strategies as well as for the modeling of climate and human impacts on forest vegetation. In this thesis I studied wind and fire disturbances in natural spruce and pine dominated forests in European Russia. In the case of Norway spruce (Picea abies (L.) Karst.) forests, the goal was to quantitatively evaluate the role of naturally formed canopy gaps and their role in canopy dynamics. In the case of Scots pine (Pinus sylvestris L.) dominated forests, I analysed the link between climate variation, human presence in the landscape, and fire activity. Here, the primary goal was to establish a relationship between tree-ring variables and independently dated fire events to infer common climatic information contained in both datasets. By doing so, an attempt was made to improve the separation of climate- and human-related influences in site fire chronologies. Finally, I analysed the link between weather variation and fire activity at the regional scale, and evaluated the value of tree-ring data as a proxy for regional-scale fire activity. My studies in the spruce-dominated forests suggested that the impact of wind disturbance on canopy dynamics may be forest-type specific at the spatial scale of 103 ha and the temporal scale of a few decades. An agreement between the outcome of gap-associated tree regeneration and canopy composition was observed in boreal stands. In the hemi-boreal stands, a large proportion of stand area under canopy gaps and poor spruce regeneration in larger gaps led to an increase in the abundance of deciduous species implying a decrease in canopy spruce and an increase in deciduous species in the coming decades. In pine-dominated forests, it was possible to establish a relationship between tree-ring chronologies and independently dated fire events. Importantly, this relationship was dependent on the seasonal timing of fire events as recorded in the scars. Joint analysis of site fire histories and local tree-ring chronologies showed possibilities to quantitatively estimate the human impact in the reconstructed fire events. At regional scale, tree-ring-based reconstruction of fire activity appears to be a good predictor of high (annual) and low (decadal) frequency variability in the half-a-century long fire record of Komi republic (East European Russia, total area 415.9 thousand km2). My results supported the view of tree-ring chronologies as potentially realistic proxies for regional fire activity during longer time periods. Generally, considerable variability of disturbance events along temporal and spatial scales needs to be incorporated in any conceptual model of vegetation dynamics. This variability is intermingled with human activities in the past and present. To provide a sound practical advice in designing conservation strategies it is important to separate purely climatic forcing of disturbance regimes from the one mediated by land use patterns.
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38.
  • Drobyshev, Igor (författare)
  • Intraspecific variability in growth response to environmental fluctuations modulates the stabilizing effect of species diversity on forest growth
  • 2017
  • Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 105, s. 1010-1020
  • Tidskriftsartikel (refereegranskat)abstract
    • 1. Differences between species in their response to environmental fluctuations cause asynchronized growth series, suggesting that species diversity may help communities buffer the effects of environmental fluctuations. However, within-species variability of responses may impact the stabilizing effect of growth asynchrony.2. We used tree ring data to investigate the diversity-stability relationship and its underlying mechanisms within the temperate and boreal mixed woods of Eastern Canada. We worked at the individual tree level to take into account the intraspecific variability of responses to environmental fluctuations.3. We found that species diversity stabilized growth in forest ecosystems. The asynchrony of species' response to climatic fluctuations and to insect outbreaks explained this effect. We also found that the intraspecific variability of responses to environmental fluctuations was high, making the stabilizing effect of diversity highly variable.4. Synthesis. Our results are consistent with previous studies suggesting that the asynchrony of species' response to environmental fluctuations drives the stabilizing effect of diversity. The intraspecific variability of these responses modulates the stabilizing effect of species diversity. Interactions between individuals, variation in tree size and spatial heterogeneity of environmental conditions could play a critical role in the stabilizing effect of diversity.
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39.
  • Drobyshev, Igor (författare)
  • Jet stream position explains regional anomalies in European beech forest productivity and tree growth
  • 2022
  • Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanistic pathways connecting ocean-atmosphere variability and terrestrial productivity are well-established theoretically, but remain challenging to quantify empirically. Such quantification will greatly improve the assessment and prediction of changes in terrestrial carbon sequestration in response to dynamically induced climatic extremes. The jet stream latitude (JSL) over the North Atlantic-European domain provides a synthetic and robust physical framework that integrates climate variability not accounted for by atmospheric circulation patterns alone. Surface climate impacts of north-south summer JSL displacements are not uniform across Europe, but rather create a northwestern-southeastern dipole in forest productivity and radial-growth anomalies. Summer JSL variability over the eastern North Atlantic-European domain (5-40E) exerts the strongest impact on European beech, inducing anomalies of up to 30% in modelled gross primary productivity and 50% in radial tree growth. The net effects of JSL movements on terrestrial carbon fluxes depend on forest density, carbon stocks, and productivity imbalances across biogeographic regions.Here the authors show that extremes in the summer jet stream position over Europe create a beech forest productivity dipole between northwestern and southeastern Europe and can result in regional anomalies in forest carbon uptake and growth.
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40.
  • Drobyshev, Igor (författare)
  • Lacustrine charcoal peaks provide an accurate record of surface wildfires in a North European boreal forest
  • 2020
  • Ingår i: Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 30, s. 380-388
  • Tidskriftsartikel (refereegranskat)abstract
    • We evaluated the skills of different palaeofire reconstruction techniques to reconstruct the fire history of a boreal landscape (Russian Karelia) affected by surface fires. The analysis of dated lacustrine sediments from two nearby lakes was compared with independent dendrochronological dating of fire scars, methods which have rarely been used in context of surface fires. We used two sediment sub-sampling volumes (1 and 3.5 cm(3), wet volumes) and three methods of calculating the Charcoal Accumulation Rate to reconstruct fire histories: CHAR number, charcoal surface area and estimated charcoal volume. The results show that palaeofire reconstructions obtained with fossil charcoal data from lake sediments and dendrochronology are similar and complementary. Dendrochronological reconstruction of fire scars established 12 fire dates over the past 500 years, and paleo-data from lake sediments identified between 7 and 13 fire events. Several 'false fire events' were also recorded in the charcoal chronologies, likely because of errors associated with the estimation of the sediment accumulation rate in the unconsolidated part of the sediment. The number of replicates, that is, number of sub-samples and lakes analyzed, had an effect on the number of identified fire events, whereas no effect was seen in the variation in the analyzed sediment volume or the choice of the charcoal-based metric. Whenever possible, we suggest the use of the dendrochronological data as an independent control for the calibration of charcoal peak series, which helps provide more realistic millennia-long reconstruction of past fire activity. We also argue for the use of 1 cm(3) sample volume, a sampling protocol involving sampling of more than one lake, and sufficient number of intra-sample replicates to achieve skilful reconstructions of past fire activity.
  •  
41.
  • Drobyshev, Igor, et al. (författare)
  • Lifespan and mortality of old oaks - combining empirical and modelling approaches to support their management in Southern Sweden
  • 2008
  • Ingår i: Annals of Forest Science. - : Springer Science and Business Media LLC. - 1286-4560 .- 1297-966X. ; 65:4, s. 401-401
  • Tidskriftsartikel (refereegranskat)abstract
    • Old oaks (Quercus robur L.) play an important role in the southern Scandinavian landscape by providing habitat for a wide range of species, a large proportion of them being currently on the National Redlists. To provide support for the management of these trees, we review data on oak mortality and formulate a mortality-driven stochastic model analysing interactions between mortality rate, oak recruitment rate into 100-150 age class, and amount of oaks older than 200 years. Empirical annual mortality rates varied between 0 and 13% with average 1.68%. Trees older 200 years had an average mortality rate of 1.1%. Oaks in the high density forests showed higher mortality (3.2%) as compared to the trees growing in the low density forests (1.2%). A 400-year long modelling exercises indicated that under current mortality rates (regular mortality being centred around 1% annually; and irregular mortality 7% with average return time of 13 years) the long-term maintenance of 20 trees older than 200 years per ha would require an input rate of 1 to 5 trees x year(-1) x ha(-1) into the 100-150 years old class. The modelling highlighted the importance of initial oak abundance affecting amount of old trees at the end of shorter (100 years) simulation period.
  •  
42.
  • Drobyshev, Igor, et al. (författare)
  • Linking tree rings, summer aridity, and regional fire data: an example from the boreal forests of the Komi Republic, East European Russia
  • 2004
  • Ingår i: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 1208-6037 .- 0045-5067. ; 34:11, s. 2327-2339
  • Tidskriftsartikel (refereegranskat)abstract
    • To evaluate the potential use of tree-ring data as a proxy for fire activity at the scale of a large boreal region, we analyzed a set of regional tree-ring chronologies of Siberian larch (Larix sibirica L.), a spatially implicit annual fire record, and monthly climate data for the Komi Republic for the period 1950-1990. In most years, annually burned area was below 0.001% of the republic's forested area and reached up to 0.7% during fire-prone years. Principal components (PC) of summer aridity resolved 64.2% of the annual variation in the number of fires, 12.2% in the average fire size, and 59.2% in the annually burned area. In turn, tree-ring PCs explained 65.2% of variation in fire-related weather PCs. Dendrochronological reconstruction of the annual number of fires and of the log-transformed annually burned area predicted 27.0% and 40.1% of the high-frequency variance of these variables, respectively. Coefficient of efficiency, a measure of reconstruction usefulness, reached 0.081 (number of fires) and 0.315 (annual area burned), supporting the obtained index as a realistic proxy for regional fire activity. Decadal variation in coefficient of efficiency values suggested improved monitoring accuracy since 1960 and more effective fire suppression during the last studied decade (1980-1990).
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43.
  • Drobyshev, Igor, et al. (författare)
  • Marginal imprint of human land use upon fire history in a mire-dominated boreal landscape of the Veps Highland, North-West Russia
  • 2022
  • Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 507
  • Tidskriftsartikel (refereegranskat)abstract
    • Dendrochronological reconstructions inform us about historical climate-fire-human interactions, providing a means to calibrate projections of future fire hazard. Most of these reconstructions, however, have been developed in landscapes with a considerable proportion of xeric sites that could potentially inflate our estimates of the historic levels of fire activity. We provide a 420-year long reconstruction of fires in a mire-dominated landscape of the Veps Nature Park, North-West Russia. The area has mostly escaped large-scale forestry operations in the past and is an example of pristine mid-boreal vegetation with a high (approximately 30% for the area studied) proportion of waterlogged areas with ombrotropic mires. The historical fire cycle was 91.4 years (90% confidence intervals, CI 66.2-137.6 years) over the 1580-1720 period, decreasing to 35.9 (CI 28.1-47.6 years) between 1730 and 1770, and then increasing again to 122.7 years (CI 91.0-178.0 years) over the 1780-2000 period. Early season fires dominated over late season fires during the reconstruction period. We documented a higher fire activity period between 1730 and 1780, resulting from the increase in early season fires. This period coincided with one of the largest multi-decadal declines in the reconstructed spring precipitation since 1600 CE, although we found no significant relationship between fire and precipitation over the whole reconstructed period. The nine largest fire years were associated with negative summer precipitation and positive summer temperature anomalies over the study region. Land-use history of the area did not appear to have an effect on historical fire dynamics. Modern (1996-2016) fire records indicate a regional fire cycle of ~ 1300 years, featuring a pronounced pattern with early (April-May) and late (July-September) season fires. The uniform fire cycle in the area since 1780, occurrence of nine largest fire years during years with spring-summer droughts, and low ignition frequencies over the last 420 years (0.005 to 0.037 ignitions per year and km2) suggest that the fire regime of the Veps Highland remained largely natural until the onset of the 20th century.
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44.
  • Drobyshev, Igor (författare)
  • Monitoring Climate Sensitivity Shifts in Tree-Rings of Eastern Boreal North America Using Model-Data Comparison : Shifts in Tree Growth Sensivity to Climate
  • 2018
  • Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 21, s. 1042-1057
  • Tidskriftsartikel (refereegranskat)abstract
    • The growth of high-latitude temperature-limited boreal forest ecosystems is projected to become more constrained by soil water availability with continued warming. The purpose of this study was to document ongoing shifts in tree growth sensitivity to the evolving local climate in unmanaged black spruce (Picea mariana (Miller) B.S.P.) forests of eastern boreal North America (49A degrees N-52A degrees N, 58A degrees W-82A degrees W) using a comparative study of field and modeled data. We investigated growth relationships to climate (gridded monthly data) from observed (50 site tree-ring width chronologies) and simulated growth data (stand-level forest growth model) over 1908-2013. No clear strengthening of moisture control over tree growth in recent decades was detected. Despite climate warming, photosynthesis (main driver of the forest growth model) and xylem production (main driver of radial growth) have remained temperature-limited. Analyses revealed, however, a weakening of the influence of growing season temperature on growth during the mid- to late twentieth century in the observed data, particularly in high-latitude (> 51.5A degrees N) mountainous sites. This shift was absent from simulated data, which resulted in clear model-data desynchronization. Thorough investigations revealed that desynchronization was mostly linked to the quality of climate data, with precipitation data being of particular concern. The scarce network of weather stations over eastern boreal North America (> 51.5A degrees N) affects the accuracy of estimated local climate variability and critically limits our ability to detect climate change effects on high-latitude ecosystems, especially at high altitudinal sites. Climate estimates from remote sensing could help address some of these issues in the future.
  •  
45.
  • Drobyshev, Igor, et al. (författare)
  • Multi-century reconstruction of fire activity in Northern European boreal forest suggests differences in regional fire regimes and their sensitivity to climate
  • 2014
  • Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 102:3, s. 738-748
  • Tidskriftsartikel (refereegranskat)abstract
    • Forest fires are one of the main disturbance agents in boreal and temperate ecosystems. To decipher large-scale temporal and spatial patterns of past fire activity in Scandinavia, we analysed the synchronicity of dendrochoronologically reconstructed fire events in a large network of sites (n=62; 3296 samples, 392 individual fire years) covering a wide geographical gradient (56.5-67.0 degrees N and 9.3-20.5 degrees E) over AD 1400-1900. We identified large fire years (LFY) as years with regionally increased forest fire activity and located the geographical centres of climatic anomalies associated with synchronous LFY occurrence across the region, termed LFY centroids. The spatial pattern of LFY centroids indicated the presence of two regions with climatically mediated synchronicity of fire occurrence, located south and north from 60 degrees N. The return intervals of LFYs in Scandinavia followed a Weibull distribution in both regions. Intervals, however, differed: a period of 40years would carry a 0.93 probability of LFY occurrence in the southern region, but only a 0.48 probability of LFY occurrence in the northern region. Over 1420-1759, the northern region was characterized by significantly higher temporal variability in LFY occurrence than the southern region. Temporal correlation of LFYs with reconstructed average summer temperature and total precipitation was evident mainly for the northern region. LFYs in this region were associated with positive temperature and negative precipitation anomalies over Scandinavia and with colder and wetter conditions in more southern parts of the European subcontinent. Synthesis. Historical patterns of the occurrence of large fire years (LFY) in Scandinavia point towards the presence of two well-defined zones with characteristic fire activity, with the geographical division at approximately 60 degrees N. The northern and mid-boreal forests, although exhibiting lower LFY frequencies, appeared to be more sensitive to past summer climate, as compared to the southern boreal forests. This would imply that fire regimes across Scandinavia may show an asynchronous response to future climate changes.
  •  
46.
  • Drobyshev, Igor (författare)
  • Multiscale variation in drought controlled historical forest fire activity in the boreal forests of eastern Fennoscandia
  • 2018
  • Ingår i: Ecological Monographs. - : Wiley. - 0012-9615 .- 1557-7015. ; 88, s. 74-91
  • Tidskriftsartikel (refereegranskat)abstract
    • Forest fires are a key disturbance in boreal forests, and characteristics of fire regimes are among the most important factors explaining the variation in forest structure and species composition. The occurrence of fire is connected with climate, but earlier, mostly local-scale studies in the northern European boreal forests have provided little insight into fire-climate relationship before the modern fire suppression period. Here, we compiled annually resolved fire history, temperature, and precipitation reconstructions from eastern Fennoscandia from the mid-16th century to the end of the 19th century, a period of strong human influence on fires. We used synchrony of fires over the network of 25 fire history reconstructions as a measure of climatic forcing on fires. We examined the relationship between fire occurrence and climate (summer temperature, precipitation, and a drought index summarizing the influence of variability in temperature and precipitation) across temporal scales, using a scale space multiresolution correlation approach and Bayesian inference that accounts for the annually varying uncertainties in climate reconstructions. At the annual scale, fires were synchronized during summers with low precipitation, and most clearly during drought summers. A scale-derivative analysis revealed that fire synchrony and climate varied at similar, roughly decadal scales. Climatic variables and fire synchrony showed varying correlation strength and credibility, depending on the climate variable and the time period. In particular, precipitation emerged as a credible determinant of fire synchrony also at these time scales, despite the large uncertainties in precipitation reconstruction. The findings explain why fire occurrence can be high during cold periods (such as from the mid-17th to early-18th century), and stresses the notion that future fire frequency will likely depend to a greater extent on changes in precipitation than temperature alone. We showed, for the first time, the importance of climate as a decadal-scale driver of forest fires in the European boreal forests, discernible even during a period of strong human influence on fire occurrence. The fire regime responded both to anomalously dry summers, but also to decadal-scale climate changes, demonstrating how climatic variability has shaped the disturbance regimes in the northern European boreal forests over various time scales.
  •  
47.
  • Drobyshev, Igor (författare)
  • Non-stationary Response of Tree Growth to Climate Trends Along the Arctic Margin
  • 2019
  • Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 22, s. 434-451
  • Tidskriftsartikel (refereegranskat)abstract
    • Climate change modulates cold-marginal forest ecosystems through changing growth constraints. Understanding spatiotemporal variations in climate-growth relationships is essential to project forest ecosystem dynamics, and climate-environmental feedbacks. We explored variations in growth and climate-growth relationships, along the Arctic margin in north-western Europe, using Scots pine radial growth chronologies, climate data and links between the geographical origin of dominant air masses and growth-controlling variables. Analyses covered nineteenth century to early twenty-first century, with emphasis on two separate warming periods (early twentieth century, and late twentieth to early twenty-first century) and the intervening cooling period. The analyses revealed spatiotemporally unstable growth responses to climate along the Arctic margin. Spatial growth patterns were most similar during the cooling period. However, climate trends (warming, cooling) were weak drivers of growth-limiting climate variables. Instead, a transition in growth-limiting variables occurred throughout the analysed period. A wide range of growing season and non-growing season climate variables limited growth during the early twentieth century. Thereafter the number of growth-limiting variables progressively decreased. This change was accompanied by a contraction in the spatial correspondence between growth and climate, and by a shift in the geographical origin of dominant air masses. This was particularly emphasized close to the Atlantic during recent warming period. The weak association between growth-limiting variables and climate trends question projections of future ecosystem dynamics based on climate variables identified during specific periods (for example, recent warming period). Such projections may be misleading as the diversity of climate conditions constraining cold-marginal forests will be underestimated.
  •  
48.
  • Drobyshev, Igor (författare)
  • North America’s oldest boreal trees are more efficient water users due to increased [CO2], but do not grow faster
  • 2019
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 116, s. 2749-2754
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to anthropogenic emissions and changes in land use, trees are now exposed to atmospheric levels of [CO2] that are unprecedented for 650,000 y [Luthi et al. (2008) Nature 453: 379-382] (thousands of tree generations). Trees are expected to acclimate by modulating leaf-gas exchanges and alter water use efficiency which may result in forest productivity changes. Here, we present evidence of one of the strongest, nonlinear, and unequivocal postindustrial increases in intrinsic water use efficiency (iWUE) ever documented (+59%). A dual-isotope tree-ring analysis (delta C-13 and delta O-18) covering 715 y of growth of North America's oldest boreal trees (Thuja occidentalis L.) revealed an unprecedented increase in iWUE that was directly linked to elevated assimilation rates of CO2 (A). However, limited nutrient availability, changes in carbon allocation strategies, and changes in stomatal density may have offset stem growth benefits awarded by the increased iWUE. Our results demonstrate that even in scenarios where a positive CO2 fertilization effect is observed, other mechanisms may prevent trees from assimilating and storing supplementary anthropogenic emissions as above-ground biomass. In such cases, the sink capacity of forests in response to changing atmospheric conditions might be overestimated.
  •  
49.
  • Drobyshev, Igor (författare)
  • Precommercial Thinning of Picea mariana and Pinus banksiana: Impact of Treatment Timing and Competitors on Growth Response
  • 2017
  • Ingår i: Forest Science. - : Oxford University Press (OUP). - 0015-749X. ; 63, s. 62-70
  • Tidskriftsartikel (refereegranskat)abstract
    • Early successional competition among boreal forest tree and shrub species and its effects on growth of commercial tree species have been a major source of uncertainty in establishing efficient precommercial thinning and brushing prescriptions. We examined the effect of prethinning competitor density, postthinning competitor regrowth density, prethinning stem diameter, and the timing of thinning operations on the growth response of black spruce (Picea mariana [Mill.] BSP) and jack pine (Pinus banksiana Lamb.). In addition, we examined the mortality rate of hardwoods after thinning and the number of new shoots produced per surviving thinned stem. For jack pine, growth response was greatest when thinning occurred between 4 and 9 years after establishment, whereas for black spruce we observed no significant relationship between growth response and the timing of treatment. For jack pine, growth response was significantly affected by pretreatment competitor density, posttreatment competitor regrowth density, and pretreatment stem diameter. For black spruce, no significant relationship was observed between growth response and any variables. Mortality rates and production of new shoots in hardwoods varied significantly between species. Considering the high regrowth potential of willow (Salix spp.) and alder (Alnus spp.), we recommend that stands exhibiting low densities of these species should be left unthinned. Our results help foresters identify stands that require precommercial thinning and call for modification of currently used thinning strategies.
  •  
50.
  • Drobyshev, Igor (författare)
  • Prolonged Absence of Disturbance Associated with Increased Environmental Stress May Lead to Reduced Seedbank Size in Picea mariana in Boreal Eastern North America
  • 2015
  • Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 18, s. 1135-1150
  • Tidskriftsartikel (refereegranskat)abstract
    • Disturbance plays an important role in the distributional range of species by affecting their colonization potential and persistence. Short disturbance intervals have been linked to reduced seedbank sizes of some species, but the effects of long intervals are largely unknown. To explore the potential existence of seedbank sizes that may also be limited by long disturbance intervals, we studied an area in boreal eastern North America where time since fire (TSF) coincides with an increase in environmental stress (accumulating organic matter measured as depth of the soil organic layer (SOL)). Along a chronosequence dating back about 710 years, we counted the number of seeds cone(-1) of black spruce (Picea mariana) and then estimated the number of seeds tree(-1) and site(-1) by upscaling. Younger sites [TSF 60-150 years] with mature first regeneration trees had average-sized seedbanks for black spruce [12.0-17.9 (10(5)) seeds ha(-1)], whereas subsequent pulse trees that established in SOL depths greater than 35 cm showed highly reduced seed numbers. Sites with second- to fourth-regeneration pulse individuals [TSF c. 350-710 years] had exceptionally small seedbanks of 0.90 (10(5)) and 0.46 (10(5)) seeds ha(-1), respectively. Radial tree growth rate showed a similarly negative response to SOL depth and could potentially be used as an indicator of seed output in plant species. Because the decline in seedbank size was possibly caused by more general environmental stress factors such as reduced nutrient availability, we suggest exploring whether other examples of ecosystems exist where long time since disturbance may lead to reduced seedbank sizes.
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