| 1. |
- Drobyshev, Igor, et al.
(author)
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Influence of annual weather on growth of pedunculate oak in southern Sweden
- 2008
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In: Annals of Forest Science. - : INRA, EDP Sciences. - 1286-4560 .- 1297-966X. ; 65:5, s. 512-512
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Journal article (peer-reviewed)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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| 2. |
- Drobyshev, Igor, et al.
(author)
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Lifespan and mortality of old oaks - combining empirical and modelling approaches to support their management in Southern Sweden
- 2008
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In: Annals of Forest Science. - : Springer Science and Business Media LLC. - 1286-4560 .- 1297-966X. ; 65:4, s. 401-401
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Journal article (peer-reviewed)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.
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| 3. |
- Drobyshev, Igor, et al.
(author)
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Relationship between crown condition and tree diameter growth in southern Swedish oaks
- 2007
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In: Environmental Monitoring & Assessment. - : Springer Science and Business Media LLC. - 1573-2959 .- 0167-6369. ; 128:1-3, s. 61-73
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Journal article (peer-reviewed)abstract
- We studied correlation between crown conditions and tree-ring widths in 260 trees of pedunculate oak (Quercus robur L.) growing on 33 sites in southern Sweden. The tree-ring increment over 1998-2002 was highest in trees with healthy crowns, intermediate in trees with moderately declined crowns, and lowest in trees with heavily declining crowns. The time period with significant correlation between crown status and tree-ring increment varied between 10 years (given autocorrelation in tree-ring chronologies preserved) and 4 years (autocorrelation removed). In pairwise comparisons of three crown classes, differences in tree-ring increment between trees with healthy crowns and trees with heavily declining crowns were the most pronounced, Fisher LSD P value staying below 0.05 over 13 years (autocorrelation preserved ) or 4 years (autocorrelation removed). Over two 5-year periods (1993-1997 vs. 1998-2002) the cumulative increment increased significantly for trees with healthy crowns, did not change in trees with moderately declining crowns, and significantly decreased in trees with heavily declining crowns. For trees with healthy crowns, this dynamics may represent growth recovery after 1992 drought. Instead, oaks with defoliation above 60% appear to reach a threshold in their ability to recover growth. At sites on nutrient-poor soils cumulative increments over 1998-2002 differed significantly among trees with different crown condition and no differences were observed at sites on nutrient-rich soils. Analyses and interpretation of the oak growth trends as recovered from tree-ring chronologies may be improved by controlling for the crown status of the trees sampled, e.g., by using sampling strategy that would represent the average crown and growth conditions of the sites.
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| 4. |
- Drobyshev, Igor, et al.
(author)
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Temporal mortality pattern of pedunculate oaks in southern Sweden
- 2007
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In: Dendrochronologia. - : Elsevier. - 1125-7865 .- 1612-0051. ; :24, s. 97-108
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Journal article (peer-reviewed)abstract
- Decline of the oak forests decline in southern Sweden has been reported for more than two decades. Little empirical data exists, however, to study the temporal pattern of the phenomenon in detail. In this study we quantified the temporal pattern of non-windfall oak mortality by analyzing the dataset of 44 dendrochronologically dated dead pedunculate oak (Quercus robur L.) trees. We compared tree-ring chronologies from recently dead and living trees from the same sites (number of sites = 13) located in the nemoral and boreo-nemoral zones in southern Sweden. For each dead tree, tree-ring chronologies were analyzed for the presence of pre-death growth depressions. A growth depression was defined as a period ( of one or more years) when growth remained below the 5%, 7%, or 10% quantiles of the ring-width distribution obtained from living trees for a particular year and site. The most recent peak in oak mortality occured around the year 2000. Growth depressions were recorded in 80% (n=35) of all dead oaks and were most prominent during the 1990s. While some oaks showed an obvious reduction in growth over several decades, 51% of the dead trees had growth depression for at least 4 years prior to death. Although diameter growth rate differed between living and recently dead trees for at least 30 years, this difference started to amplify in late 1980s-early 1990s. Presence of pre-death growth depression in tree-ring chronologies implies that (a) non-windfall mortality of oaks is a decade-long process and (b) the actual death event might be lagged behind the timing of the mortality-inducing factors. ANOVA revealed significant differences in tree responses to the drought year 1992. The cumulative growth increment ration between 1992-1994 and 1989-1991, was higher in living trees than in those that had recently died. We suggest that the spring and summer drought of 1992 resulted in the mortality of oaks that was observed in southern Sweden at the end of the 20th centurey. If this time lag exists, it may complicate analyses of decline-related factors and the choise of appropriate actions by forest managers. We conclude that studies of oak decline may benefit from widening the perspective to include several decades preceding the sampling year.
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