| 1. |
- Matthes, Heidrun, et al.
(författare)
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Sensitivity of high-resolution Arctic regional climate model projections to different implementations of land surface processes
- 2012
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 111:2, s. 197-214
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses the effects of vegetation cover and soil parameters on the climate change projections of a regional climate model over the Arctic domain. Different setups of the land surface model of the regional climate model HIRHAM were realized to analyze differences in the atmospheric circulation caused by (1) the incorporation of freezing/thawing of soil moisture, (2) the consideration of top organic soil horizons typical for the Arctic and (3) a vegetation shift due to a changing climate. The largest direct thermal effect in 2 m air temperature was found for the vegetation shift, which ranged between −1.5 K and 3 K. The inclusion of a freeze/thaw scheme for soil moisture shows equally large sensitivities in spring over cool areas with high soil moisture content. Although the sensitivity signal in 2 m air temperature for the experiments differs in amplitude, all experiments show changes in mean sea level pressure (mslp) and geopotential height (z) throughout the troposphere of similar magnitude (mslp: −2 hPa to 1.5 hPa, z: −15 gpm to 5 gpm). This points to the importance of dynamical feedbacks within the atmosphere-land system. Land and soil processes have a distinct remote influence on large scale atmospheric circulation patterns in addition to their direct, regional effects. The assessment of induced uncertainties due to the changed implementations of land surface processes discussed in this study demonstrates the need to take all those processes for future Arctic climate projections into account, and demonstrates a clear need to include similar implementations in regional and global climate models.
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| 2. |
- Wolf, Annett, et al.
(författare)
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Future changes in vegetation and ecosystem function of the Barents Region
- 2008
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Ingår i: Climatic Change. - : Springer. - 0165-0009 .- 1573-1480. ; 87:1-2, s. 51-73
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic vegetation model (LPJ-GUESS) is used to project transient impacts of changes in climate on vegetation of the Barents Region. We incorporate additional plant functional types, i.e. shrubs and defined different types of open ground vegetation, to improve the representation of arctic vegetation in the global model. We use future climate projections as well as control climate data for 1981-2000 from a regional climate model (REMO) that assumes a development of atmospheric CO(2)-concentration according to the B2-SRES scenario [IPCC, Climate Change 2001: The scientific basis. Contribution working group I to the Third assessment report of the IPCC. Cambridge University Press, Cambridge (2001)]. The model showed a generally good fit with observed data, both qualitatively when model outputs were compared to vegetation maps and quantitatively when compared with observations of biomass, NPP and LAI. The main discrepancy between the model output and observed vegetation is the overestimation of forest abundance for the northern parts of the Kola Peninsula that cannot be explained by climatic factors alone. Over the next hundred years, the model predicted an increase in boreal needle leaved evergreen forest, as extensions northwards and upwards in mountain areas, and as an increase in biomass, NPP and LAI. The model also projected that shade-intolerant broadleaved summergreen trees will be found further north and higher up in the mountain areas. Surprisingly, shrublands will decrease in extent as they are replaced by forest at their southern margins and restricted to areas high up in the mountains and to areas in northern Russia. Open ground vegetation will largely disappear in the Scandinavian mountains. Also counter-intuitively, tundra will increase in abundance due to the occupation of previously unvegetated areas in the northern part of the Barents Region. Spring greening will occur earlier and LAI will increase. Consequently, albedo will decrease both in summer and winter time, particularly in the Scandinavian mountains (by up to 18%). Although this positive feedback to climate could be offset to some extent by increased CO(2) drawdown from vegetation, increasing soil respiration results in NEE close to zero, so we cannot conclude to what extent or whether the Barents Region will become a source or a sink of CO(2).
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| 3. |
- Yurova, Alla, et al.
(författare)
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Variations in net ecosystem exchange of carbon dioxide in a boreal mire: Modeling mechanisms linked to water table position
- 2007
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Ingår i: Journal of Geophysical Research. - : John Wiley & Sons. - 2156-2202 .- 0148-0227. ; 112:G2
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Tidskriftsartikel (refereegranskat)abstract
- [1] In mires, which occupy large areas of the boreal region, net ecosystem CO2 exchange ( NEE) rates vary significantly over various timescales. In order to examine the effect of one of the most influencing variables, the water table depth, on NEE the general ecosystem model GUESS-ROMUL was modified to predict mire daily CO2 exchange rates. A simulation was conducted for a lawn, the most common microtopographical feature of boreal oligotrophic minerotrophic mires. The results were validated against eddy covariance CO2 flux measurements from Degero Stormyr, northern Sweden, obtained during the period 2001 - 2003. Both measurements and model simulations revealed that CO2 uptake was clearly controlled by interactions between water table depth and temperature. Maximum uptake occurred when the water table level was between 10 and 20 cm and the air temperature was above 15 degrees C. When the water table was higher, the CO2 uptake rate was lower, owing to reduced rates of photosynthetic carbon fixation. When the water table was lower, NEE decreased owing to the increased rate of decomposition of organic matter. When the water table level was between 10 and 20 cm, the NEE was quite stable and relatively insensitive to both changes within this range and any air temperature changes above + 15 degrees C. The optimal water table level range for NEE corresponds to that characteristic of mire lawn plant communities, indicating that the annual NEE will not change dramatically if climatic conditions remain within the optimal range for the current plant community.
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| 4. |
- Gimmi, Urs, et al.
(författare)
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Quantifying disturbance effects on vegetation carbon pools in mountain forests based on historical data
- 2009
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Ingår i: Regional Environmental Change. - : Springer Science and Business Media LLC. - 1436-3798 .- 1436-378X. ; 9:2, s. 121-130
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Tidskriftsartikel (refereegranskat)abstract
- Although the terrestrial carbon budget is of key importance for atmospheric CO(2) concentrations, little is known on the effects of management and natural disturbances on historical carbon stocks at the regional scale. We reconstruct the dynamics of vegetation carbon stocks and flows in forests across the past 100 years for a valley in the eastern Swiss Prealps using quantitative and qualitative information from forest management plans. The excellent quality of the historical information makes it possible to link dynamics in growing stocks with high-resolution time series for natural and anthropogenic disturbances. The results of the historical reconstruction are compared with modelled potential natural vegetation. Forest carbon stock at the beginning of the twentieth century was substantially reduced compared to natural conditions as a result of large scale clearcutting lasting until the late nineteenth century. Recovery of the forests from this unsustainable exploitation and systematic forest management were the main drivers of a strong carbon accumulation during almost the entire twentieth century. In the 1990s two major storm events and subsequent bark beetle infestations significantly reduced stocks back to the levels of the mid-twentieth century. The future potential for further carbon accumulation was found to be strongly limited, as the potential for further forest expansion in this valley is low and forest properties seem to approach equilibrium with the natural disturbance regime. We conclude that consistent long-term observations of carbon stocks and their changes provide rich information on the historical range of variability of forest ecosystems. Such historical information improves our ability to assess future changes in carbon stocks. Further, the information is vital for better parameterization and initialization of dynamic regional scale vegetation models and it provides important background for appropriate management decisions.
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| 5. |
- Gimmi, Urs, et al.
(författare)
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Soil carbon pools in Swiss forests show legacy effects from historic forest litter raking
- 2013
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Ingår i: Landscape Ecology. - 3311 GZ DORDRECHT, NETHERLANDS : Springer. - 0921-2973 .- 1572-9761. ; 28:5, s. 835-846
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Tidskriftsartikel (refereegranskat)abstract
- Globally, forest soils contain twice as much carbon as forest vegetation. Consequently, natural and anthropogenic disturbances affecting carbon accumulation in forest soils can alter regional to global carbon balance. In this study, we evaluate the effects of historic litter raking on soil carbon stocks, a former forest use which used to be widespread throughout Europe for centuries. We estimate, for Switzerland, the carbon sink potential in current forest soils due to recovery from past litter raking ('legacy effect'). The year 1650 was chosen as starting year for litter raking, with three different end years (1875/1925/1960) implemented for this forest use in the biogeochemical model LPJ-GUESS. The model was run for different agricultural and climatic zones separately. Number of cattle, grain production and the area of wet meadow have an impact on the specific demand for forest litter. The demand was consequently calculated based on historical statistical data on these factors. The results show soil carbon pools to be reduced by an average of 17 % after 310 years of litter raking and legacy effects were still visible 130 years after abandonment of this forest use (2 % average reduction). We estimate the remaining carbon sink potential in Swiss forest due to legacy effects from past litter raking to amount to 158,000 tC. Integrating historical data into biogeochemical models provides insight into the relevance of past land-use practices. Our study underlines the importance of considering potentially long-lasting effects of such land use practices for carbon accounting.
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| 6. |
- Göttel, Holger, et al.
(författare)
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Influence of changed vegetations fields on regional climate simulations in the Barents Sea Region
- 2008
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Ingår i: Climatic Change. - : Springer. - 0165-0009 .- 1573-1480. ; 87:1-2, s. 35-50
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Tidskriftsartikel (refereegranskat)abstract
- In the context of the EU-Project BALANCE (http://balance-eu.info) the regional climate model REMO was used for extensive calculations of the Barents Sea climate to investigate the vulnerability of this region to climate change. The regional climate model REMO simulated the climate change of the Barents Sea Region between 1961 and 2100 (Control and Climate Change run, CCC-Run). REMO on similar to 50 km horizontal resolution was driven by the transient ECHAM4/OPYC3 IPCC SRES B2 scenario. The output of the CCC-Run was applied to drive the dynamic vegetation model LPJ-GUESS. The results of the vegetation model were used to repeat the CCC-Run with dynamic vegetation fields. The feedback effect of the modified vegetation on the climate change signal is investigated and discussed with focus on precipitation, temperature and snow cover. The effect of the offline coupled vegetation feedback run is much lower than the greenhouse gas effect.
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| 7. |
- Leuzinger, Sebastian, et al.
(författare)
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A sink-limited growth model improves biomass estimation along boreal and alpine tree lines
- 2013
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Ingår i: Global Ecology and Biogeography. - HOBOKEN 07030-5774, NJ USA : John Wiley & Sons. - 1466-822X .- 1466-8238. ; 22:8, s. 924-932
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Tidskriftsartikel (refereegranskat)abstract
- Aim Despite increasing evidence for plant growth often being limited by sink (meristem) activity rather than source (photosynthesis) activity, all currently available dynamic global vegetation models (DGVMs) simulate plant growth via source-limited processes. For a given climatic region, this may lead to an overestimation of carbon stock per unit surface area, particularly if a model fails to correctly predict forest cover. Our aim is to improve the Lund-Potsdam-Jena (LPJ) DGVM by replacing the source-limited (SoL) tree growth algorithm by a sink-limited (SiL) one. Location Our analysis focuses on the cold tree line at high latitudes and altitudes. We study two altitudinal transects in the Swiss Alps and the northern tree line. Methods We limit annual net primary productivity of the LPJ DGVM by an algorithm based on the annual sum of growing degree-days (GDD), assuming that maximum plant growth is reached asymptotically with increasing GDD. Results Comparing simulation results with observational data, we show that the locations of both the northern and the alpine tree line are estimated more accurately when using a SiL algorithm than when using the commonly employed SoL algorithm. Also, simulated carbon stocks decrease in a more realistic manner towards the tree line when the SiL algorithm is used. This has far-reaching implications for estimating and projecting present and future carbon stocks in temperature-limited ecosystems. Main conclusions In the range of 60-80 degrees N over Europe and Asia, carbon stored in vegetation is estimated to be c. 50% higher in the LPJ standard version (LPJ-SoL) compared with LPJ-SiL, resulting in a global difference in estimated biomass of 25 Pg (c. 5% of the global terrestrial standing biomass). Similarly, the simulated elevation of the upper tree line in the European Alps differs by c. 400 m between the two model versions, thus implying an additional overestimation of carbon stored in mountain forests around the world.
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| 8. |
- Leuzinger, Sebastian, et al.
(författare)
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Poor methodology for predicting large-scale tree die-off
- 2009
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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. ; 106:38
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Tidskriftsartikel (refereegranskat)
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| 9. |
- Manusch, Corina, et al.
(författare)
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The impact of climate change and its uncertainty on carbon storage in Switzerland
- 2014
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Ingår i: Regional Environmental Change. - : Springer. - 1436-3798 .- 1436-378X. ; 14:4, s. 1437-1450
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Tidskriftsartikel (refereegranskat)abstract
- Projected future climate change will alter carbon storage in forests, which is of pivotal importance for the national carbon balance of most countries. Yet, national-scale assessments are largely lacking. We evaluated climate impacts on vegetation and soil carbon storage for Swiss forests using a dynamic vegetation model. We considered three novel climate scenarios, each featuring a quantification of the inherent uncertainty of the underlying climate models. We evaluated which regions of Switzerland would benefit or lose in terms of carbon storage under different climates, and which abiotic factors determine these patterns. The simulation results showed that the prospective carbon storage ability of forests depends on the current climate, the severity of the change, and the time required for new species to establish. Regions already prone to drought and heat waves under current climate will likely experience a decrease in carbon stocks under prospective 'extreme' climate change, while carbon storage in forests close to the upper treeline will increase markedly. Interestingly, when climate change is severe, species shifts can result in increases in carbon stocks, but when there is only slight climate change, climate conditions may reduce growth of extant species while not allowing for species shifts, thus leading to decreases in carbon stocks.
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| 10. |
- Manusch, Corina, et al.
(författare)
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Tree mortality in dynamic vegetation models - A key feature for accurately simulating forest properties
- 2012
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Ingår i: Ecological Modelling. - 1000 AE AMSTERDAM, NETHERLANDS : Elsevier. - 0304-3800 .- 1872-7026. ; 243, s. 101-111
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic vegetation models are important tools in ecological research, but not all processes of vegetation dynamics are captured adequately. Tree mortality is often modeled as a function of growth efficiency and maximum age. However, empirical studies have shown for different species that slow-growing trees may become older than fast-growing trees, implying a correlation of mortality with growth rate and size rather than age. We used the ecosystem model LPJ-GUESS to compare the standard age-dependent mortality with two size-dependent mortality approaches. We found that all mortality approaches, when calibrated, yield a realistic pattern of growing stock and Plant Functional Type (PFT) distribution at five study sites in Switzerland. However, only the size-dependent approaches match a third pattern, i.e. the observed negative relationship between growth rate and longevity. As a consequence, trees are simulated to get older at higher than at lower altitudes/latitudes. In contrast, maximum tree ages do not change along these climatic gradients when the standard age-dependent mortality is used. As tree age and size determine forest structure, our more realistic mortality assumptions improved forest biomass estimation, but indicate a potential decline of carbon storage under climate change. We conclude that tree mortality should be modeled as a function of size rather than age. (C) 2012 Elsevier B.V. All rights reserved.
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