| 1. |
- Kronnäs, Veronika, et al.
(författare)
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Effect of droughts and climate change on future soil weathering rates in Sweden
- 2023
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Ingår i: Biogeosciences. - Göteborg : IVL Svenska Miljöinstitutet AB. - 1726-4170 .- 1726-4189. ; 20:10, s. 1879-1899
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Tidskriftsartikel (refereegranskat)abstract
- In a future warmer climate, extremely dry, warm summers might become more common. Soil weathering is affected by temperature and precipitation, and climate change and droughts can therefore affect soil chemistry and plant nutrition. In this study, climate change and drought effects on soil weathering rates and release of Ca, Mg, K and Na were studied on seven forest sites across different climates in Sweden, using the dynamical model ForSAFE.Two climate scenarios were run, one medium severity climate change scenario from IPCC (A1B) and one scenario where a future drought period of 5 years was added, while everything else was equal to the first scenario. The model results show a large geographical variation of weathering rates for the sites, without any geographical gradient, despite the strong dependence of temperature on weathering and the strong gradient in temperature in Sweden. This is because soil texture and mineralogy have strong effects on weathering.The weathering rates have a pronounced seasonal dynamic. Weathering rates are low during winters and generally high, but variable, during summers, depending on soil moisture and temperature. According to the model runs, the future yearly average weathering rates will increase by 5 %–17 % per degree of warming. The relative increase is largest in the two southeastern sites, with low total weathering rates. At sites in southern Sweden, future weathering increase occurs throughout the year according to the modelling.In the north, the increase in weathering during winters is almost negligible, despite larger temperature increases than in other regions or seasons (5.9 ∘C increase in winter in Högbränna; the yearly average temperature increase for all sites is 3.7 ∘C), as the winter temperatures still will mostly be below zero. The drought scenario has the strongest effect in southern Sweden, where weathering during the later parts of the drought summers decreases to typical winter weathering rates.Soil texture and amount of gravel also influence how fast the weathering decreases during drought and how fast the soil rewets and reaches normal weathering rates after the drought. The coarsest of the modelled soils dries out and rewets quicker than the less coarse of the modelled soils. In the north, the soils do not dry out as much as in the south, despite the low precipitation, due to lower evapotranspiration, and in the northernmost site, weathering is not much affected. Yearly weathering during the drought years relative to the same years in the A1B scenario are between 78 % and 96 % for the sites.The study shows that it is crucial to take seasonal climate variations and soil texture into account when assessing the effects of a changed climate on weathering rates and plant nutrient availability.
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| 2. |
- Lucander, Klas
(författare)
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Direct and indirect pressures of climate change on nutrient and carbon cycling in northern forest ecosystems : Dynamic modelling for policy support
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Northern forest ecosystems play an important role in mitigating climate change by sequestrating carbon (C), while additionally providing and regulating other ecosystem services. A majority of the Swedish environmental quality objects (EQOs) that guide Swedish environmental policy and management are associated with the forest, and they have proven difficult to achieve. Several of them relate to the biogeochemical cycling of C and nutrients. Climate change increases the direct pressure on the forest ecosystems, and affects the C and nutrient cycling through direct pressures such as increasing temperatures and the risk of droughts, and through indirect pressures caused by an increasing demand of renewable energy from forests. Dynamic forest ecosystem models can be a useable tool for holistically studying, understanding and predicting the effects of increasing pressures, as a basis for policy support.This thesis aimed to compare, quantify and analyze the effects of direct and indirect pressures of climate change on forest soil and vegetation processes, and indicators related to nutrient and C cycling in forests, focusing on three of the EQOs that relate to forests, Natural Acidification Only, Zero Eutrophication and Reduced Climate Impact. The dynamic ecosystem model ForSAFE was applied on sites in different climate regions in Sweden, with different exposure to deposition. First, the effect of historical land use change on nitrogen (N) leaching and the risk of eutrophication was studied. Then, effects of intensified forest management on tree growth and concentrations of base cations (BC) and N in the soil solution were investigated. Finally, ForSAFE was used to study the effect of climate change on weathering of BC, which is an important process for providing vegetation with nutrients and for buffering against acidification.Using a combined approach with empirical data and the ForSAFE model, we could conclude that present environmental conditions alone are not enough to predict the risk of N leaching from two geographically close and comparable forest sites. Information about previous land use and moisture conditions was required to be able to correctly model the current dynamics of the soil organic matter. The effect of N fertilization on tree growth and N leaching was studied at three sites in areas with high, intermediate and low nitrogen deposition. The tree growth was the largest at the low deposition site, whereas the effect on N leaching was more pronounced at the high deposition site. These results support the Swedish Forest Agency´s current recommendations for N fertilization, which differ between regions depending on historical and present N deposition. Whole-tree harvesting (WTH), i.e. harvesting of not only stems but also branches and tops at final felling, led to a temporary reduction (20-30 years) of BC concentrations in the soil solution compared to stem only harvesting, in a study on six sites all over Sweden. This could not be explained by higher weathering rates after WTH, which has been suggested in earlier studies. Instead, it could be explained by higher BC leaching and BC uptake in trees during a period after stem only harvesting. Direct effects of climate change led to an increase in weathering rates in all of Sweden, with increased weathering rates year around in southern Sweden but not in winters in Northern Sweden. Future droughts may reduce weathering due to reduced soil moisture, and the risk is the highest in southern Sweden, where low soil moisture during summers already inhibits weathering. The study also highlighted the importance of soil texture and mineralogy for predicting weathering throughout Sweden, moderating the strong effect of temperature on weathering.The results highlighted the potential of using process-based models with high temporal resolution on well-investigated sites, for increasing the process knowledge and providing results useful for policy makers. An important message to policy makers is that site history and soil properties should be taken into account when planning for future forest management recommendations to reach the EQOs.
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| 3. |
- Lucander, Klas, et al.
(författare)
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The Effect of Nitrogen Fertilization on Tree Growth, Soil Organic Carbon and Nitrogen Leaching-A Modeling Study in a Steep Nitrogen Deposition Gradient in Sweden
- 2021
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) fertilization in forests has the potential to increase tree growth and carbon (C) sequestration, but it also means a risk of N leaching. Dynamic models can, if the important processes are well described, play an important role in assessing benefits and risks of nitrogen fertilization. The aim of this study was to test if the ForSAFE model is able to simulate correctly the effects of N fertilization when considering different levels of N availability in the forest. The model was applied for three sites in Sweden, representing low, medium and high nitrogen deposition. Simulations were performed for scenarios with and without fertilization. The effect of N fertilization on tree growth was largest at the low deposition site, whereas the effect on N leaching was more pronounced at the high deposition site. For soil organic carbon (SOC) the effects were generally small, but in the second forest rotation SOC was slightly higher after fertilization, especially at the low deposition site. The ForSAFE simulations largely confirm the N saturation theory which state that N will not be retained in the forest when the ecosystem is N saturated, and we conclude that the model can be a useful tool in assessing effects of N fertilization.
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| 4. |
- Zanchi, Giuliana, et al.
(författare)
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Modelling the effects of forest management intensification on base cation concentrations in soil water and on tree growth in spruce forests in Sweden
- 2021
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Ingår i: European Journal of Forest Research. - : Springer Science and Business Media LLC. - 1612-4669 .- 1612-4677.
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Tidskriftsartikel (refereegranskat)abstract
- The study investigated the effects of forest residue extraction on tree growth and base cations concentrations in soil waterunder different climatic conditions in Sweden. For this purpose, the dynamic model ForSAFE was used to compare theeffects of whole-tree harvesting and stem harvesting on tree biomass and the soil solution over time at 6 different forestsites. The study confirmed the results from experimental sites showing a temporary reduction of base cation concentrationin the soil solution for a period of 20–30 years after whole-tree harvesting. The model showed that this was mainly causedby the reduced inputs of organic material after residue extraction and thereby reduced nutrient mineralisation in the soil. Themodel results also showed that whole-tree harvesting can affect tree growth at nitrogen-poor forest sites, such as the ones innorthern Sweden, due to the decrease of nitrogen availability after residue removal. Possible ways of reducing this impactcould be to compensate the losses with fertilisation or extract residue without foliage in areas of Sweden with low nitrogendeposition. The study highlighted the need to better understand the medium- and long-term effects of whole-tree harvestingon tree growth, since the results suggested that reduced tree growth after whole-tree harvesting could be only temporary.However, these results do not account for prolonged extraction of forest residues that could progressively deplete nutrientpools and lead to permanent effects on tree growth.
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