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  • 1.
    Manusch, C
    et al.
    ETH, Dept Environm Syst Sci, Inst Terr Ecosyst, CH-8092 Zurich, Switzerland.
    Bugmann, H
    ETH, Dept Environm Syst Sci, Inst Terr Ecosyst, CH-8092 Zurich, Switzerland.
    Heiri, C
    Swiss Fed Inst Forest Snow & Landscape Res, CH-8903 Birmensdorf, Switzerland.
    Wolf, Annett
    Linnéuniversitetet, Universitetsförvaltningen. ETH, Dept Environm Syst Sci, Inst Terr Ecosyst, CH-8092 Zurich, Switzerland.
    Tree mortality in dynamic vegetation models - A key feature for accurately simulating forest properties2012Inngår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 243, s. 101-111Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 2.
    Manusch, Corina
    et al.
    ETH, Switzerland.
    Bugmann, Harald
    ETH, Switzerland.
    Wolf, Annett
    ETH, Switzerland.
    Sensitivity of simulated productivity to soil characteristics and plant water uptake along drought gradients in the Swiss Alps2014Inngår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 282, s. 25-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Future climate scenarios indicate a change in precipitation patterns, i.e. in frequency and intensity, and thus a change of water availability for plants. The consequences for ecosystems can be evaluated using dynamic vegetation models (DVMs), but the description of soil properties and assumptions about root distribution and functionality are rather simplistic in many DVMs. We use the LPJ-GUESS model to evaluate (i) the usage of high-quality data sources for describing soil properties and (ii) the assumptions regarding roots. Specifically, we compare simulated carbon uptake when applying the frequently used FAO global soil map vs. soil measurements from 98 sites in the driest regions of Switzerland. The multilayer soil data were used either as observed (non-aggregated) or aggregated into two layers. At sites with low water holding capacities (whc < 100 mm) and a low precipitation sum that does not compensate for small whc, the FAO data led to a higher annual net primary productivity (ANPP) than when using observed soil data. In contrast under wetter conditions, the description of soil data did not make much difference. A comparison of different rooting strategies revealed a higher importance of vertical root distribution per soil layer than variable rooting depths due to the overriding effect of the hydrological assumptions in the model. We conclude that it is pivotal to use high-quality soil data and possibly to refine the hydrological assumptions in DVMs when attempting to study drought impacts on ecosystems. (C) 2014 Elsevier B.V. All rights reserved.

  • 3. Tamburino, Lucia
    et al.
    Bravo, Giangiacomo
    University of Torino / Collegio Carlo Alberto.
    Mice in Wonderforest: Understanding mast seeding through individual-based modelling2013Inngår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 250, s. 34-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mast seeding is the synchronous production of large amounts of seeds at long intervals in plant populations. It is observed in several genera and its explanation remains controversial. To test one of the most popular hypotheses, predator satiation, we developed a virtual experiment based on an individual-based model reproducing the interaction between trees and seed predators in a simulated forest. This allowed a direct comparison between masting and no-masting cases, as would have been impossible in reality. The large differences observed between the two scenarios strongly supported the hypothesis. At the same time, a second mechanism similar to the classic paradox of enrichment seemed to play a crucial role, working in synergy with predator satiation to keep in check seed predator populations. More generally, we showed that the resource distribution over time can deeply affect population dynamics, even when the overall amount of the resource is kept constant.

  • 4.
    Wolf, Annett
    Linnéuniversitetet, Universitetsförvaltningen. Forest Ecology, Institute of Terrestrial Ecosystems, Department of Environmental Science, ETH Zurich, Universitätsstrasse 16, CH-8092 Zurich, Switzerland.
    Estimating the potential impact of vegetation on the water cycle requires accurate soil water parameter estimation2011Inngår i: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 222, nr 15, s. 2595-2605Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is well known that vegetation dynamics at the catchment scale depends on the prevailing weather and soil moisture conditions. Soil moisture, however, is not equally distributed in space due to differences in topography, weather patterns, soil properties and the type and amount of vegetation cover. To elucidate the complex interaction between vegetation and soil moisture, the dynamic vegetation model LPJ-GUESS (Smith et al., 2001), which provides estimations of vegetation dynamics, but does not consider lateral water fluxes was coupled with the hydrological TOPMODEL (cf. Beven, 2001) in order to be able to evaluate the importance of these lateral fluxes. The new model LG-TM was calibrated and validated in two climatically different mountain catchments. The estimations of runoff were good, when monthly and weekly time scales were considered, although the low flow periods at winter time were somewhat underestimated. The uncertainty in the climate induced change vegetation carbon storage caused by the uncertainty in soil parameters was up to 3–5 kg C m−2 (depending on elevation and catchment), compared to the total change in vegetation carbon storage of 5–9 kg C m−2. Therefore accurate estimates of the parameters influencing the water holding capacity of the soil, for example depth and porosity, are necessary when estimating future changes in vegetation carbon storage. Similarly, changes in plant transpiration due to climatic changes could be almost double as high (88 mm m−2) in the not calibrated model compared to the new model version (ca 50 mm m−2 transpiration change). The uncertainties in these soil properties were found to be more important than the lateral water exchange between grid cells, even in steep topography at least for the temporal and spatial resolution used here.

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