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- Badeck, FW, et al.
(author)
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Tree species composition in European pristine forests
- 2001
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In: Climatic Change. - 0165-0009. ; 51:3-4, s. 307-347
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Journal article (peer-reviewed)abstract
- The degree of general applicability across Europe currently achieved with several forest succession models is assessed, data needs and steps for further model development are identified and the role physiology based models can play in this process is evaluated. To this end, six forest succession models (DISCFORM, ForClim, FORSKA-M, GUESS, PICUS v1.2, SIERRA) are applied to simulate stand structure and species composition at 5 European pristine forest sites in different climatic regions. The models are initialized with site-specific soil information and driven with climate data from nearby weather stations. Predicted species composition and stand structure are compared to inventory data. Similarity and dissimilarity in the model results under current climatic conditions as well as the predicted responses to six climate change scenarios are discussed. All models produce good results in the prediction of the right tree functional types. In about half the cases, the dominating species are predicted correctly under the current climate. Where deviations occur, they often represent a shift of the species spectrum towards more drought tolerant species. Results for climate change scenarios indicate temperature driven changes in the alpine elevational vegetation belts at humid sites and a high sensitivity of forest composition and biomass of boreal and temperate deciduous forests to changes in precipitation as mediated by summer drought. Restricted generality of the models is found insofar as models originally developed for alpine conditions clearly perform better at alpine sites than at boreal sites, and vice versa. We conclude that both the models and the input data need to be improved before the models can be used for a robust evaluation of forest dynamics under climate change scenarios across Europe. Recommendations for model improvements, further model testing and the use of physiology based succession models are made.
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- Hickler, Thomas
(author)
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Towards an integrated ecology through mechanistic modelling of ecosystem structure and functioning
- 2004
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Doctoral thesis (other academic/artistic)abstract
- Plant physiology, population dynamics and the structure and functioning of ecosystems are closely interrelated. However, these processes are often investigated independently within different subdisciplines of ecology. Mechanistic models of ecosystem structure and functioning combine representations of processes operating at a range of scales and levels of organisation, providing a tool for the description and study of ecosystems as integrated entities. This thesis is based on the development and application of LPJ-GUESS, a modelling framework which integrates processes such as leaf-level photosynthesis, the dynamics of populations competing for resources, and the fluxes of carbon and water between soil layers, vegetation and the atmosphere. LPJ-GUESS currently includes as alternative configurations the Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM) and the General Ecosystem Simulator (GUESS). The results from a study of potential future ecosystem dynamics on the continental scale projected by two DGVMs (LPJ and MC1) suggest that changes in climate and atmospheric CO2 concentrations may severely impact North American ecosystems within the next century (e.g. through vegetation dieback caused by drought), but simulation results depended heavily on the climate scenario and alternative assumptions as to the effects of increasing atmospheric CO2 on carbon assimilation and ecosystem water balance. LPJ-DGVM simulated similar effects of elevated CO2 on forest productivity as observed during four years of CO2 fumigation at a free air CO2 enrichment (FACE) experiment, but it remains uncertain if a CO2 effect of the magnitude commonly simulated by ecosystem models is realistic in the longer term. A comparison of the structure and composition of pristine forests simulated by a number of forest gap models revealed that most of the models have restricted generality because the empirical relationships used to calculate growth are usually not applicable beyond the climatic region for which each particular model was developed. More generally applicable gap models should incorporate process representations derived from generalised plant-physiological mechanisms. The physiology-based gap-type model GUESS was demonstrated to reproduce observed patterns of vegetation dynamics at the plant-type as well as the species level. Finally, a comprehensive hypothesis on the effects of plant hydraulic architecture on water uptake in different types of plants was implemented within the LPJ-DGVM. The hypothesis was validated through a comparison of simulated ecosystem structural and functional features with available data. Comparing the predictions from a number of models that have been applied under standardised conditions has been useful for identifying major drivers and uncertainties in mechanistic ecosystem models, but the future development of the field will crucially depend on evaluation of individual process formulations by field and experimental scientists in close collaboration with modellers. Such approaches could benefit ecology through integration of knowledge from different subdisciplines and by tightening the coupling between empirical studies and models.
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- Hickler, Thomas, et al.
(author)
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Using a generalized vegetation model to simulate vegetation dynamics in northeastern USA
- 2004
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In: Ecology. - : Wiley. - 0012-9658. ; 85:2, s. 519-530
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Journal article (peer-reviewed)abstract
- Models based on generalized plant physiological theory represent a promising approach for describing vegetation responses to environmental drivers on large scales but must be tested for their ability to reproduce features of real vegetation. We tested the capability of a generalized vegetation model (LPJ-GUESS) to simulate vegetation structural and compositional dynamics under various disturbance regimes at the transition between prairie, northern hardwoods, and boreal forest in the Great Lakes region of the United States. LPJ-GUESS combines detailed representations of population dynamics as commonly used in forest gap models with the same mechanistic representations of plant physiological processes as adopted by a dynamic global vegetation model (the Lund-Potsdam-Jena [LPJ] model), which has been validated from the stand to the global scale. The model does not require site-specific calibration. The required input data are. information on climate, atmospheric CO2 concentration, and soil texture class, as 'well as information on generally recognized species traits (broad-leaved vs. needle-leaved, general climatic range, two fire-resistance classes, shade-tolerance class, and maximum longevity). Model predictions correspond closely to observed patterns of vegetation dynamics and standing biomass at an old-growth eastern hemlock (Tsuga canadensis)/hardwood forest (Sylvania Wilderness, Michigan), an old-growth forest remnant from the "Great Lakes Pines Forest" (Itasca State Park, Minnesota), and a presettlement savanna (Cedar Creek Natural History Area, Minnesota). At all three sites, disturbance (wind or fire) strongly controls species composition and stand biomass. The model could be used to simulate vegetation dynamics on a regional basis or under past or future climates and atmospheric CO, levels, without a need for reparameterization.
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