Structuring uncertainty and variability in forest dynamics models - Application to coexistence of silver fir and Norway Spruce in mountain forests

Abstract : Practitioners and decision-makers need information on how to conserve mixed Fir and Spruce forests in mountains. To answer this question, we modelled demographic (growth, mortality, recruitment) and allometric functions from field data for the two species. These functions have been implemented in a forest dynamics model to improve the knowledge on natural dynamics of the two species and to test for silvicultural practices. Parameter estimation was performed within a hierarchical Bayesian framework. Estimation permitted to quantify and underline species differences : Fir, the relatively shade-tolerant species compared to Spruce, was less sensitive to self-thinning, had a higher growth and a higher probability of recruitment at low light than Spruce. Models took into account observation errors and spatio-temporal process variability. Individual variability (or so-called intra-specific variability) and temporal variability (interannual and intraindividual variability) were significant and tended to equalize species fitness, inverting species hierarchy locally in space or sporadically in time. First simulations with simulator Samsara2 showed a better behavior of the model when including process variability. Variability led to patterns for stand structuration (tree heights and diameters) and to patterns for basal-area evolution with time which were much more realistic than without variability. Running simulations on a mixed Fir and Spruce stand, we observed a competitive exclusion of Spruce by Fir. Equalizing mechanisms associated to variability were not able to blur the competitive advantage of Fir on Spruce. Nevertheless, transient dynamics of the system was slow and apparent coexistence of the two species lasted for several hundred years.
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Submitted on : Tuesday, September 1, 2009 - 8:00:00 AM
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Ghislain Vieilledent. Structuring uncertainty and variability in forest dynamics models - Application to coexistence of silver fir and Norway Spruce in mountain forests. Sciences of the Universe [physics]. AgroParisTech, 2009. English. ⟨NNT : 2009AGPT0008⟩. ⟨pastel-00005391⟩

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