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Tree community assembly in New Caledonia's lowland forests facing a heterogeneous environment in space and time

Abstract : The aim of this thesis is to study how spatio-temporal variations of the environment affect the composition of New Caledonia's fragmented lowland forests, using a multi-scale approach - regional, landscape, local scales - and by integrating deterministic and stochastic aspects of ecological dynamics. Using a functional approach, we first analyze how regional and local water availability gradients influence community assembly processes from the regional species pool. In a second step, we combine empirical data and mechanistic modelling to assess the temporal effect of fragmentation and habitat loss on neutral extinction-immigration dynamics and environmental filters. At the local scale, we analyze the successional trajectories guiding the spatio-temporal dynamics of forest recolonization on degraded environments under the influence of edge effects. At the regional level, we show that variations in annual rainfall patterns generate environmental filters that determine the composition of species subpools at the landscape level. Topography then plays a major role in assembling communities at the landscape level, filtering species according to their drought resistance or resource use strategies based on the precipitation context. The balance between immigration and extinction in communities depends on landscape structure, but these stochastic processes are slow, and we show that their influence is delayed in case of rapid landscape change. On the other hand, edge creation affects environmental filters and entails rapid changes community composition. Finally, our results reveal that the recolonization of the forest on disturbed environments follows a succession trajectory driven by deterministic processes, and characterized by a transition from stress resistance to competition for light. Overall, this thesis provides new elements for understanding the spatio-temporal dynamics of New Caledonia's forests, as well as for planning their conservation.
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Submitted on : Wednesday, January 13, 2021 - 2:36:49 PM
Last modification on : Thursday, February 11, 2021 - 11:13:13 AM


  • HAL Id : tel-03108890, version 1


Grégoire Blanchard. Tree community assembly in New Caledonia's lowland forests facing a heterogeneous environment in space and time. Sciences de l'environnement. Université de Montpellier, 2019. Français. ⟨tel-03108890⟩



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