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Reconnaissance et dynamique récente des habitats forestiers dans le contexte de la Directive Habitats-Faune-Flore

Abstract : In 1992, European natural habitats became items to be conserved in the same way as species were, thanks to the Habitats Directive. This enlarged the scope of action of nature protection public policies to a new level of biodiversity organisation. But the late recognition of the conservation value of habitats and the gaps in their definitions partly explain the absence of time series data at the national scale. This limits our capacity to monitor and assess their conservation status and to adapt conservation measures at the national and local levels. The present thesis work first investigates rapid, formalised approaches for identifying forest habitats. Then, these approaches are used to study the recent dynamics of forest habitats in relation to two substantial changes that occurred in the past decades, i.e., climate warming and the creation of the Natura 2000 network.We first studied the uncertainties linked to the identification of forest habitats when assigning floristic surveys to habitat types by comparing five expert’s judgements with three automatic classification programs. We highlighted high variability among expert judgements, and comparable efficiency between automatic classification programs and expert judgements. We also demonstrated that a limited number of species was sufficient to identify forest habitats, and that surveys carried out in winter could be used too. We thus created time series of standardised data on forest habitats based on different floristic survey sources, whether assigned to a habitat type or not.Secondly, we created 5,701 pairs of historical (before 1987) and recent (after 1997) floristic surveys, and highlighted that 11% of the pairs located in highlands had shifted towards forest habitats characteristic of warmer climate conditions. The increased dominance of these habitats led us to conclude that thermophilisation was underway in highlands. However, no significant shift was observed in lowlands, hence a substantial difference between the thermal requirements of plant communities and current temperatures: a climatic debt is developing. In the face of these different impacts, we proposed that nature protection public policies could be more efficient if they were implemented and prioritised differently in highlands vs. lowlands.Finally, we studied 155 Natura 2000 sites distributed across mainland temperate and mountainous France, and showed that the number of very large trees in the plots where they were observed had increased significantly more inside the network than outside it since its implementation. We thus evidenced that the conservation measures implemented in Natura 2000 forests, which are managed and exploited, have already had positive effects on very large trees – considered as a characteristic of old-growth forests and also used as biodiversity and conservation status indicators of forest habitats.This thesis work was necessary to complement the numerous studies already available at the species and plant community scales, for it is indispensable to aim for the simultaneous conservation of all the levels of organisation of biodiversity to be efficient. Knowing the scope of validity of the tools used to identify forest habitats, but also understanding the recent dynamics of forest habitats and its influencing factors provide useful data to implement surveillance and adapt public policies and management actions, and thereby reach greater efficiency.
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Submitted on : Wednesday, June 23, 2021 - 2:21:22 PM
Last modification on : Friday, August 5, 2022 - 2:38:11 PM
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  • HAL Id : tel-03268758, version 1

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Lise Maciejewski. Reconnaissance et dynamique récente des habitats forestiers dans le contexte de la Directive Habitats-Faune-Flore. Sylviculture, foresterie. AgroParisTech, 2021. Français. ⟨NNT : 2021AGPT0001⟩. ⟨tel-03268758⟩

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