Remote sensing for mapping Natura 2000 habitats in the Brière marshes (France, Loire-Atlantique, 44) : setting up a long-term monitoring strategy to understand changes

Context :

This work is part of a doctoral thesis being carried out on the marshes of the regional natural park of Brière (France, Loire-Atlantique, 44). The main purpose is to study the changing dynamics of plant formations on the entire sector, in order to enable prospective modeling. The natural park of Brière would like to set up a Biodiversity Observatory in order to gain a better understanding of the functioning of this fast-changing ecosystem. Field sampling efforts are very costly and time-consuming, and are hampered by difficult access to the extensive marsh areas (over 18 000 hectares). As a result, existing maps are not spatially exhaustive and present a simplification of habitats mosaics, making modeling impossible.

Purposes :

The aim of the study is to (1) map the current distribution of plant communities (2) identify their dynamics through the historical evolution of potential habitats in relation with hydrology, invasion by trees, agro-pastoral and traditional practices and (3) deduce the marsh's capacity for stability and resilience in the coming decades.

Materiel and methods :

The first step involves an hyperspectral and LiDAR aerial survey across the whole sector. It is completed by the acquisition of a World View 3 scene, in order to assess the contributions of the different types of data. At the same time, floristic field surveys were carried out to characterize the textural and spectral variability of the images. Automatic classification methods were then applied.
Based on the results obtained from the mapping, we can assess the quality of the biodiversity in the Brière region. Indeed, plant formations differ in terms of stability and resilience.

Main results :

A complete mapping of the 18 000 hectare of marshland has been carried out, according to the Eunis declination, at a spatial resolution of 1.30 meter. This includes areas not yet mapped. In addition to these classic communities, we have also added invasive exotic species, which are very present in the Brière region. The relation between biodiversity loss and human factors from the Middle Ages to the present day has been established.
Standardized data acquisition and processing methods have been set up to enable long-term changes monitoring.