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Master Thesis

Évaluation de la pression sylvicole en fonction de l’accessibilité des parcelles : exemple du secteur des Quatre Montagnes (Isère)

Abstract : While numerous works have shown that the road network impacts forest biodiversity, the influence of the distance with forest service on the forest stands of a point of view of the management (capital on foot) and of the forestry, is not approached on the literature. With the development of airborne laser scanning (ALS), it is now possible to map the spatial variability of forest stand parameters at a resolution of about 20 m. Besides, Geographical Information Software (GIS) model and quantify forest accessibility (Sylvaccess) based on the forest network and digital terrain models. Euclidean distance was also calculated in order to reproduce the methodology on another study area do not have accessibility model. The objective of this study is to quantify the link between forest parameters and accessibility (measured as the harvesting distance), while taking into account external environmental and forest ownership. The study area is located in the Vercors mountain (French Alps), where ALS data were acquired over 50 km2. Preliminary data analysis showed that outside accessibility, the main factors affecting forest variables in this area are topographical factors, geology and forest ownership. Analyses of covariance (ANCOVA) were then performed with forest parameters as the dependent variable and slope, altitude, harvesting distance, geology and forest types as independent variable. The analysis was conducted separately for private and public forests because the characteristics are very different between these two categories. The use of the euclidean distance or the distance of the model doesn’t influence the quality of the models (R² = 43% for public forests and R² = 20% for private forests). Nevertheless, the model using the Sylvaccess distance is more operational for forest managers because obstacles and topography are integrated. The model estimates an increase of the basal area of 1m²/ha, each time the skidding distance increasing of one kilometer. The results of the modeling are the same for public and private forests. Although estimates from LiDAR data are not error-free, the very high number of pixels used as observations in the analysis allowed to detect a very weak relationship with harvesting distance, which would probably not have been possible by considering a smaller number of field plots. While those results have to be confirmed with data from another study area, they show that remote sensing data coupled with GIS models allow to highlight dynamics which are difficult to observe from the ground, quantifying the spatial variability of basal area according to the skidding distance.
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Master Thesis
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Jérémy Bellier. Évaluation de la pression sylvicole en fonction de l’accessibilité des parcelles : exemple du secteur des Quatre Montagnes (Isère). Biodiversité et Ecologie. 2014. ⟨dumas-01109332⟩

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