Abstract
The quantitative characterization of landscape structure is critical to assess conservation, and monitor and manage biodiversity. The Mediterranean Basin is a biodiversity hotspot that illustrates the strong relationship between biodiversity and the complexity of the landscape mosaic. Our objective was to test the relevance of two textural indices and one radiometric index (the normalized difference vegetation index (NDVI)) to characterize vegetation structure. These indices could be used as indicators of vegetation composition and organization of four vertical strata when derived from airborne and Pléiades space-borne VHSR imagery. More specifically, we analyzed the influence of the spatial resolution and the radiometric information on the characterization of the landscape structure. Our results indicated that NDVI information at 0.5 m spatial resolution was necessary to be able to incorporate the heterogeneity of vegetation structure. Indices derived from lower resolution NDVI images or different radiometric information than airborne images also proved to be sensitive to vegetation fragmentation and composition. NDVI images brought out details on ligneous/herbs patterns while panchromatic image brought out more details on herbs/bare soil patterns. Combined textural and NDVI indices show strong potential for vegetation structure understanding, allowing detailed mapping. NDVI information shows good potential for applications related to landscape closure dynamics; related habitat degradation indicators caused by shrub encroachment. Panchromatic derived information, on the other hand, provides information relevant in applications focusing grazing management.
Highlights
Heterogeneity of landscape structure is related to ecosystem functions, biodiversity and ecosystem services
In previous work [44], we developed a methodological framework based on textural and radiometric analysis of the normalized vegetation index (NDVI), computed from very high spatial resolution imagery: two textural indices were produced from the Fourier-based textural ordination (FOTO) method applied on NDVI, and complemented by a radiometric index corresponding to the value of the NDVI
Using NDVI information (PNDVI and PNDVIFUS) instead of panchromatic channel (PPAN) for FOTO analysis led to slightly improved estimation of landscape shape index (LSI) for herbs strata (H and G), but the performance among satellite data sources were similar when predicting other strata
Summary
Heterogeneity of landscape structure is related to ecosystem functions, biodiversity and ecosystem services. The quantitative characterization of landscape structure is critical in any evaluation for conservation to report, monitor and manage biodiversity because of the relationship that exists between landscape structure and ecological processes [1,2,3,4]. From a long term perspective, anthropic activity has contributed positively to this remarkable diversity by sustaining landscape heterogeneity with logging and pasture, preventing habitats closure and homogenization [12]. This closure by shrubs and forest is occurring, due to changes in traditional practices, combined with habitat loss and fragmentation induced by land use change [13,14]
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