Quantifying canopy fractional cover and change in Fanjingshan National Nature Reserve, China using multi-temporal Landsat imagery

This letter explores factors affecting the quantification and mapping of forest canopy fractional cover (CFC), and explores causes of CFC change. CFC was quantified using a simple linear mixture model based on the modified soil-adjusted vegetation index (MSAVI) derived from Landsat TM surface reflectance data of Fanjingshan National Nature Reserve (FNNR) in China. Different soil and vegetation endmembers were tested to analyse the sensitivity of the mixture model. Illumination effects due to topographical variability are found to influence MSAVI and therefore CFC estimates. Implementing an illumination stratification that selects different closed canopy endmembers for different topographic-related illumination strata generally minimizes these effects. The spatial distribution and possible causes of CFC change were examined. Most changes in CFC over the 15-year study period appear to have resulted from anthropogenic activities, at least based on the precision constraints of Landsat-derived CFC change estimates and limited high spatial resolution imagery used in a mostly visual verification of patches with low CFC and reduction in CFC between image dates.