Vplyv prízemnej vegetácie a podrastu na priebeh fenologickej krivky bukových porastov odvodenej z údajov MODIS / Effect of understory vegetation and undergrowth on course of phenological curve of beech forests derived from MODIS

Abstract

Vegetation index NDVI derived from satellite data MODIS (product MOD09) was used for monitoring of phenological phases of beech stands. The effect of leaves of upper story and undergrowth trees, understory vegetation, bark of thin and thick branches, trunk, and litter on NDVI value was identified and quantified for determination of the onset of phenological phases in five beech stands. The phenological observations were carried out in the spring 2011. Phenological curves were modelled for each stand. Inputs were NDVIsat derived from MODIS. The NDVI value for each component was determined from spectral analyses, and its percentage was estimated. Consequently, NDVIₘₒdₑₗ values were calculated for each stand and compared with NDVIₛₐₜ. We found out that NDVIₛₐₜ values are systematically biased from NDVIₘₒdₑₗ values a quotient q was established to revise this biased NDVIₛₐₜ values. Possibilities for satellite long-term phenological monitoring resulted from the quantified effect of individual forest components on NDVI value. The 100% leaf onset is the most suitable phase for phenological monitoring of the canopy trees component. The 100% leaf budburst is suitable phenophase for monitoring of forest stands phenology.