ASSESSMENT OF LIGHT ENVIRONMENT FOR HERBACEOUS VEGETATION IN SEMI-NATURAL GRASSLAND USING TIME-SERIES UAV DATA

Abstract. Grasslands are important ecosystems containing unique biodiversity. It has been reported that some herbaceous species inhabiting grassland reduced its number and became extremely rare. Restoring these species as well as maintaining the grassland are key issues. Light environment is crucial for plant growth and survival. It is particularly important to evaluate light environment of microsite for herbaceous vegetation. In this paper, NDVI, vegetation biomass and gap fraction were estimated using time-series UAV data, and compared to photosynthetic photon flux density (PPFD), solar radiation and gap fraction measured by traditional ground-based techniques to validate its utility in accessing light environment for herbaceous vegetation in semi-natural grassland. The results showed that UAV derived variables displayed overall good correlations with ground derived variables: relative PPFD, relative solar radiation and gap fraction. Analysis of time-series UAV data revealed that UAV derived NDVI and vegetation biomass were not suitable for evaluating light environment when vegetation attains its maturity. UAV derived gap fraction was most resilient to change of vegetation growth. UAV derived methods have advantage in evaluating light environment in microsite without disturbing valuable plants and would help restoring semi-natural grassland.