Remotely sensed vegetation biophysical parameters as proxies for primary productivity estimation

Continuous availability of Sentinel data has opened a new era for timely assessing vegetation biophysical and biochemical parameters - several identified as Essential Biodiversity Variables (EBVs) under GEOBON EBVs classes- over large areas. Such parameters like leaf area index (LAI) and chlorophyll content are important indicators of vegetation photosynthetic capacity, health, stress and productivity. While some of these relationships (e.g. the link between canopy chlorophyll content and vegetation stress) are well-studied, the relationship between plant biochemical and biophysical parameters and vegetation productivity (i.e. net primary productivity, NPP) needs further investigation. In this study, we estimated leaf area index (LAI), the fraction of vegetation functional type and canopy chlorophyll content (modulated using leaf chlorophyll content and LAI) using phenological parameters, empirical approaches and temporal Sentinel-2 data in a temperate mixed forest ecosystem of the Bavarian Forest National Park, Germany. The remotely sensed biophysical products were validated using a recent landcover map of the national park, temporal in situ measurements of LAI and chlorophyll content. The relationship between these variables and NPP calculated using vegetation index universal pattern decomposition approach was then studied to determine which of these variables is a better indicator of productivity and can be used as a proxy for estimation of NPP. Our results showed that among studied parameters, canopy chlorophyll content, which represents both leaf pigments and vegetation abundance, has a strong direct relationship with NPP and hence provide a critical understanding of plant functioning. The study demonstrates that remotely sensed vegetation biophysical parameters- that are becoming more and more readily available, thanks to the European Space Agency missions- can be used as proxies for estimation of the primary productivity, which need a wide array of canopy geometry and life-cycle dynamics, at large scales. These findings would facilitate and support the myVARIABLE pilot of the EuroGEOSS Showcases initiative (e-shape), developing primary productivity as a remotely sensed EBV describing ‘Ecosystem Physiology’ and ‘Species Physiology’.