A New Index for Assessing Tree Vigour Decline Based on Sentinel-2 Multitemporal Data. Application to Tree Failure Risk Management

ABSTRACT

Detection and monitoring of vigour decline are certainly useful for forest managers to support future interventions. In this work a new index, from Sentinel-2 retrieved NDVI (Normalized Difference Vegetation Index) time series, is proposed, hereafter called ‘normalized Vegetation Vigour Index (nVVI)’, which is specifically designed to quantify and map tree vigour decline. Results proved that nVVI is negatively correlated to tree age (r = −0.815, p < 0.001): older or unhealthy trees showed low nVVI values; younger trees showed high nVVI possibly related to vigour increase. nVVI was, finally used within a Decision Support System (DSS) specifically designed to support tree failure risk management in wide areas, like the natural parks. It was found that such approach can result in an economic saving of about 52% compared to more traditional tree stability surveys. If present, a nVVI map can highlight incipient vegetative anomalies permitting tree stability surveys to be better prioritized.