Abstract
Climate change and human activities in particular are important causes of the possible variations in Mediterranean basin forest health conditions. Over the last decades, deciduous oak-forest mortality has been a recurrent problem in central and southern Italy. Despite the perception of increasingly visible damage in oak forests in drought sites, the role of various environmental factors in their decline is not completely clear. Among the modern methods of monitoring terrestrial ecosystems, remote sensing is of prime importance thanks to its ability to provide synoptic information on large areas with a high frequency of acquisition. This paper reports the preliminary results regarding a replicable and low cost monitoring tool planned to quantify forest health conditions based on the application of the Normalized Difference Vegetation Index (NDVI), using the diachronic images provided by the Sentinel-2 satellite. The study area is represented by a peri-urban forest of natural Mediterranean deciduous oaks, characterized by a high variability in the composition of the species and in the silvicultural structures. In order to monitor the health conditions of a specific forest canopy cover with remote sensing data, it is necessary to classify the forest canopy cover in advance to separate it from other species and from the Mediterranean scrub. This is due to the spatial distribution of vegetation and the high rate of biodiversity in the Mediterranean natural environment. To achieve this, Light Detection and Ranging (LiDAR) data, forest management data and field sampling data were analyzed. The main results of this research show a widespread decline in oak health conditions over the observed period (2015–2017). Specifically, for the studied area, thanks to the specific localization of the oak canopy cover, we detected a high potential concerning the Sentinel-2 data application in monitoring forest health conditions by NDVI application.
Highlights
Forest ecosystems are an essential economic and environmental resource widespread in most regions of the world
According to Gongalton [28], this layer grid was validated referring to the kappa index of agreement (KIA) using 3737 pixels randomly distributed in the territory and validatedd by ffiield surveys and by an analysis of aerial photos referring to 2017
IInn this regard, the results show a decrease in the average Normalized Difference Vegetation Index (NDVI) value of the pixels ranging from 0.9 to 0.87, from July 2015 to JJuullyy 22001166, and this decreases further to an average value off 00..8855 iinn JJuullyy 22001177, Ffigure 5
Summary
Forest ecosystems are an essential economic and environmental resource widespread in most regions of the world. In the Mediterranean basin, a region characterized by long droughts, extreme weather events, a generally low precipitation rate coupled with fragile land susceptible to degradation processes (e.g., erosion, salinization, pollution, sealing) and human pressure due to the continuous development of both scattered and compact urban settlements, it is possible to identify a wide range of disturbing factors that threaten natural forests. For these reasons, the Mediterranean basin has been identified as one of the hot spots of climate change with major risks in the near future, including warmer and drier conditions. In Italy, since the 1980s, drought-induced deaths have been detected in the southern regions of oak forests, which show a worrying trend of increasing damage, as in other areas of the Mediterranean basin
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