Oak decline in the Mediterranean basin: a study case from the southern Apennines (Italy)

It is known that the decline of oaks forest can be triggered by an increase of climatic anomalies such as heat waves, droughts, and extreme cold. The present study aims to deepen the relationships between climate anomalies and oak decline basing on in-field observations made in the Lucanian Apennine (southern Italy) during summer 2017. Remote sensing was used to identify those areas affected by vegetation decline. A comparison of the climatic conditions recorded in 2015 and 2017 was carried out, these years being the hottest and the driest, respectively, since 1800. Satellite images and remote sensing data [Normalized Difference Water Index (NDWI), Temperature Condition Index (TCI)], and ground-based collected data [(Decline Severity (DES), Deficit/Surplus (D/S), Rainfall Anomaly Index (RAI), Standardized Precipitation Index (SPI)] were processed using GIS techniques to evaluate spatial distribution and time-scale evolution of the damage by oak decline. The results show that despite the heat peaks reached in 2015, it was not possible to highlight any clear sign of oak decline based on satellite images for that year. On the contrary, these signs were found to be evident by observing the satellite images of 2017 and confirmed by the Decline Severity assessment made in the field and further supported by NDWI and DNDWI indexes. Regarding possible factors that may have triggered the 2017’ oak decline in the study area, it is not possible to provide a definite answer, at present. In this work it was hypothesized that an important role could have been played by the drastic reduction of rainfalls during the first semester of the year