Investigating spatiotemporal changes in greenness of Zagros Oak forests in response to drought

Climate changes in Iran, which have mainly manifested in the form of intensifying periods of drought and increasing temperature, can have profound effects on the forest ecosystems of Zagros in the west of Iran. In this study, the drought trend (with PDSI index) and its effects on the spatial-temporal dynamics of EVI greenness index from MODIS sensor were investigated through correlational relationship in the statistical period from 2000 to 2020 in Zagros oak forests in Kohgiluyeh and Boyer-Ahmad province. To determine the greenness index threshold value, sampling at 20 points in the forests of the province and EVI index values in these areas were used. The results showed that the greenness threshold value of EVI in these forests was at the maximum level in June. The greenness index value and the area of the oak forests of the province have decreased during the study period. The peak greenness of the oak forests of the province had a significant sensitivity to changes in rainfall and drought at the end of the cold period of the year and in the spring season. The negative phases of the drought indices have been completely consistent with the periods of greenness loss. The EVI, as an index of forest greenness, has shown a high sensitivity to the PDSI drought index. The PDSI index has also been able to explain 0.74 of the spatial changes of EVI in the three months of April, May, and June.