Climate-induced vegetation dynamics associated with the prevalence of charcoal oak disease in Zagros forests

Abstract

Zagros forests are the important ecosystem for water and soil protection. Recently, these forests have been affected by extensive die-back associated with drought and pathogens. In this study, an epidemiological approach was adopted to investigate oak die-back in four sites of unexplored Zagros forests of western Iran, Lorestan. The pathogenic agent was identified and an index of disease severity (IDS) was designated for more than 100 trees in each site. High-risk zone mapping was determined based on disease dispersal and inverse distance weighting (IDW) was utilized for interpolation analysis. To evaluate the precipitation role in the regeneration of oak sites, remote sensing (RS) analysis (using NDVI) was carried out based on the processing of Sentinel-2A satellite images from 2016 to 2019, and the logistic regression (LR) model was used to study the correlation between disease incidence and climatic factors. Mean annual maximum temperature (MAMT), mean annual relative humidity (MARH), mean annual precipitation (MAP), and wet-bulb temperature (WBT) of 10 years were included as independent variables. An ITS-based phylogenetic analysis showed that the isolated fungus infecting the oak trees was Biscogniauxia mediterranea. Also, the Sarab-Doure area with a value of 321.5 ranked as the most infected area followed by Mela-Shabane (232.3) and Sarab-Navkesh (168.6), and Kaka-Reza was the healthy area, Kruskal-Wallis test (chi-square; p-value < 0.0001). Based on the LR model, the highest risk was predicted at MAMT of 28 °C (Waldχ2 = 6.61, p-value < 0.05), MARH of 38% (Waldχ2 = 6.20, p-value < 0.01), and wet-bulb temperature (WBT) of 11 °C (Waldχ2 = 4.84, p-value < 0.02). Compared to the infected areas, the healthy site, Kaka-Reza, had a significantly greater degree of NDVI from 2016 to 2019. In 2019, NDVI value for all studied sites increased which is promising for the rehabilitation of the infected forest areas. IDW analysis showed that the west of the province is more prone to die-back. Overall, this study showed that oak decline syndrome is extremely a drought-induced phenomenon in the Zagros regions.