Throughfall sensitivity of individual Persian oak (Quercus brantii var. persica) trees to the rainfall event in the Zagros region

The increasing trend of declining Brant`s Oak (Quercus brantii Lindl.) trees in the Zagros forests has become the main challenge of forest management in this region. The aim was to investigate throughfall sensitivity of individual Brant`s Oak trees to rainfall magnitude in the Zagros forests of Lorestan and Ilam Provinces. Long-term meteorological data of Khorramabad and Ilam stations and Mann-Kendall test were used to investigate the annual rainfall trend. Five typical individual brant’s Oak trees per region were selected to measure rainfall and throughfall within the leafed period. The mean sensitivity coefficient of throughfall was the linear regression slope between the percentages of changes in rainfall event versus the percentage of changes in throughfall. None of the selected regions showed significant trends for annual rainfall and mean rainfall event size per year (6.6 mm for KhorramAbad against 8.5 mm for Ilam) in the long-term review. In contrast, rainfalls > 10 mm in Ilam and rainfalls < 2 mm in Khorramabad presented significant decreasing and increasing trends, respectively. The sensitivity coefficient of throughfall was on average 3.3 in Ilam and 1.3 in Khorramabad. We found out that the throughfall sensitivity to events below average was more than those of events above average (Ilam 4.3 vs. 1.2 and Khorramabad 1.7 vs. 1.1). If the decreasing trend of rainfall magnitude in Khorramabad and Ilam forests continues, high sensitivity of throughfall of Brant’s Oak trees to rainfall magnitude will lead to reduced throughfall and accelerate the dieback process in these forests.