Investigating the Oak Decline in different Crown-Dimensions in Middle Zagros Forests (Case Study: Ilam)

Oak decline is an eminent factor, which has a significant role in degradation and change in Zagros forests. The goal of present study was to assess the crown surface area of oak trees in Sarableh forests, Ilam province. For this purpose, permanent sample plots were used. Eighty sample plots with 10 Ar area were applied based on systematic-random method in a 150×200 survey network in 120 ha. The crown diameters and oak decline were measured. Oak decline was classified in five classes (very high, high, medium, no decline). The inventory was conducted in 2012 and 2014. The Mann-Whitney test was used to compare the oak decline in two inventory times. The results showed that the trees in very high and high decline classes (total of two classes) were 13.6% in 2012 and it is increased to 25.4% in 2014 (to be an 11.8% increase). The changes in forest decline were significant at decline classes (P≤0.01). The highest oak decline was observed in two m2 crown area and the maximum healthy trees were found in 14 m2 crown area. Our result revealed that trees with small crown area are more engaged by forest decline. In order to managing the forest engaging to oak decline in Ilam province and the rehabilitation of these forests , it is recommended the trees with small crown area (up to seven m2) should be more considered in terms of forest rehabilitation and tending.