Analysis of the decline status of Zagrosian oak forests using spatial statistics (Case study: Zarab forests of Ilam)

Recently, forest decline has outburst in Zagros forests region in the west of Iran, especially in Ilam province. In this research, we selected an 83 ha infected forest area in Zarab, Ilam and the dried trees were fully investigated for variables including dbh, height, drought intensity, crown cover, origin and Cartesian coordinates. Their spatial structure, spatial patterns and spatial correlation were analyzed using variogram analysis, O-ring statistic and Mark correlation function (MCF), respectively. Results showed that the density of dried trees was 27 N/ha which is more comprised of coppice trees in small and medium diameter classes. A cluster spatial pattern of dried trees was determined up to 35 m and after that it was uniform, implying dried trees created patches with 3850 m2 surface area. Variogram analysis showed that only dbh and drought intensity of dried trees had strong spatial structure which was mapped using Kriging interpolation method of Geostatistics. Mark correlation function graph showed that adjacent dried trees were similar according to drought intensity while were not similar based on their dbh. In general, the results illustrated that all of the trees in the studied area were infected by drought with different biometric characteristics as well as at different geographical aspects. These results can be used as an instruction for sustainable management of the stands based on their spatial characteristics.