Spatial distribution of tree crown dieback and its relation with some environmental factors and road network

Lately, the tree crown dieback is encountered as an important problem in the northern forests. The main goal of this study is investigation on spatial distribution of the tree crown dieback in relation to primary and secondary topography characteristics and distance from river and roads using terrain analysis and GIS. A 100×500 meters random systematic sampling network with 0.1 ha sample area was designed in GIS and applied on the district 1, Dr. Bahramnia educational forest. The location of trees contain the tree crown dieback were registered using GPS in each sample and was imported to GIS. The digital elevation model (DEM) of the study area was generated using the interpolating of contour lines from 1:25000 topography map and the primary and secondary topography characteristics and distance from river and roads were produced using terrain analysis and GIS. The digital values of location of trees contain the tree crown dieback were extracted on produced maps. The impact of selected factors on the tree crown dieback was assessed using relative effect (RE) method and principal component analysis (PCA). The results showed that the north aspect, 300-400 meter mean sea level altitude, the 30-40 percent slop, the 150-200 meters distance from rivers, the 1-100 meters distance from roads, the shaded relief of 0.4-0.5, solar radiation of 1500-1750, wetness of 15-17.5, profile curvature of 0.1-0.25 and plan curvature of 0.3-0.6 were more effective on the tree crown dieback. The results of PCA analysis also showed that four factors of solar radiation distance from road and river and slop with attending on four axes and 75 percent variances have been effective on tree dieback.