The Effect of Successional stages on Density and Composition of Bird Species (Case study: Shast Kolateh Forest)

the intermediate disturbance hypothesis predicts that communities with intermediate disturbance rates will have the greatest species diversity compared to communities with high and low frequency disturbances. Therefore, a recently disturbed area should be dominated by early-colonizing species or ruderal species. A late successional area is predicted to be dominated by strong competitors and a mid-successional area by a mixture of the tow. Composition of forest community in different successional stages is important as one of the key management issues. This study was conducted to investigate the effects of successional stages on density and composition of bird species and to test the intermediate disturbance hypothesis.

The total numbers of 60 Sampling units were selected and were evenly assigned into 3 treatments. 20 samples were allocated for each of the three treatments including clear cutting, single tree selection logging, and virgin compartments equivalent to the early stage of succession, intermediate stage of succession, and climax stage of succession, respectively. Environmental variables and birds were detected within 60 circle sampling plots with 25m radius. The number of tree species, basal area, height of trees, number of snags, density of grass cover, canopy cover, and litter depth were recorded at each sampling plot. Birds were recorded using point-count method.

Forest structure variables including tree density, Shannon-Wiener diversity index, Camargo evenness index, species richness, tree basal area, density of canopy cover, the number of snags, and the number of trees with more than 20 m in height had significant differences among different successional stages. Moreover, bird community structure including Shanon-Wiener diversity index, Camargo evenness index, and richness index had significant differences among different successional stages. In the period of the study, a total of 24 bird species were recorded. Jay and Chaffinch had the highest abundance in the early successional stage; meanwhile, Black Woodpecker and Coal Tit were the most abundant in the mid successional stage. The Great Spotted Woodpecker, Wren, and Nuthatch were the most prevalent bird species at the mature forest.

bird and tree diversity and richness followed the predictions of the intermediate disturbance hypothesis, being highest in the mid successional plot.