The importance of various stages of succession in preservation of biodiversity among riparian birds in northern Iran.

Every stage of succession may provide certain species with habitat requirements which are impossible in other stages of succession. This study attempts to evaluate the different stages of succession in terms of composition and structure of bird populations in Hyrcanian forests. Bird-habitat relationships were investigated by comparing vegetation characteristics in three successional stages including late, initial stage, and urban areas. Bird richness, diversity, and abundance were measured within a 25-m radius of each of the 120 sampling points in various stages of succession and urban areas from May to April (2014) in the Ziarat catchment. This study indicated that every stage of succession may support certain species. Based on bird-habitat associations along the various stages of succession, two groups were distinguished. Conventional comparative analysis separated two groups of understory birds: interior specialists and edge specialists. The interior-specialist group was positively correlated with the number of dead trees, tall trees with high values of dbh and height and canopy cover. In contrast, edge specialists groups mainly included terrestrial insectivores and were positively correlated with open area and shrub cover, and percentage of shrub cover between 1 and 2 m in height. In summary, bird communities in Hyrcanian forests are highly dynamic in different vegetation covers suggesting that it is critical to increase diverse and abundant bird populations by conserving forests composed of mosaics of differently disturbed stands and mature forest patches.