Bird species richness and diversity along an altitudinal gradient in North of Alborz Mountain (Case study: Kheyrud forest)

A monotonic decline in species richness and diversity with increasing elevation has often been considered as a general pattern، but recent evidence suggests that the dominant pattern is hump-shaped or unimodal with maximum richness occurring at some mid-elevation point. This study was conducted in Kheyrud forest، Mazandaran province. The study area was divided into six elevation levels according to plant communities. Sampling was carried out in mid-spring at 163 random sampling points، which were located with a minimum distance of 250 m apart، as well as a minimum distance of 25 m from the edge of forest. We applied «unlimited radius point count» using «sit and wait» method to count observed and/or heard bird species from dawn until 10:00 am، lasting on average 10 minutes، and avoiding windy and rainy weathers. Our results revealed the existence of significant differences in richness and diversity between elevation classes. Also، we found a hump-shaped pattern of bird species richness and diversity against elevation، reaching the maximum at mid-elevation. These results highlight the importance of forest communities at mid-elevation in North of Alborz Mountain Range and suggest that silvicultural practices should be managed to conserve biodiversity at this elevation zone.