Forest structural complexity in habitats with presence and absence of the Caucasian grouse (Lyrurus mlokosiewiczi) in the Arasbaran biosphere reserve, Iran

Abstract Forest structural complexity can vary among different types of habitat and is defined by the dependency of species on resources. The positive relationship between structural complexity and forest functions is of increasing interest to researchers. In this study, we focused on the structural complexity of the habitat of the Caucasian grouse ( Lyrurus mlokosiewiczi ), which is an indicator species in mountain forest habitats in the Arasbaran biosphere reserve, Iran. Data were collected from previously identified presence and absence locations of this species. Three sample plots were chosen at random in each area (six sample plots in total). The main parameters measured were type of species, diameter and height of trees, shrub and regeneration, and number and diameter of coarse woody debris. Overstorey tree species richness differed in the absence and presence locations, with 16 and 12 species respectively. Understory species richness was also different in the absence (15 species) and presence (10 species) locations. The Caucasian grouse was observed in the site with trees smaller than 10 cm and a balanced density of trees smaller than 5 cm. Overall, the SCI was higher in the absence location than in the presence location. The heterogeneity of the stand structure in grouse habitats was low. The area where the Caucasian grouse was present was characterized by small numbers of dead trees and also low log volume. Maintaining a heterogenous forest structure is important for protecting this species. Conservation of fruit trees that are fed on by the grouse is also recommended.