Anthropogenic Pressures Decrease Structural Complexity in Caucasian Forests of Iran

The Arasbaran Protected Area of northern Iran encompasses 160,000 ha of deciduous, broadleaved forest with 78,560 ha recently designated as a United Nations Educational, Scientific, and Cultural Organization's (UNESCO) Biosphere Reserve. Our study objectives were to (1) quantify whether anthropogenic pressures measurably impacted the structural complexity of Arasbaran forests and (2) determine which structural complexity indices were most sensitive to anthropogenic pressures in Arasbaran forests. We identified and sampled three study sites with high, moderate, and low levels of anthropogenic pressures and used nine forest structural indices to develop structural complexity indices. High anthropogenic pressure resulted in aggregated tree distribution, uniformity in tree sizes, and less heterogeneous forest structure. The structural indices particularly sensitive to anthropogenic pressure were diameter differentiation, height differentiation, Gini coefficient, and structural diversity. Structural complexity appears to be a useful method for quantifying the impacts of anthropogenic pressure on montane deciduous forests. Regular sampling of the diameter differentiation index, height differentiation index, Gini coefficient and structural diversity index should be integrated into conservation management plans for the Arasbaran Protected Area.