Grazing Intensity and Its Effects on Functional Diversity Components in Golestan National Park Grasslands

Ruminants and vegetation in natural ecosystems are inherently interdependent, and grazing, as a major ecological disturbance, exerts profound impacts on plant functional traits. This study conducted to evaluate the effects of sheep grazing intensity and topographic aspect on plant functional traits and functional components of grasslands in Golestan National Park. Based on the distance from a watering point, three grazing sites were selected: Site 1 (nearest to the watering point) to Site 3 (farthest), across both western and eastern aspects (six sites in total). From each plant species, five plants were sampled, and two leaves per each species were collected to measure functional traits including leaf area, leaf thickness, leaf length, leaf width, leaf dry matter content (LDMC), and specific leaf area (SLA). At each site, ten 4m² quadrats were established to estimate vegetation cover, and functional indices including community-weighted mean (CWM) traits, functional diversity (FD), and Rao’s quadratic entropy were calculated. Results indicated that grazing significantly affected Rao’s index, functional diversity, and CWM of SLA, LDMC, leaf area, thickness, width, and length. Topographic aspect had no significant effect on any trait, however, the magnitude of variation differed between aspects. Overall, livestock grazing exerted relatively lower effects on Rao’s index, while its impact on FD was more pronounced under moderate grazing intensity. The CWM of leaf traits revealed divergent strategies, with plants tending to increase leaf area rather than leaf thickness as an adaptive response to grazing pressure.