Assessing the response of rare and common plant species to human induced rangeland degradation at a landscape scale in western Iran

Abstract

Knowledge of plant species distribution and abundance at different landscape scales and management-induced degradation is essential for the conservation, planning, and enhancement of the biodiversity of rangelands. In this study, additive partitioning of species diversity based on contribution diversity was used to analyze the interaction of landscape scale and grazing intensity factor to better understand the distribution of rare and common species. A total of 64 units (quadrats) were sampled by using a nested hierarchical sampling design at three scales of two regions (semi-arid vs. Mediterranean), four sites, and four quadrats in both exclosure and grazing areas. The regional-scale species richness (γs(q)) was calculated by the sum of the quadrat (αs(q)) and site (βs(q)) scale contributions to the region. The calculated rank of αs(q) indicated that an abundance of rare species for exclosures (α < 0.05) and the Mediterranean area (α < 0.01) was significantly greater than for grazing and the arid area, respectively. The highly palatable plants significantly correlated (α < 0.01) with the contribution diversity components (alpha/beta) in the exclosure areas but not in grazed areas. Furthermore, of the measured explanatory variables, the electrical conductivity (EC) of the soil was significantly negatively related to γs(q) which shows a sensitivity of rare species to the variable environmental conditions that are related to human influences interacting with soil and climatic conditions. The vegetation attributes of biomass and vegetation cover were significantly (α < 0.01) higher for managed exclosure sites than the grazed areas. The findings of this investigation demonstrate an increasing trend for rare species in managed and better environmental conditions. In conclusion, the protection and restoration of plant species diversity in semi-arid and Mediterranean grasslands in western Iran are possible through the application of sustainable management practices by decision-makers and managers.