Document Type : Research Paper
Authors
Forest and Rangeland Department, Agricultural and Natural Resources Research and Education Center of Zanjan, Agricultural Research, Education and Extension Organization (AREEO), Zanjan, Iran
Abstract
Rangelands, as one of the vital ecosystems in Iran's arid and semi-arid regions, play a crucial role in biodiversity conservation, soil erosion prevention, and forage supply. In recent years, anthropogenic pressures such as overgrazing and climate change have led to the decline in species diversity and the ecological degradation of rangelands. This study aimed to investigate the trends of plant species diversity and richness indices from 2021 to 2023 (corresponding to 1400–1402 in the Iranian calendar) in the Jishabad rangeland site of Tarom County. For this purpose, a systematic sampling design was applied, in which four main plots (each 10×10 m) were randomly selected within a one-hectare study site. In each main plot, four subplots of 1×1 m were established. Field measurements were conducted during the peak growth season (May–June) over three consecutive years. In each subplot, data on species composition, life form, percentage cover of vegetation, litter, moss, bare soil, gravels, and erosion intensity were recorded. Species identification was conducted using reliable floristic references for Iranian flora. Diversity indices including richness (Margalef and Menhinick), evenness (Pielou), and diversity (Shannon–Wiener and Simpson) were calculated and analyzed using appropriate parametric and non-parametric statistical methods.The results revealed that biodiversity indices varied significantly across the study years. Results showed significant increases in biodiversity indices over the study period (2021–2023): the mean number of species per subplot rose from 5.69 in 2021 to 7.75 in 2023 (P < 0.01); the Shannon–Wiener index increased from 1.62 to 1.96, and the Simpson index from 0.16 to 0.83 These changes, accompanied by a 10% reduction in bare soil cover and increased perennial plant frequency, were likely driven by grazing management, natural exclosure, and favorable climatic conditions.
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