Abstract
Introduction: The forest floor vegetation cover is a key factor influencing the structure and dynamics of animal communities within forest ecosystems. Ground beetles, as indicator species in biodiversity and ecological studies, show pronounced responses to habitat changes and vegetation types. The Khoshk-e-daran National Natural Monument in northern Iran—known as the last remnant of the Hyrcanian lowland forests—features heterogeneous forest floor vegetation due to the temporary waterlogged areas and unauthorized livestock grazing in certain parts of the forest. This study aimed to examine the effect of forest floor vegetation cover percentage on the biodiversity of ground beetles across different areas of the Khoshk-e-daran National Natural Monument.
Materials and Methods: Twelve plots measuring 20 × 20 m were selected across the entire area of the Khoshk-e-daran Natural Monument. Six plots were located in areas with evidence of livestock grazing and human presence (low-protection areas), and six plots in areas without signs of human or livestock disturbance (high-protection areas), selected randomly. In each plot, eight pitfall traps were installed to capture ground beetles. Specimens were identified using valid morphological keys. Biodiversity indices were calculated using Hill numbers in R, and dominance indices were computed in PAST software. Forest floor vegetation cover percentage was calculated from photographs taken in three 1×1 m microplots at fixed locations and distances within each plot, analyzed using ImageJ software. Simple linear regression was used to determine the relationship between vegetation cover and biodiversity indices, while independent t-tests (SPSS v26) were applied to assess differences between low and high protection areas.
Results: In total, 3,079 individuals belonging to 15 genera and 15 species were identified; two taxa were recognized only at the genus level. The most abundant species were Carabus sculpturatus (929 individuals) and Carabus adamsi (673 individuals). The percentage of forest floor vegetation cover explained 53.9% of the variation in species richness, 72.2% of the variation in beetle abundance, 88.1% of the variation in the Shannon index, and 79.4% of the variation in evenness index. Conversely, regression analysis showed a significant negative relationship with the dominance index. Mean species richness was significantly higher in high-protection areas (13.32 ± 1.21) compared to low-protection areas (8.31 ± 0.67). The Shannon diversity index was also significantly greater in high-protection areas (7.09 ± 0.22) than in low-protection ones (3.88 ± 0.16). Evenness index values differed significantly between high-protection (0.53 ± 0.026) and low-protection (0.26 ± 0.036) areas.
Discussion and Conclusion: Forest floor vegetation cover directly influences the diversity and abundance of ground beetles by creating favorable microclimatic conditions, enhancing food resources, and providing physical shelters. The results confirm that the conservation and proper management of forest floor vegetation in the Khoshk-e-daran Natural Monument can be an effective approach to protect soil-dwelling fauna, particularly ground beetles. Conversely, vegetation loss caused by livestock grazing can lead to a substantial decline in beetle biodiversity. This study highlights the importance of incorporating plant–invertebrate interactions into ecological conservation strategies as a key component of ecosystem preservation efforts.
Keywords: Hyrcanian Forest, Carabidae, Conservation Ecology, Livestock Grazing
Keywords: Hyrcanian Forest, Carabidae, Conservation Ecology, Livestock Grazing