Assessing the response of two soil engineering groups to reforestation in the Hyrcanian forests

Many forest ecosystems are becoming more vulnerable due to human activities and the considerable effects of forest exploitation. Furthermore, forest management practices often overlook the importance of biodiversity, focusing primarily on timber production and economic gain. The Hyrcanian forests, in particular, face significant challenges due to a combination of factors such as deforestation, climate change, and invasive species. This study aims to explore the impact of reforestation on the diversity, abundance, and community structure of two key groups of soil engineers: earthworms and ants. These groups were chosen due to findings from a previous study indicating their higher abundance in this region. Additionally, it aims to determine which of these groups is more significantly impacted. The study was conducted in both natural and planted forests across three locations in the central region of these forests. Samples were collected from 72 quadrats and 48 transects. A total of 251 samples were collected for earthworms and 410 samples for ants. Then, the samples were sorted into morphological operational taxonomic units (MorphOTUs) based on morphological characteristics. DNA barcoding studies were performed using the cytochrome c oxidase subunit 1 (COI) gene to determine the molecular OTUs. After that, the difference in OUT richness, abundance and composition between natural and planted forests was investigated using statistical analysis. In the current research, 16 and 19 OTUs were recognized for earthworms and ants, respectively. The results indicated that ant abundance was significantly higher in natural forests (n = 263) compared to planted forests (n = 147). However, the difference in earthworm numbers was negligible (n = 125 in natural and n = 126 in planted forests). The community compositions of both groups did not show significant differences between these forests. The difference between ants and earthworm abundance indicates that ants play a key role as pioneer species in the colonization process, followed by other groups (earthworms) that have settled in the planted forests. The study emphasizes the significance of a genetic approach to understanding the biodiversity of both groups. We believe that integrating both groups will improve the effectiveness of bioindicators in these areas. It is crucial to recognize the biodiversity of soil invertebrates for monitoring natural forests and developing effective reforestation policies, which are essential for fostering resilient ecosystems.