Nightmare of forests: Secondary forestation silently alters soil macroinvertebrate communities

Macroinvertebrates play a crucial role in maintaining soil structure, ecosystem function, and ecosystem services. They are highly sensitive to human disturbances and are used as bioindicators to assess interference with soil components. The primary objective of this study was to investigate the impact of secondary forestation on soil macroinvertebrates in the Caspian Hyrcanian forests. A comprehensive DNA barcoding approach was employed to examine community structures, diversity, and density of soil macroinvertebrates in relation to natural forests and re-planting strata. Macroinvertebrates were collected using transects and quadrates, and the composition of communities between natural and planted forests was compared on both broad (sampling locations/central part of the forest) and local (each forest) scales. A total of 172 OTUs (132 MOTUs and 40 MorphOTUs) were identified in this study. On the local scale, total density and diversity did not differ between the habitat types (natural and planted forests), unlike the broad scale. However, there was a significant change in community composition. The results of β-diversity and phylogenetic β-diversity approaches revealed a turnover between the two habitat types, with Hymenoptera (ants), Annelida (earthworms), and Arachnida contributing most to the dissimilarity between natural and secondary forests. Overall, despite observed changes in community composition, the stability in total populations between the two habitat types suggests that forests that have been deforested and replanted with trees for >20 years have had enough time to recover. Given the significant decrease in the Hyrcanian forests, particularly in recent decades, comprehensive information on the apparent impact of human disturbance on soil biota is necessary to address conservation issues.