Comparative systematic review on abundance and composition of selected soil microbial communities in degraded and restored forests

Land degradation is a rising environmental challenge driven by climate change, spread of invasive species, wildfires, and anthropogenic activities such as deforestation. Mitigating land degradation through ecological restoration is critical not only for the preservation of soil microbial communities but also for the recovery of the broader ecosystems they support. Ecological restoration is widely recognised as a strategy for reversing land degradation, enhancing biodiversity, and improving soil health. Soil microbial communities are integral to these processes, facilitating nutrient cycling, organic matter decomposition, and ecosystem resilience. In this paper, the abundance and composition of key soil microbial taxa in degraded and restored forest ecosystems were systematically reviewed, with a focus being on fungal and bacterial communities as well as soil enzymatic activities. A structured literature search across Web of Science, Scopus and Google Scholar databases, identified 1100 studies, of which 32 met the inclusion criteria. The results showed that microbial diversity and abundance were significantly reduced in degraded forests compared to restored sites, with ecological restoration promoting the reestablishment and restructuring of functionally important microbial assemblages. Soil physicochemical properties, vegetation characteristics, and restoration methodologies emerged as primary determinants of microbial composition and recovery dynamics. However, microbial reassembly is a protracted process, contingent on site-specific environmental factors and restoration approaches. The review also highlighted critical research gaps, particularly the need for long-term microbial monitoring and region-specific investigations, especially in tropical and sub-Saharan African forest ecosystems. Understanding of microbial responses to forest restoration can help create more effective, evidence-based strategies for enhancing soil health and ensuring ecosystem sustainability.