Monitoring organic-matter decomposition and environmental drivers in restored vernal pools

Vernal pools are small, shallow and ephemeral freshwater wetlands, often located in forests. Despite harboring high levels of biodiversity and being biochemical hotspots, they have been severely degraded by human activities. Restoration of vernal pools has become a priority for resource managers, and monitoring of restoration projects is needed to track the effectiveness of restoration techniques. In this study, we analyzed the ecological functioning of natural and restored vernal pools in the forest of Chinon (France) four years after a restoration project. Specific aims were to: (1) compare organic-matter decomposition rates between natural and restored pools, and (2) evaluate the main drivers of organic-matter decomposition in these two types of pool. In five natural and nine restored vernal pools, a standardized organic-matter decomposition assay (cotton strip) was deployed for up to 57 days. Each pool was characterised in terms of vegetation type, water and soil quality. We found that decomposition rates did not differ between natural and restored pools. The natural pools, however, had the greater stores of total organic carbon (TOC) content, and Sphagnum moss cover. Across both pool types, decomposition rates were positively associated with canopy openness and vascular plant cover, suggesting a possible ‘priming effect’ of primary producers on microbial decomposers. Sphagnum moss cover and some soil variables, such as TOC, were associated with slowed decomposition, highlighting the potential of Sphagnum spp. at influencing microbial activity. We suggest that future studies couple the cotton strip assay with biotic indices to assess the overall functioning of these wetlands.