Contrasting recovery of earthworms and enchytraeids thirty years after wildfire: tree species effects in regenerating temperate forests

Wildfires profoundly alter forest ecosystems, yet the long-term recovery of their belowground (soil) communities remains poorly understood. We investigated the recovery of earthworm (Lumbricidae) and enchytraeid (Enchytraeidae) assemblages thirty years after a catastrophic forest fire in Rudziniec Forest District, southern Poland, comparing post-fire, single-species stands of four tree species (Pinus sylvestris, Larix decidua, Betula pendula, and Quercus robur) with adjacent undisturbed mature forests on Podzols. Earthworm density showed no significant difference between sites (p > 0.05), with assemblages exclusively composed of epigeic species (Dendrobaena octaedra, Bimastos rubidus) in both post-fire and undisturbed sites, reflecting the overriding influence of acidic Podzol conditions rather than fire history. In contrast, enchytraeid density remained severely depressed in post-fire soils, with a significant tree species × site interaction. Enchytraeid density was highest under oak (66 % of reference) and lowest under birch (14 %). Soil pH emerged as the strongest predictor of enchytraeid density (r = − 0.78), with fire-induced pH elevation (from 3.42 to 4.03) and a 60 % reduction in organic horizon thickness jointly associated with increased relative dominance of Cognettia chlorophila over the acidophilic Achaeta gemmata. Our findings demonstrate that annelid density differed markedly between taxonomic groups thirty years after fire, with enchytraeids most strongly associated with reduced soil pH and organic horizon loss. These results have implications for post-fire forest management, suggesting that tree species selection significantly influences belowground ecosystem restoration outcomes.