The Impact of Tree Species and Charcoal on Soil Fauna in Post-Fire Forest Ecosystems

Soil fauna, particularly enchytraeids and earthworms, play a crucial role as soil engineers, actively contributing to nutrient cycling through the breakdown and ingestion of litter material. These organisms engage in intricate interactions with microorganisms responsible for decomposing and mineralizing detritus. The present study seeks to delve into the complex interplay among tree species, charcoal presence, and soil fauna within post-fire forest ecosystems. The investigation took place in Rudziniec, Poland, a site that witnessed one of Europe's largest fires in 1992. Two delineated areas were observed: one with post-fire charcoal presence and another with removed charcoal. Four distinct tree species—pine (Pinus sylvestris L.), larch (Larix decidua Mill.), birch (Betula pendula Roth), and oak (Quercus robur L.)—were selected as representative species for the study. Samples were obtained from locations adjacent to the trees at a depth of 0-10 cm for echytraeids and at a depth of 0-25 cm for earthworms. The study elucidates the impacts of post-fire charcoal removal or retention on soil fauna across diverse tree species. When considering the various tree species, enchytraeid density was higher in coniferous trees (pine and larch) compared to deciduous trees (birch and oak). Among these, oak trees exhibited the highest enchytraeid species diversity, yet their density was lowest (60944 ind.m-2). Among experimental plots, in birch plots with post-fire charcoal retention, enchytraeid density was lowest (27470 ind.m-2); conversely, in charcoal removal plots, it showed the highest number with 105355 ind.m-2. Regarding earthworm biodiversity, a maximum of two species were observed across all plots. Earthworm density was lower in coniferous trees (12.65 ind.m-2 in pine and 10.67 ind.m-2 in larch) compared to deciduous trees (20.09 ind.m-2 in birch and 14.67 ind.m-2 in oak). With charcoal presence, earthworm density sharply decreased in coniferous trees while increasing in deciduous trees. A similar trend was observed in earthworm biomass. Among all experimental plots, the highest biomass value was found in pine trees with charcoal removal (4.54 g.m-2) whereas the lowest value with charcoal presence (0.35 g.m-2). These differences suggest an intricate relationship between post-fire charcoal management, tree species, and their consequential impact on soil fauna. The insights gathered from this study hold valuable implications for informing ecosystem management and restoration strategies, contributing to a more comprehensive understanding of the intricate dynamics within post-fire environments. This research was funded by The National Science Centre, Poland, grant No. 2021/42/E/ST10/00248. The analyses were performed in the Laboratory of Forest Environment Geochemistry and Reclaimed Areas, University of Agriculture in Krakow.