Citation: Renˇ co, M.; Adámek, M.; Jílková, V.; Devetter, M. Post-Fire Recovery of Soil Nematode Communities Depends on Fire Severity. Diversity 2022, 14, 1116. https://doi.org/10.3390/d14121116 Academic Editors: Luc Legal, Xin Sun, Liang Chang and Pingting Guan Received: 10 November 2022 Accepted: 12 December 2022 Published: 15 December 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). diversity Article Post-Fire Recovery of Soil Nematode Communities Depends on Fire Severity Marek Renˇ co 1 , Martin Adámek 2 , Veronika Jílková 3 and Miloslav Devetter 3, * 1 Institute of Parasitology, Slovak Academy of Sciences, Hlinkova 3, 040 01 Košice, Slovakia 2 Faculty of Science, Department of Botany, Charles University, Benátská 2, 128 00 Prague, Czech Republic 3 Biology Centre, Institute of Soil Biology, Czech Academy of Sciences, Na Sádkách 7, 370 05 ˇ Ceské Budˇ ejovice, Czech Republic * Correspondence: devetter@upb.cas.cz Abstract: Following the creation of a new organic layer after a forest fire, there is an initial build-up phase of overall biota. We studied soil nematode community development in a chronosequence of post-fire coniferous forest sites in relation to different fire severity. The taxonomic and functional composition of the soil nematode community was analyzed to detect immediate changes and levels of post-fire recovery in soil food web structures, i.e., 0, 1, 4, 8, 14, 20, 45, and 110 years after the event. Unburned forest sites served as controls. With small exceptions recorded immediately after the burn (mean nematode abundance, total biomass), the low severe wildfires had no impacts on the structures of nematode communities. The structures of nematode communities were found to be stable on sites affected by low severe wildfires, without considerable fluctuations in comparison to the unburned sites during chronosequence. On the contrary, nematode communities responded considerably to fires of high severity. The significant changes, i.e., a decrease of mean nematode abundance, plant parasites, omnivores and predators, species number, and nematode diversity, the values of CI, SI, MI, but an increase in the number of bacterivores and EI were recorded immediately after the fire. Such status, one year after a fire of high severity, has been observed. Full recovery of nematode communities 14 years after the disruption was found. Overall, our results showed that fire severity was a considerable element affecting soil nematode communities immediately after events, as well as the time needed to recover communities’ structure during post-fire chronosequence. Keywords: ecosystem recovery; fire severity; nematoda; soil; diversity; coniferous forest; wildfire 1. Introduction Terrestrial nematodes, i.e., species that inhabit exclusively the soil environment, are by far the most abundant edaphic animals [1]. As estimated [2], approximately 4.4 × 10 20 nematode individuals inhabit the upper layer of soils across the globe. They interact with many other organisms, consuming and being consumed by other components of the soil fauna [3]. High diversity is the basis for their multiple functions and roles; for example, by eating bacteria and fungi, they regulate their populations [4], feeding on plant roots damages the hosts, many times at economically important levels [5]. Acting as top-down regulators of lower trophic levels, e.g., predator and omnivore nematodes, as components of the higher trophic levels of the soil food web, may play an important role in regulating plant-feeding nematode populations, particularly where bottom-up re- sources are restricted [3]. Therefore, their contribution to nutrient dynamics, energy flow, global carbon (C) cycle, organic matter decomposition or mineralization is decided [6–8]. Inhabitting the soil, nematodes are thus essentially dependent on soil characteristics and are sensitive to any modifications [9–11], e.g., after a disturbance. Disturbances, both human-induced and natural, shape forest systems by influencing their composition, structure, and functional processes [12]. Natural disturbances with Diversity 2022, 14, 1116. https://doi.org/10.3390/d14121116 https://www.mdpi.com/journal/diversity