Forgotten role of fires in Central European forests: critical importance of early post-fire successional stages for bees and wasps (Hymenoptera: Aculeata)

Abstract

Forest fire remains among the most controversial topics in nature conservation. Here, we address changes in abundance and species composition of the bee and wasp community following a temperate forest crown fire that led to nearly complete defoliation and dieback of trees within 2 years. We found a highly dynamic community of 252 bee and wasp species (representing 18.8 % of total bee and wasp species known from the Czech Republic) that utilized 1-7-year-old burned forest stands. Species richness in the burned forest stands was significantly higher than that recorded in nearby forest that had been unaffected by any recent fire. The unburned forest hosted only 88 species. We found 42 red-listed species, of which 40 were present in the burned forest, while only 12 were present in the control forest. Numerous early-and late-responding species were detected, but maximum species diversity was reached 3 years after the fire. Only 7 of the total of 261 species were limited to the forest that was unaffected by any recent fire. A management regime that supported the presence of bare sand and heather patches, and removal of all but solitary pine trees, was found to be insufficient to support the full spectrum of forest fire-dependent species. This was mainly due to the absence of charred or decaying dead wood, which is otherwise utilized by numerous redlisted cavity adopters that are absent in the surrounding cultural landscape. Retaining part of the charred trunks is suggested as a novel post-fire conservation measure.

Regional Case Studies

“…Conservation management that focuses on the formation of bare soil patches by fire (as in the first of the two above-presented case studies) supports a very diverse spectrum of organisms but is not sufficient to provide habitat for hymenopteran cavity adopters, which are associated with dead wood and would benefit from greater public acceptance of mixed-severity fire in forests and greater retention of snags after fire (Bogusch et al, 2015). Results similar to those described above have been found for various invertebrate taxa after mixed-severity fire, including increases in diversity of saproxylic (dependent on decaying wood) beetles in the Swiss Alps (Moretti et al, 2010) and enhanced species richness of ground beetles, hoverflies, bees, wasps, and spiders in the forests of the southern Alps (Moretti et al, 2004).…”

“…Among them were two species that were considered regionally extinct (Dipogon vechti and Chrysis iris), two critically endangered species (Miscophus niger and Passaloecus monilicornis), and numerous endangered and vulnerable species. In total, the burned forest stands hosted 252 bee and wasp species 1-7 years following the forest fire, which represented 19% of the total 1343 species reported so far from the Czech Republic (Bogusch et al, 2007;Bogusch et al, 2015). Importantly, the species spectrum associated with the burned forest stands differed not only from those of the unburned forest but also from the species associated with bare sand and heather patches with retained solitary pine trees at a site 12 km away (Blažej and Straka, 2010;Bogusch et al, 2015).…”

“…In total, the burned forest stands hosted 252 bee and wasp species 1-7 years following the forest fire, which represented 19% of the total 1343 species reported so far from the Czech Republic (Bogusch et al, 2007;Bogusch et al, 2015). Importantly, the species spectrum associated with the burned forest stands differed not only from those of the unburned forest but also from the species associated with bare sand and heather patches with retained solitary pine trees at a site 12 km away (Blažej and Straka, 2010;Bogusch et al, 2015). The species absent at the unburned site with bare sand and heather patches consisted mostly of those requiring dead wood, such as standing fire-killed trees (snags), which is rarely available in the current commercially exploited forests of the Czech Republic as well as surrounding countries.…”

“…At 5-7 years following the fire, both the diversity and abundance of aculeate hymenopterans decreased back to the levels experienced in the surrounding unburned forest, and the species spectrum changed. Even in these later phases of forest succession, the burned site hosted numerous species that were absent or rare in the unburned forest and absent or rare during the earlier phases of forest succession (Ammophila sabulosa, Lasioglossum punctatissimum, Arachnospila hedickei, and Crossocerus exiguus) (Bogusch et al, 2015).…”

Flight of the Phoenix

“…Dead wood thus should be considered an important habitat resource deserving conservation measures. Mosaic management of burned forest sites and retaining charred trunks are suggested as management measures supporting biodiversity at the sites of recent forest fires (Bogusch et al, 2015).…”