15 December 2019 Impact of windthrow and forest fire on Neuropterida The impact of windthrow and forest fire on Neuropterida and Mecoptera Peter Duelli1, Beat Wermelinger2, Marco Moretti1 & Martin K. Obrist1 1 WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Biodiversity and Con- servation Biology, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland; [email protected], [email protected], [email protected] 2 WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Forest Health and Biotic Interactions, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland; [email protected] Received 25th September 2018; revised and accepted 21st February 2019 Abstract. The impact of forest fires and windthrow on species compositions in the Neuroptera, Raphidioptera, and Mecoptera was assessed in Swiss forests using standardized flight intercep- tion traps. As a result, 82 % of the 50 species benefited from the disturbance and became more abundant in the years after the fire or windthrow. Only 11 species, mainly Hemerobiidae and Coniopterygidae, peaked in the undisturbed forest stands. We conclude that for Neuropterida and Mecoptera catastrophic incidences are natural ecological events which create new habitats and by this foster their occurrence and abundance. The full manuscript to this summary has been published during the preparation of these Pro- ceedings; see Duelli et al. (2019). Further key words. Neuroptera, Raphidioptera, natural disturbance, wind-fell, blow-down, wildfire, insects, Switzerland Introduction The vast majority of European Neuropterida and Mecoptera develop and live in for- ests and other arboreal habitats (Aspöck et al 1980), with a preference for forest edges (Duelli et al. 2002). We investigated the impact of massive disturbances such as forest fires and windthrows on the population dynamics of Neuroptera, Raphidioptera, and Mecoptera. Methods In four independent projects carried out in Switzerland, all based on accidental natural disturbances, the differences in species composition and relative abundances of arthro- pod species were monitored with standardized flight interception traps Moretti( et al. 2006; Wermelinger et al. 2017). In each project, two levels of disturbance were compared with controls in undisturbed forests. In the two windthrow projects (storm Vivian 1990, Figs 1−3; storm Lothar 1999, Figs 4, 5), the plots where the wind-felled trees were not removed after the storm were termed as intermediately disturbed (ID, Figs 2, 4) and the timber-harvested forest plots Proceedings of the XIII International Symposium of Neuropterology, 17–22 June 2018, Laufen, Germany163 Pages 163-172, DOI:10.5281/zenodo.3569395 Peter Duelli, Beat Wermelinger, Marco Moretti & Martin K. Obrist as heavily disturbed (HD, Figs 3, 5). In all four projects the controls were trap stations in undisturbed forest. In the winter fire project in Ticino, the intermediately disturbed plots had only burned once in the previous 40 years (Fig. 6), while the intensely dis- turbed plots had burned several times. Figure 7 shows a trap station in an unburned chestnut control plot. In the summer fire project in Leuk in south-western Switzerland, where in 2003 a forest fire destroyed the forest on an entire mountain slope, the intense- ly disturbed plots were chosen from the center of the burned area (Fig. 8), the traps for intermediately disturbed plots stood within 10 m to the edges of unburned forest, and the control plots were chosen from areas of intact forest (Fig. 9). The windthrow plots after the storm Vivian (1990) were sampled from mid-May to late September in the years 1992, 1993, 1994, 1996. The windthrow plots after the storm Lothar (1999) were sampled from late March to late September in the years 2000, 2001, 2002. The forest fire plots in Ticino were sampled from mid-March to late September 1997. The forest fire (2003) plots above Leuk (Valais) were sampled from early May to early September in the years 2004, 2005, 2006, 2008. The traps were emptied weekly. There were twice as many traps in disturbed plots (ID and HD) than in the control plots (FO), so the numbers of specimens in the intact forest plots (FO) had to be dou- bled to compare the numbers in disturbed and undisturbed plots. As an indicator for Figure 1. Windthrow above Schwanden, Canton Glarus, Switzerland, caused by storm Vivian during February 1990, af- fecting mainly conifer forests in the Alps. Photo: © WSL (1991) 164 Impact of windthrow and forest fire on Neuropterida Figure 2. Window flight interception trap with water tray below glass screen and yellow pan trap in an uncleared Vivian windthrow (ID) plot in the Alps (Schwanden, Canton Glarus, Switzer- land). Second year after the storm. Photo: © WSL (1992) Figure 3. Cleared windthrow (HD) plot with trap station in the second year after storm Vivian. Even in cleared plots there is much dead wood (trunks and slash) remaining. Photo: © WSL 1992. 165 Peter Duelli, Beat Wermelinger, Marco Moretti & Martin K. Obrist Figure 4. Storm Lothar in winter 1999 affected mainly deciduous forests in the lowlands of Swit- zerland. Uncleared forest (ID) plot near Habsburg, Canton Aargau, Switzerland, with combi- trap (plexiglass cross window flight interception trap above yellow funnel filled with water) and pitfall trap for epigeal arthropods. Photo: © Beat Wermelinger (2003) Figure 5. Cleared windthrow plot (HD) three years after storm Lothar on the Swiss Plateau near Messen, Canton Solothurn, Switzerland. Photo: © Beat Wermelinger (1992) 166 Impact of windthrow and forest fire on Neuropterida Figure 6. Combi-trap above Locarno, Can- ton Ticino, Switzerland, four years after the last of several fires (HD plot), just before bud burst in spring. Regrowth in chestnut forests is very fast. Photo: © Marco Moretti (1997) Figure 7. Refilling a combi-trap in an intact (FO, no fire in the previous 40 years) chest- nut forest. The whole trap device can be tilted to pour the water with insects through a fil- ter into a bucket. The insects are transferred with forceps from the filter into alcohol vials. Photo: © Denise Wyniger (1997) 167 Peter Duelli, Beat Wermelinger, Marco Moretti & Martin K. Obrist Figure 8. Trap station in the center (HD) of a large pine forest area burned in 2003 above Leuk, Canton Valais, Switzerland. One year after the fire there is hardly any regrowth visible, but in the following years a colorful flora appeared. Photo: © Marco Moretti (2006) Figure 9. Combi-trap in an unburned part (FO) of the forest above Leuk. The southerly exposed slopes of the Valais Valley are the most species-rich habitats for insects in Switzerland, including Neuropterida. Photo: © Marco Moretti (2006) 168 Impact of windthrow and forest fire on Neuropterida the effect of disturbance in general, the following formula was used for each species: mean (HD + ID) / [mean (HD + ID) + FO)]. Species with more than 66 % are considered winners, those with less than 33 % losers. Species rating in between were not affected or considered indifferent to the midterm effects of storms or fires. A 100 % winner spe- cies means that all specimens of that species were collected in disturbed plots, while a loser species (0 %) was not caught at all in the disturbed plots in the years after the dis- turbances. Since the disturbances in the four projects occurred in different habitats, in different years, and in different climatic zones of Switzerland, the species composition was too variable to allow statistical treatment. Only a few species were common to all four projects. Results and Discussion For the summary presented here (Table 1), all the data of the four projects were com- bined per species, but analyzed separately for the three disturbance categories, i.e., in- termediately disturbed plots (ID), heavily disturbed plots (HD), and control plots in undisturbed forest (FO). A total of 79 species and 8 285 specimens of Neuropterida and Mecoptera were col- lected. However, only 50 species represented by five or more individuals were included in the analysis. The species that can be considered ‘winners’ were those with more speci- mens collected in disturbed plots than in the intact forest (Table 1). In summary, 28 species above 66 % were rated as winners, 9 species were losers in the sense that their abundance was less than 33 % in the disturbed areas, and 13 spe- cies were ranking indifferent, between 33 % and 66 %. More species (20) had a higher abundance (bold print in Table 1) in intermediately disturbed (ID) plots than in heavily disturbed (HD) areas (17). Only 11 species, mainly Hemerobiidae and Coniopterygi- dae, peaked in the undisturbed forests (FO). Chrysopidae. Almost all winners among the green lacewings are well-known forest edge species (Duelli et al. 2002). Clear losers among the Chrysopidae were Chryso­ tropia ciliata, living in moist forests, and Peyerimhoffina gracilis, restricted to shady conifer forests. Hemerobiidae. It was a surprise to see so many brown lacewing species ranking high up as winners after disturbances, because brown lacewings are generally known to neuropterologists to prefer the forest interior (e.g., Duelli et al. 2002). Among the losers, the genus Sympherobius was dominant. Coniopterygidae. The dustywings showed the highest proportion of losers, also in terms of individuals. Myrmeleontidae. The two antlion species were favored by the mid-term effects of fire. Raphidiidae. The two most common snakefly species were winners. Dead bark of trees and trunks was an excellent habitat for their larvae. Panorpidae. The two most abundant scorpionfly species were indifferent to distur- bance, whereas the others were winners. 169 Peter Duelli, Beat Wermelinger, Marco Moretti & Martin K. Obrist Table 1. List of species with five or more individuals collected in the three treatments. FO − intact forest; ID − intermediately disturbed forest; HD − heavily disturbed forest; n − Total number of specimens per species. Bold: treatment with the highest number of individuals caught. [% d.p.] − percentage of individuals caught in disturbed plots; Species >66 % are considered winners, those <33 % losers.