Fire and landscape context shape plant and butterfly diversity in a South African shrubland

Abstract

Aim To understand effects of fire history and landscape composition on butterfly diversity in a fragmented agricultural landscape. Location We studied critically endangered renosterveld remnants within the fynbos biome in the Swartland municipality, Western Cape, South Africa, a global biodiversity hotspot. Method We selected survey sites on renosterveld fragments in the agricultural landscape along a gradient of fire history to test the response of biodiversity patterns to fire and landscape composition. We surveyed butterfly species richness, abundance and community composition as well as vegetation structure in five survey rounds on 58 sites between August 2018 and April 2019. We analysed data through linear modelling and multidimensional scaling. Results Fire was associated with reduced shrub and understorey plant cover and with increased plant species richness. Butterfly species richness was three to four times higher when natural habitat increased in the surrounding landscape (within a 2 km radius), while butterfly abundance was negatively associated with increasing time since fire, with approximately 50% fewer individuals after 9 years. Fire was indirectly associated with increased butterfly species richness and abundance through the alteration of vegetation structure, particularly through removal of shrubs and enhanced plant diversity. Low‐mobility butterfly species were more positively associated with less vegetation cover than were high‐mobility species, which were more associated with sites characterized by long absence of fire. Main conclusions Our findings suggest that species respond differently to fire, so a diversity of fire frequencies is recommended. Partially burning areas approximately every 10 years may benefit particularly low‐mobility butterfly species through gap creation and fostering plant diversity. Hence, including fire into management activities can benefit butterfly and plant populations alike in critically endangered renosterveld.

Divergent responses of butterflies and bees to burning and grazing management in tallgrass prairies

“…However, the vegetation variables we assessed (plant species richness, forb frequency, native graminoid frequency, frequency of invasive grasses Poa pratensis and Bromus inermis), site area, and the percent of prairie in the surrounding 1.5-km buffer around each site were not correlated with butterfly abundance or species richness. This is in contrast to previous studies, which found positive associations between butterflies and site area and surrounding habitat (Kral et al, 2018;Robinson et al, 2014;Topp et al, 2021), nectar resources (Öckinger & Smith, 2006;Vogel et al, 2007;Winfree et al, 2011) and host plants (Dennis et al, 2011). The lack of associations we found with local and landscape variables may be partially explained by the fact that there was no clear separation between vegetation characteristics based on management type at our study sites (Larson et al, 2020;Leone et al, 2019).…”

“…For example, plant communities were similar on burned and grazed sites (which included the sites in this study), although 28% of plant species occurred on only one or the other of the management types (Larson et al, 2020 ). Topp et al ( 2021 ) found that fire was indirectly associated with butterfly abundance and species richness through its effect on the vegetation; no such indirect effects of management were documented at our sites.…”

“…We hypothesized that both butterfly and bee communities would be affected by management practices, but that their responses to fire vs grazing would differ and be mediated by local and landscape factors such as patch size, prairie habitat availability in the landscape, floral and host plant resources, and soil texture. Habitat patch size and the amount of suitable habitat in the surrounding landscape are known to positively impact bee and butterfly communities (Denning & Foster, 2018 ; Robinson et al, 2014 ; Topp et al, 2021 ). We expected these to be positively associated with the abundance or diversity of butterflies and bees.…”

Fire ecology for the 21st century: Conserving biodiversity in the age of megafire

“…This approach provides a rapid means of identifying potentially imperilled species with just two inputs. However, species have different relationships with fire (Topp et al, 2022): some species may be minimally affected, others may be substantially affected. To account for this, Legge et al (2022) consider traits of animals that could confer vulnerability to both fire and the post‐fire landscape.…”

“…Fire is an inherently spatiotemporal process, yet fire ecology has, for much of its history, been more concerned with the temporal than the spatial effects of fire—with a particular focus on local post‐fire successional trajectories of species and communities (Keith, 2021). Studies in this Special Issue provide examples of the insights that temporal studies of fire can provide: Connell et al (2022) showed that species’ post‐fire responses are contingent on prevailing climatic conditions; Miller et al (2022) demonstrated the surprisingly long‐term (100+ year) post‐fire successional dynamics of lichen communities; Rainsford et al (2022) revealed the variable successional trajectories of different functional groups of plants and birds, and how that information can be used to assess tolerable minimum and maximum fire intervals, and; Topp et al (2022) showed that the response of butterflies to fire depends on species’ mobility, mediated through the effects of fire on vegetation structure.…”