Abstract
Tallgrass prairie and oak savanna support appreciable biodiversity and are among the most threatened habitats in Canada, yet little is currently known about which bee species occur in these habitats and how management might affect their abundance and diversity. Here, we ask how restoration and management practices in tallgrass prairie and oak savanna affect bee communities in southern Ontario. Bee communities, vegetation plots and environmental characteristics were sampled in remnant, burnt, restored, and naturalized sites at three localities. Although bee communities were markedly different at the three sampled localities (separated by at least 114 km) with only 19% of total species shared, consistent trends in bee community metrics among management types across localities were found. Remnant sites had lower abundance, species richness, and Shannon diversity than other management types in most cases. Greater canopy cover and more woody debris were associated with remnant and burn sites and greater floral abundance with restored sites. These research outcomes will have implications for restoration ecology, habitat management, and bee conservation in tallgrass prairie and oak savanna.
Introduction
In Canada, grasslands are best known from the prairies ecozone (in the provinces of Alberta, Saskatchewan, and Manitoba) with an extension of this once contiguous habitat in the mixedwood plains ecozone of southern Ontario (Robertson et al. 1997; Shorthouse 2010; Sheffield et al. 2014). Here, prairie persists as tallgrass and oak savanna, a small fraction of this habitat remains making it one of the most threatened ecosystems in Canada and a conservation priority due to the high biodiversity it supports and the presence of many rare plant and animal species (Bakowsky and Riley 1994; Kraus and Hebb 2020). The approximately 100 remaining remnants of tallgrass and oak savanna habitat in southwestern Ontario are small “isolated and biogeographically significant” fragments of the former expanses of grassland and savanna that occurred prior to European colonisation (Shorthouse 2010). In addition to being isolated from prairies in central north America, cessation of natural and historical disturbance regimes (i.e., natural and managed fires, flooding, and bison grazing) and threats from overabundance of deer (Bakowsky and Riley 1994), mis-guided management (including tree planting: Tallgrass Ontario 2019), and encroachment of weedy species and shrubs, mean that the persistence of tallgrass communities relies entirely on management.
Pollinators are important for terrestrial ecosystem function due to their close relationships with flowering plants (Klein et al. 2007; Ollerton et al. 2011). Among insect pollinators, bees are particularly important due to their dependence on flowers for their nutritional needs. The southern Ontario mixedwood plains ecozone has high bee diversity and levels of national endemism, with approximately 23% of bee species not found elsewhere in Canada (Sheffield et al. 2014; Pindar and Raine 2023). This ecozone has similar levels of endemism to the prairies ecozone in western Canada and is second only to the arid grasslands of the western interior basin ecozone of British Columbia (Sheffield et al. 2014). Within the mixedwood plains ecozone, tallgrass prairie and savanna habitats are especially important areas rich in biodiversity, particularly of plants and insects, likely due to the warm and dry microclimate (Skevington 1999; Paiero et al. 2010; Bennett et al. 2019). To conserve tallgrass associated bee species, and the habitat fragments in which they live, it is critical to understand how current management practices, or lack thereof, impacts these bee communities.
Although there has been a considerable amount of research on impacts of management practices, particularly fire, on prairie plant communities (Hulbert 1986; Brudvig et al. 2007; Pavlovic et al. 2011; Larson et al. 2020) much less is known about the impacts on animals (Rice 1932; Knapp et al. 1999; Brawn 2006; Burke et al. 2020; Guiden et al. 2021) and less still about the bees reliant on these particular plant communities (Panzer 2002; Harmon-Threatt and Chin 2016; Griffin et al. 2017; Bruninga-Socolar et al. 2022). Additionally, the majority of these studies are from larger tallgrass habitat remnants in the central Midwest United States, with much less known about the impacts of management on these smaller remnant habitats in Ontario. A substantial amount of research has documented terrestrial arthropod biodiversity in Ontario tallgrass habitats (Sugar et al. 1998; Skevington et al. 2001; Paiero et al. 2010; Shorthouse 2010) with associated reporting of new species distribution records (Skevington 1999; Paiero et al. 2003; Jones et al. 2019; Sharkey et al. 2020, 2024). However, fewer studies have specifically inventoried bees and how the role of fire (Pindar 2013), and restoration (Richards et al. 2011; Paterson et al. 2019) or lack thereof (i.e., naturalization) might impact bee communities in these habitats.
