Wild bee community change over a 26-year chronosequence of restored tallgrass prairie

Restoring pollinators is an essential component of restoring functional ecosystems, yet little is known about how bees respond to ecological restoration practices, which generally focus on plants. We studied a large-scale, long-term tallgrass prairie restoration run by the Nature Conservancy in noth-central Illinois, USA, to determine how bee abundance, richness, and community composition is affected by the restoration process. We compared bee communities across a 26 year chronosequence of 12 restored sites, to bee communities in remnant prairie sites (controls) and agricultural sites (pre-restoration condition). We used passive trapping methods to collect 2,097 specimens representing 85 bee species in 23 genera. Prairie restoration had a positive effect on bee abundance (p=<0.0001) and richness (p<0.0001), with the strongest benefits occurring within the first few years, and high abundance and richness being maintained throughout the entire restoration chronosequence. In constrast, bee community composition changed with site age (R²=0.33, p=0.029), but primarily because community composition of the youngest restored sites differed from that of remnants (R²=0.11, p=0.033); communities in restored sites converged on that of remnants by 5-7 years after restoration. Changes in community composition of restorations over the chronosequence progressed predominantly through the gradual accumulation of species, rather than species replacement. Overall, we conclude that current prairie restoration methods are successful in reestablishing diverse bee communities that resemble those in remnant habitats.