Restoration increases bee abundance and richness but not pollination in remnant and post‐agricultural woodlands

Abstract

Human land use, including agriculture, is a leading contributor to declining biodiversity worldwide and can leave long‐lasting legacies on ecosystems after cessation. Ecological restoration is an approach to mitigate these impacts. However, little is known about how animal communities and plant–animal interactions respond to the combined effects of land‐use legacies and restoration. We investigated how restoration and agricultural history affect bee (Hymenoptera: Apoidea: Anthophila) communities and pollination function. In 27 paired remnant (no history of agriculture) and post‐agricultural longleaf pine (Pinus palustris Mill.) woodlands, we established 4–10 1‐ha plots (126 total) and experimentally restored half of them, while the other half were left as unrestored controls. Restoration was accomplished through canopy thinning which reinstates open savanna‐like conditions. We collected bees in each plot using a combination of bowl trapping and standardized netting transects. Thinning increased bee abundance by 169% and bee richness by 110%, but agricultural land use had no effect on these variables. Bee community composition was affected by restoration and was marginally affected by agricultural history. To measure pollination function, we conducted a sentinel plant experiment in which potted black mustard (Brassica nigra L.) plants were placed out in a subset of these sites (n = 10) and either bagged to exclude pollinators or left open for pollinator access. Then, we measured fruit and seed set of sentinel plants to compare pollination function among the restoration and land‐use history treatments. Seed set and fruit set of sentinel plants were higher in open than bagged plants, indicating that this model system effectively measured pollination, but we found no differences in pollination based on restoration or agricultural history. These results indicate that although pollinator communities may show clear responses to restoration that are largely independent of prior land‐use impacts, this does not necessarily translate into differences in pollination function after restoration.

Canopy thinning, not agricultural history, determines early responses of wild bees to longleaf pine savanna restoration

“…Large‐bodied species may be more affected by land use, but they are also able to fly long distances between patches and so larger experimental plots would be needed to test effects on these bees. A related study incorporating net collections across additional sites suggests the patterns observed here are maintained over multiple years and also apply to a wider range of bee species (Breland et al ). Although land‐use history did not appear important for bee diversity in this study, it may play a stronger role in other species with stronger dependencies on specific floral hosts.…”

The impacts of bioenergy pine plantation management practices on bee communities

“…Thinning creates canopy gaps, which changes understorey microclimate and vegetation (Ares, Neill, & Puettmann, 2010;Nunes, Oliveira, Cabral, Branquinho, & Correia, 2014;Son, Lee, Jun, & Kim, 2004) and has been known to increase abundance and/or diversity of bees in other forests (Proctor, Burke, & Crins, 2012;Taki et al, 2010). Furthermore, another study that thinned longleaf pine forests close to our study region saw increased bee abundance and richness (Breland et al, 2018).…”

“…Thinning may lead to increases in biodiversity. A study conducted in a U.S. national forest in Georgia observed greater bee species richness in thinned compared to dense pine forests (Hanula, Horn, & O'Brien, 2015; but see Breland, Turley, Gibbs, Isaacs, & Brudvig, 2018). Fallen woody debris is another by-product of timber production that may be harvested for biomass (Riffell, Verschuyl, Miller, & Wigley, 2011a).…”

The Limits to Adaptation in Restored Ecosystems and How Management Can Help Overcome Them

“…Common garden experiments have identified candidate species for such efforts (Tuell et al, 2008;Rowe et al, 2018). Likewise, restoration management, such as thinning and burning, will often alter total pollinator abundances, community composition, and richness, sometimes negatively (Potts et al, 2003;Breland et al, 2018), in part by affecting nest sites and influencing floral resource availability (Potts et al, 2003;National Research Council of the National Academies, 2007). As a result, the scale at which disturbances are applied should be carefully considered to allow refuges for pollinators and other taxa (Shuey, 2013).…”