Pollination of a bee‐dependent forb in restored prairie: no evidence of pollen limitation in landscapes dominated by row crop agriculture

Abstract

Restoration is used to conserve biodiversity; however, it is unclear to what extent restoration impacts ecosystem functions. Pollination is an ecosystem function that is critical to plant reproduction and thus restoration success. Few studies have assessed whether pollination is restored within restoration areas themselves. Plant–animal interactions may be affected by factors beyond the scale of the restoration. For example, surrounding landscape context may influence pollinator abundance and consequently the amount of pollen deposited. Decreased pollen receipt might then limit seed set. We hypothesized that in restorations surrounded by more agriculture, pollinator‐dependent forbs would experience greater pollen limitation. This would likely be due to declines in pollinator abundance within the restorations with an increase in surrounding agriculture. We deployed potted Chamaecrista fasciculata (Fabaceae), an obligatorily bee‐pollinated forb, and sampled bee communities in restored prairies in Minnesota, U.S.A. We measured pollen limitation by comparing seed set among open and supplementally pollinated plants. We also sampled native bees in seven of the eight sites. We tested for a relationship between proportion row crop agriculture (corn and soy) surrounding a restoration and pollen limitation, as well as an effect of agriculture on bee abundance. We did not find evidence that increasing proportion of surrounding agriculture negatively affected pollen limitation or bee abundance. Our results indicate that greater surrounding agriculture may not influence pollination of C. fasciculata through declines in pollinator availability, and suggest for some plants that landscape context might not limit pollination in restorations.

Floral resource diversity drives bee community diversity in prairie restorations along an agricultural landscape gradient

“…Our results indicate that bee communities may benefit from restorations even in highly agricultural landscapes, especially in restorations with high floral diversity. This is especially important as it suggests that the creation of new habitat complexes in agriculturally dominated landscapes will effectively conserve bees, and potentially sustain bee pollination services (Ritchie, Lane, & Cariveau, 2020). Based on our results we propose that planting and managing restorations to achieve high floral diversity in restorations is an effective way of supporting diverse and heterogeneous bee communities within the highly agricultural landscapes of the tallgrass prairie region.…”

A review of the challenges and opportunities for restoring animal-mediated pollination of native plants

“…In Europe, agri-environment-based pollinator plantings are most effective at increasing relative abundance and richness of pollinators in landscapes were between 1% and 20% of the surrounding landcover was still in semi-natural habitat [105]. Ritchie et al [38] did not find a relationship between the increasing area of agriculture surrounding a restoration and overall bee abundance and pollen limitation of an annual forb, suggesting that restorations can have positive effects on pollination regardless of placement within the landscape.…”

“…Pollen supplementation studies can help to quantify the relative effect of resources and pollen receipt for limiting plant reproduction. Few studies have directly tested for pollen limitation in restorations (but see [38]) [31,39].…”

Pollinator‐mediated effects of landscape‐scale land use on grassland plant community composition and ecosystem functioning – seven hypotheses

“…Landscape configurational heterogeneity, in terms of increasing densities of field edges (Hass et al ., 2018) and connectivity between fragments (Cranmer, McCollin & Ollerton, 2012), has also been shown to lead to higher pollinator‐mediated seed set in phytometers. However, surrounding landscape‐scale context was not important in driving seed set of a bee‐pollinated forb in prairie restoration sites (Ritchie, Lane & Cariveau, 2020), and fragmentation was found to be of little importance compared to local conditions in a rockland plant (Costin, Morgan & Young, 2001; Roque, Koptur & Sah, 2017). In renosterveld fragments in South Africa, seed set and pollen limitation did not differ between fragments even though pollination rate and pollinator species richness were reduced in smaller and more isolated fragments (Hauber et al ., 2022).…”