Abiotic and Biotic Factors Affecting Restored

Pollinator Habitat in Solar Installations

In the United States, land dedicated for solar energy installations is increasing rapidly to meet renewable energy goals. However, multi-acre utility-scale solar energy have potential adverse effects caused by large-scale landscape transformation (Trainor et al. 2016; Hoffacker et al. 2017). An increasingly popular solution to mitigate negative environmental effects of solar sites involves using the space between panels as restored pollinator habitat. Planting and maintenance of pollinator-friendly plant communities in these spaces pose unique challenges that make consideration of both abiotic (e.g. soil type, nutrients, and climate) and biotic (e.g local pollinator community, hardiness of plant species) factors for long-term success. We investigated the roles of soil nitrogen and plant species on pollinator preference.

In one experiment, three cultivars of Brassica rapa (Brassicaceae) were grown under high and low nitrogen levels to determine the effects of soil conditions on pollen production and attractiveness to bumble bees (Bombus impatiens). A two-way, mixed model ANOVA was used to evaluate effects of nutrient level and plant type on plant biomass, pollen grain area, and number of pollen grains. When given 100% of recommended nitrogen, plants had a higher production of pollen grains than plants grown with low levels of nitrogen. Size of pollen grains was not affected by soil nitrogen, but rather by cultivar. These differences in size and number of pollen grains can be important for bee foraging preferences, although we found that genotype was only a marginally significant factor in bumble bee foraging preferences of these plants.

In a second experiment we evaluated the relative attractiveness of 10 species and cultivars of mints from two plant genera, Mentha and Pycnanthemum, at two semi-natural study sites known to support diverse a pollinator community in central Pennsylvania (Russo et al. 2013). Linear mixed effects models were used to examine the fixed effects of selected factors on abundance of visitors within an insect order, total visitor abundance, and diversity of visitors. The native M. arvensis had the greatest abundance of pollinator visitors, but all species and cultivars showed similar diversity of pollinators. The two mint genera also served as generalist plants within this plant-pollinator network, attracting pollinators from the insect orders Hymenoptera, Lepidoptera, Diptera, and Coleoptera. Generalist plant species are important to pollinator communities as they can attract and provide resources for generalist pollinators (those that visit a variety of plant genera/families) as well as specialists (those that visit only a select number of plant genera/families) (Martín González et al. 2010; Ollerton 2017). Thus, native Mentha and Pycnanthemum may be good additions to restored pollinator habitat at solar sites, where attractive, low-maintenance, fast-growing, hardy, and short statured plants are preferred.

The results from both studies revealed the importance of choosing the right plant species to support pollinator communities. Our results also provide better understanding into the importance of soil nutrition on pollen floral resources and ultimately the plant’s attractiveness and utility to pollinator species. Ultimately, we hope these insights will help to improve the quality of restored pollinator habitat.

Presenter:  Sarah Kania is an early career entomologist/pollination ecologist. She completed her master’s at Penn State in entomology, focusing on plant-pollinator interactions and pollinator habitat restoration. She currently works for Penn State conducting wild bee research and has more recently joined ASA as a scientist to help develop pollination-related services to ASA’s clients.

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