Bumble bee colony growth and reproduction on reclaimed surface coal mines

Reclamation of coal mine lands in the eastern United States creates pockets of grassland habitat in an otherwise predominantly forested region. These sites may represent an opportunity for pollinator conservation if they provide valuable foraging habitat for wild bees. To determine site characteristics that influence bee success on reclamation lands, we monitored growth and reproduction of 24 commercially reared bumble bee (Bombus impatiens) colonies placed on 12 former coal mines (aged 2 to 30+ years post-reclamation) in Ohio, U.S.A. Twenty colonies survived the duration of the experiment (May-August 2014). All colonies produced both new queens (mean 21.0 +/- 37.0 SD) and males (36.5 +/- 36.5), in proportion to overall colony size. Results of generalized linear models indicate that colony growth and reproduction increased with floral diversity and species turnover, and declined with site area and the proportion of forest in the surrounding landscape. The sex ratio of reproductive offspring was significantly more male-biased on sites with low flower diversity, underscoring the importance of floral diversity for meeting the higher resource demands of queen production. Floral resource composition and consistency were influenced by site age and surrounding landscape. Older sites had higher floral diversity and species turnover throughout the season than younger sites, and included high-quality native bee forage plants. We discuss the implications of this study for reclamation project managers seeking to promote bee reproduction and conservation.