Agricultural land use causes drastic changes to ecosystems which can last for decades or centuries after agricultural activity has stopped. One way to mitigate these impacts is through restoration of post-agricultural lands; however, the interplay between agricultural history and restoration remains poorly understood. This is particularly true for interactions among species, such as plant-pollinator interactions. We investigated how experimental restoration of longleaf pine (Pinus palustris) forests with differing land-use histories affects plant-pollinator networks. The experiment included 32 1-ha plots, representing a factorial cross of restored vs. unrestored and post-agricultural vs. remnant, which have no known history of agriculture (n=8 for each treatment combination). Longleaf pine forests are characterized by a sparse canopy. In restored plots, we thinned the trees down to 10 pine trees per hectare to reinstate this forest structure. Within each plot, we recorded pollinator visitations to plants and constructed pollination networks from these data. We asked: how are (1) pollinator and flowering plant communities and (2) pollination network structure affected by restoration, land-use history, and their interaction?
Results/Conclusions
We collected or observed 3041 insects from 148 species or morphospecies visiting flowers from 57 plant species. There was a marked effect of restoration on flowering plant and pollinator communities with floral and pollinator abundance and species richness all significantly higher in restored plots (all four effects: p<0.001). Both floral and pollinator communities were also affected by the interaction between land-use history and restoration. Pollinator and floral abundance, pollinator diversity, and floral species richness were all lowest in unrestored, remnant plots (p = 0.039, 0.001, 0.076, and 0.0004, respectively), while there was no effect of land-use history on floral or plant communities in restored plots. Due to the low numbers of pollinator visits observed in unrestored, remnant plots, we looked at pollinator network structure in restored plots alone. We found that after restoration, remnant plots supported more specialized networks (higher H2’, p = 0.013) than post-agricultural plots. Agricultural history did not affect network connectance, interaction evenness, or interaction asymmetry. These results illustrate large positive effects of forest restoration, along with more nuanced effects of agricultural history, for floral and pollinator communities and plant-pollinator interactions.