Restoration of pollinator diversity, function and resilience in Michigan prairie fen

While species diversity is often used as an indicator of successful habitat restoration, the restoration of ecological function and its resiliency are ultimately the critical measures of success. We examined multiple metrics of pollinator and pollination service restoration following clearing of invasive glossy buckthorn (Frangula alnus) from portions of a prairie fen wetland system in Michigan. The metrics include: 1) pollinator diversity and abundance, 2) pollinator function using the sentinel plant Asclepias incarnata, and 3) quantitative food webs describing plant-pollinator interactions. We compared each of the metrics in four different treatments: 1) uncleared controls, 2) cleared, previously buckthorn invaded areas, 3) on-site uninvaded reference areas, and 4) an off-site reference area considered among the highest quality prairie fens in Michigan. We tested the hypotheses that pollinator diversity, abundance, function, and quantitative web linkage number would be greatest in off-site, followed by on-site reference areas, cleared, and uncleared control treatments. We found no significant differences in bee or butterfly abundance or diversity between cleared and on- or off-site reference areas, while both diversity and abundance remained low in uncleared control areas. Similarly, pollination function was restored in cleared areas, but significantly more insects were still observed at sentinel flowers in the off-site reference. We used quantitative food webs to explore the potential resiliency of pollination services in restored and reference areas. We conclude that consideration of species interactions can provide a more complete picture of habitat restoration outcomes than species diversity alone.