Changes in Phenology of Flowering, Correlation with Climate Variability, and Response of Honeybees

Many studies have found that the timing of flowering has shifted temporally in response to climate change, but few have ascertained the possibility of asynchrony developing between flowering and pollinator appearance. Collapses in pollination could have serious consequences for interdependent plant-pollinator networks. Five years of plant-pollinator data collected in twelve montane meadows at the HJ Andrews Experimental Forest in Oregon provided an opportunity to examine how climate variability has affected the flowering of plants and how pollinators have responded. For nearly all plant species, the timing of flowering shifted significantly earlier from 2011 to 2015. Interestingly, the timing of first flowering, peak flowering, and last flowering did not shift uniformly with each other or consistently from year to year. The timing of flowering was highly correlated with both timing of snowmelt and cumulative degree days at June 1, probably because the growing season typically cannot commence until the snowpack melts. The earlier the snow melted, the earlier the flowering season commenced. Timing of flowering was less correlated with average Antecedent Precipitation Index from May 1 to June 1 (a proxy for soil moisture), which did not change consistently from year to year. Analysis of the timing of peak number of interactions between Apis mellifera (honeybee) and Eriophyllum lanatum from 2011 to 2015 indicated that its visitations to the flowers shifted temporally in parallel with shifts in flower timing. However, Apis mellifera is a generalist pollinator that is perhaps more adaptable to perturbations than specialists. Analysis of specialist species would give a better indication of increasing asynchrony in plant-pollinator networks over time. These findings provide a preliminary analysis of how climate variability has affected plant-pollinator networks in montane meadows at the HJ Andrews Forest and confirm the importance of maintaining species biodiversity in meadows as a way to buffer networks against the negative effects of climate change.