Thursday, August 15, 2019: 2:50 PM
M112, Kentucky International Convention Center
Background/Question/Methods
Plants in the temperate zone adjust their seasonal timing to fit windows of favorable biotic and abiotic conditions. These adjustments (phenological traits), are diverse and ecologically important, but there is little direct evidence of their role in shaping the relationship between climate and plant community composition. A better understanding of how phenology mediates the climatic filtering of traits and species within communities could improve our predictions of spatial and temporal reassembly under climate change. Here we test the hypothesis that the phenological traits of species are filtered from communities to reduce exposure to extreme climatic events (snowfall, freezing and drought) during reproduction. We combined large observational datasets on microclimate and flowering time from three communities of montane and subalpine forbs along a macroclimate gradient in the Western USA. Using Bayesian hierarchical models, we estimated phenological responses of species in the three communities to aspects of locally-measured microclimate. We then assessed the strength of regional-scale and local-scale filtering of phenological traits using null models that compared snow, freezing, and drought frequencies experienced by species in the native community to the extreme event frequencies experienced by randomly assembled groups of species from local and regional species pools.
Results/Conclusions
We found evidence of strong climatic filtering of community phenology across both microclimate and macroclimate gradients, but the amount of filtering and the aspects of climate that were strong filters differed significantly among locations. Phenological traits were most strongly filtered to avoid snow at Mt. Rainier National Park (WA), where the growing season was shortest, and were filtered to avoid freezing at Rocky Mountain Biological Lab (CO), a site with a high risk of freeze events during the growing season. In contrast, phenological traits at MPG Ranch (MT) were filtered to avoid late-summer drought. Within each study area, the strength of climatic filtering varied considerably across elevation gradients. Collectively this work suggests that the match between climate and phenological traits plays an important role in community assembly by determining which species can match their reproductive timing to periods that avoid climatic disruption. Our work also suggests that the trend towards reduced snowpack and longer growing seasons observed in high-latitude and mountain environments across the globe will weaken filtering of phenological traits in local communities. This could facilitate the invasion of species with new phenological strategies into these systems, altering both community composition and ecosystem function.