PS 26-69 - Pervasive phenological mismatches between native and nonnative temperate forest plants

Background/Question/Methods

As the climate warms, organisms are adjusting the timing of their life cycle events, or phenology, to warmer temperatures and longer growing seasons. The magnitude and direction of these phenological shifts are highly variable among species, which may lead to asynchronous phenological shifts—or phenological mismatches—between interacting species. Here, we study phenological mismatches among canopy trees, midstory shrubs, and herbaceous forbs common to North American deciduous forest ecosystems. We combine observational studies of early spring phenology with a controlled growth chamber study to ask how native and nonnative temperate forest species from 3 forest strata layers change their spring leaf-out phenology to experimental manipulation of winter chilling and spring warming temperatures. We studied the phenology of cut twigs from 4 trees and 7 shrubs, as well as potted individuals of 6 understory herbs collected at two time points (early and late winter, simulating short and long winter chilling exposure) and placed in growth chambers set to ambient and warm spring temperatures. We ask how does plant origin and strata affect phenological sensitivity to winter chilling and spring warming temperatures?

Results/Conclusions

We found evidence for phenological mismatch between natives and nonnatives as well as plants occupying different forest strata. Across all species, leaf emergence of natives was two times slower than nonnatives (natives-35.5 days ± 2.8 s.e.; nonnatives-16.4 days ± 4.4 s.e.). Leaf emergence of canopy trees (39.5 days ± 4.1 s.e.) and midstory shrubs (25.8days ± 3.8 s.e.) was 2 and 3 times slower, respectively, than emergence of herbaceous wildflowers (12.3 days ± 5.5 s.e.). Plant phenology responded strongly to experimental warming and winter chilling, advancing leaf emergence by ~25% in warmed relative to ambient chambers and ~30% in plant collected in late relative to early winter. Overall, plants were more phenologically sensitive to winter chilling relative to spring warming. Canopy trees and midstory shrubs advanced their leaf-out times by 50% when collected later in the winter but wildflowers showed no response to collection date. Native plants advanced leaf out time by 50% at later collection dates, relative to nonnative plants that had little sensitivity to collection date. Overall, our data support that forest plants will shift their phenology in response to future global warming winters and springs, but to different degrees leading to potential phenological mismatches among forest strata.