Anticipated consequences of climate change already seen in temperate regions include early spring warmup. These early warm temperatures may mean that certain species can extend their growing seasons and take advantage of favorable conditions. However, we are also seeing warm springs punctuated by intermittent hard freezes. Warm weather can accelerate leaf flush in perennial woody species, potentially exposing vulnerable young tissues to damaging frosts. Earlier warming temperatures may also limit the winter chill accumulation necessary for many temperate woody shrubs affecting timing of leaf-out and reproductive potential.
Using a combination of field observations and twig warming experiments, we study the effects of spring warming on eight different species of native shrubs considered characteristic of our study landscape. These shrubs represent a variety of plant families and reproductive strategies while also constituting the dominant, native shrubs of the study ecosystem. In addition, we investigated the phenological cycles of the eastern tent caterpillar (Malacosoma americanum) in the field, its boom and bust cycles, and host preferences.
Results/Conclusions
Responses to warming temperatures have been species-specific. Some species were able to take advantage of the earlier spring temperatures; either leafing out or producing flowers soon after the on-set of warmer temperatures (e.g. Vaccinium angustifolium and Gaylussacia baccata). These species with lower chilling requirements might profit from warming winters, potentially extending their growing seasons and reproductive potential, barring any effect of late spring frosts.
Species more reliant on winter chilling requirements cannot similarly respond to earlier warming, potentially limiting any advantage to a longer growing season. Malacosoma americanum have been shown to be particularly sensitive to temperature, hatching soon after the onset of spring. In field observations, their primary host plant, Prunus serotina, has not been as adept at initiating spring budburst with earlier warm temperatures. Our twig experiments compliment field data demonstrating that the stricter winter chill requirements of these native cherries prohibit early spring leaf out. Lack of winter chilling not only led to a considerable delay in budburst for some species, but also caused substantial changes in the chronological order of species' budburst. Differential climate sensitivities have implications for the assemblages of shrub communities with predicted warmer temperatures.