Encroachment by shrubs has the potential to alter the phenology of high-light adapted species. In arctic and alpine regions, shrubs could initiate these novel interactions, as many shrub species have been expanding their ranges over time, and increasing in abundance in response to experimental warming. Īs species shift their ranges in response to climate change, novel species interactions (such as shading by newly arriving overstory species) could arise with the potential to alter phenological and performance responses to climate change. Interspecific competition for resources could also influence phenology for instance shading by overstory species can delay flowering and reduce reproductive success in understory species. For instance, a removal experiment in alpine ecosystems found that neighbor interactions shifted from facilitative to competitive with rising mean temperature at a site. However, interactions among plant species can also vary with climate. Most attention has focused on biotic interactions such as pollination or trophic interactions for which differing phenological sensitivities among interacting species could result in mismatch and loss of interactions. Along with temperature having a high degree of influence on phenological sensitivity, species interactions can also influence phenology, and hence may contribute to the observed variation. While advanced spring phenology is often observed in response to warming, there is significant variation among species in the magnitude and even direction of phenological responses. This study demonstrates that species interactions can modify phenological responses to climate change, and suggests that indirect effects of rising temperatures arising from shifting species ranges and altered species interactions may even exceed the direct effects of rising temperatures on phenology.Īlong with range shifts, earlier spring phenology (i.e., the timing of biological events such as leaf emergence or flowering) observed worldwide provides some of the best evidence that plant species are already responding to climate change. A shading treatment delayed phenology and lowered flower production, suggesting that shading may be the mechanism by which sagebrush presence delayed flowering of the understory species.
andersonii, but less so in the presence of sagebrush.
Warming significantly increased flower production of T. Both first flowering and peak flowering were strongly accelerated by warming, but not when sagebrush was present. Here, we describe how experimental warming and the presence of a range-expanding species, sagebrush ( Artemisia rothrockii), interact to influence the flowering phenology (day of first and peak flowering) and production (number of flowers) of an alpine cushion plant, Trifolium andersonii, in California’s White Mountains. Other indirect effects of climate change, such as shifting species composition and altered species interactions, may also be contributing to shifting plant phenology. While most species display earlier phenology with warming, there is large variation among, and even within, species in phenological sensitivity to rising temperatures. Shifts in plant species phenology (the timing of life-history events such as flowering) have been observed worldwide in concert with rising global temperatures.