Investigating patterns of plant phenology provide insights into the ecological processes organizing a plant community. Although large scale patterns of phenological responses are informative on a regional scale, species-specific response to microsite differences may be more beneficial to local conservation and management efforts when determining best practices in a changing climate. We used Nantucket Island, MA as a study system where regional mainland patterns of phenological responses may not be applicable. As climate change has been shown to shift spring leaf out and flowering times, there are significant implications for the globally rare sandplain grassland and heathland habitats found on Nantucket.
We monitored eight native, dominant shrubs at eight microsites across 104 acres of sandplain grassland/heathland habitat for three growing seasons. Field observations were paired with twig warming experiments investigating the potential for species to take advantage of an earlier spring. In investigating common, native shrubs, we seek to understand how a community, driven by its dominant species, may change with warming spring temperatures. We ask: How do microsite conditions preceding leaf budburst affect the onset date for each species? Are some species potentially more vulnerable to earlier springs than others?
To date, budburst correlated primarily with minimum spring temperatures. However, temperature alone cannot explain the diverse budburst responses observed among our study species. Phenological responses were species-specific, with some species responding more to microsite variation in temperature than to site-wide temperatures. These species tend to be those that break bud first (Vaccinium angustifolium and Prunus serotina, e.g.). Early leaf-out plants are typically more resistant to late frosts with physiological trade-offs to minimize leaf damage. These species that can “take advantage” of small differences based on microsite, may be more nimble in responding to future climate change scenarios including earlier onset of spring and still be less vulnerable to late frosts.
Species with late budburst (Morella caroliniensis and Viburnum dentatum, e.g.) responded more to site-wide temperatures within each year. It is the “moderate” species (Gaylussacia baccata and Quercus ilicifolia, e.g.) that may be more vulnerable to earlier spring warming. These species are responding to microsite variation in temperature, but are more vulnerable physiologically to late frost damage. Differential climate sensitivities have implications for the assemblages of shrub communities in these threatened systems with predicted warmer temperatures.