Impacts of climate change on the phenology of temperate forest plants and birds in Massachusetts and Japan

The timing of phenological events such as flowering and bird migrations is highly sensitive to changes in climate. Phenology affects many physiological, community, and ecosystem processes, but availability of long-term data is limited. I examined historical records of plant phenology in Massachusetts and Japan, beginning with observations made in the 1850s by Henry David Thoreau in Concord, Massachusetts. By combining these records with my own observations and experiments, I found that flowering in Massachusetts shifted forward by approximately one day each decade over the past century because of warming temperatures. Importantly, these changes varied among species; some changed more, some less, and others did not change. Plants flowering early in the spring responded more to warming temperatures than did summer flowering plants. Records from Mt. Takao, Japan showed that early flowering cherry species and individual trees were the most responsive to warming temperatures. Experimental evidence showed that structural and physiological traits, such as xylem vessel diameter and inflorescence water content, might explain why some closely related species responded differently to climate change. Novel data sources such as photographs and herbarium specimens from Concord and the Arnold Arboretum showed changes in flowering times that were indistinguishable from changes indicated by conventional scientific observations.; As part of my investigations, I reviewed data on two additional spring phenomena that might vary with changes in temperature: bird migration times and Boston Marathon race results. Warming temperatures have not affected winning marathon times due to high variability in race day temperatures. However, bird migrations, like flowering times, have shifted forward about one day per decade. Moreover, the migration times of birds that winter in the southern United States respond more strongly to warming than those of birds wintering in South America. Long-term data from the Manomet Center for Conservation Sciences and Mt. Auburn Cemetery show that changes in population size or sampling effort can alter the date that bird migrations reportedly occur. Researchers who overlook these methodological issues can reach incorrect conclusions. Despite variations in responses to climate change, many responses are predictable, which will help us to manage for future climate change.