A 19th century naturalist and a 20th century hunting guide reveal phenological mismatches in temperate deciduous ecosystems

Background/Question/Methods: Advancing spring phenology is among the most visible, highly documented, and well-studied ecological impacts of anthropogenic climate change. Long-term monitoring, historical records, and experiments have established that plant phenology in general is shifting earlier in response to warmer temperatures, while populations, species, and functional groups vary in the sensitivity of their responses. These variations in phenological sensitivity may disrupt the timing of ecological interactions, causing phenological mismatch as interacting species shift their phenological events at different rates in response to environmental change. Documenting the impact of phenological mismatch is challenging because it requires detailed records of both species (establishing different rates of phenological response) and measures of the ecological effects of decoupling their interaction. The journals of Henry David Thoreau and a Maine hunting guide hold clues to trophic and non-trophic phenological mismatches in temperate deciduous forests in the northeast United States. From these historical ecological records we determine variations in phenological responses to spring temperatures among plants and migratory birds in Maine and canopy trees and understory wildflowers in Massachusetts.

Results/Conclusions: Phenological mismatch is occurring in temperate deciduous ecosystems within plant communities and between trophic levels. We establish different rates of phenological response in two case studies. Migratory bird arrivals are decoupled from spring temperatures while both wildflowers and trees advance flowering (-2.5 days/°C) and leaf out (-2.3 days/°C) in warmer Aprils in Maine. In Massachusetts, leaf out among canopy trees is more sensitive to spring temperatures (-4.4 days/°C) than understory wildflowers (-2.2 days/°C). The higher sensitivity in trees leads to a shrinking period of high light in spring for understory species. We combined contemporary field experiments with these results to estimate of the ecological effects of this phenological mismatch. We modeled the changes in carbon budgets for wildflowers under longer (cooler historical conditions, when the canopy closed later) and shorter springs. Wildflowers had 6.2–8.0% larger annual carbon budgets in the 1850s, and by 2080, their annual carbon budgets may be 5.7-12.6% lower than today. Both case studies highlight the importance of historical records in climate change research, as well as the challenges and limitations of historical data to establish potential mismatches. Further work on the ecological impacts of variations in changing phenologies is needed.