Identifying and Projecting Novel Long-Term Phenological Trends: Integrating Heterogeneous Data Sources



Garretson, Alexis

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Studies of climate change in deciduous forest communities mainly document the earlier appearance of spring leaves and later senescence in autumn. However, climate change can create novel patterns of growth or shift other aspects of plant phenology. To determine if such changes have occurred in eastern United States forests, I examined digitized herbarium specimens of sugar and red maple (Acer saccharum and A. rubrum: Sapindaceae) for the presence/absence of expanding leaves of buds, fruit, flowers, and colored leaves, as well as evidence of pathogen and herbivory damage. Available herbaria specimens ranged from 1892 to 2017 but were dominated by specimens collected in the 1970s. Citizen science records were largely dominated by specimens observed in the late 2010s and served to verify changes observed in herbaria records. Evaluations of the herbaria specimens show evidence of earlier spring phenology in maples, as well as a reduction in reproductive activity, and some evidence of aseasonal leaf production occurring before the winter dormancy. Additionally, decadal comparisons uncovered increases in fall pathogen damage and herbivory over the past 120-years, with both species showing an increase in pathogen damage and A. saccharum showing an increase in herbivory. My results also show species-specific phenological changes and differing magnitudes of responses to different climate factors, stressing the need to control for species identity and develop species-specific models of the impact of climate change on phenology. Overall, this work serves as a demonstration of the utility of herbaria specimens to document changing phenology, species interactions, and ecology while validating the results by comparisons to ongoing citizen science monitoring programs.


This thesis has been embargoed for 10 years. It will not be available until August 2030 at the earliest.


Phenology, Herbarium, Maple trees, Citizen science, Climate change, Plant-insect interactions