Abstract:
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.
