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. For example, regrowth of leaves after late spring frost damage or increases in herbivory as a result of climate change can generate aseasonal new leaf production in summer and autumn. To determine if such changes have occurred in eastern United States forests, we examined digitized herbarium specimens and citizen-science images 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 fungal and herbivory damage. Available herbaria specimens ranged from 1892 to 2017 but were dominated by specimens collected in the 1970s. Citizen science images were largely dominated by specimens observed in the late 2010s and served to verify changes observed in herbaria records.
Results/Conclusions
Comparisons of pre- and post-1960 herbaria collections show that maples experienced a lengthening of the time span of new leaf production. Specifically, we documented new leaf production in every month from April to September compared to a simple peak prior to 1960 of buds and expanding leaves in May. Additionally, decadal comparisons uncovered increases in fall fungal damage and herbivory over the past 200 years. Our results indicate that the effect of climate warming go beyond a simple lengthening of leaf life span and instead radically change the seasonal timing of new leaf production with impacts on multi-trophic interactions. Such novel phenological patterns may require modifications to current climate models of carbon and nutrient sequestration.