Abstract
Recent studies suggest climate-related delays in the timing of leaf coloration and abscission in maple trees but lack baseline data prior to the late 20th century. To better understand how autumn foliar phenology and late-season damage risks have changed for this genus over the past century, we evaluated 2,972 digitized herbaria specimens of red and sugar maple collected between 1826 and 2016 for the presence of leaves, autumn leaf coloration, and pathogen or herbivore damage. We found that the onset (first appearance) of colored leaves has shifted 0.26 days later each year, leading to a delay of more than a month in autumn phenology since 1880. We find that these shifts are related to precipitation regimes in both the fall and summer seasons and that more severe droughts are associated with higher probabilities of colored leaves. Moreover, we found that the probability of both herbivory and pathogen damage has increased significantly over the study period. In particular, we find a strong association between increasing summer drought conditions and increased probability of herbivory. Furthermore, the presence of foliar damage increased the probability of leaf coloration on herbaria specimens. However, the end-of-season abscission date (last appearance of leaves) was strongly associated with herbivory and climate in a contrary direction: Increasing yearly drought, higher fall temperatures, and the presence of herbivory were associated with earlier abscission. In fact, the last leaf dates for specimens with herbivory were nearly 2 weeks earlier than specimens without herbivore damage. Our study documents significant changes in maple senescence over the last 150 years and suggests that incorporating herbivory into models may improve our ability to predict forest responses to climate shifts.
Highlights
Scientists find that climate change has lengthened the growing season of deciduous forests by advancing spring leaf out (Badeck et al, 2004; Wolfe et al, 2005; Menzel et al, 2006; Polgar and Primack, 2011; Wolkovich et al, 2012; Ellwood et al, 2013)
To establish long-term patterns for both abiotic and biotic stressors on autumn phenology and determine whether insect and pathogen damage have changed with climate warming, we examined herbaria specimens of red and sugar maples collected over the past two centuries
Our analyses of red and sugar maple phenology suggest that autumn coloration has been delayed by approximately 0.26 days/year since 1826, leading to a delay of more than a month in recent decades (Figures 2, 3)
Summary
Scientists find that climate change has lengthened the growing season of deciduous forests by advancing spring leaf out (Badeck et al, 2004; Wolfe et al, 2005; Menzel et al, 2006; Polgar and Primack, 2011; Wolkovich et al, 2012; Ellwood et al, 2013). Findings for autumn phenology have varied, with some suggesting temperature-related advancements in leaf. Short term experiments show a delay of autumnal leaf senescence and abscission for some species, such as maple, in response to soil warming and increasing ambient temperatures (Norby et al, 2003; Wheeler et al, 2016). Remote sensing studies document a later end to the vegetation growing season of approximately 5 days since the 1980s (Liu et al, 2016). Because of the limited temporal scope of studies, many questions remain about the responses of forest ecosystems, including how long climate stress has been influencing forest phenology and if the rate is increasing in current years
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