Journal
AMERICAN JOURNAL OF BOTANY
Volume 101, Issue 8, Pages 1293-1300Publisher
WILEY
DOI: 10.3732/ajb.1400045
Keywords
climate change; forests; herbarium specimens; leaf-out; New England; phenology; remote sensing; trees
Categories
Funding
- iDigBio program of the National Science Foundation
- Div Of Biological Infrastructure
- Direct For Biological Sciences [1115210] Funding Source: National Science Foundation
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Premise of the study: There is great interest in studying leaf-out times of temperate forests because of the importance of leaf-out in controlling ecosystem processes, especially in the face of a changing climate. Remote sensing and modeling, combined with weather records and field observations, are increasing our knowledge of factors affecting variation in leaf-out times. Herbarium specimens represent a potential new source of information to determine whether the variation in leaf-out times observed in recent decades is comparable to longer time frames over past centuries. Methods: Here we introduce the use of herbarium specimens as a method for studying long-term changes in leaf-out times of deciduous trees. We collected historical leaf-out data for the years 1834-2008 from common deciduous trees in New England using 1599 dated herbarium specimens with young leaves. Key results: We found that leaf-out dates are strongly affected by spring temperature, with trees leafing out 2.70 d earlier for each degree C increase in mean April temperature. For each degree C increase in local temperature, trees leafed out 2.06 d earlier. Additionally, the mean response of leaf-out dates across all species and sites over time was 0.4 d earlier per decade. Our results are of comparable magnitude to results from studies using remote sensing and direct field observations. Conclusions: Across New England, mean leaf-out dates varied geographically in close correspondence with those observed in studies using satellite data. This study demonstrates that herbarium specimens can be a valuable source of data on past leaf-out times of deciduous trees.
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