Using herbarium specimens to study evolutionary change related to climate warming - novel uses of natural history collections through specimen and label images

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The objective of this project is to use herbarium specimens to document inter- and intra specific leaf-out times of 17 European tree species over the past c. 130 years and to infer micro- and macro-evolutionary changes in their phenological strategies that relate to climate. Within the SPP 1991, this project falls into research focus 3, novel uses of natural history collections through analyses of specimen and label images, including computer vision/machine learning. We will use (images of) thousands of specimens from throughout the range of the focal species to quantify change in (i) populations along latitude and longitude, (ii) over time, and (iii) between species of known phylogenetic relationships. Pilot data are presented in the proposal. Because the fastest increase in day length at any particular latitude occurs at the same time each year, photoperiod-sensitive species are expected to show lower spatial and inter-annual variation than photoperiod-insensitive species. Up to now, no study has tested these twin hypotheses, however, because light is difficult to control for adult trees, and saplings in climate chambers cannot be used because they leaf-out at different times than adult trees. Building on work of Unger, Merhof, and Renner (BMC Evol. Biol., in press), we also want to apply their Support Vector Machine code, which was developed for 13 of the same species. The herbarium approach to studying leaf-out times can provide long time series for tree phenology and allows going back in time to infer the magnitude and direction of tree responses to climate warming.