Herbarium specimens as tools to assess the impact of large herbivores on plant species

Abstract

Herbarium specimens can be used to reconstruct spatiotemporal changes in plant morphology caused by environmental pressures. The reliability of herbarium-derived data requires evaluation, because specimen collection is subject to biases. We used herbarium and field data to investigate the impact of large herbivore browsing on the size of a forb. White trillium (Trillium grandiflorum (Michaux) Salisbury) was studied because the impacts of white-tailed deer (Odocoileus virginianus Zimmermann) browsing on this species are well-known. A total of 692 herbarium specimens collected in Quebec (Canada) were used to evaluate leaf area. Leaf area values of herbarium specimens were compared with those of modern (2013, 2014) specimens collected in sites either with >8 deer per square kilometre or without deer. Flowering individuals in modern sites with deer had a significantly lower leaf area than herbarium specimens and modern specimens collected in sites without deer. The distribution of white trillium individuals in deer sites was also skewed towards plants with a smaller leaf area. Herbarium specimens may offer unique and inexpensive data, compared with methods traditionally used to assess the impacts of herbivores on plants, such as exclosures or clipping experiments. Unfortunately, this rich data source is seriously jeopardized by the downtrend in specimen collecting.