Effects of deer browsing on eastern hemlock growth and survival

Studies during the past six decades convincingly demonstrate that persistent browsing by native white-tailed deer (Odocoileus virginianus) eliminates the ability of eastern hemlock (Tsuga canadensis), white cedar (Thuja occidentalis), yellow birch (Betula alleghaniensis), and several other long-lived tree species to regenerate in forests of the upper Midwest and northeastern United States. The data shared here were used for three publications to date (see the Related Works section, below): The first is Alverson et al. 2019, which critically examined the relative contributions of deer versus snowshoe hare in reducing the growth and survival of eastern hemlock. The second is Alverson et al. 2024, a more detailed examination of growth and mortality rates of eastern hemlock, and the relationship of those two variables. The third is Waller et al. 2024, which explores the Regeneration Ratio, a new metric that integrates growth ("transit time" through the zone of vulnerability to browsing by deer and other herbivores) and mortality (half-life), and can be used to assess regeneration potential in populations of other tree species. (We are interested in collaborations to further test this metric for additional temperate and tropical species.)

This is a rich data set from extensive fieldwork in northern Wisconsin and the western Upper Peninsula of Michigan, USA, from 1991 to 2011. It will be useful to others who wish to check our results, or examine specific subsets of data, e.g., the growth and mortality of specific size classes of hemlocks, behaviour of cohorts during a specific decade relative to regional changes in deer or hare abundance, or the characteristics of cohorts growing in specific ownerships. Although we examined the relationship of diameter and height, we did not consider allometry in detail in these publications. We encourage others to explore the allometry of these indigenous, juvenile hemlocks and would be happy to share the limited additional data that we have, upon request.

Methods
Site selection, study plot location, assignment of individual hemlocks to plots and exclosure treatment, and protocols for growth and mortality data, and for pellet counts, are fully described in W.S. Alverson and D.M. Waller, 1997. Deer populations and the failure of hemlock regeneration in northern forests. Pp. 280-297 in W.J. McShea et al., eds. The science of overabundance: Deer ecology and population management. Smithsonian Institution Press, Washington, DC.

A description of the analyses, and a summary of protocols, are provided in W.S. Alverson, D.A. Riege, and D.M. Waller. 2024. Losing the slow race: How deer hinder growth, survival, and regeneration of juvenile hemlocks (Tsuga canadensis). Forest Ecology and Management. [https://doi.org/10.1016/j.foreco.2023.121466]