A 20-year experiment on the effects of deer and hare on eastern hemlock regeneration

Abstract

Eastern hemlock (Tsuga canadensis (L.) Carrière) is a shade-tolerant, slow-growing tree once common in forests across the Great Lakes region. It was heavily exploited in the late 19th and early 20th centuries and now experiences limited regeneration across much of its range. This failure to regenerate has been ascribed to poor seedbed conditions, insufficient canopy openings, warmer climate, and browsing by white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) or snowshoe hare (Lepus americanus Erxleben, 1777). To test whether deer or hare limit hemlock regeneration, we studied >2000 hemlock seedlings inside and adjacent to experimental deer exclosures at 59 sites randomly distributed across hemlock and hemlock-component stands in northern Wisconsin and the western Upper Peninsula of Michigan in the United States. We monitored local deer and hare abundance, seedling growth, and seedling survival for 20 years. Two First Nations reservations showed lower deer density and greater survival and growth of unprotected seedlings than three national forests of the United States. Cohorts of hemlock seedlings protected from deer survived at a rate four times higher than those exposed to deer (59.3% vs. 15.0%) and shared a combined height 5.2 times greater. Hare densities significantly affected seedling survival only within exclosures. This extensive, long-term study identifies deer as the primary factor constraining hemlock regeneration in the region.

Herbivory mediates direct and indirect interactions in long‐unburned chaparral

“…Many other studies also show community impacts of ungulates without leading to alternative ecological states (e.g., Nishizawa et al, 2016; Russell et al, 2001). However, browsing can speed or retard shifts to alternative states depending on herbivore preferences for dominant species (Alverson et al, 2019; Cote et al, 2004; Ramirez et al, 2019).…”

Where have all the flowers gone? A call for federal leadership in deer management in the United States

“…Deer are selective browsers (although elk consume a higher proportion of grasses) and at low abundance limit recruitment of species they prefer to consume; at high abundance, deer can eliminate herbaceous and woody recruitment entirely (Figure 1), a process that plays out over decades. Island and exclosure studies implicate deer as the main driver of differences in plant community composition regardless of climate or previous land-use (Mudrak et al, 2009;Goetsch et al, 2011;Martin et al, 2011;Frerker et al, 2014;Alverson et al, 2019;Kelly, 2019;Dobson et al, 2024). Wildflowers and many shrubs never escape deer browsing and so tend to disappear first.…”

“…This is not only a problem in the Northeast, nor is it only wildflowers that have vanished. Entire cohorts of tree seedlings in forest understoriesrepresenting future forestsface poor survival odds and forests in the Great Lakes, Mid-Atlantic and Northeast (including National Parks and Monuments) are in imminent danger of recruitment failure affecting landscapes for decades to come (Patton et al, 2018;Rogers and McAvoy, 2018;Alverson et al, 2019;Miller and McGill, 2019;Miller et al, 2023). In western North America, black-tailed or mule deer (Odocoileus hemionus) and elk (Cervus elaphus) create similar problems (Porter and Underwood, 1999;Binkley et al, 2006;Martin et al, 2011;Rogers and McAvoy, 2018;Chollet et al, 2021) in western forests.…”