Plant Biodiversity

Oh, deer! Overpopulation is taking a toll on Wisconsin’s forests, Isthmus, Oct 24, 2019By some estimates, there are now more deer on Wisconsin’s landscape than since the Ice Age. With 2019 herd estimates ranging between 1.9 and 2 million-plus animals, the annual fall hunt for the white-tailed deer — the state’s most iconic animal after the cow — should be a productive one for the more than half a million gun and bow hunters who will take to the field. But the abundance of deer, especially in the southern portion of the state but also in the north where the regeneration of certain tree species is now at risk, continues to be a fraught bio-political issue.
Studies by retired UW-Madison forest ecologist Don Waller, an expert on the effects of deer on forest ecosystems, have shown that plant species diversity due to an overabundance of deer has been reduced by 15 percent. Tree species such as hemlock, white cedars, yellow birch and pines, among others, are failing to regenerate, changing forest composition. Likewise, the native plant communities that make up the forest understory are listed by Waller as ‘losers’ in the deer vs. plant calculation. Native orchids, lilies and a litany of less flashy forest herbs rank high on the deer menu. “There are a lot of cascading effects on other species,” says Waller, adding that browsing deer often pave the way for invasive plants.

One of the world’s largest organisms is shrinking, Science, Oct 17, 2018The Pando aspen grove, located in central Utah, is the largest organism on the planet by weight. From the surface, it may look like a forest that spans more than 100 U.S. football fields, but each tree shares the exact same DNA and is connected to its clonal brethren through an elaborate underground root system. Scientists first noticed the Pando shrinking in the late ’90s. They suspected elk, cattle, and most prominently deer were eating the new shoots, so in the new study Rogers and colleagues divided the forest into three experimental groups. One section was completely unfenced, allowing animals to forage freely on the baby aspen. A second section was fenced and left alone. And a third section was fenced and then treated in some places with strategies to spur aspen growth, such as shrub removal and controlled burning; in other places it was left untreated. The results were surprising: Simply keeping the deer out was enough to allow the grove to successfully recover, the team reports today in PLOS ONE. Even in the fenced-off plots where there was no burning or shrub removal, young trees were thriving.

Volunteers trained to track forest health, The Altamont Enterprise, May 10, 2018The AVID focuses research and monitoring efforts on wildflower and tree species eaten by deer in New York and includes laying out monitoring plots in forested areas. Within these plots, individual plants of the focal species are counted, marked, and measured. Measuring these same plants each year will show whether browsing pressure from deer is changing over time and is expected to provide critical information for DEC biologists to guide deer management decisions.

White-tailed deer can have significant impacts on forests and the other animals in that habitat, according to a release from the DEC. The effects of deer browsing can persist for decades.

Without its ‘understory’ layer, the forest will collapse,, April 17, 2018This study uses a “treasure trove of data” collected by former Rutgers professor Murray Buell from 1948 to 1972. Buell studied forests at 13 sites in four central New Jersey counties. “Those studies were conducted prior to the deer population explosion,” Kelly said, noting that white-tailed deer essentially vanished from New Jersey prior to 1948 and did not rebound until decades later.

Kelly and his students surveyed these same forests … and the differences today are astounding. While Buell counted an average of 10 deer per square mile in central New Jersey forests, the number today is closer to 70 deer per square mile. The number of medium and large trees has decreased only slightly since Buell’s time, but saplings have plummeted by 85 percent and small trees by 90 percent.

Tribal forests in Wisconsin are more diverse, sustainable, 16, 2018“Deer are acting like a keystone species here,” says Waller. “It’s not a minor effect. It’s not affecting one or a few species. It’s not affecting one or a few sites. It’s not a temporary effect. These are pervasive, long-lasting effects that are actually shifting Wisconsin plant communities outside the Indian reservations into another state—a state of lower diversity, of different composition, more invasives.”

Wetland seed dispersal by white-tailed deer, Botany One, March 28, 2018results suggest that seed dispersal by large herbivores may be a more prevalent mechanism for wetland plants than previously recognized. This mechanism allows for the potential for long-distance dispersal over upland habitat from isolated wetland environments. [abstract]

Wetland seed dispersal by white-tailed deer in a large freshwater wetland complex, AoB Plants, Feb 1, 2018Mechanisms of long-distance dispersal are important in establishing and maintaining plant populations in isolated wetland habitats. White-tailed deer (Odocoileus virginianus) have been cited as long-distance dispersers of both native and exotic plant species in North America; however, knowledge regarding their influence in wetlands is limited. Given traditional classification methods for seed dispersal, white-tailed deer are not likely viewed as important dispersal mechanism for wetland plants. We collected naturally deposited white-tailed deer faecal pellet piles from wetlands in Canaan Valley, West Virginia, USA. Our research has suggested that endozoochory by herbivores contributes to long-distance dispersal of wetland plants.

A regional assessment of white-tailed deer effects on plant invasion, AoB Plants, Feb 1, 2018 Overall, native deer reduced community diversity, lowering native plant richness and abundance, and benefited certain invasive plants, suggesting pervasive impacts of this keystone herbivore on plant community composition and ecosystem services in native forests across broad swathes of the eastern USA.

Changes in vegetation following two reductions in white-tailed deer abundance at Eagle’s Crest and Spring Pond Nature Preserves, Eagle Creek Park, Indianapolis, Indiana, Eagle Creek final Report, 2017Following the 2014/15 and 2017reductions in
deer abundance, I observed sustained increases in the heights of jack-in-the-pulpit and white baneberry, two indicator species of deer overabundance in Indiana. Between 2013 and 2017, I also observed increased rate of flowering and increased proportion of female plants in jack-in-pulpit. This species is able to change its gender and will switch to male flowering or not flower at all under environmental stress. While deer rarely browse jack-in-the-pulpit, their movement around plants results in soil compaction and reduces litter depth, which creates stress on plants and reduces their growth. Reduced deer densities at Eagle Creek Park have likely resulted in reduced environmental stress on jack-in-the pulpit plants.

A regional assessment of white-tailed deer effects on plant invasion, AoB Plants, Nov 2017Among deer-access plots, native species richness, native and total cover, and Shannon diversity (cover) declined as deer density increased. Deer access increased the proportion of introduced species cover (but not of species richness or stem density). As deer density increased, the proportion of introduced species richness, cover and stem density all increased. Because absolute abundance of introduced plants was unaffected by deer, the increase in proportion of introduced plant abundance is likely an indirect effect of deer reducing native cover.

Effects of white-tailed deer and invasive plants on the herb layer of suburban forests, AoB Plants, Nov 2017Non-native plants and herbaceous native plants were affected very little by fencing or M. vimineum invasion. In contrast, across all forests the combination of deer access and M. vimineum addition had a strongly negative effect on woody native percent cover. Forests differed in overall fencing effects on woody natives; their cover was greater in fenced plots in just three forests, suggesting greater deer pressure in those forests during the experiment. The early invasion by M. vimineum was greatest in two of these same forests, but was not influenced by fencing.

Interactive effects of deer exclusion and exotic plant removal on deciduous forest understory communities, AoB Plants, Nov 2017We conducted a 5-year, 2 × 2 factorial experiment in three mid-Atlantic US deciduous forests with high densities of white-tailed deer (Odocoileus virginianus) and exotic understory plants. We predicted: (i) only deer exclusion and exotic plant removal in tandem would increase native plant species metrics; and (ii) deer exclusion alone would decrease exotic plant abundance over time. Treatments combining exotic invasive plant removal and deer exclusion for plots with high initial cover, while not differing from fenced or exotic removal only plots, were the only ones to exhibit positive richness responses by native herbaceous plants compared to control plots. Woody seedling metrics were not affected by any treatments. Deer exclusion caused significant increases in abundance and richness of native woody species >30 cm in height.

Assessing plant community composition fails to capture impacts of white-tailed deer on native and invasive plant species, AoB Plants, Nov 2017Excessive herbivory can have transformative effects on forest understory vegetation, converting diverse communities into depauperate ones, often with increased abundance of non-native plants. White-tailed deer are a problematic herbivore throughout much of eastern North America and alter forest understory community structure. Reducing (by culling) or eliminating (by fencing) deer herbivory is expected to return understory vegetation to a previously diverse condition. We examined this assumption from 1992 to 2006 at Fermilab (Batavia, IL) where a cull reduced white-tailed deer (Odocoileus virginianus) abundance in 1998/1999 by 90 % from 24.6 to 2.5/km2, and at West Point, NY, where we assessed interactive effects of deer, earthworms, and invasive plants using 30 × 30 m paired fenced and open plots in 12 different forests from 2009 to 2012.

An indicator approach to capture impacts of white-tailed deer and other ungulates in the presence of multiple associated stressors, AoB Plants, Nov 2017We found year and site-specific effects with high deer herbivory of unprotected individuals (70–90 % of oaks browsed by deer versus none in fenced areas) far exceeding importance of rodent attacks. Oaks planted at low earthworm density sites were at significantly higher risk of being browsed compared with oaks at high earthworm density sites, but there was no detectable negative effect of invasive plants. Surviving oaks grew (~2 cm per year) under forest canopy cover, but only when fenced.

Effects of deer on the photosynthetic performance of invasive and native forest herbs, AoB Plants, Nov 2017At a long-term Odocoileus virginianus (white-tailed deer) exclusion site in a temperate deciduous forest, we quantified deer-mediated ecophysiological impacts on an invasive biennial Alliaria petiolata (garlic mustard) and two palatable native herbaceous perennials, Maianthemum racemosum and Trillium grandiflorum. In mid-summer, we found that leaf-level light availability was higher in unfenced areas compared with areas fenced to exclude deer. Alliaria in unfenced areas exhibited 50 % higher mean maximum photosynthetic rates compared with fenced areas. Further, specific leaf area decreased by 48 % on average in unfenced areas, suggesting leaf structural responses to higher light levels. Similarly, Maianthemum had 42 % higher mean photosynthetic rates and 33 % decreased mean specific leaf area in unfenced areas, but these functional advantages were likely countered by high rates of deer herbivory. By contrast, Trillium exhibited significantly lower (26 %) maximum photosynthetic rates in unfenced areas, but SLA did not differ.

Beyond eating: Indirectly, deer change the landscape, University of Wisconsin-Madison, Feb 6, 2017scientists are looking beyond herbivory to better understand the indirect effects of deer on eastern North American forest landscapes. In particular, scientists are interested in how the animal’s presence and behaviors affect the composition and overall health of the wildflowers and other herbs — what scientists call understory communities — that blanket the forest floor.

Statement on Ann Arbor’s deer management budget amendment, CW Dick Lab, Oct 16, 2017Putting budgeted resources into the cull now, instead of later, makes sense. If we are able to reduce Ann Arbor’s urban deer population to a more sustainable level – by sustainable, I mean a deer abundance that permits natural forest regeneration – this will have an immediate positive impact on our natural areas.

Deer eating habits have lasting damage on forests, Cornell News, Sept 11, 2017When rampant white-tailed deer graze in forests, they prefer to eat native plants over certain unpalatable invasive plants, such as garlic mustard and Japanese stiltgrass. These eating habits lower native plant diversity and abundance, while increasing the proportion of plant communities made up of non-native species, according to a new study.

Impacts of Deer Browse on Managed Grasslands, Sanford Farm Nantucket, Nantucket Conservation Foundation, June 2107Studies, primarily in forests in New England and the Midwest, have shown dramatic reductions in flowering plant diversity, decreases in rare plant species and increases in some non-native invasive plants such as garlic mustard in areas where deer are not excluded. The impacts deer browsing have on plant communities is very easily studied through simple deer exclosure experiments. Tall exclosure fences designed to exclude deer from an area for 5-10 years can allow native species to germinate and flourish in the absence of deer browse pressure.

County Deer Management Program has begun , Union News Daily, Jan 12, 2017The hunts will take place each consecutive Monday until Feb. 9. In the case of bad weather, the hunt will take place on Friday. The aim is to reduce the deer population as well as protect native vegetation. “Forest ecologists recommend that white-tailed deer populations in Northeast hardwood forests should not exceed an overwintering density of 20 deer per square mile in order for deer browse to not impair forest health. In areas where the forest health is already compromised, deer density needs to be as low as 5 per square mile.

Trillium grandiflorum, Wikipedia, Dec 12, 2016Trillium grandiflorum as well as other trilliums are a favored food of white-tailed deer. Indeed, if trilliums are available deer will seek these plants, with a preference for T. grandiflorum, to the exclusion of others. In the course of normal browsing, deer consume larger individuals, leaving shorter ones behind. When foraging intensity increases, individuals become shorter each growing season due to the reduction in energy reserves from less photosynthetic production. One study determined that the ideal deer density in northeastern Illinois, based on T. grandiflorum as an indicator of overall understory health, is 4 to 6 animals per square kilometer. This is based on a 12 to 14 cm stem height as an acceptable healthy height. In practice, deer densities as high as 30 deer per square kilometers are known to occur in restricted or fractured habitat where natural control mechanisms are lacking. Such densities, if maintained over more than a few years, can be very damaging to the understory and lead to extinction of some local understory plant populations.


  • AVID: Assessing Vegetation Impacts from Deer, Draft, Oct 2016, Cornell UniversityA Rapid Assessment Method for Evaluating Deer Impacts to Forest Vegetation. AVID is a method for volunteers, foresters, landowners and others to measure the effect of deer browse on New York forests. Volunteers are encouraged to use AVID to document this aspect of New York forest health. Participants will learn about forest and woodland ecology, how to identify spring wildflowers and trees, and develop an eye for recognizing signs of deer impacts.
  • Independent Effects of Invasive Shrubs and Deer Herbivory on Plant Community Dynamics, Forests, Sept 2016
      Although evidence of synergistic interactions was minimal, the separate effects of invasive shrub control and deer herbivory on plant community composition and dynamics were profound. Plant communities remainedrelatively unchanged where invasive shrubs were not treated, regardless if deer herbivory was excluded or not. With increasing intensity of invasive shrub control, native shrubs and forbs became more dominant where deer herbivory was excluded, and native graminoids became progressively more dominant where deer herbivory remained severe. While deer exclusion and intensive invasive shrub control increased native shrubs and forbs, it also increased invasive vines. Restoring native plant communities in areas with both established invasive shrub thickets and severe deer browsing will require an integrated management plan to eliminate recalcitrant invasive shrubs, reduce deer browsing intensity, and quickly treat other opportunistic invasive species.
  • Sustainable Management of White-Tailed Deer and White-Cedar, The Wildlife Society, Oct 5, 2015Using recent and historical regeneration data from the Forest Service’s permanent sample plots, Larouche and her colleagues compared the dynamics of white-cedar to those of companion species over a 40-year period and found that white-cedar seedlings have not progressed to larger-size classes over time, while seedlings of other species have grown into sapling and merchantable-size classes (Larouche et al. 2010). Furthermore, density of white-cedar has declined in the study area since the 1960s, with close to 90 percent of sampled white-cedar seedlings and large saplings having evidence of deer browsing in 2005.
  • White-tailed Deer and Their Influence on Forest Vegetation, Long Island Natural History Conference, Tom Rawinski of the U.S. Forest Service, April 2015
  • How Bambi is Destroying the Forest, YouTube, 2011
      Dr. Walter Carson, who is presently a Bullard Fellow at Harvard Forest in Petersham, MA. This is an excellent talk, as it presents clear experimental evidence about 3 different possible causes of oak regeneration declines (absence of fire, increased canopy density, and deer over browsing).
  • New study evaluates deer damage in Ann Arbor’s natural areas, MLive, Oct 26, 2016“Ecological concerns about the impacts of deer on natural areas go beyond assessing whether deer are damaging a few plants. The larger and deeper issues are whether deer damage is leading to declines in biodiversity — in the abundance and distribution of native species — and whether that damage can lead to long-term changes in ecological communities and functions. The question is whether deer browsing might in turn lead to declining resources and habitat for pollinators, songbirds and other forest species.
  • What hungry deer mean for Michigan’s northern forests, Michigan Radio, Nov 10, 2016Foresters and conservation groups say there are still far too many deer in northern Michigan, and they are creating severe problems for forests. Most of the trees that tower overhead here are sugar maples, about 100 years old. But in the understory, where the young trees are coming up, there are almost none.
  • Deer Discovery: Invasive Plants Get Boost from too Many Deer, Smithsonian Insider, May 6, 2016A survey of the two study plots after 25 years revealed the density of Japanese barberry, wine raspberry and Japanese stiltgrass was much higher in the open plot. The presence or absence of deer, they found, was an excellent predictor of the abundance of exotic plant species.
  • Dispersing seeds is newly discovered role for deer — except the plants often are noxious weeds, Cornell ecologists report, Cornell Chronical, July 18, 2016Speaking at the Ecological Society of America (ESA) annual meeting Aug. 3-8 in Savannah, Ga., Mark Vellend will report his discovery that a significant role in seed dispersal is played by deer browsing on vegetation wherever they wish and depositing seeds, in their pellet-like feces, to germinate and produce new plants up to two miles away. The bad news, says Vellend: “Unfortunately, many of the seeds we’re finding in deer feces are from noxious weeds, including four of the top 20 invasive plants of greatest concern in New York state. The multiflora rose, for example,” he says of a pretty plant that creates impenetrable brambles.
  • Deer Discovery: Invasive Plants Get Boost from too Many Deer, Smithsonian Insider, May 6, 2016New results from a long-term Smithsonian study are providing strong evidence of the dramatic impact high numbers of white-tailed deer (Odocoileus virginianus) are having upon temperate forests in the eastern United States. Since 1990, scientists at the Smithsonian Conservation Biology Institute have been monitoring two 10-acre plots in a 63-acre forest just south of Front Royal, Va. One plot is fenced to exclude deer. The other is open.
  • Plant invasions and deer overabundance in the woodlots of Cades Cove, Great Smoky Mountains National Park., Botany, 2016We review the history of deer abundance and invasive species in the understory of woodlands in and around Cades Cove, Great Smoky Mountains National Park, TN, USA. Specifically, we synthesize data from long-term monitoring plots and exclosure studies in and around the Cove. Individual species response to historically high levels of herbivory ranged from neutral to strongly positive. Not surprisingly, exotics that were intolerant or intermediate shade tolerance declined on long-term monitoring plots, likely as a result of forest maturation. Bird-dispersed exotic shrubs, such as Rosa multifora, were relatively uncommon but appeared to benefit from perch sites provided by exclosure fences and resurgent woody regeneration within exclosures. The species exhibiting the strongest positive association with deer herbivory was Microstegium vimineum; an exotic, annual, C4 grass that is tolerant of shaded understory conditions. Results from deer exclosures and control plots suggest that this species’ ability to suppress native plants is enhanced by deer herbivory. In fact, while more abundant on exclosure than control plots initially, this species is now substantially less abundant within deer exclosures relative to control plots. Collectively, these observations lend support to the passenger model of community change and suggest that plant invasions be viewed in concert with changes in disturbance regimes and ungulate abundance.

  • Oak Savanna, DNROak savannas are rare and unique ecosystems where locally droughty (dry) environmental conditions result in sparse tree growth. Ample sunlight stimulates a diversity of herbaceous plants that are also adapted to these conditions on a fragile, sand soil. Commonly occurring plants within this ecosystem include little blue stem, coreopsis, and wild lupine.
    Deer regularly visit savannas in the summer when little blue stem and other warm-season grasses are actively growing.
  • Study finds 10 percent of 2015 soybean yield lost to white-tailed deer in Presque Isle County, MSU Extension, March 17, 2016Research has suggested that crop losses to deer greater than 10-15 percent of the total crop or $20 per acre are viewed as significant and requiring remedy by Michigan producers and hunters. Northeast Lower Michigan has been identified as a region of special concern for white-tailed deer management due to current deer population densities above Michigan Department of Natural Resources’ goals, high incidence of crop depredation and the presence of bovine tuberculosis-infected animals in the deer herd.
  • Deer Impacts on Seed Banks and Saplings in Eastern New York, [Abstract] Nrtheastern Naturalist, March 2016Deer did, however, decrease sapling density and richness at the unhunted site but not at the hunted site. We conclude that impacts of unmanaged deer populations are greater on sapling recruitment than on seed banks.
  • U-M biologists support Ann Arbor deer cull, Michigan News, Jan 14, 2016A University of Michigan evolutionary biologist says he and many of his U-M colleagues support the city of Ann Arbor’s plans to kill up to 100 deer this winter, calling the cull “a positive step toward ecological sustainability.”U-M botanists have long noted declines in native plants that deer favor, Dick said. In a 2015 study, an ecological team surveyed browsing impacts in Ann Arbor’s Bird Hills Nature Area and found browsing damage in 80 percent of the tree saplings.

  • The legacy of deer overabundance: long-term delays in herbaceous understory recovery, Canadian Journal of Forest Research, 2016Decades of white-tailed deer overpopulation have dramatically homogenized forests across much of the eastern United States, creating depauperate forest understory communities. The rate at which these communities recover once deer browsing has been reduced remains an open question. We evaluate overbrowsing legacy effects by examining how forest herbaceous layers respond in terms of biodiversity, density, and community composition over 11 years using exclosures and control plots within a mature beech–maple forest. Although little recovery occurred in the first 5 years, total density and preferred browse density rebounded substantially during the final years of the study. Although community composition began to diverge between exclosure and control plots after 5 years, diversity failed to recover even after 11 years of excluding browsers. Our findings show that vulnerable species can increase after excluding browsers but only if those species were initially present. Biodiversity recovery may be extremely slow because preferred browse species have been nearly extirpated from many forests and thus are unable to recruit into refugia. We empirically demonstrate the extent of the ghost of herbivory past or legacy effect of browsing, i.e., the substantial time delay between herbivore abatement and community response after decades of high deer densities.

  • White-tailed deer (Odocoileus virginianus) browse damage in Ann Arbor, Michigan; Bird Hills Nature Area, Winter 2015, Jacqueline Courteau, Ecologist, Moriah Young, University of Michigan, Independent Study Research This survey of 142 tree saplings (less than 2 meters tall) and shrubs in Bird Hills Nature Area shows that 80% have been browsed by deer, and 51% have half or more branches browsed. This level of browsing could interfere with forest regeneration and diminish the flowers and fruit available for birds, butterflies, and bees. Further monitoring would be necessary to track mortality, to reveal whether particular tree and shrub species of concern are browsed in future years, and to assess whether wildflower species are also being heavily browsed.The deer browse figures compiled in this survey may underestimate actual browse damage in several ways. First, the survey excluded plants that were already dead or lacked live buds for identification. Many of the excluded plants showed clear signs of deer browse, which suggests that browse damage could be contributing to mortality, but estimating browse-related mortality was beyond the scope of this study. Numerous other studies suggest that browse damage over several decades may already have eliminated or greatly reduced populations of deer-preferred species (Côté et al. 2004, Rooney and Waller 2003, Ferker et al. 2014). Second, it is not possible to count how many buds are missing from a plant, so we focused on the number of branches browsed. However, some unbrowsed branches were counted even if they were quite small, while the portions of branches browsed off may have been larger than those that remained. Third, we
    assessed browse damage on all species, rather than on a set of species known to be preferred by deer; damage on preferred species could be even higher.

  • Community-level impacts of white-tailed deer on understorey plants in North American forests: a meta-analysis, AOB Plants, Oct 20, 2015Ultimately, we show that white-tailed deer have strongly negative impacts on forest understorey plant communities in North America, but these impacts are not ubiquitous for all components of the plant community.

  • Many Native Connecticut Plants in Danger, Report Warns, Hartford Courant, March 26, 2015The report also warns that, “For the first time in 200 years, every state in New England is losing forest,” a result of human activities such as development, attacks by invasive insects, deer over-population, and the impact of climate change. .Elizabeth Farnsworth, the society’s senior research ecologist and the author of the report, said Connecticut’s and New England’s massive deer population is a major contributor to the loss of forest because deer browse on young seedlings.
  • Historically browsed jewelweed populations exhibit greater tolerance to deer herbivory than historically protected populations, Journal of Ecology, 2015Browsing by overabundant white-tailed deer has altered ecological relationships in forest communities across eastern North America. Recent but limited work suggests that deer browsing also selects for particular plant defensive traits.
  • It’s rare plants versus deer in the College Woods, William & Mary News, Jan 15, 2015What was once lush is now sparse. “This isn’t good for the forest, but it isn’t good for the deer either,” said Dalgleish. The problem is not simply that the deer are eating too many plants, but that the plants are growing back smaller and smaller each year. The deer are eating the plants so quickly that they are unable to store enough regenerative material to grow back to their original height the next year.
  • Deer account for almost half of long-term forest change, study finds, University of Wisconsin-Madison News, January 2, 2015A study released this week has linked at least 40 percent of species changes in the forests of northern Wisconsin and Michigan over the past 60 years to the eating habits of white-tailed deer.
  • Long-Term Regional Shifts in Plant Community Composition Are Largely Explained by Local Deer Impact Experiments, PlosOne, Dec 31, 2014The fact that herbivores and predators exert top-down effects to alter community composition and dynamics at lower trophic levels is no longer controversial, yet we still lack evidence of the full nature, extent, and longer-term effects of these impacts. Here, we use results from a set of replicated experiments on the local impacts of white-tailed deer to evaluate the extent to which such impacts could account for half-century shifts in forest plant communities across the upper Midwest, USA. We measured species’ responses to deer at four sites using 10–20 year-old deer exclosures. Among common species, eight were more abundant outside the exclosures, seven were commoner inside, and 16 had similar abundances in- and outside. Deer herbivory greatly increased the abundance of ferns and graminoids and doubled the abundance of exotic plants. In contrast, deer greatly reduced tree regeneration, shrub cover (100–200 fold in two species), plant height, plant reproduction, and the abundance of forbs. None of 36 focal species increased in reproduction or grew taller in the presence of deer, contrary to expectations. We compared these results to data on 50-year regional shifts in species abundances across 62 sites. The effects of herbivory by white-tailed deer accurately account for many of the long-term regional shifts observed in species’ abundances (R2 = 0.41). These results support the conjecture that deer impacts have driven many of the regional shifts in forest understory cover and composition observed in recent decades.
  • Overabundant White-tailed Deer and the Alteration of Forested Communities, Department of Ecology and Evolution, Rutgers University-School of Environmental & Biological Sciences
      Deer can have profound effects on preferred woody and herbaceous browse species. Deer browse of woody vegetation alters the subcanopy and the shrub layer which are made up of small understory trees, young recruits for future canopy openings, and shrubs. The overbrowsing of the herbaceous level affects one level and can virtually eradicate an entire plant during one browsing episode.
  • Report the Governor and the General Assembly of Maryland, Preservation of Maryland’s Botanical Heritage, January 15, 2014, Maryland Botanical Heritage Work GroupOur native plants are being devastated by the large numbers of white-tailed deer whose abundance is no longer kept in check. Deer consumption of native plants prevents forest regeneration and facilitates the spread of non-native invasive plants. Maryland has many areas where the majority of plant species are native, but the vast bulk of plant biomass is non-native and invasive. Restoration and landscaping practices, including by government agencies and private landowners, can either harm or help—but can never replace—our native plant diversity.
  • Deer density and plant palatability predict shrub cover, richness, diversity and aboriginal food value in a North American archipelago, Diversity and Distributions [Abstract], Sept 2014We provide comparative examples of endangered plant communities to demonstrate that, contrary to the intermediate disturbance hypothesis, any positive effect of deer on plant diversity on islands in the Pacific north-west of North America occurs at densities < 0.08 ha−1, if at all. This detailed example of trophic downgrading highlights the need and provides the methods to identify herbivore densities compatible with the persistence of all native species in conserved landscapes.
  • In a long-term experimental demography study, excluding ungulates reversed invader’s explosive population growth rate and restored natives, Proceedings of the National Academy of Sciences of the United States of America, vol. 111 no. 12, Mar 25, 2014, Susan Kalisz, 4501–4506. In a long-term experimental demography study, excluding ungulates reversed invader’s explosive population growth rate and restored natives.The study was long-term, over six years in a PA woodland with a deer population of 20-42 deer per km-sq (51-107 mi-sq), a population similar to some areas of Washtenaw County. There’s a lot of data and statistics in the report, and it shows that the garlic mustard population “explodes” (their “technical” term) where deer had access, but declines where deer were excluded. The ability of native plants to successfully compete with garlic mustard was dependent on the extent of deer browse. Deer never browsed on the garlic mustard, but selectively browsed the native plants.
    For our natural areas to sustain the native plants that support a community of other wildlife, the PA study shows that the deer need to be managed at a level where the native flora can survive.

  • Hunting gives deer-damaged forests in state parks a shot at recovery,, July 9, 2014A research team led by Michael Jenkins, associate professor of forest ecology, found that a 17-year-long Indiana Department of Natural Resources policy of organizing hunts in state parks has successfully spurred the regrowth of native tree seedlings, herbs and wildflowers rendered scarce by browsing deer.
    “We can’t put nature in a glass dome and think it’s going to regulate itself,” he said. “Because our actions have made the natural world the way it is, we have an obligation to practice stewardship to maintain ecological balance.”

    Indiana state parks historically did not allow hunting. But by the 1990s, white-tailed deer populations in parks had swelled to such size that many species of native wildflowers such as trillium and lilies largely disappeared, replaced by wild ginger and exotic species such as garlic mustard and Japanese stiltgrass, plants not favored by deer. Oak and ash tree seedlings gave way to highly deer-resistant or unpalatable trees such as pawpaw.

  • Excessive Deer Populations Hurt Native Plant Biodiversity, Pitt-Led Study Says, University of Pittsburgh News, March 10, 2014
  • Deer Browsing Delays Succession by Altering Aboveground Vegetation and Belowground Seed Banks, PLOSone, March 2014Browsing resulted in significantly decreased overall species richness (but higher diversity), reduced seed bank abundance, relatively more short-lived species (annuals and biennials), and fewer native species. Both seed bank richness and the relative abundance of annuals/biennials were mirrored in the aboveground vegetation. Thus, deer browsing has long-term and potentially reinforcing impacts on secondary succession, slowing succession by selectively consuming native perennials and woody species and favoring the persistence of short-lived, introduced species that continually recruit from an altered seed bank.
  • Excessive deer populations hurt native plant biodiversity, PhysOrg, March 11, 2014The study, initiated in 2003 at the Trillium Trail Nature Reserve in Fox Chapel, Pa., concludes that an overpopulation of deer (density of deer in the United States is about four to 10 times what it was prior to European settlement of North America) is the primary reason garlic mustard is crowding out native plants, such as trillium, which are preferred food for wild deer.
  • The vertical dimension of deer browse effects on forest understories, Rohleder, Linda, Ph.D., RUTGERS THE STATE UNIVERSITY OF NEW JERSEY – NEW BRUNSWICK, 2013Throughout their range, white-tailed deer (Odocoileus virginianus ) have significantly altered the diversity and productivity of plants upon which they browse in forest understories as well as the average heights of many of these species, yet traditional vegetation surveys can fail to capture changes occurring at higher levels in the vertical dimension.

  • The Science of Yellow Snow: White-tailed Deer may be Ruining their own Winter Havens, Michigan Tech News, June 2013.“Altering the nitrogen availability in a hemlock stand may affect its ability to continue functioning as a deeryard by changing the types of plants that grow there,” said Murray, first author on the journal article titled “Broadening the ecological context of ungulate-ecosystem interactions: the importance of space, seasonality, and nitrogen.” For example, he said, “high inputs of nitrogen may hasten the transition of hemlock stands to hardwood species that provide scant winter cover.”
  • Identification and Management of Multiple Threats to Rare and Endangered Plant Species, RC-1542, SERDP and ESTCP, Sept 2013Density and species composition of monitored stressor organisms (earthworms, slugs, and B. pellucidus) varied across field sites and years. Unexpectedly, it was found that earthworm density and biomass decreased in the fenced plots, indicating a possible, but unforeseen, interaction between earthworms and deer. In just five years, it was found that all three target non-native plants had significantly lower abundance (frequency, cover, and/or density) in fenced plots, in response to deer exclusion. This is particularly true for the short-lived M. vimineum and A. petiolata, which are annual and biennial, respectively. Simultaneously, native vegetation responded positively to deer exclusion. Results indicate that it may be possible to reduce abundance of non-native plants simply by substantially reducing deer density.
  • Benefits to rare plants and highway safety from annual population reductions of a “native invader,” white-tailed deer, in a Chicago-area woodland, Richard M. Engeman, etal, Environmental Science and Pollution Research, 2013We examined the benefits of culling deer at a Chicago-area woodland preserve by comparing browse rates on four endangered plant species from years before culling began with years with culling. We also examined deer–vehicle collision and traffic flow rates on area roads from years before culling began and years with culling to assess whether population reductions may have benefited road safety in the area. An economic analysis showed a cost savings during the cull years of US$0.6 million for reducing browsing to just these four monitored plant species and the reduction in deer–vehicle collisions
  • White-tailed Deer (Odocoileus virginianus) Disperse Seeds of the Invasive Shrub, Amur Honeysuckle (Lonicera maackii), Natural Areas Journal, Jan 2013White-tailed deer are known to disperse seeds of a hybrid complex of invasive honeysuckle shrubs in northeastern United States. We investigated whether they also disperse seeds of Amur honeysuckle, Lonicera maackii, a problematic invasive shrub in the Midwestern and eastern U.S. We found that deer ingest ripe fruit and void intact seeds of L. maackii. Based on tetrazolium tests, most (68%) of these voided seeds are viable. White-tailed deer are potentially important in the long-distance dispersal of this invasive shrub.
  • Effects of Deer Settling Stimulus and Deer Density on Regeneration in a Harvested Southern New England Forest, Intl Journal of Forestry Research, 2013Deer density and browse impact had a relationship with thermal settling stimulus for summer and fall months, and deer density had a relationship with browse impact in the winter on woody plants. We conclude that thermal settling stimulus is an important predictor for deer density and browsing impact.
  • Long-term effects of deer browsing: Composition, structure and productivity in a northeastern Minnesota old-growth forest, Mark A. White, The Nature Conservancy, Minnesota and the Dakotas, Forest Ecology and Management, 2012
  • Continued high browsing pressure is one of many factors contributing to the restructuring of northern Great Lakes forests away from historical variability conditions towards a novel and more homogeneous forested landscape. These simplified forests may be less resilient to the suite of emerging stressors such as climate change and less able to provide ecosystem services such as carbon storage, biological diversity and forest products. Sustained restoration efforts, along with reductions in deer density will be needed to restore species and structural diversity.

  • Deer and Forests, and the People Who Love Them , TJ Rawinski, US Forest Service, 2012?Conservation is a state of health in the land. The land consists of soil, water, plants, and animals, but health is more than a sufficiency of these components. It is a state of vigorous self-renewal in each of them, and in all collectively. Such collective functioning of interdependent parts for the maintenance of the whole is characteristic of an organism. In this sense, land is an organism, and conservation deals with its functional integrity, or health.Some would say that finding solutions to the dilemma of White-tailed Deer over­abundance has emerged as the nation’s single greatest wildlife-management – and ecosystem-management – chal­lenge of the 21st century.

  • Climate impacts on bird and plant communities from altered animal–plant interactions, Nature Climate Change, Jan 10, 2012Effects of climate on plant communities may provide an alternative, but particularly powerful, influence on animal populations because plants provide their habitats. Here, we show that abundances of deciduous trees and associated songbirds have declined with decreasing snowfall over 22 years of study in montane Arizona, USA. We experimentally tested the hypothesis that declining snowfall indirectly influences plants and associated birds by allowing greater over-winter herbivory by elk (Cervus canadensis). We excluded elk from one of two paired snowmelt drainages (10  ha per drainage), and replicated this paired experiment across three distant canyons. Over six years, we reversed multi-decade declines in plant and bird populations by experimentally inhibiting heavy winter herbivory associated with declining snowfall. Moreover, predation rates on songbird nests decreased in exclosures, despite higher abundances of nest predators, demonstrating the over-riding importance of habitat quality to avian recruitment.
  • “Dramatic” response by flora & fauna to climate change, USGS WUWT, Jan 11, 2012The U.S. Geological Survey and University of Montana study not only showed that the abundance of deciduous trees and their associated songbirds in mountainous Arizona have declined over the last 22 years as snowpack has declined, but it also experimentally demonstrated that declining snowfall indirectly affects plants and birds by enabling more winter browsing by elk. Increased winter browsing by elk results in trickle-down ecological effects such as lowering the quality of habitat for songbirds.
  • DEER AND BIODIVERSITY, Biodiversity of BC, 2012?The rapid growth of deer populations, obvious signs of browsing and extirpation of many palatable spring ephemeral plants from some islands has led to concern about the long-term effects of unregulated deer populations on the viability of many plant species, and on the abundance of island songbird populations which rely on understory plants for feeding and nesting.
  • Over-browsing in Pennsylvania creates a depauperate forest dominated by an understory tree: Results from a 60-year-old deer exclosure, Journal of the Torrey Botanical Society, 2011We compared tree diversity and density inside a 60 year-old deer exclosure to an adjacent reference site. Browsing caused a 55–100% decline in density of four tree species (Prunus serotina, Acer saccharum, Betula lenta, Cornus alternifolia) and created a forest dominated (>70% of all stems) by Acer pensylvanicum, an understory tree that is known to be highly browse-tolerant. The total density of trees that are capable of ascending into the canopy (i.e., non subcanopy tree species) declined by 85%.
  • Deer and Invasive Plant Species Suppress Forest Herbaceous Communities and Canopy Tree Regeneration, Natural Areas Journal, Nov 2017Our results suggest that intensive management of M. vimineum and deer populations as well as active re-vegetation of herbaceous communities and tree seedlings are necessary to restore plant biodiversity in suburban deciduous forests. [Abstract, full text can be downloaded]
  • Growing Deer Population Hurts Survival Of Forests, NPR, June 15, 2011The deer side of the fence has a carpet of grass, a shrubby looking thing, and some large trees – things that are either too big for deer to eat, or are among the very few plants they dont like to eat. Inside it is practically a jungle. Dozens of different almost exotic looking plants are tumbling over one another. Many of them are young trees.
    You have the old trees. And when the old trees go, there is something here [in the enclosure] to take its place. Out there, I don’t see anything out there that’s a small tree.

    One of the surprising things they’ve found with this experiment is that deer allow invasive species to flourish. And with fewer native plants, there are fewer birds who depend on them for nests and food. There are fewer mice and fewer chipmunks here when they have to compete with deer.

  • White-Tailed Deer, Their Foods and Management in the Cross Timbers (Texas), Kenneth L. Gee, Michael D. Porter, Steve Demarais and Fred C. Bryant, A Noble Foundation Agricultural Division publication, NF-WF-11-02, 2011 (3rd Edition)
  • Hardwood forests not regenerating as deer eat maple saplings, Michigan study shows, Science Daily, May 10, 2011In a sweeping study of a huge swath of Michigan’s Upper Peninsula, researchers documented that in many places, the sugar maple saplings that should be thriving following harvesting are instead ending up as a deer buffet. This means the hardwood forests are not regenerating.
  • The Responses of Rare and Common Trilliums (Trillium reliquum, T. cuneatum, and T. maculatum) to Deer Herbivory and Invasive Honeysuckle Removal (abstract), Bione, Castanea 75(4):433-443. 2010
  • Our results show that the long-term management of white-tailed deer will be important to the conservation of spring ephemeral herbs such as T. reliquum, T. cuneatum, and T. maculatum.

  • Deer Damage After Foliage Falls, Fairfield County, 2010
  • Trillium grandiflorum height is an indicator of white-tailed deer density at local and regional scales, Forest Ecology and Management, March 2010A significant negative relationship was found at 10 sites between maximum plant height and estimates of deer population densities, which were derived from counts of live or culled animals and varied from 7 to 40 deers km2. Maximum plant height could be reliably measured within a 4-week period. The underlying mechanism driving the negative relationship between plant height and deer density was attributed to deer preferentially selecting taller plants that grew less than ungrazed plants in the subsequent year. In 16 additional sites with locally high deer populations, the mean maximum height of T. grandiflorum appeared to be a more reliable indicator of deer density than estimates based on hunter returns across the broader regional scale of the Wildlife Management Unit.
  • Autumn herbivory by white-tailed deer and nutrient loss in planted seedlings, The American Midland Naturalist, 2008White-tailed deer in the agricultural Midwest are limited during fall and winter to areas of combined food and cover, usually remnant forests in a matrix of agriculture. During this period, tree seedlings may be at higher risk to herbivory because herbaceous and agricultural foods are unavailable and deer are concentrated in forest patches. We monitored planted swamp white oak seedlings to examine how autumnal herbivory affected nutrient loss and survival. Herbivory during this season resulted in significant losses of nitrogen and phosphorous stored within the stem, with nitrogen stores significantly reduced throughout the seedling’s tissues. Nutrient loss due to deer herbivory has the potential to prevent seedlings from reaching reproductive maturity, altering future successional paths and affecting forest composition. To alleviate herbivory pressure, forested refuges may benefit from hunting or sharpshooting, with treatments coinciding with peak crop harvest activity.

  • Michigan’s Natural Communities: Rich Conifer Swamp, Michigan’s Natural Features Inventory, 2007Long-term conservation of rich conifer swamps will require reducing deer densities across the landscape and allowing natural disturbances such as windthrow to create the complex structure that creates habitat for late-successional species.
  • Appetite for trouble, Wisconsin Natural Resources Magazine, Oct 2007Even small numbers of deer can have dramatic consequences where the land can’t support a larger herd. At a deer density of 12 to 15 animals per square mile of range, herbaceous plants like trillium, Indian cucumber, showy lady’s slipper and white fringed orchid decline. When deer densities reach 20 to 25 animals per square, species like pines, white cedar, hemlock, oaks and Canada yew can stop regenerating and small mammals like red-backed voles, an important prey species, starve out without the forest floor vegetation they need. At 25 to 35 animals per square mile of range, birds like hooded warblers decline from lack of needed ground, shrub and tree layers
  • The impact of deer on relationships between tree growth and mortality in an old-growth beech-maple forest, Zachary T. Long, Thomas H. Pendergast IV, Walter P. Carson, Department of Biological Sciences, University of Pittsburgh, Forest Ecology and Management 252 (2007)
  • Dr. Victor Reinstein Woods Nature Preserve Unit Management Plan, Town of Cheektowaga, New York, 2006
    One of the major threats to the continued existence of the mature forest at Reinstein Woods is the large deer population. The town of Cheektowaga has begun a town-wide bait and shoot program to reduce the size of the population. The program is expected to take several years to achieve a significant reduction in the size of the population. Therefore, DEC plans to go ahead with establishing deer exclosures in strategic locations to encourage regeneration of desirable tree species in the forest… Two deer exclosures within the Woods give visible evidence that the deer population is impacting the forest within the Woods.
  • A demographic study of deer browsing impacts on Trillium grandiflorum, Plant Ecology, 2003A moderate drought during the study could account for the negative population growth rate, but deer browsing accelerates the rate of decline. Population growth is most sensitive to the proportion of plants remaining in the nonflowering stage, and deer browsing reduces this proportion. Browsing damage was relatively low in this study (5.4% of stems in 1998, 11.5% in 1999) compared to another study of browsing impacts on T. grandiflorum, indicating deer could have far more severe demographic consequences in populations subject to higher levels of browsing.
  • and as far back as 1983
    The terrestrial vegetation and flora of North and South Manitou Islands, Sleeping Bear Dunes National Lakeshore, University of Michigan, 1983The vegetation and flora of North and South Manitou Islands in northern Lake Michigan were surveyed during the summer of 1982 and the spring of 1983, the first comprehensive study of both islands. The vegetation associations were mapped and described, and a catalogue of 490 vascular plant species was compiled. A noticeable difference in forest structure and floristic composition between the islands was observed, largely due to an introduced deer herd on North Manitou. Twenty permanent plots were established on the islands to observe any future changes at selected sites. The island distributions of eight native species listed as threatened or of special concern by the State of Michigan were mapped and fragile habitats were identified.


And More…

  • Special Issue: Deer eating the future of Pennsylvania’s Forests!, U Penn.
  • Seed dispersal by white-tailed deer: implications for long-distance dispersal, invasion, and migration of plants in eastern North America, Jonathan A. Myers, Mark Vellend, Sana Gardescu, P. L. Marks, Oecologia, 2004
  • Effects of population reduction on home ranges of female white-tailed deer at high densities, Howard J Kilpatrick, Shelley M Spohr, Kelly K Lima, Canadian Journal of Zoology, 2001 [abstract only] Population reduction programs at our study area did not cause the resident deer population to expand home range size or shift into adjacent habitat. We believe that localized deer reduction programs can be effective tools to manage problem deer herds. Deer removal efforts initiated to reduce deer damage to vegetation, particularly in urban areas, may have an added effect of reducing foraging range of the remaining resident deer.
  • The Impact of Deer on Woodland Biodiversity, Information Note, Forestry Commission, Edinborough, Aug 2000Deer can have an adverse impact on woodland vegetation and simplify vertical structure by selectively browsing on herbs, shrubs and young trees. Vegetation changes brought about by deer browsing are also detrimental to some vertebrate and invertebrate woodland fauna. Without appropriate management, deer populations will impose long-term changes on the composition of native woodlands. Available data suggest that densities of deer in upland habitats should be in the region of 4–7 per km2 to ensure adequate regeneration and to protect sensitive flora and fauna.
  • Height of White-Flowered Trillium (Trillium Grandiflorum) as an Index of Deer Browsing Intensity, Ecological Applications, Feb 1, 1994Trillium stem height was positively correlated with reproductive output by perennial herbaceous plants and negatively correlated with the percent of the herbaceous understory that is browsed. This indicates change in stem height is as indication of the general status of the herbaceous flora as influenced by deer browsing. Based on deer population densities associated with study sites supporting Trillium populations with stable stem heights and flowering plants, maintenance of deer densities of 4—6 individuals/km2 is recommended for deciduous forests in northeastern Illinois.
  • Impacts of White-tailed Deer On Endangered and Threatened Vascular Plants, Natural Areas Journal, 1992.To assess the impact of white-tailed deer on flora, a review of pertinent literature and a telephone survey of professional botanists, endangered species scientists, natural area managers, and US National Park Service resource managers was undertaken. Ninety-eight species of threatened or endangered plants were reported disturbed by deer. Monocots and dicots comprised 39.8% and 56.1%, respectively, of the species disturbed. Of the disturbed species, 38.7% belonged to families Liliaceae and Orchidaceae.

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