Shedding light on the problem of deer overgrazing in Carolinian forests (original) (raw)
Related papers
Effects of White-Tailed Deer on Populations of an Understory Forb in Fragmented Deciduous Forests
Conservation Biology, 1998
The effects of grazing by white-tailed deer ( Odocoileus virginianus ) on populations of Trillium spp. were examined in remnant, old-growth patches of the highly fragmented Big Woods forest ecosystem in southeastern Minnesota. We conducted three separate studies involving an exclosure experiment, transplant experiments, and comparisons of Trillium populations among study sites. The highest grazing intensity was observed where deer occurred at high overwinter concentrations ( ف 25-35/km 2 ); significantly lower grazing intensities occurred at low overwinter density ( ف 5-10/km 2 ). Deer focused their grazing on large, reproductive plants; at sites with high deer density, Trillium population structure was skewed toward small plants, and deer consistently caused over 50% reduction in reproduction during the growing season. Protection of individual plants from deer for two growing seasons resulted in dramatically increased flowering rates and significantly greater leaf area compared to control plants. No significant impact of current-year herbivory on reproduction in the following year was detected. Nevertheless, flowering rates at one site with high overwinter deer densities for at least the past 5 years suggest that the cumulative effects of grazing over several years can reduce reproduction in subsequent years. Transplant experiments with Trillium grandiflorum also showed that deer had significant effects on growth and reproduction where deer occur at high density. Our results suggest that changes in landscape structure and local deer abundance have altered plant-deer relationships such that grazing can lead to the local extirpation of sensitive forbs such as Trillium spp. As a result, active, long-term management of deer at low densities appears necessary for the conservation and restoration of fragmented forest communities in eastern North America.
The American Midland Naturalist, 2001
Large effects of white-tailed deer (Odocoileus virginianus) upon individual plants, plant populations and communities have been documented in a number of studies. However, well-supported experimental measures of the magnitude and geographical extent of these effects are still surprisingly scarce. Deer-caused changes in stem morphology and reductions in plant growth rates are well-documented in some parts of the North America. Furthermore, deer have been shown to affect the composition of several plant communities in the north-central and northeastern United States. There are some documented cases of deer-caused reductions in plant survival; most of these are tree seedlings and saplings. However, many studies have detected no effects on plant survival or fecundity, or have found that negative effects occur only in a fraction of years, seasons, sites or deer densities. Little is known about population-level or ecosystem-level impacts. Many regions and plant communities with large deer populations have not been studied. Whereas deer density is clearly important in determining spatial and temporal variation in the presence and magnitude of deer effects, other factors that may modify the effects of deer density are poorly understood. 1 Corresponding author 2 Present address: Department of Biological Sciences, 410 Manter Hall, University of Nebraska-Lincoln, Lincoln, 68588-0118. Telephone (402)-477-2123; e-mail: LelandRussell@msn.com 1 THE AMERICAN MIDLAND NATURALIST plants, plant populations, plant communities and ecosystem processes and identify major gaps in our current knowledge. We also review some methodological challenges in obtaining more conclusive evidence of deer effects. Management of deer populations is a contentious issue that has stirred emotional conflict between individuals who want to avoid the extirpation by overbrowsing of rare aesthetically pleasing or economically valuable plants and plant communities (Diamond, 1992; Diefenbach et al., 1997) and individuals who consider hunting deer to be cruel (McShea and Rappole, 1997), hunters who enjoy the abundance of deer (Diefenbach et al., 1997) and land managers who distrust human intervention in "natural" processes within wildlife refuges and preserves (Diamond, 1992). However, the effects of deer herbivory on vegetation are also of interest to ecologists examining the effects of herbivores on individual plants, plant populations and communities. By reviewing this literature we hope to provide information to aid land managers in evaluating the need to hunt deer to preserve rare or economically valuable plant species and to preserve or restore rare plant communities. In addition, we hope to enhance ecologists' understanding of the effects of herbivores on plants and the mechanisms that underlie these effects. This review will be confined to effects of white-tailed deer, although similarly high densities of related species present similar problems elsewhere (Gill, 1988; Clutton-Brock and Albon, 1992; Mclnnes et al., 1992; Singer and Renkin, 1995). For brevity we will use the word 'deer' to refer to white-tailed deer. There have been a number of regional reviews of effects of white-tailed deer on plants (Neils et al., 1956; Marquis and Brenneman, 1981; Alverson et al., 1988; Witmer and deCalesta, 1992), but, to date, no wider overview of the subject.
Castanea, 2017
The high abundance of ungulates in temperate zone forests is affecting biodiversity and ecosystem functions worldwide. A randomized, replicated experiment excluded white-tailed deer, Odocoileus virginianus, from six 10 3 10 m fenced plots for 10 years; six unfenced plots were maintained as controls. The effects of chronic herbivory were assayed by comparisons using the mean responses of ground-level vegetation in nine subplots within each of the 12 plots. Deer had a small effect on species richness but a strong effect on species prevalence, cover, and biomass, with repeatable differences in the responses of taxa to the treatments. Graminoids were favored in control plots, many other monocots and several dicots were favored in fenced plots, and parasitic plants and chemically defended herbs showed few detectable responses to fencing. The height of the vegetation represented by the shrub Vaccinium erythrocarpum and the herb Medeola virginiana was significantly taller in fenced than in control plots. This experiment demonstrated that many forest herbs, especially those in the Liliaceae sensu lato, tolerate repeated browsing without flowering, probably for decades. When released from browsing, the time required for these species to sequester sufficient resources to flower and successfully develop seeds varied from 1 to 10 years among species. Managers of forest ecosystems must consider the impacts of game management on biodiversity.
Overabundant suburban deer, invertebrates, and the spread of an invasive exotic plant
Wildlife Society Bulletin, 2011
White-tailed deer (Odocoileus virginianus) overabundance is a problem of serious concern for wildlife managers. At densities as low as 8 deer/km 2 , changes in vegetation due to deer feeding patterns have been demonstrated to negatively impact other wildlife species. The Middle Patuxent Environmental Area (MPEA) in Howard County, Maryland, USA, currently supports a deer population of approximately 41 deer/km 2 . We used an experimental approach to examine how deer overabundance in a suburban environment impacts both vegetation and invertebrates. Ten 20-m  20-m deer exclosures were constructed in the MPEA during the winter-spring of 1999. Vegetation and invertebrate data have subsequently been collected inside the exclosures and areas adjacent to the exclosures (control) during the summers of 1999, 2003, and 2007. There was no initial difference in vegetation variables between exclosure and control plots in 1999 (P > 0.05). Post-1999, plant species richness was greater in the exclosure than in the control. A multivariate analysis of variance revealed differences (P < 0.001) in vegetation cover variables between exclosures and controls, with a greater percentage of forbs, shrubby vegetation, and taller stems in the exclosure and more grass and exotics in the control. There were few differences in invertebrates between exclosures. The differences observed in vegetation between exclosures is believed to reflect interactions between deer feeding patterns and the invasive Japanese stilt grass (Microstegium vimineum) and unless deer density is reduced, it is likely that the exotic Japanese stiltgrass will continue to increase in abundance and native plant species will decrease. ß 2011 The Wildlife Society.
Long-term Changes in Plant Communities Influenced by Key Deer Herbivory
Natural Areas Journal, 2006
The aim of the present study was to estimate changes in plant species composition in several forest communities caused by changes in endangered Key deer (Odocoileus virginianus clavium) densities in the National Key Deer Refuge in the lower Florida Keys. Baseline vegetation quadrats from a 1990 study were resampled in 2002 (the present study) in buttonwood transition, hardwood hammock, and mangrove wetland communities (all deer habitat) on 12 islands with low, medium, and high Key deer densities. On islands with high Key deer densities (>17 deer km-2), the relative densities of preferred plant species <1.2 m tall significantly decreased over time in each deer habitat, and nonpreferred species <1.2 m tall significantly increased in hammock and mangrove habitats. No significant changes were observed in densities of plant species <1.2 m tall on islands with low and medium Key deer densities (<8 deer km-2). Relative densities of preferred plant species >1.2 m tall (midstory/canopy) also significantly decreased in hammock on islands with high deer density, suggesting that heavy browsing is deterring plant growth/recruitment, thus already affecting regeneration of certain plant species into the midstory/canopy tiers. Plant species richness did not vary significantly between 1990 and 2002 for islands with high deer densities, but tended to increase slightly on islands with low deer density in buttonwood and hammock communities. Evidence from this study suggests that high densities of Key deer influence plant species composition on certain islands. We suggest that management plans for Key deer should incorporate both species protection components and population control techniques dependent on deer density-island associations.
Comparative Effects on Plants of Caribou/Reindeer, Moose and White-tailed Deer Herbivory
ARCTIC, 2001
We reviewed the literature reporting negative or positive effects on vegetation of herbivory by caribou/reindeer, moose, and white-tailed deer in light of the hypothesis of exploitation ecosystems (EEH), which predicts that most of the negative impacts will occur in areas where wolves were extirpated. We were able to list 197 plant taxa negatively affected by the three cervid species, as opposed to 24 that benefited from their herbivory. The plant taxa negatively affected by caribou/reindeer (19), moose (37), and white-tailed deer (141) comprised 5%, 9%, and 11% of vascular plants present in their respective ranges. Each cervid affected mostly species eaten during the growing season: lichens and woody species for caribou/reindeer, woody species and aquatics for moose, and herbs and woody species for white-tailed deer. White-tailed deer were the only deer reported to feed on threatened or endangered plants. Studies related to damage caused by caribou/reindeer were scarce and often concerned lichens. Most reports for moose and white-tailed deer came from areas where wolves were absent or rare. Among the three cervids, whitetailed deer might damage the most vegetation because of its smaller size and preference for herbs. RÉSUMÉ. À la lumière de l'hypothèse de l'exploitation des écosystèmes (EEH), nous avons examiné les publications qui mentionnent les effets négatifs ou positifs, sur la végétation, du broutement du caribou/renne, de l'orignal et du cerf de Virginie. Cette hypothèse prédit que les impacts négatifs se concentrent dans des endroits où le loup a été éliminé. Nous avons pu énumérer 197 taxons végétaux affectés négativement par les trois cervidés, contre 24 qui profitaient du broutement. Le nombre de taxons végétaux affectés négativement par le broutement du caribou/renne (19), de l'orignal (37) et du cerf de Virginie (141) représentait respectivement 5, 9 et 11 p. cent des plantes vasculaires situées dans les aires de répartition spécifiques des animaux. Chaque cervidé affectait surtout les espèces consommées durant la saison de croissance végétale: lichens et plantes ligneuses pour le caribou/renne, plantes ligneuses et aquatiques pour l'orignal, et plantes herbacées et ligneuses pour le cerf de Virginie. Selon les rapports, ce dernier était le seul cerf qui broutait des plantes menacées ou en voie de disparition. Les études rapportant des dommages causés par le caribou/renne étaient rares et traitaient souvent des lichens. La plupart des rapports sur l'orignal et le cerf de Virginie couvraient des zones où le loup était rare ou absent. Des trois cervidés, celui qui causerait le plus de dommages à la végétation est le cerf de Virginie, en raison de sa taille plus petite et de sa préférence pour les plantes herbacées.
Biological Conservation, 2005
The introduction of Sitka black-tailed deer (Odocoileus hemionus sitkensis Merriam) to Haida Gwaii (Queen Charlotte Islands, BC, Canada) in the late 19th century, provided an opportunity to understand the long-term eVects of deer populations on the vegetation of temperate rain forests in the absence of their natural predators wolves (Canis lupus L.), and cougars (Puma concolor L.). Using seven small islands with diVerent browsing histories (no deer, deer for <20 years, deer for >50 years), we tested the long-term eVects of high deer densities on plant cover and species richness in the understorey of forest interior and forest edge habitats. Overall vegetation cover exceeded 80% in the lower vegetation layers on islands without deer and was less than 10% on the islands with deer for more than 50 years. Although overall plant species richness was similar on islands with or without deer, plant species richness at the plot scale (314 m 2 ) was reduced by 20-50% on islands with deer for >50 years. The diVerences were most pronounced for the speciesrich edge communities and among herb and shrub species. These results suggest that in the absence of predators, deer have the potential to greatly simplify the forest ecosystem.
A Natural Experiment on the Impact of Overabundant Deer on Forest Invertebrates
Conservation Biology, 2005
In large parts of North America and Europe, deer overabundance threatens forest plant diversity. Few researchers have examined its effects on invertebrate assemblages. In a natural experiment on Haida Gwaii (British Columbia, Canada), where Sitka black-tailed deer (Odocoileus hemionus sitkensis) were introduced, we compared islands with no deer, with deer for fewer than 20 years, and with deer for more than 50 years. We sampled invertebrates in three habitat categories: forest edge vegetation below the browse line, forest interior vegetation below the browse line, and forest interior litter. In forest edge vegetation, invertebrate abundance and species density decreased with increasing length of browsing history. In forest interior vegetation, decrease was significant only on islands with more than 50 years of browsing. Insect abundance in the vegetation decreased eightfold and species density sixfold on islands browsed for more than 50 years compared with islands without deer. Primary consumers were most affected. Invertebrates from the litter showed little or no variation related to browsing history. We attributed the difference between vegetation-dwelling and litter-dwelling invertebrates to differences in the effect of browsing on their habitat. In the layer below the browse line deer progressively removed the habitat. The extent of litter habitat was not affected, but its quality changed. We recommend more attention be given to the effect of overabundant ungulates on forest invertebrate conservation with a focus on edge and understory vegetation in addition to litter habitat.