Effects of White-Tailed Deer on Populations of an Understory Forb in Fragmented Deciduous Forests (original) (raw)
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Impact on plant communities by white-tailed deer in Mississippi, USA
Plant Ecology & Diversity, 2013
Background: The abundance of white-tailed deer (Odocoileus virginianus) in the eastern United States has escalated during the twentieth century, potentially impacting plant communities. Methods: We measured understorey plant cover and biomass five years after excluding deer from mature forests of three ecological regions in Mississippi, USA. We extended the significance of P values to 0.10 to detect developing impacts. Results: Deer impacts were limited and varied by ecological region. We recorded 151 species in cover transects. Consistent exclosure treatment effects were detected in two regions where there was greater cover of two deer forages and less cover of three non-forages. Species richness was greater in exclosures in one region, but otherwise species richness and diversity indices did not differ. We recorded 127 species in biomass quadrats. Exclosure treatment effects on biomass were inconsistent. Out of five species with significant differences, three had more biomass in controls, including two deer forages. Except for greater total biomass in controls of one region, there were no differences by growth form or total vegetation for canopy coverage or biomass. Ordination of community canopy cover demonstrated similarity of paired exclosure and controls. Conclusions: Exclosure treatment effects on canopy cover and species richness in two regions indicated limited negative impacts from deer foraging. A time frame of more than five years may be required for exclusion to allow recovery of vegetation, even with relatively open canopies and a long growing season.
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.
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.
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.
Ecological Impacts of Deer Overabundance on Temperate and Boreal Forests
2000
Deer have expanded their range and increased dramatically in abundance worldwide in recent decades. They inflict major economic losses in forestry, agriculture, and transportation and contribute to the transmission of several animal and human diseases. Their impact on natural ecosystems is also dramatic but less quantified. By foraging selectively, deer affect the growth and survival of many herb, shrub, and
Forest Ecology and Management, 2010
Obtaining accurate estimates of deer population sizes in forests is challenging, but required for herd management. Traditional means of estimating population size include using harvest data, which provide a non-representative sample of the true population structure (Mladenoff and Stearns, 1993; Anderson, 2001). The assumption of detection probability being consistent across space and time (Anderson, 2001) does not hold for local deer distribution, which is a function of local forage and cover availability (Harlow, 1984). However, harvest data are often the only information readily available to managers, and population estimates tend to be derived from regionally-collected data by state and provincial wildlife organizations. In small, fragmented forests where deer hunting is prohibited, large-scale estimates from harvest data may provide a poor reflection of local deer density and be of limited value in supporting site-level management decisions. Other methods for estimating deer densities are also limited by being highly labour intensive (Broadfoot and Voigt, 1996) or subject to observer error (e.g. fecal pellet sampling) (Smart et al., 2004).
Forest Ecology and Management, 2010
We examined the response of understory plants in mature maple-dominated forests of southern Québec, Canada, following about 30 years of high deer densities, using a deer exclosure experiment. An exclosure and a paired control of 625 m 2 each were established on six sites in 1998. An exclosure and a paired control of 16 m 2 were added at each of the same sites in 2003 but under a recent canopy gap to determine if light could enhance plant responses. We measured plant richness and abundance, and aboveground biomass of different plant groups for 8 years in the understory plots and for 3 years in the canopy gaps. Four herbaceous species were also monitored individually in the same plots. No significant differences between treatments were found in plots under forest cover, except for lateral obstruction at 0-50 cm height which was higher in the exclosures. Under canopy gaps, however, tree seedling and total plant abundance were higher in deer exclosures than in control plots. Trillium erectum recovered partially as individuals were taller, had larger leaves and more frequently produced a flower or a fruit in the absence of deer browsing under forest cover. To a lesser extent, Erythronium americanum and Maianthemum canadense also exhibited signs of recovery but were still at the single-leaf stage after 8 years of recovery. In general, the different plant groups exhibited little recovery following deer exclusion, possibly because of the low light levels that prevailed in the understory of undisturbed maple-dominated forests. The higher latitude of the present study could also contribute to the slow recovery rates of the different groups of plants compared to studies conducted in northeastern USA. Variability among sites and years had an effect on detection of statistically significant differences. Trends are however appearing over time, suggesting that many understory plants are recovering very slowly following deer exclusion. Our results emphasize the importance of studying large herbivore-forest interactions on different groups of plants, but also on specific species, and under different latitudes to be fully understood.
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.