Effects Of Deer Density Research Articles

Forest damage by deer depends on cross‐scale interactions between climate, deer density and landscape structure

Abstract Deer (Cervidae) populations are increasing across the temperate zone, threatening forest biodiversity and ecosystem services. However, the fundamental question of what factors make a forest susceptible to deer damage remains unanswered, hampering efforts to mitigate against damage. Previous research has assumed that deer density consistently increases forest damage. However, the effect of deer density is likely to be contingent on a range of other drivers, such as climate and landscape structure. Mitigation measures are expensive, so a sound understanding of these contingencies is required to inform the targeting of appropriate management to forests most at risk of damage. Using records of forest damage from Britain's National Forest Inventory, which comprises over 15,000 plots spanning environmental gradients, we applied a multiscale approach to identify the drivers of forest susceptibility to damage by deer. Damage likelihood was dependent on drivers operating at multiple spatial scales and their interactions. Broadleaved stands with low tree densities and old trees were consistently found to be at high risk across Britain. The statistical influence of surrounding forest cover within 500 m of a site was modified by regional deer density and climate, in addition to landscape‐level perennial cover. The effect of deer density on damage was therefore not straightforward, but context dependent. Synthesis and applications. We predict the likely outcome of afforestation initiatives on the likelihood that a forest site will be damaged by deer, with important implications for management and landscape planning in Britain. The complex interactive effects uncovered are difficult to interpret. We therefore provide an interactive Deer Damage Tool (R Shiny application; https://spake.shinyapps.io/DEERDAMAGETOOL/) for practitioners to visualize how afforestation is likely to influence the probability of deer damage in different forests and regions across Britain.

Contrasting Effect of Artificial Grasslands on the Intensity of Deer Browsing and Debarking in Forests

Deer can strongly affect other species as a keystone species. The intensity of their herbivory impact on forest vegetation is suggested to be affected by not only deer density but also by other environmental factors such as landscape components. Especially, artificial grasslands such as pastures and meadows possibility affect deer impact on forest vegetation by altering deer foraging behavior. Therefore, we aimed to clarify the effect of presence/absence of artificial grasslands on impact by sika deer (Cervus nippon) on forest vegetation. We compared the occurrence of debarking and the coverage of understory vegetation in two adjacent regions under similar deer density with and without artificial grasslands in Yamanashi Prefecture, Japan. The occurrence probability of debarking was more severe in forests in abundant artificial grassland region than in no artificial grasslands region despite considering the effects of deer density, tree size, and tree species. In contrast, the coverage of understory vegetation was high in abundant artificial grassland region than in no artificial grassland region despite considering the effects of light condition, vegetation type, and deer density. In conclusion, artificial grasslands modify deer impact on forest vegetation by increasing the occurrence probability of debarking but decreasing the browsing pressure on understory vegetation.

Does Supplemental Feeding of White-tailed Deer Alter Response of Palatable Shrubs to Browsing?

The impact on palatable shrubs when herbivores have access to high-quality food is unclear. We determined if providing high-quality food and increasing white-tailed deer (Odocoileus virginianus) density reduced growth and altered nutritional quality of two palatable shrub species. We maintained target densities of 13, 31, or 50 deer km−2 in six 81-ha−1 enclosures on each of two ranches. We provided nutritious, dry feed ad libitum in one of each pair of enclosures with similar densities on each ranch. We measured height and width of Texas kidneywood (Eysenhardtia texana Scheele) and spiny hackberry (Celtis ehrenbergiana [Klotzsch] Liebm), measured hackberry thorns, and estimated crude protein. Plants were protected from browsing with wire exclosures in 2005; a similar-sized unprotected plant was paired with each protected plant. We estimated density of shrub species using twenty 3 × 50 m belt transects/enclosure June 2005, 2007−2012. Growth of protected and unprotected kidneywood was similar (P ≥ 0.88) at 13 deer km−2, but growth was reduced (P ≤ 0.05) by higher deer densities. Protection from browsing and increasing deer density did not influence (P ≥ 0.25) size of spiny hackberry. Browsed kidneywood plants had a 34% lower crude protein (P ≤ 0.01) compared with protected plants when deer did not have access to feed. Spiny hackberry protein was greater (P ≤ 0.05) in unprotected plants compared with protected plants at 50 deer km−2. Response of Texas kidneywood density at > 1.5-m tall to deer density depended on year (P = 0.04), with no effect of deer density (P ≥ 0.10) on spiny hackberry density. Density of both shrubs was similar (P > 0.14) with and without supplement. Access to feed does not alter effects of browsing on these sympatric shrubs; however, responses to increasing herbivore density contrast. Texas kidneywood is less tolerant of herbivory than spiny hackberry.

広葉樹造林地におけるシカによる剥皮状況の違いにシカ密度・嗜好性・樹木のサイズが与える影響

広葉樹造林地におけるシカによる剥皮状況の違いにシカ密度・嗜好性・樹木のサイズが与える影響

Effects of Deer Density and Land Use on Mass of White-Tailed Deer

Abstract Local and regional land use changes, such as the expansion of cropland for cellulosic biofuels, and the population density of white-tailed deer can affect the health and body mass of white-tailed deer Odocoileus virginianus. We collected hunter-harvest data for 1,731 white-tailed deer from DeSoto National Wildlife Refuge in eastern Nebraska and western Iowa from 2003 to 2010. We used linear mixed-effects models and information theoretic methods to estimate effects of density of white-tailed deer and proportion of total landcover area converted from cropland to cool- or warm-season grassland on body mass of white-tailed deer. Density of white-tailed deer at DeSoto National Wildlife Refuge ranged from 36.5 to 50.6 deer/km2, and the proportion of landcover at DeSoto National Wildlife Refuge that remained cropland each year ranged from 14.9 to 23.2%. Body mass was inversely related to population density (−1.4 kg/5.5 deer/km2) and proportion of cropland (−1.3 kg/3.1% conversion of total land area from cropland to grassland). We used auxiliary harvest data collected at Boyer Chute National Wildlife Refuge to validate our models and found our models performed well. We estimate densities of white-tailed deer must be reduced by 1.7 (SE = 0.6) deer/km2 for every 1% change in total landcover from cropland to grassland in order for white-tailed deer to maintain body mass. Our results indicate increased harvest of white-tailed deer, resulting in a reduction in population density, may offset negative effects that a decline in the amount of available cropland could have on the body mass and health of white-tailed deer.

Effects of deer density on tick infestation of rodents and the hazard of tick-borne encephalitis. I: Empirical assessment

Tick borne encephalitis (TBE) is endemic to eastern and central Europe with broad temporal and spatial variation in infection risk. Although many studies have focused on understanding the environmental and socio-economic factors affecting exposure of humans to TBE, comparatively little research has been devoted to assessing the underlying ecological mechanisms of TBE occurrence in enzootic cycles, and therefore TBE hazard. The aim of this study was to evaluate the effect of the main ungulate tick hosts on the pattern of tick infestation in rodents and TBE occurrence in rodents and questing adult ticks. In this empirical study, we considered three areas where endemic human TBE occurs and three control sites having no reported human TBE cases. In these six sites located in Italy and Slovakia, we assessed deer density using the pellet group count-plot sampling technique, collected questing ticks, live-trapped rodents (primarily Apodemus flavicollis and Myodes glareolus) and counted ticks feeding on rodents. Both rodents and questing ticks were screened for TBE infection. TBE infection in ticks and rodents was positively associated with the number of co-feeding ticks on rodents and negatively correlated with deer density. We hypothesise that the negative relationship between deer density and TBE occurrence on a local scale (defined by the minimum overlapping area of host species) could be attributed to deer (incompetent hosts) diverting questing ticks from rodents (competent hosts), know as the ‘dilution effect hypothesis’. We observed that, after an initial increase, the number of ticks feeding on rodents reached a peak for an intermediate value of estimated deer density and then decreased. Therefore, while at a regional scale, tick host availability has already been shown to be directly correlated with TBE distribution, our results suggest that the interactions between deer, rodents and ticks are much more complex on a local scale, supporting the possibility of a dilution effect for TBE.

Effect of deer density on tick infestation of rodents and the hazard of tick-borne encephalitis. II: Population and infection models

Tick-borne encephalitis is an emerging vector-borne zoonotic disease reported in several European and Asiatic countries with complex transmission routes that involve various vertebrate host species other than a tick vector. Understanding and quantifying the contribution of the different hosts involved in the TBE virus cycle is crucial in estimating the threshold conditions for virus emergence and spread. Some hosts, such as rodents, act both as feeding hosts for ticks and reservoirs of the infection. Other species, such as deer, provide important sources of blood for feeding ticks but they do not support TBE virus transmission, acting instead as dead-end (i.e., incompetent) hosts. Here, we introduce an eco-epidemiological model to explore the dynamics of tick populations and TBE virus infection in relation to the density of two key hosts. In particular, our aim is to validate and interpret in a robust theoretical framework the empirical findings regarding the effect of deer density on tick infestation on rodents and thus TBE virus occurrence from selected European foci. Model results show hump-shaped relationships between deer density and both feeding ticks on rodents and the basic reproduction number for TBE virus. This suggests that deer may act as tick amplifiers, but may also divert tick bites from competent hosts, thus diluting pathogen transmission. However, our model shows that the mechanism responsible for the dilution effect is more complex than the simple reduction of tick burden on competent hosts. Indeed, while the number of feeding ticks on rodents may increase with deer density, the proportion of blood meals on competent compared with incompetent hosts may decrease, triggering a decline in infection. As a consequence, using simply the number of ticks per rodent as a predictor of TBE transmission potential could be misleading if competent hosts share habitats with incompetent hosts.

Effects of supplemental feeding and density of white‐tailed deer on rodents

AbstractSpatial distribution, population density, and reproductive success of many wildlife species may be altered by changes in vegetation composition, habitat structure, and availability of food. Altered distributions of key herbivores such as white‐tailed deer (Odocoileus virginianus) may impact all of these factors. Our objective was to determine the direct and indirect effects of supplemental feeding of deer on rodent populations in south Texas. We modeled effects of supplemental feeding and habitat change due to deer browsing through surveys of rodents. Rodents have a short generation time and populations respond quickly to change, so they are a suitable indicator of changes in habitat structure brought about by deer browsing pressure. We sampled rodent populations near to and far from deer feeders within twelve 81‐ha enclosures containing three different densities of deer with and without supplemental feed. The three deer densities were low (8.1 ha/deer), medium (3.2 ha/deer), and high (2 ha/deer). We conducted rodent trapping during March and April of 2007 and 2008. Abundance of rodents was much higher (P < 0.001) in 2008 than in the previous year due to an increase in rainfall. However, we found little effect of deer density, supplemental feeding of deer, or distance from deer feeders on rodent populations. Thus we conclude that supplemental feeding of deer and deer density had little influence on rodent communities in this environment. Rodent species native to semi‐arid environments are probably adapted to large changes in vegetative productivity brought about by the highly variable annual rainfall patterns, therefore they can adapt to the less abrupt habitat changes resulting from changing densities of deer. Conservation concerns that providing supplemental feed to deer in semi‐arid rangeland will disrupt the ecology of the land through changes in rodent populations were not supported. © 2011 The Wildlife Society.

Conifer leader browsing by roe deer in English upland forests: Effects of deer density and understorey vegetation

At moderate to high densities ungulates can impact negatively on forest crops and these may be managed by lethal control. In production forestry an understanding of the relationship between ungulate density, habitat-related factors and the incidence of tree damage may promote more efficient ungulate damage management than by lethal control alone. In plantation forests in the north east of England, the incidence of conifer leader browsing by roe deer ( Capreolus capreolus) was positively associated with an index of deer density (at the site scale) and planted crop tree density (at the feeding patch scale) and was negatively associated with the relative abundance of palatable understorey vegetation (at the site scale). An interaction between the deer density index and palatable understorey browse abundance was positively associated with leader browsing. Coefficients from the optimal model were used to construct a browse probability surface across a matrix of values of deer dung density and palatable understorey vegetation abundance. This illustrated a very different relationship between dung density and conifer leader browsing probability across the various levels of palatable understorey vegetation abundance. From this we hypothesise that in areas of limited palatable understorey vegetation abundance, higher levels of culling may be required to achieve reductions in the incidence of conifer leader browsing than would be necessary in areas with moderate to high palatable understorey vegetation abundance. Improvements to understorey vegetation in concert with roe deer population control may enhance the efficiency of deer damage management in upland areas with nutrient-poor soils.

Glycoprotein composition of the zona peilucida (ZP) of the white-tailed deer (Odocoileus virginianus)

The impact on palatable shrubs when herbivores have access to high-quality food is unclear. We determined if providing high-quality food and increasing white-tailed deer (Odocoileus virginianus) density reduced growth and altered nutritional quality of two palatable shrub species. We maintained target densities of 13, 31, or 50 deer km− 2 in six 81-ha− 1 enclosures on each of two ranches. We provided nutritious, dry feed ad libitum in one of each pair of enclosures with similar densities on each ranch. We measured height and width of Texas kidneywood (Eysenhardtia texana Scheele) and spiny hackberry (Celtis ehrenbergiana [Klotzsch] Liebm), measured hackberry thorns, and estimated crude protein. Plants were protected from browsing with wire exclosures in 2005; a similar-sized unprotected plant was paired with each protected plant. We estimated density of shrub species using twenty 3 × 50 m belt transects/enclosure June 2005, 2007 − 2012. Growth of protected and unprotected kidneywood was similar (P ≥ 0.88) at 13 deer km− 2, but growth was reduced (P ≤ 0.05) by higher deer densities. Protection from browsing and increasing deer density did not influence (P ≥ 0.25) size of spiny hackberry. Browsed kidneywood plants had a 34% lower crude protein (P ≤ 0.01) compared with protected plants when deer did not have access to feed. Spiny hackberry protein was greater (P ≤ 0.05) in unprotected plants compared with protected plants at 50 deer km− 2. Response of Texas kidneywood density at > 1.5-m tall to deer density depended on year (P = 0.04), with no effect of deer density (P ≥ 0.10) on spiny hackberry density. Density of both shrubs was similar (P > 0.14) with and without supplement. Access to feed does not alter effects of browsing on these sympatric shrubs; however, responses to increasing herbivore density contrast. Texas kidneywood is less tolerant of herbivory than spiny hackberry.