High Deer Densities Research Articles

Spatiotemporal plasticity of prey selection in the wolf

AbstractUnder an optimal foraging scenario, prey selection would be expected to occur when food resources are abundant. A positive frequency‐dependent prey selection would elicit prey switching when the abundance of main food resources decreases, potentially favouring community resilience to the effects of intensive, selective predation on a single prey. We assessed whether a positive frequency‐dependent prey selection by the wolf Canis lupus occurred in two areas hosting abundant populations of wild ungulates, one in northern (Słowiński National Park, Poland) and the other one in southern (Maremma Regional Park, Italy) Europe, throughout a cold semester. In Słowiński, ungulate community was dominated by red deer Cervus elaphus (57% availability) over wild boar Sus scrofa (35%) and roe deer Capreolus capreolus (8%); wild boar and fallow deer Dama dama (43–37%) were more abundant than roe deer (20%) in Maremma. In both areas, wolf diet was dominated by wild ungulates, with a major use of red deer in Słowiński and wild boar in Maremma. Prey selection occurred in both areas, and it was addressed towards the most abundant prey in Słowiński, that is, the red deer, but only towards the wild boar in Maremma, where the fallow deer was used according to availability. In Slowinski, high red deer density may have driven wolf prey selection, while the shifting of activity rhythms of the fallow deer in the Maremma as antipredator response to wolf presence may have reduced predation. Despite its comparable densities between the two areas, the wild boar was selected in Maremma and under‐used in Słowiński. Results provide partial support to positive frequency‐dependent selection, emphasising the spatiotemporal plasticity of wolf–prey relationships. The relative role of prey density and other factors (e.g., antipredator behavioural responses) should be assessed at longer temporal scales.

Deer grazing drove an assemblage‐level evolution of plant dwarfism in an insular system

Abstract Plant dwarfism, a syndrome characterised by a significant reduction in plant height and organ size, is a widely observed pattern of stress‐tolerant life‐form evolution that results from local adaptation to harsh environmental conditions. The drivers of assemblage‐level dwarfism have primarily been attributed to abiotic factors, such as low temperature, aridity, poor soil fertility or frequent fires. While biotic factors such as grazing pressure from herbivores can contribute to the establishment of plant dwarfism, these factors have rarely been tested at assemblage levels. Focusing on a dwarf plant assemblage comprising over 80 taxa on a small continental island in Japan with a high deer density, we hypothesised that historical deer grazing could also be a factor contributing to the large‐scale convergent evolution of dwarfism. To test this hypothesis, we measured the size of 1908 individual plants of 40 taxa pairs, comprising both palatable and unpalatable pairs from the island and their counterpart taxa from neighbouring regions, and sought to assess which factors (i.e. low solar radiation, estimated divergence time, low nutrient conditions and grazing pressure from deer) may have contributed to the formation of the dwarf plant assemblage on the island. We also performed genetic analysis to infer the time frames for the establishment of dwarf taxa. Statistical analyses revealed that plant size was significantly reduced mainly among the palatable taxa growing on the island, with preferential grazing by deer being identified as the most significant factor influencing plant size. Furthermore, genetic analyses revealed that dwarf ecotypes may have evolved over tens of thousands of years. Synthesis: To the best of our knowledge, this study is the first to demonstrate that interactions with herbivores can shape the assemblage‐level convergence of plant dwarfism. These findings enhance our current understanding of the formation of plant functional diversity.

Wild ungulate effects on soil fungal diversity in Mediterranean mixed forests

The effect of wild ungulate density on ecosystems varies according to different factors: climate and physiography conditions, forest type, management history, and herbivore identity. In this study, we evaluated the effect of historically high densities of red deer (Cervus elaphus L.) on the soil fungal communities in Mediterranean ecosystems using 30 paired plots, open on the one hand and exclosure plots on the other one. Plots were established at the end of 2020 in a perimeter-fenced hunting estate of 6600 ha in Toledo, Spain. Three months after plots were established, we analysed fungal communities in 60 soil samples using Illumina 250-bp paired-end sequencing. We estimated changes in total fungal richness and in the richness of trophic groups through Linear Mixed Effects models using fenced/unfenced type and deer habitat use as fixed variables and the location of the plots and the main tree host species as random variables. Fungal composition was analysed using non-metric multidimensional scaling and permutational multivariate ANOVA; edaphic characteristics were incorporated to explain differences. Soil fungal communities were not differentially affected by excluding ungulates for three months. Areas with high deer densities had a richer saprotrophic community and where lowland environments were dominated by the main tree hosts Quercus faginea and Quercus ilex. Arbutus unedo was found in mountain areas where there was less herbivore pressure, a greater richness of ectomycorrhizal and lichenized fungi and soils positively associated to nitrogen, phosphorus, potassium and organic matter levels.

Effects of root-colonizing fungi on pioneer Pinus thunbergii seedlings in primary successional volcanic mudflow on Kuchinoerabu Island, Japan.

Root-colonizing fungi, such as mycorrhizal fungi and dark septate endophyte fungi, are often found on pioneer plant species during early primary succession. However, little is known about which fungal species are responsible for the establishment of pioneer plants when these symbionts colonize simultaneously. We investigated the root-colonizing fungal communities of Pinus thunbergii that established prior to lichens, bryophytes, and short-lived herbaceous plants in a primary successional volcanic mudflow site on Kuchinoerabu Island, Japan. We collected a total of 54 current-year and 1- to 2-year-old seedlings. The colonization of root fungi was evaluated by direct observation of key structures (e.g., mantle, arbuscule, microsclerotia, and hyphae) and molecular analysis. Of the 34 current-year seedlings collected, only 12 individuals were colonized by ectomycorrhizal (ECM) fungi. By contrast, all 1- to 2-year-old seedlings were colonized by ECM fungi. Seedlings colonized by pine-specific ECM fungi, specifically Rhizopogon roseolus and Suillus granulatus, showed higher nitrogen and phosphorus contents in their needles compared to non-ECM seedlings. Arbuscular mycorrhizal fungi and dark septate endophyte fungi were found in only two and three individuals, respectively. The high density of mycophagous deer on Kuchinoerabu-jima may contribute to the favored dispersal of ECM fungi over other root-colonizing fungi. In conclusion, the seedling establishment of P. thunbergii at the volcanic mudflow may be largely supported by ECM fungi, with negligible effects of arbuscular mycorrhizal fungi and dark septate endophytes.

Long-term interactive impacts of the invasive shrubLonicera maackiiand white-tailed deer (Odocoileus virginianus) on a deciduous forest understory

AbstractWhite-tailed deer (Odocoileus virginianus) (hereafter, ‘deer’) and invasive plants affect forest understories, but few studies have investigated their interaction. We investigated long-term (11-yr) effects of excluding deer and removing the invasive shrub, Amur honeysuckle [Lonicera maackii(Rupr.) Herder], on plants in southwest Ohio. Deer exclusion enhanced tree seedling richness and density, but reduced annual and bare ground cover. Vine density was reduced byLonicera, especially where deer were excluded. Seedlings of several tree species, the invasive shrub, burning bush [Euonymus alatus(Thunb.) Siebold], and the invasive vine, winter creeper [Euonymous fortunei(Turcz.) Hand.-Maz.], were indicator species of the deer exclosure byLoniceraremoval treatment combination. The effect of deer on cover of native species depended onLoniceratreatment: where shrubs were removed, cover was higher where deer were excluded, but where shrubs were present, cover was higher where deer had access. We attribute these interactions to the reduced growth of, and shading by,Lonicerawhere deer had access and browsed this invasive shrub. Some of these effects were evident in the first 6 yr, but are now larger. Other effects were not evident in the earlier evaluation. These findings inform management of areas with high densities of deer and invasive shrubs palatable to deer. Control of only invasive shrubs will reduce native cover and not improve tree regeneration. Managing only deer will increase woody plants but reduce native cover. Management of both stressors is needed to promote tree regeneration and restoration of plant communities.

Successful forest restoration using plantation at high deer density: How neighboring vegetation drives browsing pressure and tree growth

Browsing can be an environmental stress to forest ecosystems, where the composition and structure of plant communities depend on the balance between ungulate browsing and the ability of plants to tolerate and acclimate to this stressor. Tree planting is a management tool for restoring forest whose integrity has been compromised by the intensity and repetition of browsing. This tool may be insufficient when the stress leading to forest degradation is ongoing. Balsam fir (Abies balsamea (L.) Mill.) plantations are used on Anticosti Island (Quebec, Canada) to restore winter habitat for white-tailed deer (Odocoileus virginianus Zimmermann, 1780). To promote natural regeneration and growth of planted firs that are the staple winter forage of deer, enclosures were temporarily erected and deer densities reduced to decrease browsing pressure. The stress induced by heavy browsing at the time of fence removal and the density of competitors in regenerating cutblocks, however, could compromise fir growth and forest recruitment. Our objective was to identify factors influencing browsing intensity and balsam fir’s growth following fence removal. We aimed to identify factors influencing lateral browsing intensity and number of trunk reiterations on fir at the landscape scale, including distance and size of the surrounding forests, and at the local scale through intraspecific density-dependence and interspecific associative effects. We then sought to identify the stressors most influencing balsam fir growth among browsing variables and a neighborhood crowding index (NCI). We measured browsing intensity and growth of 114 balsam firs 8 years following planting and again 2 and 4 years after dismantling two management enclosures. At the landscape scale, our results showed that when balsam fir was more than 150 m from a forest edge, the probability of browsing was close to zero and consistently a low percentage of shelter area surrounding a focal fir led to a decrease in browsing pressure. At the local scale, intensity of lateral browsing increased with the NCI of white spruce (Picea glauca (Moench) Voss). Fir growth was negatively influenced by the additive effects of browsing and NCI. Finally, our results showed that 19.7% (95 %CI: 4.5%, 42.6%) of the effect of the surrounding vegetation on growth was mediated by browsing. The success of forest ecosystem restoration through planting depends on density of neighboring tree species that can generate environmental stress by influencing growth indirectly through browsing as well as directly through competition for resources.

Fences are more effective than repellents in reducing deer browsing on planted two conifer species but their effectiveness is reduced by higher deer density, deeper snow, and steeper slope

Population expansion of deer and the damage to planted trees caused by them is becoming a serious conflict between deer and humans. Although there are many methods for tree protection, their effectiveness varies from case to case, and the determinant of effectiveness has rarely been clarified. We investigated the following three specific questions: 1) What factors influence forest managers' choice of protection methods? 2) What factors were important in reducing tree damage by each protection method? 3) Which of the repellents and fences was more effective in reducing tree damage? In 2018, we obtained data of plantation tree damages caused by sika deer (Cervus nippon) and tree protection methods from 1424 plantations in Japan. No protection was chosen at low deer densities, and repellents and fences were chosen at middle and high densities by forest managers. In the case of repellents, the damage rank increased with increasing deer density, tree age, and maximum snow depth, but was not affected by planted tree species (Cryptomeria japonica and Chamaecyparis obtusa). In the case of fences, the damage rank increased with increasing deer density, tree age, maximum snow depth, slope, and decreasing net height. The damage rank also increased with the usage of separable digging prevention net and the net without stainless wire. When the age of planted trees is seven, repellents can suppress the tree damage under 50% only when the deer density is below 10 deer/km2 (no snow) or 6 deer/km2 (snow depth is 16 cm). Fences can suppress tree damage below 50% when deer density was below 38 deer/km2 (snow depth: 0, slope: 35°) or 25 deer/km2 (snow depth: 16, slope: 35°). Deer protection methods should be selected according to environmental conditions such as deer density, snow depth, and slope degree in the case of our treated tree species.

Anthropogenic disturbances alter responses of understory plants to deer density: A 9-year deer density control experiment

The increasing deer population and their expanding distribution have altered the diversity and biomass of the plant community in the northern hemisphere. Furthermore, anthropogenic disturbances such as nitrogen deposition and logging threaten plant diversity in many parts of the forests. Therefore, it is necessary to investigate the effects of deer on plant communities under nitrogen deposition and logging conditions to understand and conserve plant diversity in forest ecosystems. We conducted a field experiment that controlled three levels of deer densities (exclosure: 0 deer/km2, low: 10 deer/km2, and high: 20 deer/km2) and four anthropogenic disturbances (without anthropogenic disturbances [control], nitrogen addition, logging, and nitrogen addition and logging combined) in a cool temperate secondary forest in northern Japan for nine years. We surveyed the effects of deer density and anthropogenic disturbance treatments on species richness and vegetation cover of life forms (forbs, ferns, trees, graminoids, unpalatable species, vines, and shrubs) and all species of understory vascular plants. We estimated the constant effect (without the elapsed year) and the temporary effect (with the elapsed year) of deer density, anthropogenic disturbances, and their interactions on the species richness, vegetation cover, and Simpson’s index as separate parameters in full models and selected the best model. The high deer density negatively affected the species richness of some life forms and all species and accelerated these effects over time for all species. The vegetation covers of most of the life forms were negatively affected by high deer density, and the effect was reduced over time. In contrast, the exclosure negatively affected the species richness of some life forms and positively affected the vegetation cover of most of the life forms and all species. The effect on the cover accelerated over time. Nitrogen addition accelerated the negative effect of high deer density on the species richness of shrubs. On the other hand, logging reduced the negative effect of high deer density on the species richness of all species. The cover of unpalatable species in the high deer density site with logging was approximately nine times higher than that in the high deer density site without anthropogenic disturbances in the last surveyed year. The high deer density and logging decreased the Simpson’s diversity index score. These results indicate that the effects of deer density, anthropogenic disturbances, and their interactions vary with time. These interactions must be considered to manage deer’s effect on forest ecosystems.

Deer browse susceptibility limits chestnut restoration success in northern hardwood forests

Efforts to develop American chestnuts [Castanea dentata, (Marsh.) Borkh], with improved resistance to the chestnut blight fungus, Cryphonectria parasitica (Murr.) Barr, and Phytophthora root rot, caused by Phythophthora cinnamomi Rands, are ongoing. Establishing founder populations of improved chestnut will require understanding the ecological and silvicultural requirements of the species. In areas where white tailed deer (Odocoileus virginianus Zimmerman) hinder tree regeneration success, understanding how browsing will affect the establishment of planted chestnut is critical. We evaluated the impact of browsing by deer on survival, growth and competitive status of hybrid chestnuts planted in 15 northern hardwood sites in Pennsylvania. We found that after six years, chestnuts planted in fences were 65 percent taller and 35 larger in basal diameter than chestnuts in unfenced areas. Browsing by deer shifted the competitive dynamics faced by the chestnuts by favoring slower growing, browse tolerant species and reducing the heights of competing woody stems. Nevertheless, the competitive status of chestnuts in unfenced plots remained stagnant over time due to repeated browsing, while it increased in fenced plots over time. Our results suggest that fencing or other means of reducing herbivory will be necessary to protect planted chestnuts in areas with moderate or high deer densities.

Large herbivores trigger spatiotemporal changes in forest plant diversity.

Large herbivores can exert top-down control on terrestrial plant communities, but the magnitude, direction, and scale dependency of their impacts remain equivocal, especially in temperate and boreal forests, where multiple disturbances often interact. Using a unique, long-term, and replicated landscape experiment, we assessed the influence of a high density of white-tailed deer (Odocoileus virginianus) on the spatiotemporal dynamics of diversity, composition, and successional trajectories of understorey plant assemblages in recently logged boreal forests. This experiment provided a rare opportunity to test whether deer herbivory represents a direct filter on plant communities or if it mainly acts to suppress dominant plants, which, in turn, release other plant species from strong negative plant-plant interactions. These two hypotheses make different predictions about changes in community composition and alpha and beta diversity in different vegetation layers and at different spatial scales. Our results showed that deer had strong effects on plant community composition and successional trajectories, but the resulting impacts on plant alpha and beta diversity patterns were markedly scale dependent in both time and space. Responses of tree and non-tree vegetation layers were strongly asymmetric. Deer acted both as a direct filter and as a suppressor of dominant plant species during early forest succession, but the magnitude of both processes was specific to tree and non-tree vegetation layers. Although our data supported the ungulate-driven homogenization hypothesis, compositional shifts and changes of alpha diversity were poor predictors of beta diversity loss. Our findings underscore the importance of long-term studies in revealing nonlinear temporal community trends, and they challenge managers to prioritize particular community properties and scales of interest, given contrasting trends of composition and alpha and beta diversity across spatial scales.

Woody plant secondary chemicals increase in response to abundant deer and arrival of invasive plants in suburban forests.

Plants in suburban forests of eastern North America face the dual stressors of high white‐tailed deer density and invasion by nonindigenous plants. Chronic deer herbivory combined with strong competition from invasive plants could alter a plant's stress‐ and defense‐related secondary chemistry, especially for long‐lived juvenile trees in the understory, but this has not been studied. We measured foliar total antioxidants, phenolics, and flavonoids in juveniles of two native trees, Fraxinus pennsylvanica (green ash) and Fagus grandifolia (American beech), growing in six forests in the suburban landscape of central New Jersey, USA. The trees grew in experimental plots subjected for 2.5 years to factorial treatments of deer access/exclosure × addition/no addition of the nonindigenous invasive grass Microstegium vimineum (Japanese stiltgrass). As other hypothesized drivers of plant secondary chemistry, we also measured nonstiltgrass herb layer cover, light levels, and water availability. Univariate mixed model analysis of the deer and stiltgrass effects and multivariate structural equation modeling (SEM) of all variables showed that both greater stiltgrass cover and greater deer pressure induced antioxidants, phenolics, and flavonoids, with some variation between species. Deer were generally the stronger factor, and stiltgrass effects were most apparent at high stiltgrass density. SEM also revealed that soil dryness directly increased the chemicals; deer had additional positive, but indirect, effects via influence on the soil; in beech photosynthetically active radiation (PAR) positively affected flavonoids; and herb layer cover had no effect. Juvenile trees’ chemical defense/stress responses to deer and invasive plants can be protective, but also could have a physiological cost, with negative consequences for recruitment to the canopy. Ecological implications for species and their communities will depend on costs and benefits of stress/defense chemistry in the specific environmental context, particularly with respect to invasive plant competitiveness, extent of invasion, local deer density, and deer browse preferences.

Do invasive species provide a refuge from browsers? A test of associational resistance in a peri-urban habitat plagued by deer

White-tailed deer (Odocoileus virginianus) overbrowsing over the past several decades has caused substantial changes to plant communities in eastern deciduous forests. Deer-preferred species have declined or become locally extirpated in many areas while deer-tolerant species have greatly increased in abundance. Moreover, the abundance of nonnative invasive species has also increased over the last few decades, outcompeting many native species. Native shrubs such as Sambucus canadensis (American elderberry) are now much less common, particularly in urban forests and forests with high deer densities. Here, we performed a short-term study in which we introduced propagations of a native shrub into a replicated field experiment in which we factorially manipulated deer presence or absence and invasive species presence or absence by using exclosures and removing invasive species. We monitored metrics of S. canadensis fitness including leaf count and plant height over two growing seasons. Browsing substantially reduced survival whereas invasive species provided a modest degree of associational resistance. Browsing significantly decreased both leaf count and plant height. By the end of the study, individuals within exclosures had over twice the number of leaves, were five times taller, and had much lower mortality versus those exposed to browsing. Removing invasive species did not change plant height, however, S. canadensis individuals experienced marginally higher leaf counts inside exclosures where we had removed invasive species. This trend was opposite in individuals outside of fences such that those growing within patches where invasive species remained had slightly higher leaf counts, especially during the first growing season. Until the final census date, elderberry growing within patches of invasive species had slightly lower mortality versus those growing in patches where invasive species had been removed. The results from our short-term study indicate that browsing is more inimical to a native shrub than competition from invasive species and we did not find evidence of associational resistance to browsing from invasive cover.

Habitat selection by nestbox-breeding birds and Roe Deer are incongruent within a heterogeneous woodland landscape

Conserving species relies upon acquiring an understanding of their use of habitat, yet our understanding of the use of habitat by co-existing species of different guilds at microgeographic scales remains poor. In particular, the use of habitat by woodland species is of conservation concern because of widespread declines in woodland biodiversity. Woodland bird declines have been ascribed, in part, to high deer densities because their browsing reduces the availability of nesting sites and food. We quantify the microgeographic use of habitat by Roe Deer (Capreolus capreolus) and of Great Tits (Parus major), Blue Tits (Cyanistes caeruleus) and Pied Flycatchers (Ficedula hypoleuca) in a heterogenous woodland landscape. We examined the use of habitat at microgeographic scales by the deer and the three bird species in relation to whether the local habitat was flat or wet or had a path, fence or wall within a 25-m radius of 206 randomly selected locations. We first examined if the occupancy rates of nestboxes in those locations were correlated with the number of Roe Deer lays and second, examined if the use of habitat by the Roe Deer and the bird species were associated with each of the habitat features that we quantified. We begin by showing that the use of habitat by Roe Deer is incongruent with the use of habitat by Great Tits, Blue Tits and Pied Flycatchers during the breeding season. Also, whilst all three bird species showed no, or weak, habitat preferences, the Roe Deer preferred daytime lay sites that were in flat areas of wet woodland close to paths, whilst there were no significant effects of the presence of fences and walls. These findings show that the Roe Deer and the three bird species differ in the use of habitat within a heterogenous woodland landscape, meaning that their use of habitat did not overlap at microgeographic scales. Meanwhile, the deer showed preferences for flat areas of wet woodland, whilst none of the bird species exhibited such preferences, and we discuss the implications of our findings for the management of woodlands.

The long‐term impacts of deer herbivory in determining temperate forest stand and canopy structural complexity

Abstract Ungulates place immense consumptive pressure on forest vegetation globally, leaving legacies of reduced biodiversity and simplified vegetative structure. However, what remains unresolved is whether browse‐induced changes occurring early in succession ultimately manifest themselves in the developed forest canopy. Understanding the development and persistence of these legacies is critical as canopy structure is an important determinant of forest ecosystem functions such as carbon sequestration and wildlife habitat. We measured how white‐tailed deer Odocoileus virginianus browse during stand initiation affected canopy structure, tree species richness, diversity, stem density, and basal area on Pennsylvania's Allegheny Plateau using a portable canopy LiDAR system. We capitalized on an historic deer enclosure experiment where forests were subjected to four deer densities (4, 8, 15, and 25 deer/km2) for 10 years following stand initiation. Deer browsing impacts on the forest canopy are apparent nearly four decades since stand initiation. The highest deer density treatment experienced a significant reduction in tree species diversity, density, and basal area with stands becoming dominated by black cherry Prunus serotina. Reductions in overstorey diversity and tree density resulted in a more open canopy with low leaf area and high horizontal leaf variability. Canopies were tallest at the lowest and highest deer densities. Synthesis and applications. Using a portable canopy LiDAR system and a former deer enclosure experiment, we show that high deer browsing pressure during stand initiation can have a decades‐long impact on stand and canopy structure. High deer densities led to stands with lower species diversity and tree density, which resulted in canopies that were taller and less dense. As remote sensing of the canopy becomes more prevalent, considering the legacy of ungulate herbivory on canopy structure may inform both land management and our understanding of ecological function, such as forest carbon sequestration, maintenance of diverse understory communities, and creation of wildlife habitat

Experimental evidence for opposing effects of high deer density on tick-borne pathogen prevalence and hazard

BackgroundIdentifying the mechanisms driving disease risk is challenging for multi-host pathogens, such as Borrelia burgdorferi sensu lato (s.l.), the tick-borne bacteria causing Lyme disease. Deer are tick reproduction hosts but do not transmit B. burgdorferi s.l., whereas rodents and birds are competent transmission hosts. Here, we use a long-term deer exclosure experiment to test three mechanisms for how high deer density might shape B. burgdorferi s.l. prevalence in ticks: increased prevalence due to higher larval tick densities facilitating high transmission on rodents (M1); alternatively, reduced B. burgdorferi s.l. prevalence because more larval ticks feed on deer rather than transmission-competent rodents (dilution effect) (M2), potentially due to ecological cascades, whereby higher deer grazing pressure shortens vegetation which decreases rodent abundance thus reducing transmission (M3).MethodsIn a large enclosure where red deer stags were kept at high density (35.5 deer km−2), we used an experimental design consisting of eight plots of 0.23 ha, four of which were fenced to simulate the absence of deer and four that were accessible to deer. In each plot we measured the density of questing nymphs and nymphal infection prevalence in spring, summer and autumn, and quantified vegetation height and density, and small mammal abundance.ResultsPrevalence tended to be lower, though not conclusively so, in high deer density plots compared to exclosures (predicted prevalence of 1.0% vs 2.2%), suggesting that the dilution and cascade mechanisms might outweigh the increased opportunities for transmission mechanism. Presence of deer at high density led to shorter vegetation and fewer rodents, consistent with an ecological cascade. However, Lyme disease hazard (density of infected I. ricinus nymphs) was five times higher in high deer density plots due to tick density being 18 times higher.ConclusionsHigh densities of tick reproduction hosts such as deer can drive up vector-borne disease hazard, despite the potential to simultaneously reduce pathogen prevalence. This has implications for environmental pathogen management and for deer management, although the impact of intermediate deer densities now needs testing.Graphical abstract

Herbivory and flooding impacts on planted bottomland hardwood seedlings

Abstract Bottomland hardwoods forests (BLHW) are increasingly subject to active management for water quality improvement, streambank stabilization, to mitigate for urban expansion and to improve habitat for wildlife. Since the majority of remaining BLHW are degraded, restoration attempts are becoming commonplace within the Western Gulf Coastal Plain (WGCP) of the US. However, restoration success in terms of obtaining high stem densities of desirable species has been mixed, with managers observing survival rates <15 per cent for planted oak and hickory seedlings in some situations due to a variety of limitations. Over two growing seasons, we investigated the effectiveness of portable electric fences, individual tree shelters and 2.4-m woven wire high fences for mitigating herbivory by white-tailed deer (Odocoileus virginianus) and feral swine (Sus scrofa). Treatments fell within degraded forested areas and abandoned agricultural fields where we tested four species of interest: Nuttall oak (Quercus texana Buckley), Shumard oak (Q. shumardii Buckley), bur oak (Q. macrocarpa Michx.) and pecan (Carya illinoinensis K. Koch). Where herbivory occurred, mitigation techniques produced a higher survival rate ($\bar{\rm{X}} $ = 17.6 per cent) than unprotected areas ($\bar{\rm{X}} $ = 9.1 per cent). In areas of high white-tailed deer density, prominent browsing was evident, resulting in two-growing-season height growth of seedlings being less in non-fenced ($\bar{\rm{X}} $ = 2.33 cm) and electric ($\bar{\rm{X}} $ = 4.33 cm) fenced plots compared with high fences ($\bar{\rm{X}} $ = 13.02 cm) and individual tree shelters ($\bar{\rm{X}} $ = 24.23 cm). Additionally, we observed a negative relationship between survival and the number of days seedlings that were inundated with flood waters during the growing season. Matching species of interest to the site conditions, specifically the local hydrologic regimes, should carry a high priority in planning a restoration project within BLHW in the WGCP.

Using Shrubs as Nurse-plants to Reduce Browsing and Rubbing Damage by Roe Deer: An Experimental Approach

ABSTRACT We conducted a field experiment to evaluate the effectiveness of neighboring vegetation to protect cherry-wood (Prunus avium) saplings against roe deer browsing and rubbing, and determine whether this protection varies according to the attractiveness of – and the physical barrier provided by – a variety of nurse shrubs. Our results show that nurse shrubs may delay roe deer browsing and rubbing on highly attractive cherry-wood saplings, even in a situation of high deer density. The most obstructing shrubs at roe deer knee to shoulder height (Populus x canescens and Cytisus scoparius) appeared to be efficient barriers, whereas the spiny shrub (Elaeagnus angustifolia) did not protect saplings more efficiently than thornless species. Yet, obstruction appeared to be less effective against browsing when the nurse species was itself browsed (Cornus sanguinea and Alnus cordata). Since roe deer may help to reduce plantation cleaning through the control of the shrub layer, especially brambles, we argue that natural methods of protection using surrounding vegetation should represent an economic and sustainable alternative to artificial protection of saplings.

Addressing regional relationships between white-tailed deer densities and land classes.

White‐tailed deer (Odocoileus virginianus) populations have recovered to about 30 million animals in the United States, but land cover has changed during the interval of recovery. To address the relationship between deer densities and current land cover at regional scales, I applied random forests and extreme gradient boosting classifiers to model low and high deer density classes, at two different thresholds (5.8 and 11.6 deer/km2), and land classes in three regions during approximately 2003. For low and high deer density classes divided at 5.8 deer/km2, deciduous broadleaf forest overall was the most influential and positive variable in the central east and central regions and crop and pasture were the most influential and negative variables in the southeast region. Deer density increased with area of deciduous and mixed forests, woody wetlands, and shrub in all regions. Deer density decreased with area of crop, developed open space, and developed low and medium residential density in all regions. For density classes divided at 11.6 deer/km2, deer density had the strongest relationship with woody wetlands in the central east region, mixed and deciduous forest in the southeast region, and woody wetlands and herbaceous vegetation in the central region. Deer density increased with deciduous and mixed forests, woody wetlands, and shrub in all regions. Conversely, deer density decreased with herbaceous vegetation, crop, and developed low residential densities in all regions. Therefore, at regional scales, deer overall occurred at greater densities in forests and woody wetlands and lower densities in agricultural and residential development, which did not appear to support more deer. Deer preference for forests does result in damage to forest products, but alternatively, some may consider that deer provide important socioeconomic and ecological services by reducing number of small trees, particularly in the absence of other disturbances that historically controlled tree biomass.

Clear‐cutting triggers regeneration of abandoned secondary forests but risks alternative successional trajectories with high deer density

AbstractQuestionsDoes clear‐cutting intended to boost regeneration of abandoned secondary forests lead to an irreversible shift to non‐forest vegetation under high deer density?LocationWarm‐temperate forests in Boso Peninsula, Chiba Prefecture, Japan.MethodsWe designed a factorial experiment including two levels of forest canopy treatment (clear‐cutting or intact canopy) and two levels of herbivory control (presence or absence of deer) using 24 plots of 10 m × 10 m. Vegetation dynamics occurring under each experimental treatment were tracked for 7.5 years.ResultsGround vegetation under the closed canopy did not change significantly for 7.5 years both inside and outside the deer fences. However, plots were rapidly covered by early‐seral plants till 1.5 years after the cutting event. The quick growth of ground vegetation after clear‐cutting was supported by plants that are known to have soil seed banks, as suggested by their ubiquity immediately after clear‐cutting. Species richness of ground vegetation was maximized at that time and gradually decreased afterward, suggesting biological filtering. This filtering process worked differently inside and outside the deer fences, resulting in different types of vegetation. The clear‐cut‐and‐fence plots became dominated by tree recruits that will recover secondary forests in the future. Contrastingly, vegetation outside the fences lacked many species (e.g., common tree species) that were found inside the fences and became dominated by shrubs and plants unpalatable to deer. This post‐cutting vegetation outside the fences was not similar to that inside the deer fences at any seral stage. This means that the vegetation outside the fences could be tracking an alternative successional trajectory rather than a case of arrested succession.ConclusionsHere, abandoned secondary forests still seem to maintain a high regeneration potential that would be triggered by clear‐cutting, but reducing herbivory pressure by deer is necessary to avoid the risk of alternative successional trajectories.

Density-related effect of red deer browsing on palatable and unpalatable tree species and forest regeneration dynamics

Large herbivores play a key role in terrestrial ecosystems, and their populations alter the plant composition in many ecosystems. One example is deer, whose populations in the Northern Hemisphere have increased over the last decades. This has resulted in increased browsing pressure on saplings and, as a consequence, has hampered forest regeneration in some areas. Such herbivore-induced changes in the regeneration of forest stands have changed their composition and biodiversity. Although there is an established link between the deer population density and the level of damage caused by browsing, the question remains open: What is the effect of increasing deer density over years on the regeneration of palatable and less browsing-resistant tree species? In this study, we investigated the relationships between the regeneration dynamics of five tree species (European beech Fagus sylvatica, silver fir Abies alba, sycamore Acer pseudoplatanus, hornbeam Carpinus betulus, and oak Quercus spp.) and browsing pressure in two years with low and high red deer (Cervus elaphus) density and at similar roe deer (Capreolus capreolus) density. We set up experimental plots in Roztocze National Park (central-eastern Poland), a protected area where natural predators of deer are constantly present. In addition to deer density, we analysed parameters that may affect browsing intensity: height of saplings, forage availability (sapling density), sapling diversity and light intensity (canopy openness). We found that increasing red deer density significantly increased browsing on all tree species, with saplings taller than 50 cm being under the strongest pressure. Moreover, higher deer density altered deer forage selection – it increased their selection for unpalatable European beech and decreased for highly preferred sycamore. Additionally, more species-diverse patches and closed canopy attracted deer and increased the probability of browsing on saplings. Contrary to our predictions, sapling density decreased browsing intensity. The study confirms that high ungulate density has significant effects on tree recruitment and may alter tree species composition of the forest stand. We provide clear evidence that deer herbivory plays a crucial role in tree regeneration in top-down processes in natural ecosystems.