Deer Exclosures Research Articles

Herbivore-induced expansion of generalist species as a driver of homogenization in post-disturbance plant communities

We used a controlled experiment to investigate how disturbance scale (canopy gap area) and herbivory influence post-disturbance plant community dynamics. Twenty canopy gaps were installed in a temperate hemlock-hardwood forest during the winter of 2002–2003: seven small gaps (50–150 m2), seven medium gaps (151–250 m2), and six large gaps (251–450 m2). Within each gap, we established 4–12 sample plots (depending on gap size); 1–3 of which were enclosed with wire mesh white-tailed deer (Odocoileus virginianus) exclosures in 2005. Gaps were revisited and intensively sampled in 2007. After five growing seasons, ground-layer plant communities in non-exclosed plots were more similar compositionally than exclosure plots. Non-exclosed plots in small and medium gaps were more similar to non-exclosed plots in large gaps than they were to exclosed plots in their respective gap size class. Shade-tolerant forbs and trees were less common outside exclosures, while generalist species associated with higher understory light levels and exotics were more prevalent outside exclosures. Our results suggest that even in forests with relatively low deer densities (6.5–9.3 deer km−2), white-tailed deer herbivory may influence the developmental trajectory of post-disturbance plant communities and be a mechanism for decreasing β-diversity along environmental gradients.

Acer saccharum response to concurrent disturbances: the importance of stem layering as an adaptive trait

For shade-tolerant saplings persisting under heavy forest shade, the probability of release by disturbance is directly related to longevity. We examined the effects of two concurrent disturbances, overstory removal and herbivory, on the regeneration dynamics and release response of Acer saccharum Marsh. within 20 artificial canopy gaps ranging in size from 50 to 450 m2. To examine the influence of herbivory, we constructed arrays of deer exclosures within each canopy gap. Five years after gap creation, A. saccharum dominated the taller sapling classes across the entire range of gap sizes examined, and evidence of stem layering in this species was common across all treatments (52%), especially in taller saplings. The presence of stem layering was significantly associated with greater postdisturbance height growth (P < 0.001), regardless of gap area or herbivory. The increase in height of layered A. saccharum on control plots was in spite of the fact that 70% of these saplings were browsed at least once following gap creation; compared with 46% of nonlayered individuals. Consequently, our results suggest that stem layering likely fosters resilience in the face of complex or interacting disturbances and may be an important trait for forecasting gap capture and succession.

Slow responses of understory plants of maple-dominated forests to white-tailed deer experimental exclusion

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.

Editor’s choice: landscape‐level vegetation recovery from herbivory

Tanentzap, A., Burrows, L., Lee, W., Nugent, G., Maxwell, J. & Coomes, D. ( 2009 ) Landscape-level vegetation recovery from herbivory: progress after four decades of invasive red deer control . Journal of Applied Ecology , 46 , 1064 – 1072 Given the ubiquity with which ungulates are becoming increasingly common in temperate terrestrial systems, partly because of anthropogenic influences (i.e. removal of predators, milder winters and supplementary feeding), understanding the responses of herbivore-degraded ecosystems is a highly desirable objective. Current knowledge of how vegetation communities respond to ungulate browsing is largely drawn from comparisons between fenced (unbrowsed) and unfenced (browsed) areas. Replicated exclosure treatments, if imposed for long enough and distributed across a suitable environmental gradient, can provide novel insights into the complex interplay among woody plants, herbivore and the environment (e.g. Olofsson et al. 2009). Yet for practical reasons such experimental approaches are often limited in size, replication and/or location. An alternative approach is to assess the impact on vegetation communities of natural reductions or human culling of ungulate populations. Interpreting the response of vegetation to natural declines in ungulate population is complex since the same factor (e.g. climate change) responsible for ungulate declines may also impact directly on vegetation (Vors & Boyce 2009). While culling can avoid such pitfalls it is rarely undertaken over a large enough spatial and temporal scale to provide a detailed picture of ecosystem response. For this reason, the research by Tanentzap et al. (2009) is distinctive and represents one of the few studies to explicitly examine long-term (>30 years) patterns of change across multiple vegetation communities following herbivore reductions. Such an analysis bears important consequences for the management of wild herbivores and for linking ecological understanding to restoration actions (sensuOrmerod 2003). Between 1861 and 1919, more than 250 red deer (Cervus elaphus scoticus) were released in New Zealand for recreational hunting and further releases continued until 1926. By the 1960s, red deer ranged over most of the country measurably impacting forest composition and structure by reducing populations of the most palatable plant species (Elton 1958). In the Murchison mountains of southern New Zealand, limited red deer control began in 1948, but population reductions were considered minimal until systematic culling began in 1962. To assess the response of vegetation to reduced deer densities, permanent plots were established in the area as early as 1969. As a result of systematic culling, deer numbers were reduced by 92% and it was generally believed that continuous deer control since 1962 would reduce deer densities to levels at which regeneration of palatable species may occur. Tanentzap et al. (2009) report the results arising from recent resurveys of these long-established plots. Although some metrics did recover over time in response to reductions in browsing (i.e. recruitment of palatable tree seedlings and shrubland and grassland structure), the overall rate was slow (c. 30 years for relatively small but significant increases). While herbivore control is essential in restoring herbivore-disturbed ecosystems, the results suggest that solely manipulating herbivore population numbers may not always be a useful management objective in allowing for vegetation recovery. Vegetation recovery in response to long-term and significant herbivore reductions may be limited by several factors, including the slow growth rates of New Zealand species, density-dependent diet switching by deer, altered successional trajectories and below-ground processes. As a result, after 39 years, even low densities of herbivores may restrict ecosystem recovery, and restoration may require a long-term perspective on the order of decades. Management strategies can accelerate recovery by protecting existing palatable plants within deer exclosures, and planting or seeding palatable species within these refugia. However, in addition to increasing seed sources, restoration may only become apparent following large-scale disturbance events and canopy turnover.

Landscape‐level vegetation recovery from herbivory: progress after four decades of invasive red deer control

Summary 1. Ungulates have reached such high densities in some natural ecosystems that culling is frequently used to reduce their impacts on vegetation. However, much is still unknown about the outcomes of landscape‐level control, in part because monitoring vegetation recovery requires decades. 2. We report long‐term vegetation changes in permanent plots located in forest, shrubland and grassland communities across a mountain range in southern New Zealand. We test whether c. 92% reduction in the population of invasive non‐indigenous red deer Cervus elaphus since 1964 has led to the recovery of deer‐preferred species. 3. Tree seedlings, saplings and the number of seedlings per adult tree increased over time. There was lower recruitment, however, of highly palatable forest species compared with less palatable species, and the recruitment of saplings was lower in browsed forest plots compared with deer exclosures. 4. The total number of occurrences and absolute number of palatable species per plot increased over time in shrublands and grasslands respectively. The height of both shrublands and palatable grassland snow tussocks Chionochloa spp. increased, although the occurrences of most individual species remained unchanged over time. 5. Vegetation recovery at our site in response to long‐term and significant herbivore reductions may be limited by several factors, including the slow growth rates of New Zealand species, density‐dependent diet switching by deer, altered successional trajectories and below‐ground processes. 6. Synthesis and applications. Our results suggest that after nearly four decades, even low densities of introduced herbivores may restrict ecosystem recovery, and therefore, restoring herbivore‐disturbed ecosystems by solely manipulating herbivore population numbers may require a long‐term perspective. Management strategies can accelerate recovery by protecting existing palatable plants within deer‐exclosures, and planting or seeding palatable species within these refugia. However, in addition to increasing seed sources, restoration may only become apparent following large‐scale disturbance events and canopy turnover.

Death and Taxus: the high cost of palatability for a declining evergreen shrub, Taxus canadensis

Taxus canadensis Marsh., a shade-tolerant evergreen shrub, is in decline as a result of past anthropogenic disturbances and increased cervid browsing. To identify factors that may be influencing establishment for this species, we planted 1080 T. canadensis cuttings in a hemlock–hardwood forest in the spring of 2004. Cuttings were planted across a gradient of light environments, consisting of artificial canopy gaps (61–441 m2) and closed-canopy conditions, and half were protected with deer exclosures. Following four growing seasons, T. canadensis survival in exclosures was 92% compared with 75% in controls. A mixed-effects binary logistic regression analysis revealed that deer exclusion had the most influence on the probability of survival; all else being equal an individual was nearly seven times more likely to survive if planted inside an exclosure (P < 0.001). Increasing light intensity had a counterbalancing effect on growth and survival; light increased leader growth (P = 0.019) but reduced an individual’s probability of survival (P < 0.001), possibly owing to enhanced herbivory and elevated moisture stress. Consequently, enhancing resource availability and growth may not decrease the impact of biomass loss to herbivory. These results suggest that even with relatively low herbivore densities, exclosures are required for the recovery of highly palatable species.

Maintaining a Pine Legacy in Itasca State Park

ABSTRACT: Itasca State Park, located in the northern central portion of Minnesota, is challenged with maintaining a pine forest covertype, yet regeneration failures may allow much of the park to succeed to northern hardwoods. Efforts to improve pine regeneration and growth have included deer exclosures and prescribed burning to reduce competing vegetation. We revisited Itasca's Mary Lake deer exclosure 66 years after establishment to compare stand development, structure, and white pine (Pinus strobus L.) regeneration and growth with that of adjacent plots that have been: (1) untreated and (2) recently repeatedly under-burned. Overstory structure and composition was similar among all three treatments, and mid- and understory structures were similar in the treatments subject to deer browse. Sapling and midstory white pine were only present in the exclosure. White pine regeneration was present in all treatments and most abundant in the burned treatment, but was restricted to the smallest height class and con...

Effect of host populations on the intensity of ticks and the prevalence of tick-borne pathogens: how to interpret the results of deer exclosure experiments

Deer are important blood hosts for feeding Ixodes ricinus ticks but they do not support transmission of many tick-borne pathogens, so acting as dead-end transmission hosts. Mathematical models show their role as tick amplifiers, but also suggest that they dilute pathogen transmission, thus reducing infection prevalence. Empirical evidence for this is conflicting: experimental plots with deer removal (i.e. deer exclosures) show that the effect depends on the size of the exclosure. Here we present simulations of dynamic models that take into account different tick stages, and several host species (e.g. rodents) that may move to and from deer exclosures; models were calibrated with respect to Ixodes ricinus ticks and tick-borne encephalitis (TBE) in Trentino (northern Italy). Results show that in small exclosures, the density of rodent-feeding ticks may be higher inside than outside, whereas in large exclosures, a reduction of such tick density may be reached. Similarly, TBE prevalence in rodents decreases in large exclosures and may be slightly higher in small exclosures than outside them. The density of infected questing nymphs inside small exclosures can be much higher, in our numerical example almost twice as large as that outside, leading to potential TBE infection risk hotspots.

DEER HERBIVORY ALTERS FOREST RESPONSE TO CANOPY DECLINE CAUSED BY AN EXOTIC INSECT PEST

Hemlock woolly adelgid (HWA; Adelges tsugae) infestations have resulted in the continuing decline of eastern hemlock (Tsuga canadensis) throughout much of the eastern United States. While the initial impacts of HWA infestations have been documented, our understanding of forest response to this disturbance remains incomplete. HWA infestation is not occurring in isolation but within a complex ecological context. The role of potentially important interacting factors, such as elevated levels of white-tailed deer herbivory, is poorly understood. Despite the potential for herbivory to alter forest successional trajectories following a canopy disturbance, little is known about herbivory-disturbance interactions, and herbivory is rarely considered in assessing forest response to a co-occurring disturbance. We used repeated censuses of deer exclosures and paired controls (400 paired plots) to quantify the impact of deer herbivory on tree seedling species abundance in 10 eastern hemlock ravines that span a gradient in HWA-induced canopy decline severity. Use of a maximum likelihood estimation framework and information theoretics allowed us to quantify the strength of evidence for alternative models developed to estimate the impacts of herbivory on tree seedling abundance as a function of varying herbivore density and canopy decline severity. The exclusion of deer herbivory had marked impacts on the abundance of the studied seedling species: Acer rubrum, Acer saccharum, Betula lenta, Nyssa sylvatica, Quercus montana, and Tsuga canadensis. For all six species, the relationship between seedling abundance and deer density was either exponential or saturating. Although the functional form of the response varied among seedling species, the inclusion of both deer density and canopy decline severity measures consistently resulted in models with substantially greater support. Canopy decline resulted in higher proportional herbivory impacts and altered the ranking of herbivory impacts by seedling species. Our results suggest that, by changing species' competitive abilities, white-tailed deer herbivory alters the trajectory of forest response to this exotic insect pest and has the potential to shift future overstory composition.

Impacts of endangered Key deer hervivory on imperiled pine rocklands: a conservation dilemma?

In the lower Florida Keys, endangered Key deer (Odocoileus virginianus clavium) herbivory, along with fire, can affect pine rocklands, an endangered plant community. We compared pineland vegetation from three studies over approximately 50 years on four islands with either high or low deer density (historical analysis). We also compared extant vegetation samples between two islands with high or low deer density, which contained pinelands burned 10 years and 14 years prior to sampling and control areas (unburned for > 50yr). In addition, experimental deer exclosures and control plots established in pineland were prescribe burned and analyzed for deer effects on an island with high density of Key deer. The historical analysis suggests that, over time, deer-preferred plant species declined while less-preferred species increased, regardless of fire history on islands. The extant vegetation analysis suggests that fire and Key deer herbivory both reduce hardwood plant density and growth. Densities of deer-preferred woody species were higher on an island with low deer density than on an island with high deer density in burn treatments, but relatively similar in control areas. On the high deer density island, a fire effect was evident in that the control area had higher densities of woody species than burned areas, and herbaceous species richness was higher in the control area, indicating a possible refuge from deer herbivory. In deer exclosures, preferred woody species and herbaceous species tended to increase after fire, but decrease in adjacent open plots. Results suggest that Key deer herbivory, along with fire, shapes pine rockland plant communities, and that overbrowsing might have substantial impacts on preferred herbaceous and woody species in pinelands. Therefore, efforts could be confounded in managing both the endangered Key deer and the endangered pine rocklands that they affect.

LOCALIZED DEER ABSENCE LEADS TO TICK AMPLIFICATION

Deer support high tick intensities, perpetuating tick populations, but they do not support tick-borne pathogen transmission, so are dilution hosts. We test the hypothesis that absence of deer (loss of a dilution host) will result in either an increase or a reduction in tick density, and that the outcome is scale dependent. We use a complementary methodological approach starting with meta-analysis, followed up by a field experiment. Meta-analysis indicated that larger deer exclosures reduce questing (host-seeking) tick density, but as the exclosure becomes smaller (<2.5 ha) the questing tick density is increased (amplified). To determine the consequences for tick-borne pathogen transmission we carried out a field experiment, comparing the intensity of ticks that fed on hosts competent for tickborne pathogen transmission (rodents) in two small (<1 ha) deer exclosures and their replicated controls. Intensity of larval ticks on rodents was not significantly different between treatments, but nymph intensity, the tick stage responsible for tick-borne encephalitis (TBE) transmission, was higher in deer exclosures. TBE seropositive rodents were found in a deer exclosure but not in the controls. We propose that localized absence of deer (loss of a dilution host) increases tick feeding on rodents, leading to the potential for tick-borne disease hotspots.

Isolating the Effects of White-tailed Deer on the Vegetation Dynamics of a Rare Maritime American Holly Forest

Effects of multiple herbivores were isolated in a rare, old-growth, maritime forest that has been affected by high white-tailed deer (Odocoileus virginianus) populations for several decades. Three decades of change in the plant community was described using permanent plots and nearly two decades of recovery using deer exclosures. Additional short-term exclosure experiments were used to separate the effect of rabbit and vole herbivory and the influence of canopy type on understory vegetation. We assessed whether natural enclosures formed by high densities of greenbrier (Smilax rotundifolia and S. glauca) provide spatial refugia for plant species from deer. Significant differences in fenced plots indicate that deer, rabbits and voles individually affect the understory vegetation, though rabbits and voles are secondary to deer that are the major herbivore in the American holly (Ilex opaca) forest. Plant cover decreased within permanent plots from 1967 to 1986; during the same time period deer densities increased drastically island-wide. Since plots were fenced in 1986 no additional significant changes were detected, but this is likely due to an inadequate sample size. The cover of all species depended on the interaction of fencing and canopy type with significantly higher plant cover in fenced plots beneath mixed or exclusively deciduous canopy. The proportion of woody stems surpassing 0.5 m tall was significantly higher when stems were fenced. Browsing impacts were apparent on approximately a quarter of the vegetation in June 2003. Plant cover, richness and diversity were higher within natural greenbrier enclosures. Overall the exclosure studies indicate the potential natural recovery that could occur within the forest if deer herbivory were limited. Few species have been extirpated, although several are confined to the greenbrier enclosures. Under the current level of herbivory, the maritime holly forest composition will be altered, changing the characteristic canopy of a critically imperiled plant community.

Effects of Environmental Salinity on Vertebrate Florivory and Wetland Communities

Iris hexagona is a perennial freshwater species indigenous to Louisiana wetlands. Coastal iris populations that are exposed to saline conditions often suffer heavy floral browsing. This paper is the first to photographically document florivory by white-tailed deer (Odocoileus virginianus Zimmerman), which consume iris flowers and immature seed capsules. Severe florivory can prevent sexual reproduction in plants and eliminate habitat for floral arthropods. In this three-year study, we monitored environmental salinity, assessed natural levels of florivory, and established deer exclosures to test the effects of florivory on arthropod abundance and diversity. In two out of three years, florivory rates were positively correlated with the level of salinity at individual I. hexagona populations. In all three years, florivory in the brackish marsh was an order of magnitude greater than florivory in intermediate and freshwater sites. In 2003, the number and diversity of arthropods was significantly greater on unbrowsed (caged) than browsed (open) irises. In October 2002, Hurricane Lili struck our main study site, causing extensive damage to the landscape and heavy deer mortality. Despite this, floral browsing was high (88%) in spring 2003, and arthropod numbers and diversity declined significantly. Our results suggest that salinity may facilitate floral browsing, which can have direct effects on plant fitness and indirect consequences for arthropod communities in wetland plant populations.

Effects of Key deer herbivory on forest communities in the lower Florida Keys

Ungulate herbivory can have strong impacts on plant communities, but these impacts are rarely considered in recovery plans of endangered species. This study examined the effects of the endangered Key deer ( Odocoileus virginianus clavium) on its environment in the lower Florida Keys. The Key deer population has increased to over 700 deer from approximately 50 deer in the 1950s; however, approximately 75% of the population resides on only a few islands (Big Pine, No Name, Big Munson) where Key deer herbivory on forest communities may be substantial. Effects of deer herbivory on plant densities were estimated on these islands using vegetation quadrats in hardwood hammock, buttonwood transition, and mangrove wetlands and compared to nine other islands with intermediate or low deer densities. On islands with high deer density, densities of preferred woody plant species <1.2 m tall (within Key deer reach) were significantly lower than islands with lower deer densities, while densities of some nonpreferred species were significantly higher. Deer exclosures established in hardwood hammock on a high-density deer island revealed a mean increase in abundance/height of preferred woody species inside exclosures, while nonpreferred species significantly increased in open plots. We conclude that on high deer density islands, highly preferred plant species might eventually fail to regenerate and unpalatable plant species may become dominant. Careful criteria need to be developed to maintain Key deer numbers above an endangered species status yet below levels that are destructive to local forest species.

Influence of deer exclusion on soil nutrients in oak forests of a central European low mountain range

High densities of red deer can have severe impacts on soil nutrient status by removing the ground vegetation and enhancing erosion of the fertile soil layers. We compared four fenced deer exclosures with adjacent unfenced sites to evaluate the effect of deer grazing and trampling on the soil nutrient status (Corg, Nt, PO43−, Ca2+, Mg2+, K+) in sloping oak forests of a central European low mountain range. The investigation was set up as a three-factor randomized complete block design (RCBD) with the factors: ‘fencing’ (fenced/unfenced), ‘gradient’ (gentle/steep) and ‘aspect’ (windward/leeward). We hypothesized that exclusion of red deer by fencing would increase soil nutrient contents independent of slope gradient and aspect. Fencing increased the contents of Corg, Nt, Ca2+ and PO43−, but only at the windward sites. This effect was less pronounced at the gently sloping site than at the steep site, which exhibited the lowest contents of Corg, Nt and PO43− of all sites. We did not find increased soil nutrients in the fenced exclosures at the leeward sites, neither at the steep nor at the gently sloping site. At both slope aspects nutrient contents (Corg, Nt, PO43−, K+) tended to be higher on the gentle than at the corresponding steep slopes. Our results suggest that red deer trampling and grazing enhance the loss of soil nutrients at predisposed sites such as windward locations with a high slope gradient. Only at such sites did the exclusion of red deer increase several soil nutrients. Copyright © 2005 John Wiley & Sons, Ltd.

Effects of harvesting and deer browsing on attributes of understory plants in northern hardwood forests, Upper Michigan, USA

Both forest harvesting and browsing by white-tailed deer ( Odocoileus virginianus Zimmerman) affect the composition and structure of forest vegetation throughout the eastern deciduous forest in the United States. We studied their affect and their interaction by measuring the composition, richness, cover, physical stature, and reproductive potential of vascular plants in the understory of three thinned (uneven-aged, even-aged, managing for old-growth characteristics) and two unthinned (second-growth, old-growth) forests dominated by sugar maple ( Acer saccharum Marsh.) in western Upper Michigan. Based on measurements taken five years after deer exclosures were established, we found consistent and strong statistical differences in species richness and percent cover related to forest harvest but not to deer browse. Percent cover of the understory vegetation showed weakly significant interactions between deer browse and forest harvest. Thinned forests had a greater average richness and cover of graminoid species, average cover of wild red raspberry ( Rubus strigosus L.) and sugar maple compared to unthinned forests. Measurements of plant morphology and the frequency of flowering and fruiting were more sensitive indicators of deer browse than community measurements such as richness and cover. Based on measures of physical stature and reproductive potential, sugar maple, red-berried elder ( Sambucus racemosa L.), bluebead-lily ( Clintonia borealis (Aiton) Raf.), small Solomon-seal ( Polygonatum pubescens (Willd.) Pursh.), false Solomon-seal ( Smilacina racemosa (L.) Desf.), rosy twisted stalk ( Streptopus roseus Michaux), and trillium species ( Trillium grandiflorum (Michaux) Salisb. and T. cernuum L.) all experienced significant browse damage. A better understanding of the interaction between forest harvest and deer browse and their effect on community composition and structure is critical to maintaining and enhancing biodiversity in managed northern hardwood forests.

Effects of white-tailed deer on the population dynamics of acorns, seedlings and small saplings of Quercus buckleyi

To measure the effects of white-tailed deer (Odocoileus virginianus) herbivory on seeds, seedlings, and young saplings of Quercus buckleyi on the eastern Edwards Plateau of central Texas, USA, experimental fenced deer exclosures were constructed. Acorns or small Q. buckleyi transplants were placed in each exclosure and in each unfenced control plot. Deer did not significantly affect acorn survival and germination, but did significantly reduce transplant survival and growth rates. The results support the hypothesis that deer are responsible for the failure of recruitment into adult size classes in Q. buckleyi populations in this region. Without adult recruitment of Q. buckleyi, the species composition and possibly even the physiognomy of woodlands on the eastern Edwards Plateau will change markedly. The results of this experiment also indicate that, although juniper (Juniperus ashei) and Q. buckleyi presumably compete for water, light, and nutrients, in the presence of deer junipers can have a positive effect on seedlings and saplings of Q. buckleyi, a case of facilitation. In the presence of deer the transplants increased in height significantly more slowly away from juniper saplings than they did beneath juniper saplings, probably due to the physical protection from browsing that junipers provided to the transplants.

Herbivory Constrains Survival, Reproduction and Mutualisms When Restoring Nine Temperate Forest Herbs

RUHREN, SCOTT AND STEVEN N. HANDEL (Department of Ecology, Evolution, and Natural Resources, and Center for Urban Restoration Ecology, Rutgers, The State University of New Jersey, 1 College Farm Road, New Brunswick, NJ 08901-1582). Herbivory constrains survival, reproduction and mutualisms when restoring nine deciduous forest herbs. J. Torrey Bot. Soc. 130:34-42. 2003.-Restoration of perennial herbs may be influenced by plant-animal interactions. For example, projects may be aided by native pollinators or seed dispersers or impeded by herbivores. Our previous work at Jockey Hollow, a U.S. National Park, indicated that abundance of native woodland herbs was low and herbivory by Odocoileus virginianus Zimmerman (white-tailed deer) was intense. The goal of our experiment was to test the feasibility of herbaceous plant restoration in spite of a large 0. virginianus herd. By examining small-scale reintroductions of nine species of native herbaceous perennials (Asarum canadense L., Geranium maculatum L., Mitella diphylla L., Polemonium reptans L., Sanguinaria canadensis L., Smilacina racemosa (L.) Desf., Tiarella cordifolia L., Uvularia grandiflora J.E. Smith and Viola spp.) we determined which plants survived and reproduced. After 3 years, 46% of plants survived and 5% flowered inside exclosures, while 23% of plants planted outside survived; no plants surviving outside exclosures flowered. Within deer exclosures, native bees visited five species and ants dispersed Sanguinaria seeds in experimental depots. However pollination and seed dispersal occurs only with protection from 0. virginianus. Overabundant 0. virginianus and the relatively long generation time of perennial herbs may prevent restoration of similar plant communities at this time.

Deciduous woodland conservation under heavy deer browsing on Devils Tower National Monument, USA

Native deciduous woodlands comprise <5% of the vegetation in the Black Hills and northern plains of the USA and appear to be in decline. Because deciduous woodlands comprise 18% of the land cover on Devils Tower National Monument (DTNM), this natural area is potentially important for the conservation of these plant communities. Lack of tree regeneration and accumulation of dead wood suggest that the native deciduous woodlands on DTNM may die out under persistent, heavy deer (Odocoileus virginianus, O. hemionus) browsing. We monitored vegetation changes for seven years (1989–1996) inside and outside 6 deer exclosures on DTNM to determine the resilience of native woodland communities when protected from browsing, and to parameterize models that evaluate specific fencing scenarios for managing woodland communities. The herbaceous woodland understory was not directly, but indirectly affected by deer browsing because graminoid biomass declined as tall shrubs recovered. Tall shrubs, dominated by Prunus spp. showed the most rapid and consistent recovery across sites. Models of shrub growth indicated that rotational fencing for short durations (∼10 years) produced the highest long-term increase in tall-shrub densities and the greatest evenness among size classes. Because deciduous woodlands currently are resilient and occur in small patches, fencing may provide a practical management alternative to deer culling programs.

Forest regeneration and the influences of white-tailed deer ( Odocoileus virginianus) in cool temperate New Zealand rain forests

Cool temperate rain forests on Stewart Island, southern New Zealand, have had little direct human modification, but introduced white-tailed deer ( Odocoileus virginianus) have influenced forest understoreys. Changes in life stages (seedlings, saplings and adult trees) of common tree and shrub species were recorded over at least 18 years in permanent plots in these forests. Faecal pellet indices of deer frequency in the forests were slightly greater in the most recent survey. However, during this period overall seedling and sapling densities increased, including species browsed preferentially by deer. In deer exclosures maintained over 21 years, densities of woody seedlings and saplings increased, but not of highly palatable species. While deer frequency was a significant predictor of increased seedling densities of unpalatable species and decreases of palatable species at a plot scale, so also were measures of local seed availability and competition from other seedlings and ferns. Seedling density increases were not uniform across species in response to stand structural attributes, and there were interactions between effects of browsing by deer and stand structural attributes. Therefore, relationships between deer frequency and seedling regeneration need to be set in the context of other biotic influences in these forests.