Managing an invasive predator pre-adapted to a pulsed resource: a model of stoat (Mustela erminea) irruptions in New Zealand beech forests

The stoat (Mustela erminea) is a specialist predator that evolved to exploit the unstable populations of northern voles and lemmings. It was introduced to New Zealand, where it is pre-adapted to respond with a population irruption to the resource pulses that follow a heavy seedfall of southern beech (Nothofagus spp.). Culling stoats during an irruption is necessary to reduce damaging predation on nesting endemic birds. Culling might not reduce the stoat population long term, however, if high natural mortality exceeds culling mortality in peak years. During other phases of the beech-mast cycle, culling might have a greater effect on a smaller stoat population, whether or not damage prevention is critical. We developed a 4-matrix model to predict the effects of culling on λ, the annual rate of change in the size of the stoat population, through the four annual phases of an average masting cycle, explicitly distinguishing between apparent and real culling. In the Post-seedfall phase of the cycle, large numbers of stoats are killed, but little of this extra mortality is additive; in other phases, culling removes larger proportions of smaller total numbers of stoats that would otherwise have lived. Culling throughout all phases is most effective at reducing stoat populations, but is also the most expensive option. Culling in Post-seedfall plus Seed or Crash years is somewhat less effective but better than culling in one phase only. Culling has different short-term effects on stoat age distribution depending on the phase of the cycle when culling begins.     

Applicability of a Bayesian state-space model for evaluating the effects of localized culling on subsequent density changes: sika deer as a case study

At the landscape scale, localised culling is often conducted to achieve various deer management aims. However, few studies have assessed the effects of localised culling on deer population dynamics, owing to the spatially and temporally insufficient datasets of deer abundance that are derived from limited survey efforts. In this study, we estimated the population dynamics of a sika deer (Cervus nippon) population in the Tanzawa Mountains, central Japan, by Bayesian state-space modelling using spatiotemporally insufficient abundance indices and evaluated the effects of unit-specific culls on subsequent density changes in 56 units. The responses of deer density to unit-specific culls differed greatly among units, and a very weak correlation was observed between the intensities of unit-specific culls and the reduction in density. Deer populations in some units tended to resist density decreases despite high culling pressure, whereas those in other units were susceptible to density decreases with little to no culling pressure. Because the spatial scales of each unit were relatively small, annual density changes in each unit were largely influenced by deer movement in this estimation. The obscured effects of unit-specific culls, which were probably derived from deer movement among units in this case study, re-emphasized that deer migration should be incorporated into the planning of localised culling and that deer management should be coordinated over a wide area beyond landscape components and landownerships. Thus, we conclude that Bayesian state-space modelling is valuable for practical deer management programs at a large spatial scale even if different abundance indices are used.     

Different facets of tree sapling diversity influence browsing intensity by deer dependent on spatial scale

Browsing of tree saplings by deer hampers forest regeneration in mixed forests across Europe and North America. It is well known that tree species are differentially affected by deer browsing, but little is known about how different facets of diversity, such as species richness, identity, and composition, affect browsing intensity at different spatial scales. Using forest inventory data from the Hainich National Park, a mixed deciduous forest in central Germany, we applied a hierarchical approach to model the browsing probability of patches (regional scale) as well as the species‐specific proportion of saplings browsed within patches (patch scale). We found that, at the regional scale, the probability that a patch was browsed increased with certain species composition, namely with low abundance of European beech (Fagus sylvatica L.) and high abundance of European ash (Fraxinus excelsior L.), whereas at the patch scale, the proportion of saplings browsed per species was mainly determined by the species’ identity, providing a “preference ranking” of the 11 tree species under study. Interestingly, at the regional scale, species‐rich patches were more likely to be browsed; however, at the patch scale, species‐rich patches showed a lower proportion of saplings per species browsed. Presumably, diverse patches attract deer, but satisfy nutritional needs faster, such that fewer saplings need to be browsed. Some forest stand parameters, such as more open canopies, increased the browsing intensity at either scale. By showing the effects that various facets of diversity, as well as environmental parameters, exerted on browsing intensity at the regional as well as patch scale, our study advances the understanding of mammalian herbivore–plant interactions across scales. Our results also indicate which regeneration patches and species are (least) prone to browsing and show the importance of different facets of diversity for the prediction and management of browsing intensity and regeneration dynamics.     

Herbivory on planted oak seedlings across a habitat edge created by timber harvest

Edge habitats create environmental gradients that affect plant community composition and herbivore behavior. Silvicultural disturbance creates edge habitat with direct (via changes in light) and indirect (via changes in herbivore behavior) consequences for the growth and survival of tree seedlings, and thus, the composition of the future forest stands. Herbivores, particularly ungulates, can be a major limiting factor in oak regeneration, and silvicultural disturbance may alter the abundance or behavior of herbivores following harvest. We measured the severity of herbivory on experimentally planted white (Quercus alba) and black oak (Quercus velutina) seedlings by white-tailed deer (Odocoileus virginianus) and eastern cottontail rabbits (Sylvilagus floridanus), as well as foliar damage from insects, across gradients created by clearcuts in a deciduous forest in Indiana, USA. Overall browse pressure on oaks was low in our study. Nonetheless, spatial variation in herbivory depended on herbivore taxa; herbivory by rabbits was highest inside harvest openings, whereas foliar damage by insects peaked in the forest. Intensity of deer herbivory was constant across the edge. In addition, we observed indirect interactions among herbivore species mediated by a seedling’s browsing history. Herbivore damage by deer was positively related to past browsing by rabbits, and foliar damage from insects was positively related to past browsing by both deer and rabbits. Increasing woody plant competition reduced herbivory on seedlings by both deer and rabbits. Given the lack of spatial variability in deer herbivory and low overall herbivory by rabbits, we suspect that interactions between timber harvesting and herbivory did not have a strong impact on oak seedlings at our study sites.     

Spatial epidemiology of chronic wasting disease in Wisconsin white-tailed deer

Chronic wasting disease (CWD) is a fatal, emerging disease of cervids associated with transmissible protease-resistant prion proteins. The potential for CWD to cause dramatic declines in deer and elk populations and perceived human health risks associated with consuming CWD-contaminated venison have led wildlife agencies to embark on extensive CWD control programs, typically involving culling to reduce deer populations. We characterized the spatial distribution of CWD in white-tailed deer (Odocoileus virginianus) in Wisconsin to facilitate CWD management. We found that CWD prevalence declined with distance from a central location, was locally correlated at a scale of 3.6 km, and was correlated with deer habitat abundance. The latter result is consistent with patterns expected for a positive relationship between density and prevalence of CWD. We recommend management activities focused on culling in geographic areas with high prevalence to have the greatest probability of removing infected individuals. Further research is needed to elucidate the factors involved in CWD spread and infection rates, especially the role of density-dependent transmission.     

Getting the biggest birch for the bang: restoring and expanding upland birchwoods in the Scottish Highlands by managing red deer

High deer populations threaten the conservation value of woodlands and grasslands, but predicting the success of deer culling, in terms of allowing vegetation to recover, is difficult. Numerical simulation modeling is one approach to gain insight into the outcomes of management scenarios. We develop a spatially explicit model to predict the responses of Betula spp. to red deer (Cervus elaphus) and land management in the Scottish Highlands. Our model integrates a Bayesian stochastic stage‐based matrix model within the framework of a widely used individual‐based forest simulation model, using data collected along spatial and temporal gradients in deer browsing. By initializing our model with the historical spatial locations of trees, we find that densities of juvenile trees (<3 m tall) predicted after 9–13 years closely match counts observed in the field. This is among the first tests of the accuracy of a dynamical simulation model for predicting the responses of tree regeneration to herbivores. We then test the relative importance of deer browsing, ground cover vegetation, and seed availability in facilitating landscape‐level birch regeneration using simulations in which we varied these three variables. We find that deer primarily control transitions of birch to taller (>3 m) height tiers over 30 years, but regeneration also requires suitable ground cover for seedling establishment. Densities of adult seed sources did not influence regeneration, nor did an active management scenario where we altered the spatial configuration of adults by creating “woodland islets”. Our results show that managers interested in maximizing tree regeneration cannot simply reduce deer densities but must also improve ground cover for seedling establishment, and the model we develop now enables managers to quantify explicitly how much both these factors need to be altered. More broadly, our findings emphasize the need for land managers to consider the impacts of large herbivores rather than their densities.     

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.     

Achieving landscape-scale deer management for biodiversity conservation: The need to consider sources and sinks

Hyper-herbivory following predator removal is a global issue. Across North America and Europe, increasing deer numbers are affecting biodiversity and human epidemiology, but effectiveness of deer management in heterogeneous landscapes remains poorly understood. In forest habitats in Europe, deer numbers are rarely assessed and management is mainly based on impacts. Even where managed areas achieve stable or improving impact levels, the extent to which they act as sinks or persist as sources exporting deer to the wider landscape remains unknown. We present a framework to quantify effectiveness of deer management at the landscape scale. Applied across 234 km² of Eastern England, we assessed management of invasive Reeve's muntjac (Muntiacus reevesi) and native roe (Capreolus capreolus), measuring deer density (using thermal imaging distance transects 780 km/year), fertility, neonatal survival, and culling to quantify source-sink dynamics over 2008–2010. Despite management that removed 23–40% of the annual population, 1,287 (95% CI: 289–2,680) muntjac and 585 (454–1,533) roe deer dispersed annually into the wider landscape, consistent with their ongoing range expansion. For roe deer, culled individuals comprised fewer young deer than predicted by a Leslie matrix model assuming a closed population, consistent with age-dependent emigration. In this landscape, for roe and muntjac, an annual cull of at least 60% and 53%, respectively, is required to offset annual production. Failure to quantify deer numbers and productivity has allowed high density populations to persist as regional sources contributing to range expansion, despite deliberative management programs, and without recognition by managers who considered numbers and impacts to be stable. Reversing an unfavorable condition of woodland biodiversity requires appropriate culls across large contiguous areas, supported by knowledge of deer numbers and fertility. © 2013 The Wildlife Society.     

Opposing deer and caterpillar foraging preferences may prevent reductions in songbird prey biomass in historically overbrowsed forests

Overbrowsing by ungulates decimates plant populations and reduces diversity in a variety of ecosystems, but the mechanisms by which changes to plant community composition influence other trophic levels are poorly understood. In addition to removal of avian nesting habitat, browsing is hypothesized to reduce bird density and diversity through reduction of insect prey on browse‐tolerant hosts left behind by deer. In this study, we excluded birds from branches of six tree species to quantify differences in songbird prey removal across trees that vary in deer browse preference. Early in the breeding season, birds preyed on caterpillars at levels proportional to their abundance on each host. Combining these data with tree species composition data from stands exposed to experimentally controlled deer densities over 30 years ago, we tested whether overbrowsing by white‐tailed deer reduces prey biomass long after deer densities are reduced. Our analysis predicts total prey availability in the canopy of regenerating forests is fairly robust to historic exposure to high deer densities, though distribution of prey available from host species changes dramatically. This predicted compensatory effect was unexpected and is driven by high prey abundance on a single host tree species avoided by browsing deer, Prunus serotina. Thus, while we confirm that prey abundance on host trees can act as a reliable predictor for relative prey availability, this study shows that quantifying prey abundance across host trees is essential to understanding how changes in tree species composition interact with ungulate browse preference to determine prey availability for songbirds.     

Temporal shifts of DNA‐microsatellite allele profiles in roe deer (Capreolus capreolus L.) within three decades

DNA‐microsatellite polymorphism (four loci) was studied in 56 male roe deer (Capreolus capreolus) from a 900‐ha hunting territory in the Vosges du Nord Mountains (France), culled over 34 years (1956–1990). Changed allele frequencies at two loci within this period, and increased allelic diversity, were traced to a phase of reduced population density and subsequent immigration. Decadic population samples collected within 900‐ha were distinguished by higher genetic variability measures than were certain geographical samples across Central Europe (4–900 km). On average, the decadic cohorts were distinguished by a gene diversity index of G_ST = 0.0286, and a genetic distance of D = 0.0938, which reflect 54% (G_ST) and 69% (D) of the respective geographic (350 km) differentiation indices of roe deer in Central Europe. The importance of demography and population ecology effects for microevolution in a large mammal is demonstrated, as is the risk of artefact by composing population samples of deer over several years. Population genetic screening should cover various demes of roe deer from the same general region, and be based on many unlinked polymorphic loci, to minimize the distorting effects of genetic dynamics at the small spatial scale.     

Effects of deer browsing on the early stage of pyrogenic succession on Miyajima Island,southwestern Japan

The early stage of forest regeneration on Miyajima Island, southewstern Japan, was studied for three years after a fire in 1984, with respect to the effects of deer browsing. The regeneration patterns of woody species, in terms of the biomass increment and browsing damage to plants, were classified into the following three groups: non- or rarely browsed species with little increment of biomass, heavily browsed with little increment, and heavily browsed with large increment. The aboveground biomass increased from 0.4 kg to 2.7 kg per 100 m² during three years, and was less than half of the biomass obtained in other burnt pine forests on the adjacent deer-free islands. About 28% of the plant biomass was consumed by deer. The effects of browsing on forest regeneration were heavier at lower than that at the higher altitudes. On this island, deer browsing seems to have an important effect on vegetational succession in the burnt areas.     

Assessing spatial variation in browsing history by means of fraying scars

Aim We used fraying scars to understand spatial variation in browsing history. Information on browsing history is an essential background in studies on the long‐term effect of deer browsing on the flora and fauna and of its variation in space. Location We focused on two small neighbouring islands of Haida Gwaii (British Columbia, Canada), Reef Island and South‐Skedans Island, colonized by introduced black‐tailed deer (Odocoileus hemionus sitkensis). Methods We searched for sites where trees with fraying scars were clustered. We studied the trees that deer selected (species, size) and the characteristics of scars (number, position, size). Using a cross‐dating procedure, we dated fraying scars with dendrochronology, obtaining an accurate estimate of the year the scar was formed. Results On Reef Island, Thuja plicata was the tree species chosen for fraying. On South‐Skedans Island, where Thuja plicata is missing, deer chose Salix sp. and Alnus rubra. Deer chose only trees with a circumference of less than 50 cm. About two to three fraying scars were recorded per tree. All of them extended between 30–40 and 70–80 cm from the ground and were between 5 and 6 cm in width. On Reef Island, 95% of the scars were formed during the last 50 years. On South‐Skedans Island, 95% were formed over the last 10 years. Age distribution of scars showed a constant increase of the number of scars over time. It indicated that deer had colonized Reef Island 53 years prior to this study but were absent or rare on South‐Skedans Island until 13 years prior to this study. Main conclusions These results indicate different colonization dates and thus different length of browsing histories for the islands studied and provide the historical background necessary to analyse the involvement of deer in the current differences in the flora and fauna observed between islands.     

Test of Localized Management for Reducing Deer Browsing in Forest Regeneration Areas

ABSTRACT White-tailed deer (Odocoileus virginianus) browsing in forest regeneration sites can affect current and future stand structure and species composition. Removal of deer social units (localized management) has been proposed as a strategy to alleviate deer overbrowsing in forest systems. We conducted an experimental localized removal in a high-density deer population in the central Appalachians of West Virginia, USA, during winter 2002. We removed 51 deer within a 1.1-km² area that encompassed 2 forest regeneration sites (14 ha). During the summer following removal, we detected decreases in distance from the removal area in 8 of 30 (26.7%) adult females having pretreatment mean telemetry locations <2.5 km from the center of the removal area. We measured browsing rates during the summers of 2001–2004 from forest regeneration sites to examine efficacy of localized management. Browsing rates declined annually in both removal and control areas, due in part to increased timber harvesting on the larger study site, suggesting that increasing forage availability may be more effective at reducing impacts on forest regeneration than localized reductions in deer populations. Three years after the initial removal, we removed an additional 31 deer from the original 1.1-km² removal area. Home range shifts of adjacent deer coupled with the large number of animals collected in the second removal suggests that localized management only produces temporary voids within high-density deer herds. Localized management may not effectively reduce negative impacts of deer in areas of high deer density.     

Fine‐scale habitat heterogeneity influences browsing damage by elephant and giraffe

Effects of large mammalian herbivores on woody vegetation tend to be heterogeneous in space and time, but the factors that drive such heterogeneity are poorly understood. We examined the influence of fine‐scale habitat heterogeneity on the distribution and browsing effects of two of the largest African terrestrial mammals, the elephant and giraffe. We conducted this study within a 120‐ha (500 x 2,400 m) ForestGEO long‐term vegetation monitoring plot located at Mpala Research Center, Kenya. The plot traverses three distinct topographic habitats (“plateau,” “steep slopes,” and “valley”) with contrasting elevation, slope, soil properties, and vegetation composition. To quantify browsing damage, we focused on Acacia mellifera, a palatable tree species that occurs across the three habitat categories. Overall tree density, species richness, and diversity were highest on the steep slopes and lowest on the plateau. Acacia mellifera trees were tallest and had the lowest number of stems per tree on the steep slopes. Both elephant and giraffe avoided the steep slopes, and their activity was higher during the wet season than during the dry season. Browsing damage on Acacia mellifera was lowest on the steep slopes. Elephant browsing damage was highest in the valley, whereas giraffe browsing damage was highest on the plateau. Our findings suggest that fine‐scale habitat heterogeneity is an important factor in predicting the distribution of large herbivores and their effects on vegetation and may interact with other drivers such as edaphic variations to influence local variation in vegetation structure and composition.     

Ungulate browsing in winter reduces the growth of <Emphasis Type="Italic">Fraxinus</Emphasis> and <Emphasis Type="Italic">Acer</Emphasis> saplings in subsequent unbrowsed years

Browsing by ungulates has become a hotly debated issue in many European mountain forests in the past century. Acer pseudoplatanus L. and Fraxinus excelsior L. are broadleaved tree species that are preferentially browsed by roe deer (Capreolus capreolus) in central Europe. We analyzed growth data from shaded saplings of both tree species to quantify the extent to which height growth after game browsing is reduced in subsequent, unbrowsed years in forest stands. Sixty saplings of F. excelsior and A. pseudoplatanus from forest stands at Albisriederberg (Switzerland) were available to us that had been dissected into pieces that then were split in the middle for counting tree rings and assessing ungulate damage. We fitted the von Bertalanffy growth equation to these height growth data and included a reduction factor for winter browsing. Both tree species showed significantly reduced height growth in unbrowsed years after one to several browsing events in winter, and this effect increased with the number of browsing events. Saplings with a high growth rate showed a higher growth reduction. After winter browsing, height growth of A. pseudoplatanus saplings was less affected in unbrowsed years than that of F. excelsior saplings. We conclude that browsed saplings of these species in forest stands are not able to compensate browsing-induced height loss, but that height differences between browsed and unbrowsed saplings probably increase over time. A comparison between our analysis and the parameters estimated using equations published by Eiberle for predicting age at 130 cm height suggests that our parameter values are rather conservative estimates of the growth reduction effect after winter browsing. Neither F. excelsior nor A. pseudoplatanus show a distinct pattern in browsing-induced growth reduction with respect to soil moisture, nutrient level, and altitude. We thus conclude that our results are likely to be valid for a wide range of forested sites.     

Culling intervals and culling risks in four stages of the reproductive life of first service and reserviced female pigs in commercial herds

The objectives of this study were to measure culling intervals and culling risks in the four stages of the reproductive life of female pigs and to compare culling intervals between the number of services and between herd groups, based on herd productivity. We also compared survival patterns of females pigs between these herd groups. Our data set included lifetime records of 52,792 females born between 2001 and 2004 in 101 commercial herds. Two herd groups were selected on the basis of the upper 25th percentile of pigs weaned per mated female per 5 yr between 2002 and 2006, namely the high-performing herds, and ordinary herds. Culled females were also allocated into four groups based on the stages of their reproductive life when culled: unmated gilts, mated gilts, unmated sows, and mated sows. Culling intervals in unmated gilts and mated gilts were defined as the number of days from birth to culling and from first mating to culling, respectively. Culling intervals in unmated sows and mated sows were the number of days from weaning to culling. The number of services was categorized into two groups: first service and reservice groups. Multilevel linear mixed-effects models and survival analysis were performed. Culling intervals (±SEM) in unmated gilts, mated gilts, unmated sows, and mated sows were 302.9 ± 1.16, 98.4 ± 0.92, 14.3 ± 0.12, and 89.6 ± 0.42 d, respectively. Culling risks in the four groups were 5.6%, 7.1%, 58.0%, and 29.3%, respectively. In unmated gilts, mated gilts, and mated sows, the culling intervals in the high-performing herds were 43.0, 18.9, and 16.0 d shorter than those in ordinary herds, respectively (P < 0.05), but no difference was found between the herd groups for the culling interval of unmated sows. For mated sows in the reservice group, culling intervals of high-performing herds were ≥13.7 d shorter than those of the ordinary herds (P < 0.05), but for mated sows in the first service group, there was no difference in the culling interval between the herd groups. The culling hazard from 8 wk postweaning for mated sows in high-performing herds increased more rapidly than that in ordinary herds. In conclusion, to reduce culling intervals and improve herd productivity, we recommend implementing a strict culling policy for mated gilts and mated sows, especially reserviced females.     

Effects of Deer Browsing, Fabric Mats, and Tree Shelters on Quercus rubra Seedlings

We examined the effects of deer browsing, fabric mats, and tree shelters on the growth and survival of Quercus rubra (northern red oak) seedlings planted as part of a reforestation project in southcentral Minnesota. Browsing by white-tailed deer occurred on 68.6% of the seedlings growing without tree shelters, whereas only 3.6% of the trees were browsed by mice or voles and 2.5% were browsed by rabbits. Fabric mats, used to control competition from herbaceous plants for roughly half of the seedlings included in the study, had a detrimental effect overall. Seedlings grown with mats had a greater frequency of deer browsing and a greater chance of dying than seedlings grown without mats. Stem height for seedlings browsed by deer was less overall than for nonbrowsed seedlings, although this pattern varied with use of fabric mats and plot location. The use of plastic tree shelters effectively prevented deer browsing and reduced the mortality rate from 34.6% to 3.2%. Our results indicate that fabric mats should not be used in restoration projects with large deer populations. They also suggest that planting seedlings away from existing forest edges and using seedling protection measures such as tree shelters will increase seedling survival and growth in future restoration projects.     

Adaptive management of sika deer populations in Hokkaido, Japan: theory and practice

We investigated the utility of adaptive management (AM) in wildlife management, reviewing our experiences in applying AM to overabundant sika deer (Cervus nippon) populations in Hokkaido, Japan. The management goals of our program were: (1) to maintain the population at moderate density levels preventing population irruption, (2) to reduce damage to crops and forests, and (3) to sustain a moderate yield of hunting without endangering the population. Because of significant uncertainty in biological and environmental parameters, we designed a “feedback” management program based on controlling hunting pressure. Three threshold levels of relative population size and four levels of hunting pressure were configured, with a choice of four corresponding management actions. Under this program, the Hokkaido Government has been promoting aggressive female culling to reduce the sika deer population since 1998. We devised a harvest-based estimation for population size using relative population size and the number of deer harvested, and found that the 1993 population size (originally estimated by extrapolation of aerial surveys) had been underestimated. To reduce observation errors, a harvest-based Bayesian estimation was developed and the 1993 population estimate was again revised. Analyses of population trends and harvest data demonstrate that hunting is an important large-scale experiment to obtain reliable estimation of population size. A serious side effect of hunting on sika deer was inadvertent lead poisoning of large birds of prey. The prohibition of the use of lead bullets by the Hokkaido Government was successful in reducing the lead poisoning, but the problem still remains. Two case studies on sika population irruption show that the densities set by maximum sustainable yield may be too high to prevent damage to agriculture, forestry, and/or ecosystems. Threshold management based on feedback control is better for ecosystem management. Since volunteer hunters favor higher hunting efficiency in resource management (e.g., venison), it is necessary to support the development of professional hunters for culling operations for ecosystem management, where lower densities of deer should be set for target areas. Hunting as resource management and culling for ecosystem management should be synergistically combined under AM.     

Disentangling the causes of damage variation by deer browsing on young Thuja plicata

Long‐lived trees experience different levels of damage due to mammalian herbivores. To untangle the mechanisms that underlie this variation, we combined chemical with dendrochronological analyses to study variation in browsing on Western redcedars (Thuja plicata) on Haida Gwaii (British Columbia, Canada). Since the last glaciation, Haida Gwaii forests had lacked large herbivore browser until Sitka black‐tailed deer (Odocoileus hemionus sitkensis) were introduced at the beginning of the 20th century. Dendrochronology yielded information on radial growth and plant annual responses to environmental stresses including herbivory. Secondary metabolite content and plant nutritional quality provided insights into proximate causes of food choices made by herbivores. We sampled lightly‐ and heavily‐browsed young trees at four sites: three clear‐cut sites with high browsing pressure and one old‐growth forest site where browsing pressure had, until recently, been lower. Heavily‐browsed young trees had lower concentrations of secondary metabolites and were of lower nutritive value than lightly‐browsed trees at all sites. Under high browsing pressure, tree growth patterns suggested that all young trees were initially severely browsed until some trees, currently scored as lightly‐browsed, started to escape deer. At the old‐growth site, both lightly‐ and heavily‐browsed trees tended to have lower overall average secondary metabolite concentrations than those of all other sites, a trend possibly related to greater canopy closure. Lightly‐browsed trees were older than heavily‐browsed ones which resulted, during the period of lower browsing pressure, in higher growth rate and a same pattern of change in growth from one year to the next year. This suggests that, under low browsing pressure, selection of young trees related to chemical defense was weak and that growth differences due to other factors than browsing could be expressed. Under strong browsing pressure, however, all young trees had equally low growth rates until trees with better genetic potential to produce effective defenses were able to escape deer. This suggests that selection by deer could occur on a long‐lived tree.     

Development of Tree Regeneration in Fern-dominated Forest Understories After Reduction of Deer Browsing

Dennstaedtia punctilobula (hay‐scented fern) can act as a native invasive species in forests in eastern North America where prolonged deer browsing occurs in stands with partially open overstory canopies. Ferns dominate the understory with a 60‐cm tall canopy, with little regeneration of native tree species. It has been hypothesized that, once established, ferns may continue to inhibit tree regeneration after deer browsing has been reduced. To test this hypothesis, we documented the pattern of recovery of the tree seedling understory in plantations of Pinus strobus (white pine) and Pinus resinosa (red pine) on the Quabbin Reservation watershed protection forest in central Massachusetts, where after 40 years of intensive deer browsing the deer herd was rapidly reduced through controlled hunting. Dense fern understories occur on nearly 4,000 ha of the predominantly oak–pine forest. Three years after deer herd reduction, stands with the highest density fern cover (77% of plots with>90% cover) had significantly fewer seedlings at least 30 cm in height, compared with stands with lower fern density, and those seedlings consisted almost entirely of Betula lenta (black birch) and white pine. Height growth analysis showed that black birch and white pine grew above the height of the fern canopy in 3 and 6 years, respectively. In contrast, two common species, Fraxinus americana (white ash) and Quercus rubra (red oak), grew beneath the dense fern cover for 5 years with height growth less than 5 cm/yr after the first year. A study of spring phenology indicated that the ability of black birch to grow through the fern canopy might have been due to its early leaf development in spring before the fern canopy was formed, in contrast to oak and ash with delayed leaf development. Thus, the ferns showed differential interference among species with seedling development after reduction of deer browse.