Ungulate Browsing Research Articles

Abschätzung des Einflusses von Verbiss durch wildlebende Huftiere auf die Baumverjüngung

Assessment of the impact of ungulate browsing on tree regeneration Browsing percentage is an objective and reproducible measure of the frequency of browsing by wild ungulates on tree regeneration. However, this relative number of browsed terminal shoots accounts for little of the effective long-term influence of browsing on tree regeneration. Apart from browsing percentage, the following four factors are important for estimating the influence of browsing: the density of tree regeneration, the within-tree browsing intensity, the height growth of the tree regeneration (and thus the time needed to grow out of the reach of browsers and the browsing-induced loss of height increment), and the mortality induced by browsing. At least the first three of these factors can be obtained easily and should thus be included in future browsing inventories.

Ungulate browsing on introduced pines differs between plant communities: Implications for invasion process and management

AbstractThe effects of herbivory on plant invasions are broadly discussed, and many studies have led to widely debated theories. In particular, the effects of herbivores on pine invasion found in different studies vary; in some cases, they controlled their expansion, and in others, they promoted it. On the other hand, vulnerability to invasion by pines differs between community types. Sites with dunes and bare ground are the most heavily invaded, followed by grasslands, while shrublands and forests are least invaded. Because current evidence is mostly observational, some of the varying responses of pine invasions to herbivory should be examined further through replicated experiments. Here, we address experimentally the extent to which preference for the non‐native invasive Pinus contorta by domestic sheep (Ovis aries) depends on the vegetation type. We installed experimental enclosures within two adjacent communities, grassland and shrubland, and in each one, we planted seedlings of P. contorta Douglas and established a sheep density typically recommended for the study area. The number of browsed seedlings, the number and type of branches browsed per seedling, the reduction in height and probability of survival immediately after browsing period were recorded. The number of browsed seedlings and damage to the terminal bud were higher in grassland than in shrubland, while the number of browsed branches per seedling was higher in shrubland than grassland. The reductions in height and probability of survival immediately after browsing were similar in both communities. These results show that moderate levels of sheep herbivory could reduce 20% seedling survival in both communities; nevertheless, the damage patterns differ between them. The sheep browsed more substantial number of seedlings in grasslands than in shrublands. However, if sheep find the seedlings, they damage it more in shrublands. These results suggest that experimental studies comparing communities are important for pine invasion management.

Ungulate Herbivory Is Correlated with High Aspen Suckering Density but Reductions in Aspen Growth Rates and Recruitment

Aspen is a foundation species that provides vital habitat for hundreds of plant and animal species. However, changing ungulate herbivory regimes may be altering recruitment success and resilience of aspen forests. The objective of this observational study was to quantify the impacts of ungulate herbivory on aspen recruitment potential. We sampled 36 aspen dominant stands on the Fishlake National Forest in Utah for browse of apical meristems, suckering density (< 180 cm in height), and recruitment density (≥ 180 cm). Our analysis indicated that for each 10% of apical meristems browsed, annual vertical and radial growth rates and recruitment density were reduced by 1.2 cm, 0.02 mm, and 17 ha−1, respectively. In contrast, aspen suckering density increased by 1 230 suckers ha−1, with each 10% browse of apical meristems. This suggests that ungulates contribute to aspen suckers persisting in the understory for longer periods and may alter recruitment success of aspen stands. Aspen that were under high ungulate browse pressure were associated with lower growth rates and persisted for twice as long in the understory. For example, a 5-yr-old sucker was predicted to be 115 cm without browse of apical meristems and 60 cm with 100% browse of apical meristems. Further, aspens of the same height with 100% browse of apical meristems were nearly 4 yr older on average than aspens with no evidence of browse of apical meristems. Approximately 34% of aspen suckers had persisted in the understory < 100 cm for ≥ 6 yr, and 7% of suckers had persisted in the understory for ≥ 10 yr. Our results suggest that high rates of meristem removal are correlated with increased aspen suckering yet reduced aspen growth and recruitment.

Growth and quality of Fagus sylvatica saplings depend on seed source, site, and browsing intensity

AbstractLocal climate and ungulate browsing are two major factors that affect tree regeneration and genetic adaptation in Central European forests. Owing to climate change and increasing ungulate numbers, the abiotic and biotic environments of trees are changing remarkably, making it necessary to investigate the separate and joint effects of seed source (i.e., location of tree population origin) and ungulate herbivory. We used a common garden experiment to study the growth and morphology of Fagus sylvatica saplings from 77 Swiss seed sources. The experiment was set up at two sites and included a clipping treatment (i.e., terminal shoot clipped at two intensities) applied before budburst to simulate winter ungulate browsing. We studied F. sylvatica sapling growth and morphology before and two years after clipping. Measured growth traits included sapling height, stem diameter, and biomass. Morphological traits included multi‐stemming, stem and crown form, stem quality, and reaction to clipping. Seed source, test site, and simulated leader browsing were all important in determining the growth and quality of F. sylvatica saplings. The effects of seed source on growth and quality indicate that F. sylvatica possesses a large pool of diverse genotypes across Switzerland and thus has the potential to adapt to local conditions through gene flow. Growth and morphology differed significantly between the two test sites, indicating that local environments should be considered carefully when a new plantation is established. The effect of the single simulated browsing event disappeared over time for the growth traits, owing to growth compensation. However, sapling quality decreased after clipping, suggesting that browsing may lead to persistent quality losses in production forests. Neither the growth nor the morphological reaction after clipping depended on the effect of population, meaning that resilience to browsing was independent of seed source. Consequently, interactions with ungulate browsing do not have to be taken into account when selecting F. sylvatica populations for particular climatic and site conditions.

Demography of evergreen and deciduous oaks in a mixed oak savanna: insights from a long‐term experiment

AbstractThe co‐existence of evergreen and deciduous oaks in Mediterranean‐climate savannas has motivated comparative studies on species’ physiological adaptations to light and drought, establishment niche differences in acorn production, dispersal and seedling herbivory, and differential sapling tolerance of ungulate browsing. Understanding how species’ differences collectively affect co‐occurrence or segregation requires long‐term studies that consider multiple life stages. We compare survival, height growth, and modeled population growth rate of the evergreen sclerophyll, Quercus agrifolia, to those of the winter‐deciduous, broadleaved Q. lobata in southern California savanna sites where the species naturally co‐occur. We evaluate species’ performances after 8.7 yr for four cohorts sown as acorns in 1997, 1998, 2000, and 2001 under four different levels of protection from cattle, deer, and rodents. Survival curves for the two species were closely similar, with large differences between cohorts associated with precipitation in the year acorns were sown. Survival and growth rates of Q. agrifolia seedlings and saplings were slightly lower, and were more reduced by ungulates and rodents, than those of Q. lobata. No Q. agrifolia plants (0/1431) exposed to ungulates (cattle and/or deer) and rodents survived to the end of the experiment. Of 1421 Q. lobata acorns planted in these treatments, only 19 plants (1.3%) survived 8.7 yr and none of these plants progressed out of the ungulate browse layer. However, when protected from both ungulates and rodents, survival rates increased significantly for both species, and Q. agrifolia increased height faster than Q. lobata. Simulated population growth rates increased slightly for plants protected from ungulates, and 95% confidence intervals spanned the stable population growth rate of 1. With exclusion of ungulates and rodents, sapling and small tree recruitment rates for both species far exceeded those needed to offset the rate of recent adult mortality, with modeled population growth rates of 1.07–1.11. Our results underscore the essential role of occasional high rainfall years for initial establishment, plus the key role of consumers in limiting early survival and growth of both evergreen and deciduous oaks in mixed oak savannas.

Can novel pest outbreaks drive ecosystem transitions in northern‐boreal birch forest?

Abstract The boreal biome exhibits distinct alternative ecosystem states with high and low levels of tree cover. Insect outbreaks facilitated by climate warming could potentially drive transitions from high to low tree cover states. We investigated whether two key premises for such outbreak‐induced transitions—critical thresholds (tipping points) and positive feedbacks that could maintain alternative states—are present in the northern‐boreal mountain birch forest of Fennoscandia. Here, climate warming has promoted range expansions of defoliating geometrid moths, resulting in novel, severe multispecies outbreaks, most recently during 2002–2010. We conducted regional‐scale field surveys of forest damage and recovery in 280 mountain birch stands in a northeast Norway immediately after the outbreak (2010) and 6 years later (2016). Satellite‐derived time series of the Normalized Difference Vegetation Index (NDVI) provided an index of stand defoliation during the outbreak period. The proportion of dead stems per stand displayed a bimodal distribution, with stands generally being either lightly or severely damaged. This was due to a critical threshold in the relationship between defoliation and stem mortality, with mortality rates increasing abruptly in stands experiencing a mean drop in NDVI of more than 4% during the outbreak. The two key forest regenerative pathways—basal sprouting and sapling production—both displayed positive feedbacks with surviving stems and trees, so that regeneration success declined with increasing damage to the mature tree layer. These feedbacks imply that stands which have been forced across critical defoliation thresholds and suffered collapses of living tree cover may struggle to recover, especially if the loss of positive regenerative feedbacks is compounded by ungulate browsing on birch recruits. Synthesis. The north Fennoscandian mountain birch forest displays critical thresholds and positive feedbacks that conform to theoretical expectations for a system that could be vulnerable to abrupt and persistent changes of state in the face of novel, climatically facilitated insect outbreaks. These findings deepen the understanding of the persistent losses of tree cover that have occasionally been observed after outbreaks in this system in the past, and add to the list of mechanisms that could help explain the bistability of tree cover across the boreal biome.

The relationship of ungulate δ13C and environment in the temperate biome of southern Africa, and its palaeoclimatic application

The relationship between ungulate stable carbon isotope values and environmental variables (temperature, relative humidity, precipitation) remains poorly understood. In this paper, we evaluate this relationship for, predominantly, C3 ecosystems in the winter rainfall areas of southern Africa. In our dataset (290 individuals representing 23 species), δ13C values of ungulate enamel are significantly correlated with mean annual precipitation (MAP), moisture index (MI) and summer aridity index (SAI), variables that also influence the distribution of C3/C4 grasses. Our study confirms previous findings that faunal δ13C values in C3 ecosystems are most strongly correlated with variables related to precipitation. δ13Cenamel values for ungulate browsers are more strongly correlated with a larger number of environmental variables than values for grazers and mixed feeders and vary according to vegetation type. We apply regressions derived from the modern dataset to estimate palaeoclimatic shifts based on δ13Cenamel values of browsing fauna at the Pleistocene sites of Hoedjiespunt and Elandsfontein in South Africa.

Selective browsing behaviour of ungulates influences the growth of Abies alba differently depending on forest type

Ungulate densities and browsing have increased over the past decades in many forests in Europe. Browsing on tree saplings is a selective process dependent on forest type. This study tested whether the impacts of browsing are altered by differences in tree vigour and within-tree browsing intensity (browsing only buds vs. browsing a large part of the annual leader shoot), and if these effects are modulated by forest type.The growth rate and within-tree browsing intensity of leader shoots were investigated for different height classes and species compositions at 18 sites (each with 14–64 plots) in spring before budburst and at 6 sites in autumn. The sites were situated in northeast Switzerland and comprised four major forest types that had Abies alba regeneration. Linear mixed-effects models were fitted for the relative growth rate of Abies and for the ratio of the relative growth rate of Abies to the relative growth rate of Picea abies.More Abies saplings were present in Fagus-dominated forests than in Fagus-Abies or Picea-Abies forests, and within-tree browsing intensity on their leader shoots was lower. Lightly browsed Abies saplings grew better than those that were not browsed, which in turn grew better than strongly browsed saplings. This pattern, which occurred irrespective of forest type, was caused by selective browsing on vigorously growing trees and led to a greater impact of strong browsing in comparison to light browsing on the growth of Abies saplings.The ratio of the relative growth rate of Abies to Picea was altered by within-tree browsing intensity, forest type and soil depth. Generally, this ratio was highest in shallow soiled Fagus-dominated forests after light browsing and lowest in Fagus-Abies forests after strong leader shoot browsing, indicating a browsing-induced shift in the relative difference in growth rate between species towards Picea in Fagus-Abies and Picea-Abies forests but not in Fagus-dominated forests.Because the main factor influencing the growth of Abies saplings was the amount of tissue loss on the leader shoots (bud vs. entire or large parts of leader shoots), browsing inventories neglecting to assess the within-tree browsing intensity are not recommended. The within-tree browsing intensity of leader shoots is a simple but objective measurement that should be used in forest regeneration inventories of Abies for improving estimates of the impact of ungulate browsing.

Ungulate browsing affects subsequent insect feeding on a shared food plant, bilberry (Vaccinium myrtillus)

Browsing by ungulates may induce plant responses and affect subsequent plant food quality for other animals. Populations of many deer species have increased to unprecedented levels in Europe and North America. In Norway, population densities of red deer (Cervus elaphus) have increased over the past decades, but little is known about how increased deer browsing pressure may change the palatability of key food plants for other taxa in the boreal ecosystem. We conducted a cafeteria experiment to assess if long-term deer-browsing intensity affected the palatability of bilberry (Vaccinium myrtillus) leaves for leaf-eating larvae (mainly Lepidoptera). We found that leaf-eating insect larvae preferred bilberry leaves from the lightly browsed bilberry plants; the larvae consumed twice as much leaf biomass from the lightly browsed plants than from the unbrowsed and moderately browsed ones, and four times more than from highly browsed plants. Larvae never selected leaves from highly browsed plants as their first choice. Our study suggests that browsing-induced changes in the quality of shared food plants may be important in mediating indirect interactions between browsers of widely separated taxa. Whereas low levels of long-term red deer browsing increases the palatability of bilberry leaves for leaf-eating larvae, high browsing pressure reduces food consumption. Whether changes in palatability lead to changes in population densities of leaf-eating larvae remains to be studied, but any such adverse effects could have cascading ecological consequences for insectivorous birds and mammals.

Wolves and Tree Logs: Landscape-Scale and Fine-Scale Risk Factors Interactively Influence Tree Regeneration

Large carnivores can reduce ungulate numbers by predation and via induced risk effects alter ungulate behavior, indirectly affecting lower trophic levels. However, predator-induced risk effects probably act at different spatial scales, which have often been ignored in trophic cascade studies. We studied how a fine-scale risk factor (distance from tree logs) affects ungulate browsing intensity and how this is modified over a landscape-scale risk gradient (distance from human settlements to wolf core) in the Białowieża forest, Poland. We found that landscape-and fine-scale risk factors strongly interacted in determining the strength and magnitude of carnivore-induced risk effects on lower trophic levels. In low-risk areas, tree logs reduced browsing intensity in small patches (approx. 4–6 m from logs), whereas in high-risk areas browsing intensity was reduced up to at least 16 m from tree logs. Moreover, the magnitude of these effects changed, with the strongest reduction in browsing intensity around tree logs in high-risk areas (up to 37%) and the smallest in low-risk areas (< 20%). Overall, the results of this study indicate that perceived risk factors act at different spatial scales, where impediments (objects blocking view and escape routes) act as a risk factor at a fine scale and carnivore distribution shapes perceived risk at the landscape scale. Moreover, these risk factors strongly interact, thereby determining the functional role of large carnivores in affecting ecosystem processes. These interactive effects should be incorporated in predator-induced trophic cascade studies to understand patterns of tree regeneration in ecosystems where large carnivores and herbivores live together.

Differential effects of cattle, mule deer, and elk herbivory on aspen forest regeneration and recruitment

The abundance and composition of ungulate herbivore communities are changing globally, which can impact the resilience and function of Earth’s ecosystems. Impacts from herbivory are compounded in areas where multiple ungulates overlap, which is common in forest ecosystems. The objective of this study was to examine the differential and combined effects of ungulate communities (deer, elk, and cattle) on aspen forest recruitment after fires that occurred in 2012. Eight sets of differential ungulate exclosures, monitored by camera traps, were established across three National Forests in Utah. We identified the differential effect of each of three ungulate species using fencing that allowed for deer-only, native ungulate only (deer and elk), all ungulates and a complete ungulate exclosure. Over a three year period (2013–2016) we quantified ungulate species impacts on aspen height, density, and browse rates using camera trap photos. Ungulate activity was nearly 10-fold higher in two National Forests compared to the third, and gradually decreased over time. Meristem removal by ungulates in unfenced plots across sites averaged 60% which we identified as a critical threshold point for aspen recruitment failure. All three ungulate species had significant and similar effects on aspen regeneration success, but when adjusted for differences in estimated forage intake (animal unit months), differential impacts became apparent (deer > elk > cattle). We estimated that 4 cattle per camera−1 day−1 and 2.5 deer or elk per camera−1 day−1 was sufficient to reach the critical recruitment threshold of 60% removal of apical meristems. We conclude that ungulates species differentially influence aspen regeneration and recruitment, and that ungulate browsing above 30% meristem removal impairs aspen recruitment with recruitment failure occurring above 60% meristem loss.

An annotated transcriptome of highly inbred Thuja plicata (Cupressaceae) and its utility for gene discovery of terpenoid biosynthesis and conifer defense

Western redcedar (Thuja plicata; Cupressaceae; WRC) is an ecologically and economically important conifer species of the Pacific Northwest. Regeneration of WRC forests is affected by ungulate browsing, which removes current growth and hampers development of young trees. Monoterpenes make WRC foliage less palatable and can deter browsing. Genomic resources are required to advance knowledge of terpene accumulation and breeding of WRC for herbivore resistance. Unlike most conifers, WRC readily selfs to produce genotypes of reduced heterozygosity. We used seedlings of eight different fifth-generation selfed lines for monoterpene analysis and transcriptome sequencing. Trinity, Velvet/Oases, TransABySS, and SOAPdenovoTrans were used to generate independent transcriptome assemblies for each line. Sequence redundancy was reduced using the EvidentialGene pipeline. The best assembly, as determined by metrics of completeness, contiguity, and accuracy, was used to produce a WRC reference gene set of 28,279 sequences, of which 77% were annotated with significant BLASTp hits and 89% with significant InterProScan hits. An orthology-based approach was used to annotate gene families. Manually curated annotation identified 33 putative full-length terpene synthases (TPS). A maximum likelihood phylogeny revealed that WRC TPS cluster apart from those of Pinaceae within the gymnosperm TPS-d clade. Use of selfed lines enabled the development and annotation of a reduced-redundancy gene set for a gymnosperm of the Cupressaceae family. This gene set serves as a foundation for future functional characterization of WRC TPS and other defense genes and as a resource for the annotation of protein coding sequences in the WRC genome.

Functional composition of temperate forest trees under chronic ungulate herbivory

AbstractQuestionFunctional plant traits often express consistent changes along ecological gradients and, hence, are often used as indicators of environmental change (e.g. nutrient availability, temperature changes). Besides being driven by edaphic conditions, functional plant composition is filtered by herbivory, and traits responsive to nutrient availability often coincide with those related to palatability or resistance to browsing. We hypothesized that herbivory may distort the ways in which traits are expressed along environmental gradients.LocationBiałowieża National Park, Poland.MethodsWe used a long‐term controlled, exclosure experiment in the Białowieża National Park to study tree functional trait expression and plant indicator values, with and without large ungulate browsing, along a natural soil fertility gradient.ResultsBrowsing largely reduced the functional diversity of regenerating trees, indicated by multivariate analysis and Rao's Quadratic Entropy (RQE), and altered how several traits change with increasing fertility. Browsing led to an increase in specific leaf area (SLA) on poorer sites. RQE showed a hump‐backed trend along the fertility gradient, indicating the largest functional diversity at intermediate fertility. However, this pattern was not affected by browsing. Unlike the morphological tree traits, trends of light and N plant indicator values along the gradient were unaffected by browsing.ConclusionsThese results highlight how the expression of plant traits resulting from one driver (soil fertility) can be modified by another driver (herbivory,) and stress the importance of taking herbivory into account when using plant traits as indicators of large‐scale processes (e.g. climate change). Furthermore, the results suggest that plant indicator values may be more robust towards these effects, while compiled indices such as RQE could mask considerable functional turnover. Several traits (e.g. SLA) are strongly connected to nutrient cycling. The development, driven by browsing, towards higher SLA on poorer sites may thus cause a positive feedback effect on site fertility that drives an increase in nutrient availability. This may in turn have implications for ecosystem functionality. Hence, the large reduction in functional diversity revealed at the scale of this study may in the long term have implications on multiple ecosystem processes.

A stoichiometric perspective of the effect of herbivore dung on ecosystem functioning.

Ungulate herbivores play a prominent role in maintaining the tree–grass balance in African savannas. Their top‐down role through selective feeding on either trees or grasses is well studied, but their bottom‐up role through deposition of nutrients in dung and urine has been overlooked. Here, we propose a novel concept of savanna ecosystem functioning in which the balance between trees and grasses is maintained through stoichiometric differences in dung of herbivores that feed on them. We describe a framework in which N2‐fixing trees and grasses, as well as ungulate browsing and grazing herbivores, occupy opposite positions in an interconnected cycle of processes. The framework makes the testable assumption that the differences in dung N:P ratio among browsers and grazers are large enough to influence competitive interactions between N2‐fixing trees and grasses. Other key elements of our concept are supported with field data from a Kenyan savanna.

Herbaceous competition and browsing may induce arrested succession in central European forests

Abstract Arrested succession, that is, an ecosystem permanently halted in an early successional, typically non‐forested state, has been suggested to result from intense competition by understorey vegetation, high browsing pressure and additional disturbances, but the relative importance of these factors is unclear. In addition, distinguishing between permanently arrested succession or merely delayed succession may be highly challenging, if not impossible, due to the large time‐scales involved. We used the dynamic vegetation model LandClim to systematically explore the effect of multiple factors on delayed and arrested succession over a time span of 1,000 years, starting from an unforested state. We included abiotic and biotic factors as well as large‐scale overstorey disturbance, in four Central European landscapes. Arrested succession occurred in 1%–14% of the simulations. Among the non‐arrested simulations, 95% reached a forested state (defined as ≥10% canopy cover) within 100 years. Large herbaceous biomass was the most important predictor for arrested succession, followed by browsing and large‐scale disturbances. Combinations of factors were important at particular locations in the landscape, where understorey competition and browsing jointly induced a strong establishment filter. Abiotic conditions consistently influenced the probability of arrested succession, with a low probability under mesic conditions and increased likelihood in more xeric parts of the landscapes. Synthesis. We demonstrated that permanently arrested succession has the potential to occur in temperate forests, particularly under a combination of high amounts of herbaceous biomass and ungulate browsing in drought‐constrained landscape positions. We thus conclude that considering environmental heterogeneity at the landscape scale is key for understanding the conditions that lead to delayed and arrested succession.

Phenolic Glycosides in Populus tremuloides and their Effects on Long-Term Ungulate Browsing.

In the aspen-grassland ecotone of Riding Mountain, Manitoba, lightly browsed vigorous clones of trembling aspen (Populus tremuloides Michx.) occur in close proximity to heavily browsed dieback clones. This study examines whether intraspecific variation in the production of phenolic glycosides is correlated with this strong dichotomy in clonal vigor. Individual clones were sampled over four years at three sites located along a gradient of increasing soil moisture stress. At each site, eight aspen clones of similar size and age were sampled: four vigorous and four dieback clones (total of 24 individual clones). The severity of wapiti (elk) browsing was assessed as the ratio of browse-damaged to total branches per aspen ramet. Statistically significant differences in foliar concentrations of the phenolic glycosides salicortin and tremulacin were observed between vigorous and dieback clones: a mean of 14.8% dry mass for lightly browsed (vigorous) clones, versus just 7.0% for heavily browsed (dieback) clones. Mean concentrations of foliar phenolics were also significantly greater in more moisture-stressed sites. These results demonstrate that the strong dichotomy in clonal vigor (vigorous versus dieback clones) is associated with large differences in phenolic glycoside production. Vigorous clone ramets produce high amounts of phenolic glycosides and have low levels of herbivore browsing and low mortality rates, whereas dieback clone ramets have low amounts of phenolic glycosides and much higher herbivore browsing and mortality rates. This suggests that intraspecific variation in phenolic glycosides in trembling aspen is an important predisposing factor leading to ramet mortality, and by extension to the decline of aspen clones.

Salvage logging of mountain birch after geometrid outbreaks: Ecological context determines management outcomes

Abstract Outbreaks of pest insects occasionally cause mortality of entire forest stands. Salvage logging of affected stands is the most common management response to such events. Logging may aid stand recovery by increasing the production and establishment of saplings, or stimulating the production of basal sprouts in sprouting tree species. However, the outcome of logging may depend on the ecological context in which it is implemented, with both herbivory and local growing conditions being potentially important factors. We conducted a field experiment to assess how logging affects recovery by saplings and sprouts in stands of mountain birch that have been damaged by outbreaks of geometrid moths. The study was conducted at the two locations Luftjok and Bugoyfjord in subarctic Norway, where moth outbreaks have caused widespread mortality of mountain birch during the last two decades. Logging generally caused a strong increase in the production of basal sprouts, and also improved sprout growth in Luftjok, resulting in a substantial production of new stems in the logging plots at this location within the six-year period of the study. In Bugoyfjord, sprout growth was retarded in logging plots compared to controls, resulting in complete failure to produce new stems during the study period. This appears to have been caused by ungulate browsing, possibly in interaction with regional, geologically determined, gradients in growing conditions. The outcome of logging also depended on local site quality, with limited sprouting occuring in rich meadow type stands, which traditionally have been assumed to have low capacity for sprout production. Birch saplings were less abundant in logging plots than in controls by the end of the study, especially in Bugoyfjord, suggesting that logging did not improve sapling production. We conclude that logging may stimulate damaged mountain birch stands to recover by means of basal sprouting, but that the positive effects of logging may be reduced by browsing in some areas. Logging should also be practiced with care in rich meadow type stands, which have limited capacity for sprouting.

Spatio-temporal variation in foodscapes modifies deer browsing impact on vegetation

Ungulate browsers often alter plant composition and reduce diversity in forests worldwide, yet our ability to predict browse impact on vegetation remains equivocal. Theory suggests, however, that ungulate distribution and foraging impacts are shaped by scale-dependent decisions based on variation in habitat composition and structure encountered within their home range. Examine how variation in habitat composition at landscape (259 ha) scales modulates browse impact on vegetation at local scales. We measured vegetation richness and abundance in plots with and without white-tailed deer (Odocoileus virginianus) at 23 northern hardwood forest sites distributed across a 6500 km2 area in Pennsylvania, USA. Experimental sites were embedded within landscapes with varying levels of habitat composition and deer densities. Browsing reduced vegetation richness and cover by as much as 53 and 70%, respectively; however, we found browse impact was modulated by variation in the relative abundance of managed habitats that alter forage availability. Specifically, relative to fenced areas, browse impact weakened and ultimately disappeared as the proportion of forage-rich habitats (e.g., recent harvests) increased to ≥20%. Conversely, vegetation grew increasingly depauperate as landscapes contained greater proportions of forage-poor habitats (i.e., older harvests), particularly when browsed. Our results underscore how management actions that alter forage availability to ungulates throughout the landscape (i.e. the foodscape) can shape forest-ungulate interactions and suggest a new paradigm whereby managers evaluate and undertake actions at the appropriate spatio-temporal scales to proactively limit the deleterious impact of browsing on plant biodiversity.

Individual and interactive effects of white-tailed deer and an exotic shrub on artificial and natural regeneration in mixed hardwood forests.

Underplanting tree seedlings in areas where natural regeneration is limited may offer a tool by which desired overstory composition can be maintained or restored in forests. However, invasive plant species and ungulate browsing may limit the effectiveness of underplanting, and in-turn, the successful restoration of forest ecosystems. Individually, the invasive shrub Lonicera maackii and browsing by white-tailed deer (Odocoileus virginianus) have been found to negatively affect the regeneration of native tree species in the Midwestern United States, but few studies have examined their interactive or cumulative effects. Using exclosures and shrub removal at five sites, we examined the effects of white-tailed deer and L. maackii both on underplanted seedlings of Castanea dentata and Quercus rubra and on the composition, species richness and diversity of naturally regenerated native tree seedlings. Individually, both deer and L. maackii had negative effects on the survival of underplanted seedlings, but we identified no interactive effects. The presence of L. maackii or deer alone resulted in similar declines in the survivorship of Q. rubra seedlings, but the presence of deer alone resulted in lower survival of C. dentata seedlings than the presence of L. maackii alone. Lonicera maackii reduced light levels, increased seedling moisture stress and decreased relative basal diameter growth for Q. rubra seedlings. Deer reduced the relative growth in height of underplanted C. dentata and Q. rubra seedlings and increased moisture stress of C. dentata seedlings. No effects of L. maackii or deer were found on soil or foliar nitrogen or the overall abundance, species richness and diversity of naturally regenerated seedlings. However, L. maackii and white-tailed deer did affect the abundance of individual tree species, shifting composition of the regeneration layer towards shade tolerant and unpalatable and/or browse tolerant species.

Species composition, elevation, and former management type affect browsing pressure on forest regeneration in the Tatra National Park

Abstract Effects of ungulate pressure on the development of young generation of trees is one of the most important issues in ecology and forestry. Ungulate pressure influence on the development of natural regeneration has been also reported from several national parks. Our study on the effects of ungulate browsing on the young generation of trees was conducted on more than 500 sample plots controlled during one growing season. The overall browsing pressure ranged from 7.6% in seedlings to 20.3% in low saplings. The pressure of ungulates on the regeneration of Picea abies, the dominant species in the Tatra National Park, was by and large below 1%. Broadleaved species were browsed more frequently. The relationship between the plot altitudes and browsing intensity was statistically significant for seedlings and low saplings; at the higher altitudes, the browsing pressure was greater. There was also observed a statistically significant relationship between the type of former management and the browsing degree in seedlings; in the areas subjected to “landscape protection”, the intensity of browsing was higher when compared to strictly protected areas. Pressure exerted by ungulates on tree regeneration was very unevenly distributed, i.e. some plots were heavily browsed and many others - not browsed at all. The most affected tree species were Salix caprea and Sorbus aucuparia, although the percentage of browsed individuals rarely exceeded 50%. Other species favored by ungulates was Acer pseudoplatanus; despite the high browsing pressure, this species was present among seedlings and tall saplings, suggesting that it would be able to recruit to the tree layer. Abies alba was browsed less frequently than the deciduous trees; however, among the tall saplings it was the third most browsed species.