Moose Browsing Research Articles

Interactive effects of moose browsing and stand composition on the development of mixed species seedling stands

The moose (Alces alces L.), a common large herbivore in the boreal region, impairs forest regeneration by browsing on tree seedlings and saplings. Moose prefer deciduous species, but during winter more coniferous seedlings are used. We used meta-analyses, separately for deciduous and coniferous seedlings, for evaluating whether excluding moose browsing affected seedling density and height. In addition, we compared (1) deciduous seedling proportion, (2) stand density, (3) elapsed time from fencing and (4) estimated moose density with moose exclusion effect sizes. Fencing had a positive effect on coniferous seedling height. With more deciduous trees in a seedling stand, the fencing effect for both seedling height and density of coniferous seedlings decreased. On the other hand, the fencing effects increased with denser stands. At some point effect sizes turned to negative, and conifer species varied in their response to browsing. This implies that deciduous seedlings can protect conifers from browsing by moose up to some mixing ratio, but when deciduous seedling densities are too high, their negative effect increases, presumably through increased competition. Our results suggest that a moderate deciduous admixture in conifer-dominated mixed seedling stands can decrease moose damage but also underline the significance of timely silvicultural measures to minimize the negative effects of excessive deciduous seedlings and too dense stands. Due to differences in coniferous and deciduous species, as well as their compositions and amounts in studied experiments, more studies adjusted to local conditions are still needed to give exact measures for silvicultural recommendations.

The natural ‘exclosure effect’ and tree regeneration following post‐windstorm salvage logging

Abstract Understanding the influence of post‐disturbance forest management on tree regeneration is critical for assessing ecosystem recovery and guiding future responses. In particular, the influx of elevated coarse woody material (CWM) following wind disturbance, if left in situ, may impede herbivore access, thereby protecting saplings from browsing damage through a natural ‘exclosure effect’. In 2013, a tornado in northcentral Maine, United States and subsequent salvage logging operations created three clear ‘treatments’ for evaluation of the exclosure effect: blowdown, blowdown plus salvage logging and an undamaged control. Nine years post‐tornado, we inventoried tree regeneration within these treatments to evaluate differences in sapling abundance, species composition, size structure and browsing intensity. We also inventoried CWM, including the height above forest floor. Results revealed significant differences in sapling composition and browsing intensity among treatments. The salvage treatment had the highest proportion of browsed saplings (56 ± 28%; mean ± standard error), followed by the control (9 ± 10%) and blowdown (5 ± 8%). Blowdown had by far the greatest mean (50 ± 9 cm) and average maximum (169 ± 43 cm) heights for CWM. Binomial generalized linear models revealed that browsing probability was a function of mean CWM height and an interaction between sapling density and proportion of sapling hardwoods. Thus, browsing damage was less likely in plots with greater CWM heights and more likely in plots with greater sapling density and more hardwood saplings. Synthesis and applications. This study furthers our understanding of ecosystem recovery following blowdown and salvage logging. Results suggest that salvage logging created important differences in coarse woody material (CWM) abundance and height distribution, when compared to un‐salvaged areas, and that these differences in turn altered sapling size structure and browsing intensity. These findings highlight the potential long‐term effects of successive disturbances, as the differences evident in these early stages may persist for decades or longer. Importantly, we provide evidence of the exclosure effect, suggesting that CWM retained in the un‐salvaged area protected saplings from moose browsing. Thus, in post‐disturbance areas where browsing threatens regeneration, we recommend that managers consider retaining CWM to serve as a natural exclosure.

Harvest block aggregation as a driver of intensive moose browsing pressure on hardwood regeneration in a temperate forest

In many regions of the world, browsing pressure by ungulates has increased over the last century, often reaching unsustainable levels. Overbrowsing by ungulates is threatening biodiversity and causing delays in the establishment of forest regeneration. Moose (Alces alces) is considered as an ecological engineer, as it can cause severe impacts on stand structure, composition, quality, and succession through overbrowsing. In conifer-dominated stands, moose browsing pressure has been shown to vary with the distribution of forage and cover patches across the landscape, but such spatial relationships have not been explored in hardwood-dominated landscapes, where intensive forest management can create clustered patches of good-quality forage and cover, ideal conditions for wintering moose. We investigated the influence of local and landscape variables on browsing by North American moose (Alces alces americana) on commercial and non-commercial woody regeneration in an intensively managed forest landscape of northwestern New Brunswick, Canada. We predicted that browsing pressure at the local scale (vegetation sampling plot) would increase with moose winter counts in the surrounding landscape (1 to 3 km radius). We modeled moose counts as a function of environmental features and road density, using a quasi-Poisson regression. According to an aerial survey (25 km2 sampling plots), moose counts increased with the proportion of forage patches (disturbed stands < 20 years old), whereas they decreased with the proportion of mixed mature stands > 80 years old, which offer both forage and cover. We extrapolated this model to a 2770 km2 study area and used predicted counts as an independent variable to assess its influence on browsing pressure. In 720 plots of 4.15 m2, browsing pressure was quantified using occurrence (i.e. proportion of seedlings/saplings with at least one twig browsed during the previous winter) and intensity (i.e. mean proportion of twigs browsed per stem) on commercial and non-commercial tree seedlings and saplings. We explained variation in occurrence and intensity using zero-inflated models with snow precipitation and local vegetation variables as covariates. Browsing pressure increased with predicted moose counts within a 3 km radius, with snow precipitation and with the proportion of coniferous trees in the canopy, whereas it decreased with sapling density. These results highlight the importance of seedlings and saplings in moose winter diet and confirm the attraction of moose toward recent (<20-year-old) harvest blocks during winter. Therefore, we should avoid aggregating harvest blocks to decrease their attractiveness to moose and browsing pressure on natural hardwood regeneration.

Heavy browsing pressure by moose (Alces alces) can interfere with the objectives of ecosystem-based forest management

Forest management can enhance the ecosystem services forests provide, but it can also alter the capacity of forests to provide those services in the future. Ecosystem-based management has been widely implemented to mitigate the deterioration of forest ecosystems by reducing dissimilarities between managed and natural forests. Ecosystem-based management objectives generally aim to maintain community composition, stand structure, ecosystem functions and services. Heavy browsing pressure by ungulates at densities unrepresentative of past abundance could interfere with these objectives by chronically and selectively browsing tree regeneration following logging.Using a browsing exclusion experiment, we investigated how the effects of different moose browsing pressures on tree regeneration could interfere with ecosystem management objectives in boreal forests of Quebec, Canada. Management objectives in this region include, among others, reaching targeted coniferous trees densities for commercial harvest, favouring the conservation of birches (Betula spp.) to maintain soil quality and conserving fruit-bearing trees due to their ecological significance for biodiversity. We used path analyses to differentiate direct and indirect effects of moose on seedling density and mixed models to investigate how browsing affected sapling recruitment and whether resulting densities are compatible with ecosystem management objectives.By directly reducing the overall sapling density, moose browsing indirectly increased seedlings densities of all deciduous species. This indirect effect increased with browsing pressure and favoured raspberry cover, which was positively or negatively linked to seedling density, depending on tree species. Moderate and heavier browsing pressures reduced coniferous sapling density below the ecosystem management target. Moose suppressed birch saplings so that the minimal target of 50 birches ha−1 was not met under heavier browsing pressure. Sapling density of fruit-bearing trees was low under all browsing pressures when compared to exclosures.Policy implicationsHeavy moose browsing is preventing the achievement of ecosystem management objectives in our study area. Positive indirect effects on seedling densities suggest that reducing moose density could allow released seedlings to replenish the sapling layer, but we discuss why this would not guarantee reaching ecosystem management objectives. To help forest managers evaluate and respond to challenges posed by high ungulate densities, we suggest incorporating browsing inventories in national forest surveys to monitor this chronic disturbance and modulate decisions for forest ecosystem management.

The effects of moose browsing on balsam fir and forest recovery vary with bioclimatic and human use across the island of Newfoundland

Moose present a complex management problem because they generate a mixture of benefits and costs to humans, some of which are caused by browsing of regenerating trees. We developed a Lotka–Volterra model, parameterized by moose management areas, to link moose browsing to spruce and balsam fir dynamics on the island of Newfoundland. The model predicts the distribution of moose, adult fir, and spruce well. Empirical estimates of juvenile fir biomass were variable, and our model predicted its biomass poorly. Our model predicts a small negative effect of moose on adult fir biomass (−0.06%) and juvenile fir biomass (−1.65%) and a small positive effect on spruce biomass (+0.02%) under baseline assumptions, but larger effects (±10%–60%) if moose browse commercial softwoods preferentially. Small effects of moose on trees at steady state do not fully reflect the importance of moose because moose parameters (e.g., growth rate and harvesting rate) impacted the return time of our model from disturbance. Our model analysis demonstrates one way to add animal effects into vegetation growth models and suggests that parameterizing ecological models by management unit is useful when the data to support more detailed models are not available.

Net Climate Effects of Moose Browsing in Early Successional Boreal Forests by Integrating Carbon and Albedo Dynamics

AbstractMoose (Alces alces) is a large herbivore that can mediate boreal forest regeneration after timber harvest through selective browsing of tree species. Despite increasing evidence of moose browsing influence on tree growth in early successional forests, climate effects due to changes in carbon sequestration rates and biophysical factors such as albedo remain largely unexplored. We used 11 years of data from 44 pair‐sites of herbivore exclosures within clear‐cut forests in Norway to investigate how moose browsing alters aboveground tree biomass and albedo. We find a higher total aboveground tree biomass (mainly deciduous species) in unbrowsed than browsed forest plots, as moose browsing limited the growth of tree biomass. The effect of moose exclosure on relative tree abundances differed between sites, suggesting that moose browsing has stronger effects on forest structure than composition. At the same time, moose increased forest albedo relative to un‐browsed forests, driving biophysical cooling. When averaged at regional levels, climate effects due to changes in biomass and albedo are of similar magnitude, but contributions can diverge in specific locations. In a region with intensive forestry operations and high moose density, CO2 emissions from moose browsing in post‐harvested sites can be equal to about 40% of the annual emissions of fossil fuels from that region. Cooling effects from increased albedo can offset about two thirds of this impact. Given its influence on tree growth rates and climate impacts, management of moose browsing density should be integrated into forest management plans to optimize climate change mitigation and forest productivity.

The relationship between moose browsing, habitat structure and predation pressure on insect herbivores

Grazing and browsing by large ungulates can have a strong effect on habitat composition and structure. Associated effects can be reduction in the abundance of palatable tree species and alter understory properties, thereby affecting habitat complexity. Changes in habitat structure and complexity can in turn affect arthropod predation pressure, as arthropod predators are strongly influenced by habitat characteristics. This may be increasingly important in production forests, as such systems are often more vulnerable to disturbances such as pest insects. However, studies exploring this indirect link between ungulates and predation rate are sparse. We explore this link through the comparison of fenced plots excluding ungulates (for four years) with associated control plots replicated in 16 forest stands covering a large geographical area. We measured vegetation characteristics to assess the effect of exclusion on habitat structure. We used plasticine models to compare predation rates in fenced and control plots on pine trees. In addition, we sampled herbivorous insects to explore the potential relationship between predation and herbivore abundance. We could only demonstrate a weak effect of browser exclusion on habitat structure, suggesting that the time of exclusion was too short to cause a vegetation response. In terms of arthropod predation, we found that predation was positively affected by understory cover, but not related to herbivore abundance. Understory properties such as species composition and biomass has been demonstrated to be affected by ungulates in other studies. Therefore, we propose that ungulate browsing – despite weak effects of browsing exclusion in our study – can affect arthropod predation via changes in the understory, which could potentially affect pest populations. Our study is one of the first attempts to connect effects of mammalian browsing to changes in predation rates on herbivorous insects.

Winter browsing in absence of an apical predator: Do high moose densities compromise tree regeneration?

Over the last decades, the increasing intensity of timber harvesting and the changes in forestry practices have impacted the population dynamics of many wildlife species. Moose (Alces alces americana) densities have strongly increased, leading to an extensive pressure on vegetation but also to the growing popularity and socioeconomic benefits of sport hunting. On the south shore of the St. Lawrence River, eastern Québec (Canada), moose densities have been on a constant rise for 3 decades, reaching unprecedented levels due to the absence of its main predator (wolf Canis lupus), conservative sport hunting regulations (females protected 1 year out of 2) and increases in early seral forests induced by logging. Resource managers now need to find the balance between ensuring adequate regeneration of cutblocks and maintaining quality habitat to support the hunting industry, a task that requires identifying the level of use and damages on commercial tree species, and the variables related to such damages. We evaluated the effect of 4 common silvicultural treatments and time elapsed since treatment on proxies of resource use and suitability for moose in the mixed forest of the Bas-Saint-Laurent region. Besides silvicultural treatments, we evaluated the effect of various characteristics – at the stand and landscape scales – on the habitat use of moose and the damage they caused in 440 sampling plots. We found no difference in use and damage between all types of treatment, suggesting that local conditions vary between replicates of a given treatment. At the stand scale, variations of occurrence of browsed commercial and non-commercial stems and severe damages to commercial stems were strongly related to forage diversity, relative nitrogen availability and the proportion of alternative species that are browsed. At the landscape scale, the area occupied by naturally regenerating stands around our sample plots increased the occurrence of severe damages to commercial species. The variations in occurrence and in the number of moose feces were best explained by relative moose density and the proportion of browsed stems. Our results showed the importance of considering stands characteristics to provide quality habitat for moose. We recommend that managers avoid the aggregation of naturally regenerating stands, and prioritize high-density plantations without pre-commercial thinning or low-density plantations to reduce the probability of severe damage by moose. These approaches promote stand diversity, forage quality and availability, and favor quality habitat for moose while ensuring maximum timber yield from planted spruce, which is not targeted by moose browsing.

Exploitative Competition between Mountain Hare and Moose-Qualitative Effects on Hare Winter Forage?

Simple SummaryMountain hares in Scandinavia are classified as Near Threatened in the Norwegian and Swedish Redlists assessing the risk of species extinction. This is due to a possible population decline witnessed during the last decades in Scandinavia. Competition between large herbivores such as moose, red deer, roe deer on one hand and hares on the other, is one of several hypotheses that has been put forward to explain this decline. In a cafeteria trial (providing several types of forage to determine food preference) we investigate the effects of previous moose winter foraging on the food selection (i.e., amount consumed, bites per minute and bitediameter) of downy birch and goat willow by captive hares. We find that hares do not differentiate among levels of previous moose foraging on downy birch but have larger bite diameters of goat willow earlier eaten on by moose, compared to plants not fed on by moose. Thus, effects of moose on hare winter food quality seem to be limited. We highlight the need for studies focusing on (1) effects of previous moose foraging using wild hares in a natural experimental design, and (2) effects of moose foraging on available hare food at a landscape scale during winter.Mountain hares (Lepus timidus) in Scandinavia are classified as Near Threatened in the Norwegian and Swedish Redlists. This is due to a possible population decline witnessed during the last decades in Scandinavia. Competition between large herbivores and mountain hares is one of several hypotheses that has been put forward to explain this decline. In a cafeteria trial we investigate the effects of previous moose (Alces alces) winter browsing on the food selection (i.e., biomass consumed, bites per minute and bitediameter) of downy birch (Betula pubescens) and goat willow (Salix caprea) by captive mountain hares. We find that mountain hares do not differentiate among previous browsing levels of downy birch, but have larger bite diameters of goat willow earlier browsed by moose, compared to non-browsed plants. Thus, effects of moose on mountain hare winter food quality seem to be limited. We highlight the need for studies focusing on (1) qualitative effects of moose browsing using wild mountain hares in a natural experimental design, and (2) quantitative effects of moose browsing on available mountain hare forage at a landscape scale during winter.

Intensive moose browsing and small-scale domestic woodcutting impacts on forest successional trajectories in Gros Morne National Park, Canada

Moose (Alces alces L.) browsing in Gros Morne National Park has damaged its balsam fir (Abies balsamea (L.) Mill.)-dominated forest. A forest estate model was used to evaluate (i) the impacts of moose browsing and woodcutting on forest succession and (ii) strategies of forest restoration through planting and moose population management. The simulation results show that under current heavy browsing pressure growing stock of balsam fir decreases by 38%, but the area of spruce (Picea mariana (Mill.) BSP and P. glauca (Moench) Voss) increases by 32% over a 100-year planning horizon, compared to that under light browsing scenario which is assumed to be similar to the forest outside the Park due to moose population management. Annual allowable cut (AAC) for the Park’s 19 400 ha domestic harvest area is estimated to be around 120 979 m3 in a light browsing scenario, 21% higher than the sustainable harvest level in a heavy browsing scenario. The model forecasts a 97% reforestation of the Park’s 7 194 ha disturbed area by planting in the heavy browsing scenario, leading to an increase in total forest growing stock by 22% and AAC by 12%. Integration of planting with moose population management could be a more efficient way of restoring forest under high browsing pressure in GMNP.

Associate Editors/Corédacteurs

Moose (Alces alces L.) browsing in Gros Morne National Park has damaged its balsam fir (Abies balsamea (L.) Mill.)dominated forest. A forest estate model was used to evaluate (i) the impacts of moose browsing and woodcutting on forest succession and (ii) strategies of forest restoration through planting and moose population management. The simulation results show that under current heavy browsing pressure growing stock of balsam fir decreases by 38%, but the area of spruce (Picea mariana (Mill.) BSP and P. glauca (Moench) Voss) increases by 32% over a 100-year planning horizon, compared to that under light browsing scenario which is assumed to be similar to the forest outside the Park due to moose population management. Annual allowable cut (AAC) for the Park’s 19 400 ha domestic harvest area is estimated to be around 120 979 m3 in a light browsing scenario, 21% higher than the sustainable harvest level in a heavy browsing scenario. The model forecasts a 97% reforestation of the Park’s 7 194 ha disturbed area by planting in the heavy browsing scenario, leading to an increase in total forest growing stock by 22% and AAC by 12%. Integration of planting with moose population management could be a more efficient way of restoring forest under high browsing pressure in GMNP.

Frugivore zoogeochemistry in tropical forest ecosystems

Frugivore zoogeochemistry in tropical forest ecosystems

Roads, forestry, and wolves interact to drive moose browsing behavior in Scandinavia

AbstractAs wild ungulate densities increase across Europe and North America, plant–herbivore interactions are increasingly important from ecological and economic perspectives. These interactions are particularly significant where agriculture and forestry occur and where intensive grazing and browsing by wild ungulates can result in economic losses to growing crops and trees. We studied plant–herbivore interactions in a moose (Alces alces)‐dominant system where forestry is a primary economy, the primary and secondary road networks are extensive, and wolves (Canis lupus) are recolonizing. Wolves and humans use low‐traffic, secondary roads, yet roadsides provide high‐quality and quantity browse for moose. Foraging theory predicts that moose will respond to riskier landscapes by selecting habitats that reduce predation risk, sacrificing feeding time or food quality. As food becomes limiting, however, animals will accept higher predation risk in search of food. We predicted that road avoidance behavior would be strongest within wolf territories. In areas without wolves, moose should select roadsides for their high forage availability. To test these predictions, we measured moose browsing and counted pellet groups as a proxy for habitat use each spring in Norway and Sweden between 2008 and 2018, in areas with and without wolves and at different distances from primary and secondary roads. We used generalized linear mixed models to evaluate drivers of the probability of browsing occurrence and browsing pressure. We found that browsing occurrence increased closer to secondary roads but decreased closer to primary roads. We also found browsing patterns to vary among tree species. For Scots pine (Pinus sylvestris), the browsing occurrence was two times higher in young forests relative to non‐young forests and decreased further from secondary roads. Wolf territory presence and probability had neutral or positive effect on browsing occurrence and pressure for all species. However, wolf territory presence had negative effects on browsing occurrence and pressure when interacting with secondary roads, young forest, or snow cover. We showed that roads can influence browsing patterns in Norway and Sweden. However, further research is needed, particularly in the face of continued infrastructure development in Scandinavia.

Moose Browsing Tends Spruce Plantations More Efficiently Than a Single Mechanical Release

Forest vegetation management can improve planted seedling survival and growth and is thus widely used in plantation silviculture. In some jurisdictions, mechanical release using brushsaws has replaced the traditional use of chemical herbicides for forest vegetation management purposes. However, its associated costs and the increasing difficulty of finding qualified labor represent a challenge. The browsing of competition by large herbivores may represent an alternative to mechanical release when planted seedlings are resistant to browsing. Here, we compare the efficacy of moose browsing relative to mechanical release in controlling competing vegetation and in promoting white spruce growth in plantations. In a high moose density region, we used an experimental design consisting of four pairs of moose exclosures and unfenced plots; fifty percent of both the access-restricted and unrestricted study areas received a mechanical release treatment. Moose browsing was more efficient than mechanical release in diminishing the sapling density and basal area of competing species. Mechanical release only reduced the sapling density of taller competitors (height &gt; 201 cm), whereas browsing reduced the sapling densities of competitors across a greater size range (height &gt; 130 cm). These effects of moose browsing on competition translated into a greater positive effect of moose browsing on the basal area of planted spruces. We attribute the higher effectiveness of moose browsing relative to mechanical release to its chronic nature. Moose browsed continuously throughout the year and for multiple years, whereas mechanical release was applied only one time between the second and fourth years after planting. Our results suggest that pairing wildlife management and silviculture decisions could be in the best interest of both the hunting and forestry industries in regions where plantations are frequent and use browse-resistant crop trees. Favouring browsers in controlling the density of competing species could increase the hunting experience and income, while providing an effective, cost-free, and socially acceptable forest vegetation management service.

Drivers of arboreal lichen community structure and diversity on Abies balsamea and Betula alleghaniensis in the Avalon Forest Ecoregion, Newfoundland

There is debate about what drives and maintains the structure of arboreal lichen communities and the relative importance of substrate vs. local environment. Here, we examined which lichen species are unique to two tree species [Abies balsamea (L.) Mill. and Betula alleghaniensis Britton] in the boreal forests of the Avalon Peninsula, Newfoundland, and which environmental variables are most important for lichen colonization and community structure. We collected data on lichen diversity from tree boles along with environmental data (tree size, bark pH, canopy cover) for each tree and each site. Multivariate analyses were used to determine the relationship between community structure and environmental data. The results show that a diverse range of tree characteristics are needed to support a diverse range of lichen species. Certain stands, such as old B. alleghaniensis stands, are more suitable to host a unique community of lichens than others. These results can inform land managers on the Avalon, recommending strategies for protected areas and providing forest harvest guidelines that limit clear-cutting of A. balsamea to maintain a diverse community structure and limit harvest of B. alleghaniensis trees in sites less optimal for lichen growth. These baseline data can also be used to monitor changes caused by moose browse and selective harvesting, two locally important threats to lichen diversity.

From delayed succession to alternative successional trajectory: How different moose browsing pressures contribute to forest dynamics following clear‐cutting

AbstractAimsSelective browsing can be a chronic disturbance that reduces the survival, growth and reproduction of individual species and shapes the composition and structure of plant communities. Along with other disturbances that perturb the forest ecosystem, browsing may thus affect forest regeneration and successional trajectories after an acute perturbation such as clear‐cutting. However, effects of different browsing pressures on plant species, communities and ultimately succession remain hard to predict.MethodsWe implemented a browsing exclusion experiment (n = 15 sites) along a gradient of moose browsing pressure to investigate how this factor influenced the early‐successional trajectory of boreal forests following clear‐cutting in eastern Canada. We used Principal Response Curve analyses to compare the trajectory of the plant communities depending on site‐specific moose browsing pressure and analyzed the trajectory of individual species leveraging these curves.ResultsOur results show that all browsing pressures lead to alterations in plant communities when compared to exclosures, but the effect was stronger under heavier browsing pressure. Under heavier browsing pressure, we observed a lower ground cover of balsam fir, an increased ground cover of raspberry, reaching more than 60%, and a lower abundance of saplings for balsam fir, birches and rowan.ConclusionsThis study demonstrated that forest response to browsing is a function of local browsing pressure and that moose mainly slowed forest succession toward a closed canopy. However, heavier browsing pressure, through reduced sapling abundance and the resulting increased cover of competitive raspberry, may delay forest succession and push the ecosystem toward an alternative successional trajectory. As heavy selective browsing can interact with anthropogenic disturbances to determine forest succession, we recommend strong integration of the forest and wildlife management sectors to promote sustainability.

Climate Change Is Likely to Alter Future Wolf – Moose – Forest Interactions at Isle Royale National Park, United States

We evaluated how climate change and variable rates of moose browsing intensity, as they relate to wolf predation, might impact the forests of Isle Royale National Park, MI USA by conducting a simulation modelling experiment. The experiment consisted of contrasting three different scenarios of wolf management and with a static (current conditions) and changing climate (high emissions). Our results suggest that the interactive effects of wolf predation and climate change are likely to be temporally variable and dependent on biogeographic and forest successional processes. During the first 50 years of simulations, when the effects of climate change were minor, higher simulated rates of predation by wolves reduced moose population densities, resulting in greater forest biomass and higher carrying capacities for moose. However, over the longer term, early successional and highly palatable aspen and birch forests transitioned to late successional spruce and fir forests, regardless of climate or predation intensity. After 50 years, the effects of climate change and predation were driven by effects on balsam fir, a late successional species that is highly palatable to moose. High-intensity predation of moose allowed balsam fir to persist over the long term but only under the current climate scenario. Climate change caused a reduction in balsam fir and the other boreal species that moose currently feed on, and the few temperate species found on this isolated island were unable to compensate for such reductions, causing strong declines in total forest biomass. The direct effects of moose population management via reintroduction of wolves may become increasingly ineffective as the climate continues to warm because the productivity of boreal plant species may not be sufficient to support a moose population at all, and the isolation of the island from mainland temperate tree species may reduce the likelihood of compensatory species migrations.

Natural browsing repellent to protect Scots pine Pinus sylvestris from European moose Alces alces

A major problem within forestry is winter browsing on young Scots pine (Pinus sylvestris) by European moose (Alces alces). Moose are selective foragers and make foraging decisions on many scales, for example, they avoid trees with high levels of plant defensive compounds, which reduce digestibility. Bark extract from Norway spruce (Picea abies) is known to have high levels of such defensive compounds. The aim of this study was to evaluate the effects of Norway spruce bark extract as a repellent to European moose. Spruce bark was extracted in a conventional way with ethanol as the solvent, creating a solution that was applied to the apical leader of young pine trees in planted forests. In two field trials in northern Sweden (winter 2017–2018 and winter 2018–2019), the apical leader of young pine trees (height 1–2.5 m) were sprayed with bark extract from Norway spruce. A total of 5247 pine trees were included in the study. The field trials showed that spruce bark extract lowered the number of browsed apical leader of pine trees, and directed moose to browse less valuable lateral shoots, and neighboring trees. During the first field trial, apical leaders were treated every second meter along transects with a concentration of the spruce bark extract of 2.8% by dry weight. The level of browsed apical leaders changed from 15.1% to 6.8% of all apical leaders. During the second field trial, apical leaders were treated in circular plots, in which all main stems inside the circle were treated with a concentration of the spruce bark extract of 5.0% by dry weight. The level of browsed apical leaders changed from 19.5% to 4.7% of all apical leaders. Hence, results show that spruce bark extract (a non-toxic forest byproduct) can function as an efficient repellent. The bark extract can control browsing to a level that is considered acceptable – generally a maximum of 5% of all apical leaders browsed every year. This would result in approximately 7 out of 10 trees, in treated small scale areas, having unbrowsed apical leaders when the trees reach a height at which the apical leaders are safe from moose browsing.

Does recolonization of wolves affect moose browsing damage on young Scots pine?

Ungulates frequently cause damage to human livelihoods, such as agriculture, livestock or forestry. In Sweden, forestry is the dominating land use and is a very important source of income. Moose (Alces alces) browsing commonly causes damage to young forest stands, mainly Scots pine (Pinus sylvestris). Factors known to affect the level of moose browsing damage are moose density, forage availability, site productivity, tree species composition, snow depth, and infrastructure. One hypothesis is that the recent recolonization of wolves (Canis lupus) in Sweden may lead to a decrease in browsing damage levels, through an effect of wolf predation on moose density or moose behaviour. We used data from annual moose browsing damage surveys, long-term wolf monitoring, moose harvest statistics, habitat composition, snow depth, and road network to investigate the effect of wolf recolonization on moose browsing damage on Scots pine. Contrary to predicted, wolf territory establishment and duration showed an increase in the level of moose damage on young Scots pine. But, the effect size was small and it is questionable if it can be considered as biologically relevant. Overall, other factors were more important than wolves in explaining browsing damage on pine by moose. Presence and cover of deciduous species increased the occurrence of moose browsing damage on pine but reduced the level of damage. Decreasing snow depth and increasing road density both resulted in a lower level of damage. We suggest that the strong human impact on all trophic levels on the Swedish forest ecosystem through harvest and intense forestry practices is likely to override wolves’ effects on density and behaviour of moose, as well as their potential effects on preferred browsing species for moose.

Growth and chemical responses of balsam fir saplings released from intense browsing pressure in the boreal forests of western Newfoundland, Canada

For ungulates, balsam fir (Abies balsamea (L.) Mill.) is thought to be a low quality forage due to high levels of indigestible fiber and secondary metabolites. Regardless, intensive browsing of fir saplings by overabundant moose (Alces alces L.) populations has led to the failure of fir-dominated forests in Newfoundland, Canada to regenerate following disturbance. The construction of moose exclosures in Gros Morne National Park (GMNP), western Newfoundland, presented an opportunity to compare levels of secondary metabolites (e.g. phenols and tannins), thought to act as anti-herbivore allelochemicals in balsam fir, under extremes of moose browsing pressure. We examined browsing damage to fir saplings and compared levels of carbon (C), nitrogen (N), total phenols and condensed tannins in current-year foliage outside and inside of eight moose exclosures. Outside of exclosures, 74% of fir saplings showed apical browsing while 97% were browsed laterally. At five exclosures, exposed saplings had significantly greater total phenol concentrations than inside exclosures. Such trends for condensed tannins were observed at only two exclosures, both locations having relatively high moose density and browsing damage. Unlike condensed tannins, total phenols were responsive to different patterns and levels of browsing. Foliar phenol concentration was negatively related to canopy closure, and to height and diameter of saplings, and positively related to the foliar C level. Foliar tannin level was unrelated to canopy or growth characteristics but positively related to the foliar N concentration. Moose browsing affected the defense chemistry of balsam fir; however, phenols and tannins responded differently, this likely being influenced by time of year. Foliar nitrogen levels were greater for inside saplings at only the two exclosures having highest moose density and browsing damage. Our data suggest that balsam fir employs constitutive chemical defense; however, this investment appears to be ineffective in deterring moose browsing.