Environmental variation and moose Alces alces density as determinants of spatio-temporal heterogeneity in browsing

Understanding temporal variation in habitat selection and browsing intensity by large herbivores is fundamental because of their large impact on the ecosystems. I studied the annual variation in winter browsing pressure on young trees and habitat selection by moose Alces alces over a ten year period. Specifically, the relationships between browsing pressure on Scots pine Pinus sylvestris and two birch species ( Betula ssp.) and three explanatory variables – 1) availability of forage, 2) moose density (estimated by pellet group counts) and 3) snow cover was studied. At a larger spatial scale (forest stand level) the relationship between moose habitat selection between three different habitat types (forest <30 yr, forest>30 yr and mire) and two explanatory variables, 1) snow condition and 2) moose density, were studied. Browsing pressure on Scots pine, the dominating food plant, was related to forage availability, moose density and snow condition. No significant relationships between any of the three explanatory variables and browsing pressure on the two birch species were found. Moose selection for certain habitats varied between years and was affected by number of days with >0.10 m of snow.
Habitat selection was not significantly related to moose density and the relationship between overall moose density and habitat specific moose densities was proportional within the studied density range. These findings have implications for understanding varying browsing patterns – and will affect both the ability to predict herbivores' effect on the forest ecosystem. A snow dependent browsing pattern also indicates that one can expect a long term decrease in browsing pressure on the tree and shrub layer as a consequence of the ongoing large-scale climate change.     

The impact of simulated moose densities on conifer aphids along a productivity gradient

Large herbivores have a significant impact on boreal forest ecosystems. The modification of resources through their feeding induces changes in trophic dynamics and affects the direction of interactions in a community. Moose Alces alces may decrease the available plant biomass for herbivorous insects on one of their main winter forage species in Fennoscandia, Scots pine Pinus sylvestris, and indirectly alter the abundance of invertebrates through exploitative competition. Moose browsing can also induce chemical, morphological, and phenological changes in plants, changing their nutritive value to insect herbivores such as aphids. Habitat productivity may further modify the responses of aphids to moose browsing. We studied the responses of the gray pine aphid Schizolachnus pineti to different moose densities, and their relations to habitat productivity by sampling pine branches and measuring the number of aphids on pine needles. The experimental setup consisted of 8 exclosures along a productivity gradient, where the feeding, defecation, and urination of 4 densities of moose had been simulated for 7 yr. We here show that high levels of simulated browsing decrease the amount of gray pine aphids in areas with high productivity. In areas with low productivity, however, simulated browsing had no such effect. Habitat productivity should therefore be considered as an important factor that may determine the strength of an areas buffering capacity to high moose densities. Low resource environments appear to be favourable to specialist conifer aphids on pines under high browsing pressure, but the performance of generalist insect herbivores might be lowered.     

Female Moose Prioritize Forage Over Mortality Risk in Harvested Landscapes

Since 2010, several moose (Alces alces) populations have declined across North America. These declines are believed to be broadly related to climate and landscape change. At the western reaches of moose continental range, in the interior of British Columbia, Canada, wildlife managers have reported widespread declines of moose populations. Disturbances to forests from a mountain pine beetle (Dendroctonum ponderosae) outbreak and associated salvage logging infrastructure in British Columbia are suspected as a mechanism manifested in moose behavior and habitat selection. We examined seasonal differences in moose habitat selection in response to landscape change from mountain pine beetle salvage logging infrastructure: dense road networks and large intensive forest harvest cutblocks. We used 157,447 global positioning system locations from 83 adult female moose from 2012 to 2016 on the Bonaparte Plateau at the southern edge of the Interior Plateau of central British Columbia to test whether increased forage availability, landscape features associated with increased mortality risk, or the cumulative effects of salvage logging best explain female moose distribution using resource selection functions in an information-theoretic framework. We tested these hypotheses across biological seasons, defined using a cluster analysis framework. The cumulative effects of forage availability and risk best predicted resource selection of female moose in all seasons; however, the covariates included in the cumulative models varied between seasons. The top forage availability model better explained moose habitat use than the top risk model in all seasons, except for the calving and fall seasons where the top risk model (distance to road) better predicted moose space use. Selection of habitat that provides forage in winter, spring, and summer suggests that moose seasonally trade predation risk for the benefits of foraging in early seral vegetation communities in highly disturbed landscapes. Our results identified the need for intensive landscape-scale management to stem moose population declines. Additional research is needed on predator densities, space use, and calf survival in relation to salvage logging infrastructure. © 2020 The Wildlife Society.     

Foraging by moose on two species of birch when these occur in different proportions

The two tree-like birch species Betula pendula and B. pubescens are of medium preference to moose during winter in northern Sweden. Because these birches are abundant in many biotopes, they form a major part of the moose diet. The two birches are very similar in appearance and often occur in mixed stands. Twenty-one birch stands where B. pendula formed from 2 to 97% of the birches were investigated to determine how the relative composition of the stands affected browsing of the two species by moose. In stands composed of 60% or less of B. pendula , there was a preference for this species when regarding 1.5–3.0 m high birches, which carry the largest amount of available browse per tree. At higher proportions B. pendula was still preferred, but use was closer to availability. However, in all stands there were significantly more moose bites per tree of B. pendula than of B. pubescens . In four birch stands browsing on 1.0–1.5 m high birches was also investigated. For this height class there was still a preference for B. pendula , but the difference between the two species was less pronounced than for the 1.5–3.0 m height class.     

Browse biomass production an.regrowth capacity after biomass loss in deciduous and coniferous trees: responses to moose browsing along a productivity gradient

To understand how large herbivores interact with their food resources and the ecosystem, it is necessary to understand plant growth responses to biomass loss. Tolerance to biomass loss, and the ability to regrow new photosynthetic tissue after herbivore attack, is one such important mechanism. Here we experimentally studied how year-round browsing corresponding to four different levels of moose, Alces alces , population density affected total annual browse biomass production, which also serves as a proxy for production of new photosynthetic tissue, in birch ( Betula pubescens and B. pendula ) and Scots pine, Pinus sylvestris , along a habitat productivity gradient. Our results revealed that habitat productivity index was the most important variable determining annual browse biomass production for birch, and that a high moose density and biomass removals of 25–40% annually actually could stimulate birch above-ground productivity in more productive sites. Contrary to birch, pine was not affected by habitat productivity index, and appeared to have much lower regrowth capacity than birch. For pine, percent biomass removed was the most important factor affecting annual browse biomass production, which decreased with increasing levels of biomass removal. We also tested if birch and pine responded to biomass removal by allocating more resources to browse biomass production at in the lower portion of the stem (0–0.5 m), which was protected from biomass removal in winter. Birch did not allocate more resources to biomass production in the lower portion of the stem, whereas pines subjected to high biomass removal had more biomass in the lower portion of the stem than those protected from losses. Our study thus shows that plant responses can be linear or non-linear along the range of herbivore densities we studied, and that responses can change from negative to positive along underlying habitat productivity gradients.     

Moose and vole browsing patterns in experimentally assembled pure and mixed forest stands

Plants growing in diverse communities are believed to exhibit associational resistance to herbivores, but this hypothesis has seldom been tested experimentally for vertebrate herbivores in forest ecosystems. We examined browsing patterns of the two principal mammalian herbivores of Finnish boreal forests, moose and voles, in young stands where tree species diversity and composition were experimentally manipulated. The stands were composed either of monocultures or different 2–5 species mixtures of Norway spruce, Scots pine, Siberian larch, silver birch, and black alder. Voles and moose showed contrasting responses to stand diversity and species composition. In accordance with the predictions of the associational resistance hypothesis, vole damage was higher in tree monocultures than in mixed stands, although stand diversity effects were statistically significant only at one of the three study areas. Voles also damaged more trees in coniferous than in deciduous stands. In contrast, moose browsing tended to increase with the number of tree species in a stand and with the presence of the preferred tree species, birch, in a mixture. The observed differences in vole and moose responses to stand diversity and species composition are likely to be due to different feeding specialisation, foraging patterns, and movement ability of these herbivores. Voles switched to trees only when the supply of a more preferred food (grasses and forbs) was depleted and restricted their feeding choice only to the most palatable tree species regardless of the number of tree species present per stand. In contrast, tree branches and foliage represented an important part of moose diet throughout the year; moose may be able to tolerate secondary plant metabolites of different tree species better than voles and may thus benefit from diet broadening when more tree species are available. Furthermore, the home range size and foraging ability of these two very differently sized herbivores may partly explain the observed differences in utilisation of different tree species. Finally, both moose and voles showed high spatial and temporal variation in their feeding; in particular, vole damage was more influenced by tree species diversity in areas and years with high vole densities. Thus, diversification of forest stands may have very different effects on mammalian browsing depending on the herbivores present, their densities, and the tree species used in reforestation.     

Trait‐mediated indirect interactions: Moose browsing increases sawfly fecundity through plant‐induced responses

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Effects of competition,herbivory and substrate disturbance on growth and size structure in pin cherry (Prunus pensylvanica L.) seedlings

We examined separate and interactive effects of intraspecific competition, vertebrate browsing and substrate disturbance on the growth and size structure of pin cherry (Prunus pensylvanica L.) in the first two seasons of growth after clearcutting, in a hardwoods forest in New Hampshire, United States. Over the 15-month study period, 97.5% of 1801 individuals survived, and mean plant height increased from 4-fold at high density to 5-fold at low density. Relative height growth was significantly lower at higher plant densities in two of the three growth periods examined. Vertebrate browsers (moose and deer) significantly preferred taller plants. Browsed plants had higher relative height growth following browsing than unbrowsed plants (compensatory growth) at low and intermediate densities. The degree of compensation declined with density and compensation was not significant at the highest density level. At low and intermediate densities, plants browsed early in life regained height dominance through compensatory growth; they failed to regain dominance at high density. Because compensatory growth tended to offset the effects of size-selective browsing, there was no difference in the degree of size inequality between browsed and unbrowsed plots. However, size inequality increased with plant density. Substrate disturbance caused by logging had no significant effects on either relative height growth or size inequality. The slope of the relationship between relative height growth and initial height increased significantly with density and time, and was higher in unbrowsed than in browsed plots, suggesting that competition among plants was size-asymmetric. Despite the preference of browsers for large plants, there was a clear net growth advantage for plants of large initial size, when the effects of competition, browsing and compensatory growth were combined. The interactive effects of density and browsing demonstrate the importance of a multifactorial approach to the analysis of individual plant performance and population structure.     

Cascading effects of moose (<Emphasis Type="Italic">Alces alces</Emphasis>) management on birds

Large herbivores often have key functions in their ecosystems, and may affect ecosystem processes with cascading effects on other animals. The mechanisms often involve relocations of resources of various kinds, including reduction in resource availability following foraging and increase in resources from animal excreta. As large herbivore populations in Europe generally are intensely managed, management activities may interact with the activities of the herbivores themselves in the effect on other ecosystem components. We investigated the effects of moose (Alces alces) winter browsing, together with the effect of net nutrient input via supplementary winter feeding of moose on functional composition and species richness of birds in a boreal forest. Supplementary feeding stations for moose had a net zero effect on bird species richness and abundance, because negative effects of moose browsing were balanced by positive effects of nutrient input. Sites with a similar browsing intensity as at feeding stations but without nutrient input had lower abundance and species richness than feeding stations. Functional groups of bird species showed differing responses: birds nesting at or below browsing height were negatively affected by moose browsing, whereas species nesting above the browsing zone were positively affected by moose browsing. Insect-eating species responded negatively to moose browsing on birch but positively to nutrient input at feeding stations, whereas seed-eating species responded positively to birch browsing and negatively to feeding stations. This study showed that both high levels of cervid activity and human management interventions influence bird communities.     

Comparative Space Use and Habitat Selection of Moose Around Feeding Stations

ABSTRACT The practice of feeding cervids in winter, either as a supplement to enhance nutritional status or to divert animals away from roads, railways, or vulnerable habitats, is rising noticeably. Moose (Alces alces) densities in Scandinavia are currently at historically high levels, resulting in amplified damage to economically important young Scots pine (Pinus sylvestris) forest stands. Nevertheless, there is limited information as to how diversionary feeding affects herbivore space use and habitat selection. We followed 32 female moose marked with Global Positioning System collars to evaluate 1) if feeding stations serve as attraction points to the extent that habitat-selection patterns resemble those of central-place foragers (i.e., high usage and more uniform selection close to the attraction point), and 2) if moose using feeding sites select young pine stands less than those not using feeding sites. Moose that used diversionary forage concentrated their space use around feeding stations and selected habitats as predicted for a central-place forager with a decreasing probability of using areas away from feeding sites and a low degree of habitat selectivity close to feeding sites. However, moose that used feeding sites continued to select young pine stands to the same extent as moose that did not use feeding sites. Feeding sites were, therefore, not successful in diverting moose away from valuable natural browse, so we recommend wildlife managers establish feeding sites in sacrifice areas where moose browsing is permissible and, if possible, >1 km from young pine plantations.     

Linking Moose Population and Plant Growth Models with a Moose Energetics Model

Selective foraging by large mammals can change ecosystem properties such as plant species composition, nutrient cycling rates, and soil fertility. These changes, in turn, alter the availability of forage and could affect the relative efficiencies of foraging strategies used by these animals. We used a simulation model to predict how alternate foraging strategies affected the net annual energy balance of moose (Alces alces), moose density, and distribution of browse across the landscape. The model simulates the spatial distribution of vegetation in an 8-ha landscape of 1-m² cells with seasonal changes in the energetic needs of free-ranging moose and plant phenology. The energetics model was integrated with a moose population model and a plant-growth model for long-term simulations. Changes in bite density in each feeding station are predicted with height and biomass logistic curves modified by a quadratic response to browsing. We tested foraging strategies using random, fractional, and marginal value theorem (MVT) algorithms on landscapes with a range of bite densities and differing spatial distributions. Small-scale disturbances (that is, tree-fall gaps) were required to maintain browse supply and prevent moose population extinction under all foraging strategies. Populations using a fractional stopping rule survived the 100-year simulations because moose browsed across much of the landscape and did not overbrowse patches with high bite density. Populations using random and MVT stopping rules became extinct in about 25 and about 50 years, respectively. Moose using a random stopping rule were in negative energy balance because travel time was high and the net energy intake rate was low on an annual basis. Moose using the MVT stopping rule were initially in positive energy balance, but as the high-density browse patches were overbrowsed and low-density unbrowsed patches grew out of reach, bite density decreased, and energy balance became negative in subsequent years. Thus, the foraging strategy used by individual moose resulted in creation of landscapes that strongly affected browse density, browse distribution, moose population density, and moose survival. Received 30 April 1997; accepted 5 August 1997.     

Moose density and habitat productivity affects reproduction,growth and species composition in field layer vegetation

Question: What is the effect of a gradient in moose density on reproduction, growth and functional composition of the field layer vegetation in a boreal forest, and how is this effect modified by habitat productivity? Location: Northwest of Umeå, Västerbotten, northern Sweden. Methods: Field layer vegetation was surveyed in an experimental setup with simulation of three different moose densities and a control in eight study sites along a gradient of habitat productivity. Results: We found that increased moose density led to decreased cover and reproductive effort of a browsed dwarf shrub (bilberry, Vaccinium myrtillus L.) and increased cover and reproductive effort of a non‐browsed graminoid (wavy hair‐grass, Avenella flexuosa (L.) Drejer). Increased moose density led to increased light availability and probably reduced competition from V. myrtillus. Total reproductive effort in the field layer vegetation increased, height decreased and cover of light‐demanding species and graminoids increased with increasing moose density. The effects of moose density were modified by the productivity gradient, leading to a higher relative increase in light availability and reproductive effort in highly productive areas than in low productive areas. Conclusions: Increased light availability was an important indirect effect of moose density, leading to less competition for light and a shift towards early successional species. The effect of moose density on light availability was modified by habitat productivity, leading to stronger relative effects in highly productive areas than in low productive areas.     

Moose summer and winter diets along a large scale gradient of forage availability in southern Norway

Studies on dietary functional responses in large herbivores are traditionally conducted by following individual animals. The method is very time-consuming, and hence, typically provides only a narrow array of forage species compositions. Here we use a range level approach to look at moose (Alces alces) selectivity for and utilization of forage species in relation to availability in both summer and winter. We compare 12 Norwegian ranges representing a large scale gradient in plant communities. The most important forage species in the diet were birches (Betula spp., comprising 43% of all trees browsed in summer and 27% in winter), rowan (Sorbus aucuparia, 25% of trees browsed in summer, 37% in winter), and bilberry (Vaccinum myrtillus, 42% of herbaceous epidermal fragments in summer feces). Selectivity for birches was positively related to its availability and negatively related to availability of rowan, Salix spp., and aspen (Populus tremula) together (all more selected for than birches). Multiple regression models including availability of several forage species were thus superior to single-species models in explaining the diet content of main forage plants. Selectivity for birches was also stronger in summer than in winter, while the opposite pattern was found for rowan. The finding is relevant for our evaluation of the quality of summer and winter ranges, and hence, their relative influence on population productivity. Our study underlines the need to incorporate species composition of available forage when quantifying dietary functional responses in selective herbivores such as moose. Furthermore, care should be taken when extrapolating data on moose diet across ranges or seasons.     

Selectivity by moose vs the spatial distribution of aspen: a natural experiment

Patch use theory predicts that herbivores perceive food as patches and spend more time in high quality patches, i.e. feeding sites providing a high net rate of intake of energy and/or limiting nutrients. The herbivores should accordingly not discriminate among food items in such high quality patches, and food items should thus be eaten in proportion to availability. In contrast, classical diet theory assumes food selection to take place at the level of individual plants, and predicts that the forager should concentrate on the most profitable item until availability drops below some critical threshold.
Here we address how the spatial distribution of European aspen Populus tremula , a highly preferred browse species, affects the selectivity by moose Alces alces at the patch and the tree level. The study was performed in a managed boreal forest landscape in coastal northern Sweden, where aspen occurs highly aggregated almost exclusively in discrete patches. We compared moose' selectivity for aspen and browsing intensity on aspen ramets and other browse species in aspen patches versus at randomly located sites.
Random sites and aspen stands were utilised equally by moose in terms of overall use of forage. There was no difference in total coverage of forage species and relative moose density. Selectivity for aspen was stronger at random sites than at aspen sites, and the browsing intensity on aspen was similar. We conclude that moose did not perceive aspen stands as discrete patches, and used aspen ramets more in accordance with diet theory. These findings agree with the idea that large generalist herbivores strive to maintain a mixed and balanced diet, causing rare species to be over-utilised (negative frequency-dependent food selection). By such selective feeding, moose may reinforce the aggregated distribution of aspen in the managed boreal forest landscape.     

Cascading Effects of Climate Change on Forest Ecosystems: Biogeochemical Links Between Trees and Moose in the Northeast USA

The relationship between herbivores, plants and nutrient dynamics, has been investigated in many systems; however, how these relationships are influenced by changing climate has had much less attention. In the northeastern USA, both moose populations and winter climate have been changing. Moose, once extirpated from the region, have made a comeback; while locally, snow depth and duration of snow cover have declined. There is considerable uncertainty in how these changes will interact to influence forested systems. We used small experimental plots and transects along with snow removal (to elicit soil freezing and expose potential forage plants), mechanical browsing, and fecal additions (labeled with ¹⁵N) to examine ecosystem responses. We found that snow removal changed moose browsing behavior, with balsam fir more heavily browsed than sugar maple or Viburnum under low snow conditions. Soil freezing alone did not significantly alter N dynamics or selected plant responses, but there were significant interactions with moose activity. The combined effects of moose fecal additions, mechanical browsing, and soil freezing resulted in higher levels of NO₃ ^? leaching under fir and maple, whereas Viburnum had essentially no response to these multiple factors. Our results suggest that declines in snow depth can initiate a cascade of ecosystem responses, beginning with exposure of plants to increased browsing that then triggers a series of responses that can lead to higher N losses, precipitated by decreased N demand in plants compromised by soil freezing damage. Balsam fir may be particularly susceptible to this cascade of multiple stresses.     

Browsed twig environmental DNA: diagnostic PCR to identify ungulate species

Ungulate browsing can have a strong effect on ecological processes by affecting plant community structure and composition, with cascading effects on nutrient cycling and animal communities. However, in the absence of direct observations of foraging, species‐specific foraging behaviours are difficult to quantify. We therefore know relatively little about foraging competition and species‐specific browsing patterns in systems with several browsers. However, during browsing, a small amount of saliva containing buccal cells is deposited at the bite site, providing a source of environmental DNA (eDNA) that can be used for species identification. Here, we describe extraction and PCR protocols for a browser species diagnostic kit. Species‐specific primers for mitochondrial DNA were optimized and validated using twigs browsed by captive animals. A time series showed that about 50% of the samples will amplify up to 12 weeks after the browsing event and that some samples amplify up to 24 weeks after browsing (12.5%). Applied to samples of natural browsing from an area where moose (Alces alces), roe deer (Capreolus capreolus), fallow deer (Cervus dama) and red deer (Cervus elaphus) are sympatric, amplification success reached 75%. This method promises to greatly improve our understanding of multispecies browsing systems without the need for direct observations.     

Winter home range and habitat use by porcupines in Alaska

Habitat selection results from trade-offs between availability and use of resources under constraints of predation, competition, or other threats, which can vary spatially and temporally. For northern herbivores, winter food availability and quality can limit population size and may drive habitat preference. North American porcupines (Erethizon dorsatum) are widespread generalist herbivores that range from Mexico to the northern reaches of Alaska. During the long Alaskan winter, porcupines deal with high energetic demands resulting from low ambient temperatures while subsisting on low quality forage. We tracked free-ranging porcupines over 3 winters in southcentral Alaska to determine habitat selection and home range size in relation to diet. Porcupines maintained larger than expected home ranges, and selected for conifer-hardwood forests at the home range level. Individual variation among porcupines was too large to determine a pattern of microhabitat selection among trees. Regardless, direct observations revealed that porcupines used only white spruce and paper birch trees for foraging. White spruce may provide some nutritional and thermoregulatory advantage over paper birch; however, porcupines did feed on paper birch cambium, suggesting some nutritional requirement is met by eating paper birch. Porcupines most likely feed on paper birch cambium when detoxification pathways used to process plant toxins in white spruce needles are saturated. Maintaining mixed conifer-hardwood forests in southcentral Alaska would provide suitable winter habitat for porcupines and may alleviate damage to single species stands of conifers or hardwoods that are preferred by commercial forestry operations. © 2012 The Wildlife Society.     

Generation of Spatial Patterns in Boreal Forest Landscapes

Boreal forests are composed of a few plant species with contrasting traits with respect to ecosystem functioning and spatial patterning. Early successional deciduous species, such as birch and aspen, disperse seeds widely, do not tolerate low light and nitrogen availabilities, have rapidly decaying litter, and are highly preferred by herbivores. These later succeed to conifers, such as spruce and fir, which disperse seeds locally, tolerate low light levels and low nitrogen availability, have litter that decays slowly, and are unpalatable to most mammalian herbivores. Although there are also early successional conifers, such as jack pine and Scots pine, the aspen-birch-spruce-fir successional sequence is the most common over much of North America, and (without fir) in Fennoscandia and Siberia. The course of succession in these forests is controlled partly by seed dispersal and selective foraging by mammalian herbivores. Both of these processes are spatially dynamic, but little is known about how their spatial dynamics may affect ecosystem processes, such as nitrogen cycling or productivity. We present spatially explicit models that demonstrate the following: (a) Spatially explicit seed dispersal results in more clumped distribution of tree species and persistence of greater paper birch biomass than uniform seed rain across the landscape. Such results are consistent with current spatially explicit population models of dispersal and coexistence. (b) With localized seed dispersal, the concentrations of available soil nitrogen are distributed in larger patches with sharp transitions from low to high nitrogen availability near patch edges. In contrast, with a uniform seed rain, the distribution of soil nitrogen availability was more uniform and “hotspots” were more localized. Thus, the spatial pattern of an ecosystem process (nitrogen cycling) is determined by seed dispersal and competition for light among competing populations. (c) A dispersing herbivore, such as moose, that selectively forages on early successional deciduous species with high quality litter, such as aspen or birch, and discriminates against late successional conifers, such as spruce or fir, imposes higher-order repeated patterns of plant species and biomass distribution on the landscape. Thus, seed dispersal and herbivore foraging correlate properties in adjacent patches but in different ways, and different spatial patterns emerge. Other processes, such as insect outbreaks, fire, and water flow, also may correlate properties between adjacent patches and result in additional patterns. Received 8 February 1999; accepted 28 May 1999.     

Moose herbivory,browse quality,and nutrient cycling in an Alaskan treeline community

Moose (Alces alces) browsing on diamondleaf willow (Salix planifolia pulchra) caused significant increases in subsequent growth of stems and leaves in treeline plant communities in central Alaska, USA. Willows growing in the shade were significantly more palatable for moose than those growing in the sun. Moose density had strong effects on rates of nutrient cycling, ostensibly through effects of browsing and inputs from fecal and urinary nitrogen. Moose are a keystone herbivore that likely mediate rates of nutrient cycling in northern ecosystems.     

Choice of feeding sites by moose during summer, the influence of forest structure and plant phenology

We observed forage and habitat selection in radio-collared moose at feeding sites in southeast Norway. Use of older forest increased from spring to autumn. Birch Betula spp. and bilberry Vaccinium myrtillus accounted for c. 75% of the diet. Occurrence of important forage plants, height of browse, and difference in phenology between plant species all appeared to play a role in moose selection of feeding sites. Shading influences moose forage by delaying plant phenology and possibly through its effect on leaf content of water and secondary compounds. On single birch trees, feeding was concentrated to the top branches at midsummer; during spring and autumn more leaves from side branches were eaten. Greater discrimination as vegetation matured was also evident from the wider variety of forage species used at midsummer. Selection of feeding sites was not related to density of important browse species. We propose that variations in light/shade conditions may play a role in moose choice of feeding sites and that moose on summer range will benefit from a heterogeneous mixture of plantations and older forest stands.