Johan Månsson

Evaluation of four methods used to estimate population density of moose Alces alces

Abstract Various survey methods are used to monitor and manage ungulate populations. The choice of optimal method depends on estimation accuracy, management objective and financial constraints. Here we compare estimates produced by four different methods for estimating population size, i.e. aerial counts, hunter observations, pellet group counts and cohort analysis. A Swedish moose Alces alces population was studied during 1973–2005 in the Grimsö Wildlife Research Area (135 km2). The highest correlation was found between cohort analysis and aerial counts (r=0.69, P<0.05), and the hunter observations and the aerial counts (r=0.76, P<0.10). The different methods produced relatively consistent trends in population estimates over years. Pellet group counts prior to 1997 were not significantly correlated with the other methods, probably due to unrepresentative spatial sampling. A comparison of the aerial and pellet group counts in 2002 and 2006, showed that the average defecation rate was estimated at approximately 14 pellet groups per day per moose. Our results show the importance of having representative spatial sampling in pellet group surveys and indicate that hunter observations can be a useful tool for estimating long-term population trends even in moderately sized areas.

Quantitative estimates of tree species selectivity by moose (Alces alces) in a forest landscape

Abstract An extensive literature is available on browsing preference for certain tree species. However, useful predictive tools for estimating the impact of deer on forests production and biodiversity can still be improved. A step in that direction is not only to rank preference among tree species but also to quantify the relative risk of being browsed. The foraging selectivity of moose was evaluated using three different statistical methods developed to study habitat utilization. The general pattern for the three methods was consistent. From the results, groups of forage species were clustered and a quantitative index of selectivity was calculated for the groups. The selectivity index showed that rowan (Sorbus aucuparia), willow (Salix ssp.) and aspen (Populus tremula) had a 14 times higher probability of being browsed than a group consisting of Scots pine (Pinus sylvestris) and downy birch (Betula pubescens), while juniper (Juniperus communis) and silver birch (Betula pendula) had a 3.5 times higher probability than Scots pine and downy birch. Since the most preferred species were the least abundant, one should be cautious about the generality of the index between areas, as it may indicate that preference depends on plant species composition. The method used can easily be applied in forest management. Information on quantitative selectivity indices may improve the possibility of managing moose in accordance with acceptable browsing damage.

Moose browsing and forage availability: a scale-dependent relationship?

Scale dependence is a fundamentally important topic in ecology because it determines whether results can be generalized over different spatial scales. We studied the relationship between forage consumption by moose (Alces alces (L., 1758)) and forage availability across six nested spatial scales in south-central Sweden. By using multiple regression, we concluded that the amount of available forage was the best single variable explaining absolute consumption, irrespectively of scale. Forage species diversity, site productivity, and moose density were also important for predicting forage consumption, but their effects differed across the different spatial scales. A multiple regression including forage availability, moose density, site productivity, and forage diversity explained between 31% and 49% of the variation in forage consumption. The importance of a moose index as an explanatory variable decreased with increasing spatial scale, whereas the importance of site productivity increased. According to mode...

Can supplementary feeding be used to redistribute moose Alces alces

Abstract Foraging patterns, behaviour and the distribution of animals are affected by the availability and distribution of food in the landscape. Increasing numbers of ungulates may also be in conflict with agriculture, timber, infrastructure and conservation interests. Understanding foraging habits of ungulates and how these are affected by a change in forage availability or composition are, therefore, issues of major importance both from ecological and management perspectives. Supplementary feeding (i.e. artificial supply of food) is being used to improve local habitat, and thereby affecting ungulate movements, habitat choice and migration patterns. We experimentally tested the predictions that supplementary feeding redistributes moose Alces alces during two different migration phases (early, i.e. during the onset of migration and late, i.e. in the wintering areas). We used individually marked moose and pellet group counts to investigate the effect of supplementary feeding both at the individual and population level. We monitored 30 moose with GPS-collars before, during and after the supplementary feeding experiment, corresponding to 8-10% of the moose population in two different valleys in Northern Scandinavia. During early migration, moose ignored supplementary feeding sites even though migration routes were close to the sites. At the end of the migration route, supplementary feeding affected moose movement, distribution and behaviour. In conclusion, we suggest that there is a clear difference in response to supplementary feeding by moose due to the phase of migration. We conclude that supplementary feeding can be used under certain conditions to redistribute moose in relation to browsing, or to traffic, preferably at the end-point of migration.

The impacts of landscape structure on the winter movements and habitat selection of female red deer

An area of research that has recently gained more attention is to understand how species respond to environmental change such as the landscape structure and fragmentation. Movement is crucial to select habitats but the landscape structure influences the movement patterns of animals. Characterising the movement characteristics, utilisation distribution (UD) and habitat selection of a single species in different landscapes can provide important insights into species response to changes in the landscape. We investigate these three fields in female red deer (Cervus elaphus) in southern Sweden, in order to understand how landscape structure influences their movement and feeding patterns. Movements are compared between two regions, one dominated by a fragmented agriculture–forest mosaic and the other by managed homogenous forest. Red deer in the agriculture-dominated landscape had larger UDs compared to those in the forest-dominated area, moved larger distances between feeding and resting and left cover later in the day but used a similar duration for their movements, suggesting faster travelling speeds between resting and feeding locations. The habitat selection patterns of red deer indicate a trade-off between forage and cover, selecting for habitats that provide shelter during the day and forage by night. However, the level of trade-off, mediated through movement and space use patterns, is influenced by the landscape structure. Our approach provides further understanding of the link between individual animal space use and changing landscapes and can be applied to many species able to carry tracking devices.

Felled Scots pine (Pinus sylvestris) as supplemental forage for moose (Alces alces): Browse availability and utilization

Abstract Old trees felled by forestry actions or natural disturbances can supply large herbivores with a substantial amount of forage and thereby potentially affect browsing patterns. To explore the felling of mature Scots pine (Pinus sylvestris L.) as a management practice (and potentially divert moose from young pine forests) this study identified how much browse there is available on felled trees and to what extent this browse is used by moose (Alces alces L.). Pine trees were surveyed in two study areas in Sweden and one in Norway. Pine crowns from thinning-stage trees held on average 8 kg of potential moose forage (dry weight). Corresponding figures for mature trees and seed trees were 29 kg and 12 kg, respectively. When the trees were processed during commercial felling, much of the potential forage became unavailable, and only approximately 1.5 kg per tree was available for moose after processing. The utilization of the forage on felled trees ranged between 5 and 15%. No significant difference in utilization between tree ages or between tops and bases within the tree crowns were found. However, the bite diameters on twigs differed between parts and age stages of the trees. This study illustrates that felling of trees can influence the availability of winter forage for moose and thereby has the potential to decrease browsing pressure on young forest stands. The substantial effect that storms can have on short-term forage supply for moose is also emphasized.

Wolves, people, and brown bears influence the expansion of the recolonizing wolf population in Scandinavia

Interspecific competition can influence the distribution and abundance of species and the structure of ecological communities and entire ecosystems. Interactions between apex predators can have cascading effects through the entire natural community, which supports broadening the scope of conservation from single species to a much wider ecosystem perspective. However, competition between wild large carnivores can hardly be measured experimentally. In this study, we analyzed the expansion of the Scandinavian wolf (Canis lupus) population during its recovery from the early 1990s. We took into account wolf-, habitat-, human- and brown bear (Ursus arctos)-related factors, because wolf expansion occurred within an area partially sympatric with bears. Wolf pair establishment was positively related to previous wolf presence and was negatively related to road density, distance to other wolf territories, and bear density. These findings suggest that both human-related habitat modification and interspecific competition have been influential factors modulating the expansion of the wolf population. Interactions between large carnivores have the potential to affect overall biodiversity. Therefore, conservation-oriented management of such species should consider interspecific interactions, rather than focusing only on target populations of single species. Long-term monitoring data across large areas should also help quantify and predict the influence of biotic interactions on species assemblages and distributions elsewhere. This is important because interactive processes can be essential in the regulation, stability, and resilience of ecological communities.

Bark-stripping on Norway spruce by red deer in Sweden: level of damage and relation to tree characteristics

Abstract Red deer are increasing and spreading in Scandinavia. The species is capable of causing severe damage to Norway spruce through bark-stripping. We studied occurrence of bark-stripping on 18,000 trees in six study areas within two different regions in Sweden. The susceptibility for damage was related to morphological characters of the trees (bark thickness, branchiness, stem diameter) and whether the trees had old damage or not. In southernmost Sweden, 83, 89 and 92% of the stems were damaged in the three study areas, whereas 2, 8 and 46% was damaged in the three study areas in the region further north. Gnawing was the most common type of damage. Peeling was rare in the northern region but more frequent in the southern region. Bark-stripped trees had on average fewer branches, thinner bark and smaller diameter compared to undamaged trees. Furthermore, the risk of fresh damage was higher for already damaged trees in the northern region whereas the opposite pattern was evident in the southern region. Silvicultural measures may indirectly affect the risk of damage since it may affect branchiness, diameter and number of damaged trees left after thinning.

Managing landscapes for multiple objectives: alternative forage can reduce the conflict between deer and forestry

Deer (Cervidae) cause considerable damage to forest plantations, crops, and protected habitats. The most common response to this damage is to implement strategies to lower population densities. However, lowering deer density may not always be desirable from hunting, recreational, or conservation perspectives. Therefore, knowledge is needed about additional factors beyond deer density that affect damage levels, and management actions that consider competing management goals. We studied the relationships between levels of bark-stripping by red deer (Cervus elaphus) on Norway spruce (Picea abies) and (1) relative deer density indices (pellet group count and deer harvest data), (2) availability of alternative natural forage (cover of forage species) and (3) proportion forest in the landscape, both at a forest stand scale and at a landscape scale. Extensive variation in damage level was evident between the six study areas. On a stand scale, the proportion of spruce damaged was positively related to pellet group density, indicating the importance of local deer usage of stands. In addition, available alternative forage in the field layer within spruce stands and proportion forest surrounding stands was negatively related to damage level. On the landscape scale, damage level was negatively related to availability of forage in the field and shrub layers and proportion forest, but was not related to any of the relative deer density indices. Increasing alternative forage may thus decrease damage and thereby reduce conflicts. Additionally, the proportion of forest in the landscape affects damage levels and should thus be considered in landscape planning and when forecasting damage risk. The relationship between local deer usage of stands and damage level suggests that future studies should try to separate the effects of local deer usage and deer density.

Food plots as a habitat management tool: forage production and ungulate browsing in adjacent forest

A key challenge for wildlife management is to handle competing goals. High ungulate densities may be desirable from hunting and recreational perspectives, but may come in conflict with needs to limit or reduce browsing damage. Since browsing intensity is negatively related to forage availability it may be possible to mitigate damage on forest by increasing forage availability within the landscape. A commonly used method to increase the attractiveness of a localized part of the landscape is to establish food plots. In a multiyear setup using enclosures, wildlife observations, field surveys, and controlled biomass removal, we studied food plots to document forage production, utilization by ungulates, and browsing on adjacent forests in southern Sweden. The fenced parts of the food plots produced on average 2230 to 5810 kg ha-1 marrow-stem kale, second-year clover mix or early-sown rapeseed. The biomass of target crops was generally higher within ungrazed (exclosures) compared to grazed (controls) quadrats on the food plots, which demonstrates that the crops were used as forage by ungulates. Browsing on deciduous trees in the adjacent forest was higher within 70–135 m from the food plots compared to areas further away. For wildlife management, our study shows that establishment of food plots provides substantial amounts of forage both during growing season and at the onset of the dormant season, and that a large share of this food is consumed. Finally, our study documents that forage availability for ungulates at the onset of the often-limiting dormant season can be increased by fencing food plots throughout the growing season.