Regeneration failure of Scots pine changes the species composition of young forests

How seedling mortality and browsing affects species composition of regenerating forests has been mostly studied on a small scale. Yet, large-scale analyses based on extensive data are essential for robust prediction of species composition in young forests. In this study, we used a dataset from a national inventory of young forests (1-4 metres in height) to investigate the species composition of young forests across Sweden. We found that most of the regenerated forest area (almost 90%) was planted with Norway spruce (southern Sweden) and Scots pine (northern Sweden). Regeneration of Norway spruce was generally relatively successful but as a consequence of seedling mortality and browsing, almost 40% of the area regenerated with Scots pine will probably not develop into pine-dominated stands. Thus, low survival of Scots pine seedlings and trees can profoundly change the trajectory of species composition of the young forest from what was originally intended, and a large proportion of the young stands may develop into mixtures of conifers and broadleaves. While such mixtures may benefit certain biodiversity and ecosystem services, a loss of Scots pine dominated stands may also have adverse impacts on the economic returns as well as pine-dependent biodiversity and recreational values

Using citizen data in a population model to estimate population size of moose (Alces alces)

Long-term and wide-ranging citizen science programs provide a unique opportunity to monitor wildlife populations and trends through time while encouraging stakeholder participation, engagement, and trust. Hunter observations is such a program that in Sweden is used on a regular basis to monitor population trends of moose. However, hunter observations are not reliable to determine the actual population size. We developed a mechanistic moose population model that integrated citizen science data and used it at various geographical scales to estimate moose population size between 2012 and 2020. A sensitivity analysis, specifically performed for recruitment, adult sex ratio and calf sex ratio, showed that the simulated population size was most sensitive for variation in recruitment. According to the results, Sweden had a total moose population of -311 000 (+/- 4%) individuals pre-hunt and -228 000 (+/- 4%) post-hunt in 2020. The post-hunt moose abundance has decreased nationwide with 15%, from 0.72 to 0.61 moose per km2 during the 2012 - 2020 period. The present post-hunt moose density was estimated at 0.39, 0.78, 0.84 and 0.54 per km2 for the regions northernmost, northern, central and southern Sweden, respectively. The simulation model can be used for strategic and operative management at various geographical scales and is publicly available. By integrating citizen data with a mechanistic population model, a new low-cost method of estimating population size and relevant population dynamics was established

Predictors of browsing damage on commercial forests – A study linking nationwide management data

Population sizes and species distributions of wild ungulates in Europe have increased during the past decades, and continue to do so. As a result, browsing pressure in forests is increasing and concerns about the effects of increasingly common multi-species deer communities on forestry are rising. However, we currently lack an understanding of how the composition of deer communities affects browsing damage, particularly with respect to the role of species with different dietary requirements. Further, the relative importance of predictors of browsing damage in systems with multiple browsers remains elusive. Here, we used data from Swedish management, which is monitoring ungulates and their damage to forests, to test how deer densities, forage availability, and winter severity predict browsing damage on commercially important Scots pine (Pinus sylvestris) at national and regional scales. Moose (Alces alces) is the main browser of Scots pine, but competes with other deer over more preferred forage. During winter, a higher index of moose density was associated with higher browsing damage in northern Sweden, where there is low competition from other deer. In southern Sweden, competition from other deer is higher and a higher density index of roe deer (Capreolus capreolus) was associated with higher winter damage. However, there was no relationship between moose density and damage. We suggest that moose are forced to browse more pine due to interspecific competition over alternative forage resources in the south, yielding stronger relationships between densities of competing deer species and damage than between moose density and damage. Pine density, a proxy for forage availability, was an equally or more important determinant for browsing damage as deer density indices in most regions. Increasing pine density was associated with reduced browsing damage caused in winter in all regions and reduced damage caused in summer in central Sweden. Increased winter severity, as an index of snow depth, predicted increased winter damage in the northern region only. To reduce winter damage, our results suggest that management should consider deer densities and forage availability simultaneously, while adopting a multi-species approach. Results varied among regions, with densities of other deer being more relevant in the south and winter severity more relevant in the north. Management data did not predict summer damage well. Since national models did not capture regional variations, we conclude that management decisions and actions need to be tailored to the regional or local scale

Browsing Damage on Scots Pine: Direct and Indirect Effects of Landscape Characteristics, Moose and Deer Populations

Reducing browsing damages from cervids (Cervidae) on economically valuable tree species is a challenging task in many countries. Apart from cervid abundance, landscape characteristics, such as forest composition, land use, forage availability and climatic conditions, may affect the degree of browsing through both direct and indirect effects. A better understanding of basic mechanisms in this complex system is needed to design efficient and convincing management strategies. Focusing on Sweden as a case, which has been widely studied using regression analyses only, we applied path analysis to test the validity of a model on the indirect and direct links between landscape characteristics, cervid populations, and browsing damages on Scots pine (Pinus sylvestris). Our results validated the tested model in which moose (Alces alces) density and pine availability directly influence browsing damages. Increasing amounts of pine forests, preferred deciduous trees, and young forest had positive direct effects on moose densities and thereby indirectly contributed to increased browsing damages. The density of smaller deer species showed no direct effect on browsing damages on pine. Path analysis corroborated our attempt to disentangle direct and indirect potential causal drivers of browsing damages and shows that the choice of statistical method may alter the understanding of mechanistic driving forces

SIMULATING SELECTIVE HARVEST AND IMPACT ON AGE STRUCTURE AND HARVEST EFFICIENCY OF MOOSE IN SWEDEN

I simulated selective harvest strategies of moose (Alces alces) using antler point restrictions and protection of cows with calves to assess the impact of these strategies on population age structure and potential harvest efficiency (proportion of allowed shooting opportunities). The post-hunt, adult bull:cow ratio was held constant throughout the simulations, but age structure of the bull cohort was allowed to vary. The simulation showed that protecting bulls with few antler points (<5) reduced the average bull age in the post-hunt population, whereas protecting bulls with more points (4 – 8) yielded a higher average age. Regardless of type, restrictions caused a measurable drop in harvest efficiency, and subsequently, substantially more hunting days to achieve the harvest quota. Only 33% and 55% of the bulls in the population were eligible for harvest under the <5 points and 4-8 points restrictions, respectively. For cows, the post-hunt, average age was unaffected when cows accompanied by calves were protected during the first 3 weeks; likewise, harvest efficiency was unaffected by harvest restrictions on cows. However, restrictions protecting reproductive cows reduced harvest efficiency of calves, making it more difficult to reach calf harvest quotas. I suggest that antler point and cow hunting restrictions be abandoned in favour of sex-differentiated harvest quotas

Forest Development and Interactions with Large Herbivores

This thesis discusses aspects of feeding habits of moose (Alces alces) and their impact on forest development. The development of forage that is available to moose was studied by sampling the amount of edible biomass on pine and birch trees. A strong relationship was found between foliage (and twig) biomass and tree diameter, which corroborates the hypothesis that sapwood area limits the amount of leaves that can be supported by a tree. The vertical distribution of crown biomass could be described with a sinusoidal function. Tree diameter, tree height, the vertical length of the crown and the physical constraints of the animal determine the amount of available food. The diet preferences of the moose result in uneven browsing patterns in forest landscapes. A managed forest area was studied with respect to twig consumption, and it was found that trees were not consumed in proportion to availability. The probability that the most preferred species (rowan, aspen and willow) would be selected for browsing was found to be about 14 times higher than the corresponding probabilities for Scots pine or downy birch, and about three times higher than for common juniper and silver birch. Spruce was strongly avoided by the moose. When the resource value of a tree was defined by both its preference value and amount of biomass we were able to explain more of the spatial distribution than if biomass was accounted for alone. By introducing browsing into an individual-based gap model (FORSKA) the long-term impact of browsing in a forest stand was studied. As browsing intensity increased, the relative abundance of preferred tree species decreased. Tree species composition was more or less linearly related to browsing intensity. Hence, the impact of browsing on tree species composition is dependent not just on browsing intensity and abiotic factors such as climate, but also on the animals' preference for different tree species. The optimal balance between browsing damage and recreational hunting was addressed by developing a simulation model. An extensive sensitivity analysis on the input parameters revealed that the most influential parameters, together explaining 72% of the variation in optimal density of herbivores, were: edible biomass produced in young pine stands, the number of days in a season that animals predominately feed on trees, the daily consumption of moose, and the effects of browsing on stand growth. Multiple use of the forest resource, i.e. combining rational forestry with recreational hunting, was found to be more beneficial than single use from a socio-economic perspective. While modelling tools for analysing the impact of large herbivores on forest stands is of interest for both ecological research and resource management, it is complicated by our limited understanding of animal behaviour and forest dynamics. In future research, trees responses' to browsing and the spatial movement of animals will be of particular interest

Forage availability for moose of young silver birch and Scots pine

Forestry in Sweden suffers from browsing damage caused by large herbivores, mainly moose (Alces alces) and roe deer (Capreolus capreolus). Silviculture affects the availability of forage for these animals, and thus the browsing pressure. A step towards modeling the response of trees or to predict browsing damage is to gain more knowledge on the availability of food in forest stands. Individual gap-models are a genre of computer models widely used in studying forest dynamics. Since few of these models include browsing effects, however, they are of limited use for evaluating the effects that silvicultural strategies have on forage availability and browsing damage. The aim of this study was to collect data useful in developing a model for describing the amounts of biomass of young birch (Betula pendula) and pine (Pinus sylvestris) trees available to moose. Birch and pines trees were harvested and were divided into different biomass fractions (leaves and twigs of different diameters). The distribution of leaf/needle and twig biomass in the crown was recorded by dividing the trees into sections. The results showed the distribution of the crown biomass to be best described by a sinusoidal model. On average, the model described 79 and 86% (pine and birch, respectively) of the variation in the different fractions. A significant relationship was found between the basal area and the amounts of both leaves and twigs of the different fractions. The biomass available for consumption increased with tree height up to a maximum of 0.6 and 1.0 kg per tree (pine and birch, respectively), 4 m in height. The correlations obtained can be used for introducing browsing into existing gap-models. (C) 2003 Elsevier B.V All rights reserved

Forest acidification and the socio-economic costs.

Abstract is not availabl

Älgbete i tid och rum

• Älgens biotopval och betesmönster är föränderliga i tid och rum – t.ex. mellan olika ungskogar och mellan år. • Tillgång och fördelning av olika foderväxter och markens produktionsförmåga påverkar dessa val. • Vanliga händelser som förändrar fodersituationen i landskapet, såsom skogsbruk, storm och brand blir därigenom viktiga för betningens och skogskadornas fördelning. • Snöförhållandena bidrar till en mellanårsvariation i betestryck och skogskador. Resultaten från skadeinventeringar blir därför svåra att använda i lokal förvaltning. • Betestrycket på tall kan förutsägas utifrån information om älgtäthet, fodertillgång och snöförhållanden, men det är svårare att förutsäga bete på vårt- och glasbjörk. • Älgen föredrar vissa trädslag framför andra. Rönn, asp och sälg löper störst risk att betas

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

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