Lars Edenius

Effects of Large Mammalian Browsers on Architecture, Biomass, and Nutrients of Woody Plants

Large generalist browsers commonly feed on many species of woody plants, which are used at different intensities and frequencies. Some plant species are used during all seasons, while others are taken only during a short period of time. We have chosen to concentrate our review on a relatively well-studied system, the large generalist herbivore the moose ( Alces alces ) and its use of and impact on some species of woody plants. By this choice, we can examine a set of mammal-plant interactions within a single environment in different seasons. As a result of our review, we conclude that there is no single coherent response of woody plants to herbivory by moose. Winter browsing and summer leaf-stripping generally lead to the following responses: decreased food resources for moose in terms of plant biomass (in some situations the response may be neutral or even slightly positive); shoot size increases after medium and high levels of winter browsing, especially for deciduous species, but shoot size decreases after summer browsing; branching of annual shoots increases after winter browsing, but decreased by summer browsing; leaf size increases after winter browsing, but the response to summer browsing is variable (no response to increase); winter browsing has a neutral or negative impact on nutrient characteristics of shoots, and fiber concentration increases; winter browsing increases leaf concentrations of K, Ca, and N, while the concentration of protein-precipitating compounds decreases; early-summer browsing decreases nitrogen concentration in leaves of the next summer, while late-summer browsing has the opposite effect, at least for 1 year. Repeated leaf-stripping during late summer, however, tends to decrease nitrogen concentration. Some of these responses (e.g., changes in plant biomass and size of food item) have the potential of being important to the herbivores that feed on the plants. As the food production of a whole tree most often decreases after browsing and some of the chemical properties are affected negatively from the animals point of view, the most logical response by the herbivores should be to avoid browsed plants. However, some studies have shown that there is a higher probability for a browsed tree than for an unbrowsed tree to be browsed 1 year later.

Potential Effects of Climate Change on Treeline Position in the Swedish Mountains

Climate change may strongly influence species distribution and, thus, the structure and function of ecosystems. This paper describes simulated changes in the position of the upper treeline in the Swedish mountains in response to predicted climate change. Data on predicted summer temperature changes, the current position of the treeline, and a digital elevation model were used to predict the position of the treeline over a 100-year timeframe. The results show the treeline advancing upward by 233-667 m, depending on the climate scenario used and location within the mountain chain. Such changes hypothetically caused a 75-85% reduction in treeless alpine heaths, with 60-93% of the remaining areas being scree slopes and boulder fields. For this change to occur, the migration rate of the trees would be in the order of 23-221 m yr -1 , which is well within published migration rates for wind-dispersed deciduous trees. The remaining alpine areas would be strongly fragmented. These drastic changes would influence all aspects of mountain ecosystems, including biodiversity conservation and human land-use patterns.

Conflict resolution by participatory management: remote sensing and GIS as tools for communicating land-use needs for reindeer herding in northern Sweden.

Abstract When seeking to resolve complex land-management issues, geographical assessment of resources that are in short supply or in dispute can aid the communication of knowledge and the understanding among and between different stakeholders. In this paper, we illustrate how remote sensing and GIS can be used to gather and compile information regarding land-use activities and patterns among reindeer herders and other land users (forestry, mining, tourism, etc) in northern Sweden. The project represents a novel user-oriented effort largely based on the work carried out by the principal end user, i.e. the reindeer herders themselves. The basis for development of land-use plans for reindeer husbandry, was the following: to collect and digitally systemize traditional ecological and landscape knowledge of reindeer habitat use; to integrate this information with results from field inventories and satellite-based vegetation classifications; to map activities of other land users. The resulting land-use plans provide information that can facilitate consultation between the reindeer herders and other stakeholders and can facilitate operational work in reindeer management. This project can serve as a model for participatory involvement and planning, bringing indigenous knowledge and advanced remote-sensing techniques together in an interactive process.

Ungulates as drivers of tree population dynamics at module and genet levels

Abstract Forest ungulates affect woody plant species in many ways, e.g. by removing shoots and leaves, stripping bark, fraying, trampling, defecation and urination. High densities of ungulates can have a profound impact on plant populations, forest structure and ecosystem processes. We focus here on plant responses at two levels of population organisation in woody plants: modules and genets. Modules are defined as leaves and winter shoots, and genets as the original zygotes. Our main concern is with boreal and temperate deciduous forests, but examples from other systems are included where appropriate. Our aims are: (1) to describe and evaluate the effect of ungulate browsers on the number and other characteristics of plant population units (modules and genets), and (2) to identify consequences of the resulting changes in module and genet populations for woody plants, the browser and the forest ecosystems. At the module level , the ungulate browsers can easily change not only the number, but also the size and quality of modules. The browser–module system is more dynamic than we commonly believe, and there is a strong seasonal effect of browsing. At medium to high ungulate densities we can expect different food selection processes and food intake rates of ungulates compared to those found at low densities. At the genet level , browsers affect the number of genets of preferred plant species, as well as their size and other qualities. Reductions in the abundance of one plant species can lead to increases in other species, followed by cascading effects involving many different biota. If species increasing in abundance differ in important respects from those being replaced (e.g. if nitrogen-fixing or deciduous trees replace non-fixing or coniferous species, respectively) there may be dramatic long-term changes in ecosystem function. Both module and genet populations respond to ungulate activities, but over somewhat different time scales: the module responses being more short-term, with apparently more dynamic components. We need to better understand the dynamics of trees at both the module and genet levels, especially at high ungulate densities, and to monitor the responses of the woody plants as well as the ungulates. A better understanding of the interactions between population dynamics of ungulates and woody plants is also required.

Impact of herbivory and competition on compensatory growth in woody plants: winter browsing by moose on Scots pine

The potential for compensatory growth in plants can depend on growth form and environmental conditions experienced by individual plants. We determined the degree to which a conifer, Scots pine (Pinus sylvestris), compensates for biomass losses. By systematically clipping current annual shoots at four different intensities during three consecutive years we simulated winter browsing by moose (Alces alces). To assess the impact of between-tree competition on compensatory growth, clipping was performed at two different tree densities. In terms of current annual shoot growth, individual pines did not overcompensate in response to clipping in any of the treatments, although a tendency towards overcompensation was observed at low clipping intensities under crowded conditions

Landscape level effects of modern forestry on bird communities in North Swedish boreal forests

We address effects of large-scale forestry on landscape structure and the structure and composition of boreal bird communities in North Sweden. Specifically, we ask: after controlling for the effect of patch size, forest age and tree species composition, is there any residual effect attributable to the reduction in area of old forest? Pairs of landscape blocks (25 by 25 km) were selected to maximize area difference in human-induced disturbance, clear-cut as opposed to semi-natural old forest.Median distance to natural edge (wetlands, open water) from randomly selected points in forest was 250 and 200 m in high and low impact landscapes, respectively, indicating a high degree of ‘natural’ fragmentation of the pristine boreal landscape in the area. By contrast, median distance to clear-cut in uncut forest was 750 and 100 m, respectively. Clear-cuts in high impact landscapes were disproportionally more common in areas with contiguous forest land than in areas with spatially disjunct forest, implicating that forestry increases natural fragmentation of the landscape by subdividing larger forest tracts.Point counts along forestry roads showed that species richness and relative abundance of forest birds were higher in landscapes with low forestry impact. These differences can partly be explained by differences in age composition of forest and composition of tree species. After controlling for patch size, forest age and tree species composition, a significant effect of forestry impact remained for Sibirian species and the Tree pipitAnthus trivialis. Our results thus imply that this group of species and the Tree pipit may be sensitive to forest fragmentation.In contrast to previous Finnish studies, we found relatively small negative effects on relative abundance of species hypothesized to be negatively affected by large-scale clear-cutting forestry. However, our picture of the present does not contradict results from Finnish long-term population studies. Five factors may account for this: 1) clear-cut areas are not permanently transformed into other land use types, 2) planted forests are not completely inhabitable for species preferring older forest, 3) the majority of species in the regional pool are habitat generalists, 4) the region studied is still extensively covered with semi-natural forest, and 5) our study area is relatively close to contiguous boreal forest in Russia, a potential source area for taiga species.

Field Test of a GPS Location System for Moose Alces alces under Scandinavian Boreal Conditions

This paper reports on field tests of an animal-borne GPS telemetry system for moose Alces alces in northern Sweden. Tests involved accuracy of locations (standard mode GPS), percentage of successful location attempts under different canopy conditions, effect of movement, and performance of the GPS telemetry system on free-ranging moose. Locational accuracy was better than 92 and 183 m 95% of the time, and better than 42 and 74 m 50% of the time, respectively, dependent on whether the GPS receiver recorded a 2- or 3-dimensional location (3 or 4 satellites used to calculate the location). Percentage of successful location attempts ranged within 69–100%, and varied inversely with over-storey canopy cover and basal area of stems. Thick canopy cover and high stem basal area reduced locational accuracy and the percentage of successful location attempts. A backpack trial indicated that movement rate of 3–4 km/hour may reduce the percentage of successful location attempts under forest canopy. On moose, approximately 75% of attempts resulted in a location, the success rate being highest during winter/spring and lowest during fall. It is concluded that GPS has a great potential in wildlife telemetry studies, but effects of movement and habitat selection have to be addressed further.

The effect of resource depletion on the feeding behaviour of a browser : winter foraging by moose on Scots pine

(1) The foraging dynamics of a browser, the moose Alces alces L. exploiting depleting resources was studied experimentally. It was hypothesized that: (a) differences in the intake of twig biomass between tree stands in early foraging sessions would tend to even out as resource depletion progressed; (b) food item selectivity within stands would decrease, and (c) bite diameters would increase with time. (2) Artificial stands, composed of one browse species or a mixture of species, were set up in a forest area. The species included were Scots pine Pinus sylvestris L., aspen Populus tremula L. and grey alder Alnus incana (L.) Moench. Special attention was paid to the analysis of the pattern of Scots pine exploitation because this tree is of commercial interest. Moose browsing was assessed by counting bites and by measuring bite diameters. (3) Initially the total consumption of twig biomass in the pine + aspen stand was twice as high as that in the other two stands. This difference remained until almost half of the available biomass in the pine + aspen stand had been consumed. Within stands the preference for aspen over pine increased over time, whereas the preference for pine over alder decreased. Bite diameter on Scots pine showed a significant decline over time. (4) Browsing on Scots pine was only slightly affected by the species composition of the tree mixtures. Browsing intensities on individual pines was positively correlated with the amounts consumed on adjacent stems.

Factors affecting browsing by moose (Alces alces L. ) on European aspen (Populus tremula L.) in a managed boreal landscape

Abstract There is considerable circumpolar concern regarding the regeneration of several tree species in the temperate and boreal landscape due to heavy browsing. We analyzed the risk of browsing on aspen (Populus tremula L.) at two different scales in a managed boreal forest in northern Sweden with one dominating browser in the system, the moose (Alces alces L.). At the stand level, we found that a high density of aspen ramets in connection to or surrounded by young forest (predominantly Scots pine Pinus sylvestris L.) attracted moose relatively more than aspen stands in mature forest and interior forest, respectively. If a stand was being used, a single aspen ramet faced the best chance of escaping browsing in a stand with a high density of aspen ramets, located far from arable land. This utilization pattern by the herbivores suggests that older forest may function as a temporal refuge for aspen regeneration in the managed boreal landscape, but this situation may change as remaining old forest stands eventually turn into young forest. Although cutting will favour aspen regeneration, our study highlights an apparent paradox, as the emerging aspen ramets will face a high browsing risk from attracted herbivores.

Patterns of Stem Damage by Moose (Alces alces) in Young Pinus sylvestris Stands in Sweden

The incidence of recent moose browsing of the main stem on young Scots pine (Pinus sylvestris L.) trees, and correlations with tree or stand characteristics, were examined using data from a large-scale survey in Sweden. On average, 10% of all Scots pine main stems showed one or more types of recent damage, with browsing of the apical leader accounting for about 75% of all damage recorded. Stripping of bark off the main stem occurred most frequently in the southern area, where site productivity is highest. Apical leader browsing was negatively correlated with height of the main stems, length of the apical leader and incidence of pre-commercial thinning, whereas bark stripping and stem breaking were positively correlated with the same variables. All types of recent stem damage correlated positively with the extent of previous stem damage and also with the extent of recent browsing of lateral shoots.