Papers by Roger Bergström
Apex predators may buffer bottom-up driven ecosystem change, as top-down suppression may dampen h... more Apex predators may buffer bottom-up driven ecosystem change, as top-down suppression may dampen herbivore and mesopredator responses to increased resource availability. However, theory suggests that for this buffering capacity to be realized, the equilibrium abundance of apex predators must increase. This raises the question: will apex predators maintain herbivore/mesopredator limitation, if bottom-up change relaxes resource constraints? Here, we explore changes in mesopredator (red fox Vulpes vulpes) abundance over 220 years in response to eradication and recovery of an apex predator (Eurasian lynx Lynx lynx), and changes in land use and climate which are linked to resource availability. A three-step approach was used. First, recent data from Finland and Sweden were modelled to estimate linear effects of lynx density, land use and winter temperature on fox density. Second, lynx density, land use and winter temperature was estimated in a 22 650 km2 focal area in boreal and boreo-nemoral Sweden in the years 1830, 1920, 2010 and 2050. Third, the models and estimates were used to project historic and future fox densities in the focal area. Projected fox density was lowest in 1830 when lynx density was high, winters cold and the proportion of cropland low. Fox density peaked in 1920 due to lynx eradication, a mesopredator release boosted by favourable bottom-up changes - milder winters and cropland expansion. By 2010, lynx recolonization had reduced fox density, but it remained higher than in 1830, partly due to the bottom-up changes. Comparing 1830 to 2010, the contribution of top-down limitation decreased, while environment enrichment relaxed bottom-up limitation. Future scenarios indicated that by 2050, lynx density would have to increase by 79% to compensate for a projected climate driven increase in fox density. We highlight that although top-down limitation in theory can buffer bottom-up change, this requires compensatory changes in apex predator abundance. Hence apex predator recolonization/recovery to historical levels would not be sufficient to compensate for widespread changes in climate and land use, which have relaxed the resource constraints for many herbivores and mesopredators. Variation in bottom-up conditions may also contribute to context dependence in apex predator effects
Scandinavian Journal of Forest Research, 2001
... GOČRAN BERGQVIST1, ROGER BERGSTROČM2 and LARS EDENIUS3 1Holmen Skog, SE-891 80 OČ rnsköldsŨik... more ... GOČRAN BERGQVIST1, ROGER BERGSTROČM2 and LARS EDENIUS3 1Holmen Skog, SE-891 80 OČ rnsköldsŨik, Sweden, 2Research Unit, Swedish Association ... be-tween the incidence of bark stripping and length of the apical leader, in agreement with Hjelm (1995) and ...
Scandinavian Journal of Forest Research, 2001
Deciduous seedlings are valuable for the forest industry and, at the same time, often palatable f... more Deciduous seedlings are valuable for the forest industry and, at the same time, often palatable for large herbivores. Therefore, browsing on seedlings of seven deciduous tree species and on Picea abies(L.) Karst., as a reference species, was tested in a field experiment with the species presented at feeding stations. Twenty stations, each with one seedling per species, were established in each of 15 clear-cuts in southern Sweden. The planting took place in October. Depending on species, between 16 and 85% of the seedlings were browsed after one winter. The descending order, based on number of browsed seedlings, was Quercus robur L . > Alnus glutinosa (L.) Gaertn.> Fagus silvatica L.> Tilia cordata Mill.> Prunus avium L.> Betula pendula Roth> Picea abies (L.) Karst. > Fraxinus excelsior L. On 83% (range 45-100%) of the browsed seedlings the leader was damaged. On average, browsing reduced seedling hight by 32% (range 12-47%). Within species, initially taller seedlings were more often selected than shorter ones.
Scandinavian Journal of Forest Research, 2010
Old trees felled by forestry actions or natural disturbances can supply large herbivores with a s... more 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.
Polar Biology, 2010
To evaluate the movement rates of semidomesticated reindeer (Rangifer tarandus tarandus) during t... more To evaluate the movement rates of semidomesticated reindeer (Rangifer tarandus tarandus) during the bare-ground season, we used successive GPS positions from 48 female reindeer. Data were collected during the summers of 2002 and 2003 in two Sámi reindeer herding districts in the Swedish mountains, Handölsdalen, and Sirges. The movement rates were analysed at Wve diVerent time periods: over the whole season, and over the sub-seasons spring, and early summer, mid summer and early autumn. Variation in movements were analysed in relation to vegetation type, altitude, terrain ruggedness, temperature, wind speed, and proximity to hiking trails. We hypothesised that the foraging quality and diVerent weather conditions is an important factor in determining movement rates. We found that reindeer movement rates were similar between study areas and were dependent on vegetation type and on weather conditions. Studying the circadian movements, in mid summer period when daytime oestrid activity are expected to be high, the reindeer stayed at higher altitudes where food quality was low, but moved to low altitudes at night where the food quality was higher. Therefore, we suggest that oestrid activity forces the reindeer to stay in low-quality vegetation types. Reindeer movements were linked to disturbance in areas of intermediate human activity. We found that in Handölsdalen, where hikers are abundant, the movement rates of reindeer decreased closer to the trails whereas in Sirges, where hikers are less abundant, the movement rates of reindeer increased closer to the trails.
Oikos, 2005
Recent studies of ungulates have revealed that selective foraging seems to be an important mechan... more Recent studies of ungulates have revealed that selective foraging seems to be an important mechanism by which they can affect the structure and species composition of the plant community, and thus quantity (dry mass) and quality (chemical composition) of litter ...
Oikos, 2004
To investigate patterns of plant defence, a study was conducted on 13 tree species in Botswana. W... more To investigate patterns of plant defence, a study was conducted on 13 tree species in Botswana. We tested the hypotheses that (1) shoots on small, young trees are more defended than shoots at the same height on tall, mature individuals and (2) shoots within browsing height are more defended than shoots above the reach of browsers, on mature trees. Plant traits studied were total phenolics, tannin activity, nitrogen (N), acid‐detergent fibre (ADF), and degree of spinescence (in three species). We found some support for the first hypothesis. Overall young trees had a significantly higher concentration of total phenolics than mature trees and on species level these differences were significant for three of the 13 species. However, we found no differences in tannin activity, spinescence or ADF concentration between young and mature trees, and four species had higher levels of N in young trees, suggesting higher overall palatability. Contrary to our second hypothesis, shoots within brows...
The Journal of Wildlife Management, 1989
Journal of Tropical Ecology, 2004
Increased shoot growth has recurrently been recorded following real or simulated shoot browsing, ... more Increased shoot growth has recurrently been recorded following real or simulated shoot browsing, although responses may vary between different woody species. We investigated morphological responses to simulated dry-season browsing on Colophospermum mopane, Acacia tortilis, Grewia flava, Peltophorum africanum and Ziziphus mucronata, which differ in growth rate, occurrence of spines and use by mammalian herbivores. Treatment groups included a control, four clipping intensities and cutting at ground level. Responses were monitored during the following growth season on three annual shoots, located in the bottom, middle and top height interval, on each sapling. All five species showed compensatory growth responses, although no obvious relation was found between the strength of responses and growth rate or natural browsing pressure. The general pattern was an increased shoot length, shoot diameter, number of lateral shoots and shoot biomass with increased clipping intensity. These respons...
Journal of Arid Environments, 2007
We tested the theories on hierarchical foraging by large herbivores by studying selection of wood... more We tested the theories on hierarchical foraging by large herbivores by studying selection of woody browse by goats in a semi-arid savanna. In the smallest scale, we compared characteristics of woody plants browsed by observed goats with those of all woody plants available for the goats along their feeding paths. Particularly we recorded food selection in relation to plant species,
Journal for Nature Conservation, 2003
In recent decades considerable attention has been focused on plant-ungulate interactions at vario... more In recent decades considerable attention has been focused on plant-ungulate interactions at various spatial and temporal scales. The cascading effects following ungulate actions are also attracting increasing interest. Our knowledge of the effects of ungulates on plants, communities, landscapes and ecosystems is, therefore, growing. At the same time, shifts in ungulate populations (increases and decreases) in various forested parts of the world together with mounting interest in biodiversity issues have heightened management concerns about plant-ungulate interactions. This paper reviews methodologies commonly applied to the study of ungulate-induced effects at various scales. Non-experimental comparisons have long been used, while simulation and exclosure methods were developed decades ago. However, these methods have been progressively refined, the objectives of studies based on them have broadened, and the results obtained have increasingly highlighted the interactive and dynamic nature of plant-ungulate interactions. Recent research has exploited various new techniques, such as remote sensing, to gather and process data over larger spatial scales, while others, such as GIS and powerful modelling and statistical methods are opening up new ways to analyse data and present information. The nature, design and use of the various commonly used methods, as well as their potentials and limitations, are discussed.
Forest Ecology and Management, 2013
We investigated the spatial distribution of browsing and damage by moose (Alces alces) in young S... more We investigated the spatial distribution of browsing and damage by moose (Alces alces) in young Scots pine (Pinus sylvestris) stands of central Sweden. The study involved four spatial scales from landscape to individual trees and aimed at evaluating the possibilities of using selective thinning of damaged pine stands as a tool for reducing the economic losses for forestry. As expected, we found that damage on pine main stems is unevenly distributed between young pine forest stands in the landscape, but without any spatial autocorrelation at this scale. On stand scale however, there was a positive spatial autocorrelation of survey plots including pine trees damaged by moose. This relationship was strongest at short distances and ceased at around 350 m between plots. Both percent recent and previous damage on pine main stems were negatively correlated with the number of pine stems per plot, suggesting that keeping a higher pine stem density may reduce the damage levels. However, an increasing density of birch instead increased the probability of recent damage to the pines. The most important explanatory variable for recent damage on pine main stems on plot level was previous damage on the same. Therefore damaged pines that are spared during pre-commercial thinning may continue to be eaten by moose and possibly lighten the browsing pressure on previously undamaged trees. We also found that both recent damage and browsing on a particular pine enhances the risk of recent damage and browsing, respectively, also on the nearest neighboring pine. Removing damaged trees while thinning may therefore create undesired gaps within the stands. On tree level browsing of lateral shoots increased the chances of stem damages on individual trees and vice versa, suggesting that individual trees may simultaneously be affected by moose foraging in more than one way, i.e. damage may cause permanent change in stem structure, while browsing of lateral shoots may retard stem growth. In conclusion, we argue that there are means of reducing damage levels in pine stands while performing pre-commercial and commercial thinning, but that the actions have to be evaluated in relation to additional factors on the relevant spatial scale.
Forest Ecology and Management, 2003
The effects of moose rebrowsing on damage development in young Scots pine stands, ages 6±18 years... more The effects of moose rebrowsing on damage development in young Scots pine stands, ages 6±18 years, were examined using data from a large-scale survey in northern Sweden. Recent stem damage from moose browsing (browsing of the apical leader, breaking of the main stem, or stripping bark off the main stem) from the winter immediately preceding the survey was noted in 10% of the Scots pine main stems. The corresponding ®gure for previous stem damage was 17%. In total, 36% of all recorded recent stem damage occurred in previously damaged Scots pine stems, about twice as much as expected from random tree browsing. At low levels of previous stem damage the observed rebrowsing was about four times higher than that would be expected from random tree browsing. When more than 50% of all Scots pine main stems displayed previous stem damage, the observed rebrowsing rate was approximately the same as would be expected from random tree browsing. The observed rebrowsing and the rebrowsing expected from random tree browsing increased with increasing stand age. However, the rebrowsing expected from random tree browsing was considerably lower than the observed rebrowsing at all stand ages studied. Rebrowsing affects the calculation of undamaged Scots pine main stems after moose browsing. At 2% annual damage, the number of undamaged pine trees in a stand aged 18 years increased by 10% when rebrowsing was considered. At 10% annual damage no undamaged trees remained when rebrowsing was disregarded, but around 400 trees ha À1 remained when rebrowsing was taken into consideration. Taking rebrowsing into consideration makes it possible to make more accurate calculations of the ®nal effects of moose browsing on future stands.
European Journal of Forest Research, 2013
A major problem within forest industry is unwanted browsing on seedlings from mammalian herbivore... more A major problem within forest industry is unwanted browsing on seedlings from mammalian herbivores. The aim of this study was to evaluate the effects of birch bark extracts as repellents towards fallow deer. Birch bark was extracted in a conventional way with ethanol as solvent at ambient temperature and with a new method, liquid CO 2 extraction. An analysis of the ethanol-extracted birch bark showed that it contained large amounts of terpenoids, of which the most abundant was betulin. In seven different treatment trials, we used 15 individually handled fallow deer. To investigate the binary taste preferences, birch bark extract was added to food and presented in two bowls in typical two-choice tests. We found that the amount of a food type consumed during a trial and the number of shifts between food bowls were dependent on the amount of the birch extract the food contained. Concentrations of above 1 % by dry weight of birch extract acted as a repellent. In addition, such concentrations produced shorter feeding bouts by a greater willingness to change bowls. Therefore, our conclusion is that birch bark extract acts as a repellent towards fallow deer and is therefore likely to act as a repellent against other deer species. In addition, we show that birch bark extract produced by the new and more environmentally sustainable method employing liquid CO 2 mixed with ethanol has the same repellent effect as the traditional ethanol extraction. Keywords Betula Á Birch bark Á Browsing Á Fallow deer Á Plant secondary metabolites Á Repellents Communicated by G. Brazaitis.
Environmental Pollution, 1989
The 137Cs activity concentrations of muscle samples taken from moose collected from the central p... more The 137Cs activity concentrations of muscle samples taken from moose collected from the central part of Sweden were determined. Pre-Chernobyl samples had a mean 137Cs activity concentration of 23 Bq kg-1. Samples collected during the hunting season (mainly October) had, on average, 760 Bq kg-1 in 1986 and 664 Bq kg-1 in 1987. No significant differences between various muscles (neck, thigh and leg) could be seen. The correlation between ground deposition of 137 Cs and activity concentration in moose muscle was significant. There seems, however, to be other important parameters. One is the percentage oJfarmland within the home range of the moose-less farmland gives higher 137Cs activity concentrations.
Ecography, 2008
Large herbivores can affect vegetation structure and species composition as well as material and ... more Large herbivores can affect vegetation structure and species composition as well as material and energy flows in the ecosystem through their selective feeding, defecation, urination and trampling. These changes have a large potential to indirectly affect other trophic levels, but the mechanisms are poorly known. We studied the impacts of moose Alces alces browsing along a gradient of site productivity by experimentally simulating four different moose densities. Here we show that moose can affect the richness and abundance of three trophic levels in Swedish boreal forests through complex direct and indirect impacts, but in qualitatively different ways depending on how the physical habitat or food resources of a trophic level are affected. Vegetation richness had a hump‐shaped (unimodal) response to increased moose density. Leaf litter production decreased when browsing increased, which in turn depressed the abundance of flying prey for spiders. Consequently, spider abundance and rich...
Ecography, 2008
Large herbivores generally depend on and interact with a food resource that is heterogeneous at d... more Large herbivores generally depend on and interact with a food resource that is heterogeneous at different spatial scales. Plants allocate resources to rapid growth or to defence mechanisms depending on the availability of resources relative to loss of resources from herbivory. Herbivores select food and feeding habitats in order to maximize intake rate of nutrients and digestible energy, while avoiding chemical and structural deterrents. To optimize foraging, herbivores select habitats and food items in a hierarchical way, and different attracting and deterring factors may govern selection at different scales. We studied the impact of twig biting by a guild of indigenous browsers in three vegetation types in a semi‐arid savanna in Botswana. The heaviest browsing pressure was in the vegetation type richest in preferred plant species, although that type was also richest in defended species. There were large differences in relative utilization between plant species, and ranking of spec...
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Papers by Roger Bergström