Jonas Bergquist

Browsing damage by roe deer on Norway spruce seedlings planted on clearcuts of different ages. 1. Effect of slash removal, vegetation development, and roe deer density

Abstract A two-year long field experiment was established in May 1993, on clearcuts ranging in age from fresh to 4 years old at four sites in southern Sweden. The aim of the experiment was to study the effect of clearcut age and removal of slash (i.e., twigs, branches, and tops of harvested trees) on browsing damage by roe deer ( Capreolus capreolus L.) on planted Norway spruce ( Picea abies (L.) Karst) seedlings. The cover and height of the vegetation, as well as the number of plant species increased rapidly during the first two years after cutting, whereafter these variables continued to increase, although more slowly. Hairy grass ( Deshampsia flexuosa L.) made up about 90% of the vegetation cover. The nitrogen concentration of hairy grass was highest in two- and three-year old clearcuts. The height of the slash was lower on older clearcuts. Roe deer density increased with clearcut age. Browsing occurred during winter and the frequency of browsed seedlings was 31.2% in the 1993–1994 period and 24.8% in the 1994–1995 period. During both years the browsing damage tended to be highest on the one-year old clearcuts, but the effect was not statistically significant ( p =0.058). The level of damage was about equal on the clearcuts of other ages. The level of browsing damage was not correlated with the quantity or quality of associated vegetation, slash quantity, or roe deer density on the clearcuts.

Effects of roe deer browsing and site preparation on performance of planted broadleaved and conifer seedlings when using temporary fences

Abstract The effects of fencing and site preparation on performance of birch (Betula pendula Roth), oak (Quercus robur L.), pine (Pinus sylvestris L.) and spruce [Picea abies (L.) Karst.] seedlings were studied over four growing seasons in southern Sweden. The experiment was composed of four browsing treatments, from which roe deer (Capreolus capreolus L.) were excluded for 0, 12, 24 or 42 months, and four soil treatments. Natural browsing was combined with artificial browsing (clipping). It was demonstrated that browsing by roe deer could be isolated from browsing by moose (Alces alces L.) by selective fencing. Except for birch, browsing had little effect on seedling survival. Browsing reduced height growth by more than 100% for oak and pine, and more than 60% of pine seedling developed multiple stems. Except for oak, site preparation increased seedling survival. Inverting site preparation, in combination with or without fertilization, produced positive growth responses in seedlings, whereas patch scarification did not. There was no interaction between browsing and soil treatments on seedling performance. It was concluded that long-term protection against browsing by roe deer is needed for oak and pine, whereas short-term fences might be used for birch, and that spruce is relatively unaffected by browsing.

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.

Browsing damage by roe deer on Norway spruce seedlings planted on clearcuts of different ages: 2. Effect of seedling vigour

The effects of browsing damage by roe deer (Capreolus capreolus L.) on Norway spruce (Picea abies (L.) Karst) seedlings planted on clearcuts of different ages were studied in a field experiment. The experiment was established in 1993 on 0- to 4-year-old clearcuts in four sites, and seedling observations were made until May 1995. Half of the seedlings were planted in May and the other half was planted in October. Planting in two different seasons allowed the separation of the different effects of surroundings on the risk for a seedling to be browsed. Seedling vigour was estimated, using a needle colour index ranging from yellow to dark green. In addition, concentrations of nitrogen in needles and shoot axes were analysed. The needle colour index was well correlated with nitrogen concentration in both needles and shoot axes. The frequency of browsing was higher for seedlings with a dark green colour (high nitrogen concentration) than for seedlings with a light green or yellow colour (low nitrogen content). The average needle colour index was also correlated with the average frequency of browsing damage over different sites and years. Browsing damage tended to decrease with the height of surrounding vegetation, mainly owing to reduced seedling vigour, as long as the vegetation was shorter than the seedling. In cases where the vegetation was higher than the seedling, the physical protective afforded by the vegetation seemed to dominate. The needle colour index of seedlings tended to increase with height of slash which was most likely explained by a fertilising effect from decaying plant tissues. Browsing damage tended however to be reduced with increasing slash height. The increasing risk for a seedling to be browsed because of higher vigour, as a result of higher slash, seems to be balanced by the physical protection afforded by slash.

Browsing deterrent and phytotoxic effects of roe deer repellents on Pinus sylvestris and Picea abies seedlings

The abilities of eight repellents to reduce browsing damage by roe deer (Capreolus capreolus) were tested on 2‐year‐old containerized seedlings of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L.) in two field tests. The study was performed on 10 773 seedlings on 17 newly planted clearcuts in southern Sweden. The frequencies of untreated pine and spruce seedlings that had been browsed were 31% and 37%, respectively, in the first test performed during the winter of 1991–1992. In the second test, performed in the winter of 1992–1993, the frequency of browsing among untreated spruce seedlings was 70%. Gyllebo Blood meal, Gyllebo Seedling Protection, Gyllebo Granulate, I.A.‐Game Repellent, Cervacol Extra, freeze tape, fish oil and Dendrocol Extra showed significant deterrent effects. Anipel had no significant deterrent effect at the recommended dose. Anipel, fish oil, Gyllebo Blood meal and Cervacol Extra caused significant phytotoxic effects. The results of these tests should help in decidi...

Interactions among forestry regeneration treatments, plant vigour and browsing damage by deer.

In a large field experiment we studied the influence of regenerationmethods on the extent to which roe deer (Capreoluscapreolus L.) browse on spruce (Picea abies L.Karst) seedlings. Our objective was to evaluate if treatments that are good atstimulating regeneration may increase browsing damage by deer. Data werecollected between 1993 and 1995, and in the winters of 1993–94 and1994–95 the frequency of browsed seedlings was 13.2% and 13.4%,respectively. The frequency of browsing damage varied considerably betweensitesand clearcuts. Browsing damage was more frequent when the regeneration methodsincluded insecticide treatments. Among insecticide-free treatments, browsingwasheavier on scarified plots than on herbicide-treated or control plots (in whichseedlings were planted on untreated ground and given no post-plantingtreatment). Containerised seedlings were browsed more than bare-rooted ones.Neither the age of clearcut when planting, nor removal of slash, had any effecton browsing. It was demonstrated that regeneration methods that increased plantvigour (as assessed by leader growth and needle colour index) led to morebrowsing damage. Thus, our results support the plant vigour hypothesis, whichstates that many herbivores prefer to feed on vigorous plants because they aremore nutritious. However, the difference in browsing damage betweencontainerised and bare-rooted seedlings could not be explained solely by theplant vigour hypothesis.

Simulated effects of browsing on the production and economic values of Scots pine (Pinus sylvestris) stands

ABSTRACT Effects of browsing damage on Scots pine (Pinus sylvestris) production and economic value were simulated on sites ranging in fertility from relatively poor to relatively high. Effects of browsing damage on growth and survival after trees had exceeded browsing-height were estimated using data from a browsing study. Stem lists were produced when stems had reached a height of about 4 m. Individual tree data were then imported into the Heureka simulation system to generate predictions about stand production and economic value. Six browsing levels were simulated: 0, 2, 5, 10, 15 and 27% browsing damage annually. The 2% and 5% browsing levels had only minor effects on production, whilst higher browsing levels significantly reduced production. However, the effect on economic value was more pronounced and even the 2% browsing level had significant effects on estimated land expectation values. Results from this simulation may support discussions about acceptable browsing levels in young Scots pine stands.

Effects of timing, duration, and intensity of simulated browsing on Scots pine growth and stem quality

This study examines a large number of structural and growth-related responses of young Scots pine in relation to simulated browsing from large herbivores. We combined different modes of intensity, timing, and duration of clipping for nine consecutive years from 2000 to 2008. Data on tree responses were collected yearly during this period, as well as in 2011, and were analyzed using ordination techniques and generalized linear models. A key result demonstrated is the serious effects of clipping on the youngest pines. Mortality was high when clipping started the first year, indicating that the trees are vulnerable at that stage, but after that increasing intensity and duration of clipping were the main causes of mortality. Among the different treatment factors, intensity of clipping had the largest influence on altering the final growth responses, some of the quality responses, and mortality. Timing of clipping was the most important factor for explaining the occurrence of the majority of responses related to stem structure. Duration of clipping had the largest effect on the responses that included repeated-measures data, such as height development and number of stems. We discuss the long-term consequences of browsing for the trees and the implications for forest management.

Assessing effects of wildlife on forestry

The populations of moose and roe deer increased dramatically in Sweden during the latter half of the 20th century (Hornberg 1995; Cederlund and Markgren 1987; Cederlund and Liberg 1995). A significant increase in the cervine population was also observed in most other European countries during this period. The regulation of hunting, the decline in predators and changes in land use are believed to be the major causes of this population increase (Kuiters et al. 1996). Both moose and roe deer feed (browse) on young trees and can thus inflict damages on them and reduce the economic yield for the landowners (Gill 1992 ab). Although landowners can derive some benefits from game hunting, they show little tolerance for browsing damages. Most deer species are selective feeders, utilising and only certain plant species for feeding purposes (Hofmann 1989). Moose and roe deer prefer to feed on certain species of shrubs, on young trees and on herbs but avoid grasses (Cederlund et al. 1980). Forest management has a strong influence on the species composition and abundance of ground vegetation, and thus has a variety of possible alternatives influencing deer forage production to selecting between (Hannerz and Hanell 1993; Bergquist et al. 1999), although forestry today seldom utilises the selection opportunities this provides.