Browsing and damage inflicted by moose in young Scots pine stands subjected to high-stump precommercial thinning

In Fennoscandia, young stands of Scots pine (Pinus sylvestris L.) are intensively used by moose (Alces alces L.) during winter. We studied whether forage amounts on high-cut pines in high-stump commercial thinning influenced browsing intensity and damage incidence on retained (i.e. uncut) pine stems. High-cut pines were browsed, but to a lesser extent than retained pines. At a scale corresponding to individual feeding sites (≈40 m²), browsing intensity on retained pines was not influenced by the amount of forage on high-cut pines but was positively related to moose pellet group counts. The incidence of lower-height damage (stem breakage and bark stripping) was positively related to the amount of forage on high-cut pines, whereas higher damage (leader shoot browsing) was not. Overall browsing damage incidence on retained pines was positively related to the density of deciduous trees and negatively related to the amount of forage on retained pines. Our results suggest that although high-stump thinning supplies additional food resources for moose, larger amounts of forage on high-cut pines may increase the risk for bark stripping and stem breakage on retained trees. Further research is needed at larger spatial scales to assess the feasibility of high-stump thinning as a damage mitigation measure.     

Browsing by large herbivores on Scots pine (Pinus sylvestris) seedlings in mixture with ash (Fraxinus excelsior) or silver birch (Betula pendula)

Abstract

Food selection by large herbivores occurs at a hierarchy of scales, for example landscape, patch or plant. Several hypotheses regarding food plant selection on patch or plant level have been developed. In this cafeteria-type design field experiment, conducted during one winter immediately after planting, we tested the effect of species mixture on browsing by large herbivores (mainly roe deer) on Scots pine seedlings in mixture with seedlings of ash (highly preferred) or silver birch (less preferred). Browsing on Scots pine was not affected by species mixture, neither in terms of the number of browsed pines nor browsing intensity. Instead, browsed biomass was positively and significantly correlated to the total biomass available for browsing. Also, there were differences due to species, with ash being most browsed (44.6%), followed by Scots pine (18.9%) and silver birch (11.6%). Browsed biomass per browsed seedling, however, was largest for Scots pine. In addition, browsed seedlings were initially taller compared to unbrowsed seedlings for all species. The main management implication in this study is that the species mixture did not influence large herbivore browsing on Scots pine seedlings. Hence, removing or discouraging more (or less) attractive browse species in early stages of pine regeneration activities seems unnecessary from the point of large herbivore browsing.     

Development of Pinus sylvestris Main Stems Following Three Different Precommercial Thinning Methods in a Mixed Stand

Reducing competition by point cleaning may be an attractive alternative to conventional precommercial thinning in forestry. In this study, survival and development of main stems of Scots pine (Pinus sylvestris L.) following point cleaning were examined in a mixed stand of mainly Scots pine and birch (Betula pendula Roth and Betula pubescens Ehrh.) in northern Sweden. Treatments studied were: no precommercial thinning, conventional precommercial thinning, point cleaning of all secondary stems, and point cleaning of only the secondary stems that were higher than the main stem, within a radius of 0.8 m from the main stem, respectively. A randomised complete block design with three replicates was used. Measurements taken 13 growing seasons after these treatments showed that conventional precommercial thinning was the best treatment for retaining Scots pines as main stems. However, conventional precommercial thinning resulted in the poorest timber quality of the remaining Scots pines in terms of stem taper, thickest branch diameter and relative live crown height. In conclusion, point cleaning has to be followed by a complementary cleaning operation if the objective is to retain Scots pines as main stems in such mixed stands.     

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

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.     

Long-term browsing impact around diversionary feeding stations for moose in Southern Norway

Diversionary winter feeding of browsing ungulates is an increasingly common management practice although evidence for its efficacy to reduce excessive browsing remains ambiguous. Moreover, comparative estimates on changes in browsing pressure (proportion of available shoots browsed) following long-term winter feeding are currently lacking. We quantified spatiotemporal changes in browsing pressure of moose (Alces alces L.) on commercial and non-commercial tree species around 30 feeding stations after 15–20 years of winter feeding. The results were compared with browsing pressure indices recorded at the same feeding stations 10 years previously. We expected leader stem and lateral twig browsing to have increased over time at a fine spatial scale (≤200 m from feeding station) and to have increased in spatial extent away from feeding stations. Furthermore, we tested whether moose browsing patterns conformed to central-place foraging theory. Despite 2–3-fold higher faecal pellet group numbers in the vicinity of feeding stations, leader stem browsing increased only on the commercially valuable Norway spruce (Picea abies (L.) Karst), a species normally avoided by moose. Lateral twig browsing largely decreased within 200 m of feeding stations while at a broader scale (≤1 km from feeding stations), leader stem browsing was high on most tree species (ca. 60% of available stems browsed) as expected, Peak browsing on lateral twigs of Scots pine (Pinus sylvestris L.) occurred further from feeding stations after 15–20 years of winter feeding than 10 years earlier. Browsing pressure on active feeding stations (n = 18) was comparable to that on inactive feeding stations (n = 12), suggesting the occurrence of rebrowsing. The ability of central-place foraging theory to explain fine-scale browsing patterns around feeding stations decreased as diversionary feeding continued over time. Long-term diversionary winter feeding of moose in unproductive boreal forests has serious implications for the intensity of fine-scale browsing pressure, which may lead to resource depletion close to feeding stations followed by high browsing pressure at distances further away from feeding stations. Our study emphasizes the importance of considering the longevity of a winter feeding programme at its inception.     

Predicting lumber grade and by-product yields for Scots pine trees

The purpose of this study was to develop models for estimating yields of lumber grades and by-products of individual Scots pine (Pinus sylvestris L.) trees using stem and crown dimensions as explanatory variables. Two separate data sets were used: (1) one simulated by the process-based growth model, PipeQual, which provides information about stem form and branch properties. The model was used to predict the 3D structure of Scots pine stems from thinning regimes of varying intensity and rotation periods and (2) an empirical data set with detailed 3D measurements of stem structure. The stems were sawn using the WoodCim sawing simulator and the yields and grades of the individual sawn pieces, as well as by-products, were recorded. The sawn timber was classified on A, B, C and D-grades for side and centre boards separately (Nordic Timber grading). By-products were pulpwood, sawmill chips, sawdust and bark.     

Scarification and Seedfall affects Natural Regeneration of Scots Pine Under Two Shelterwood Densities and a Clear-cut in Southern Sweden

A study was undertaken to evaluate the effect of Scots pine (Pinus sylvestris) shelterwood density and timing of removal on the regeneration of forests with improved wood quality. This paper focuses on the effect of scarification and seedfall on the success of natural regeneration of Scots pine under two shelterwood densities and in a clear-cut. Wood quality aspects will be addressed later in the study. After 4 yrs, natural regeneration of Scots pine under a 200 stems ha^-1 shelterwood reached 90000 seedlings ha^-1, 53000 under a 160 stems ha^-1 shelterwood and 3700 in a clear-cut. The high natural regeneration under the densest shelterwood resulted from a high seedfall, slower invasion by competing vegetation, consequent prolonged recruitment and low mortality. Since mortality largely decreased for both shelterwood densities and recruitment seems to continue, the success of regeneration should be maintained in the future if proper release operations are conducted. The latter could begin when seedlings reach a height of about 0.5 m and the cover should be maintained until they reach a height of about 6 m. Therefore, it may be possible to use 200 stems ha-1 Scots pine shelterwoods in southern Sweden to obtain dense stands and thus improve wood quality (stem taper, wood density, etc.).     

Damage by pine weevil Hylobius abietis to conifer seedlings after shelterwood removal

Abstract

Pine weevil (Hylobius abietis L.) damage to seedlings after overstorey removal was investigated in a survey study in six shelterwoods in the south–central part of Sweden. The shelterwoods predominantly consisted of Scots pine, except at one site where the shelter trees mainly consisted of Norway spruce. Before final cutting, 10 plots were laid out at each site and measurements of shelter trees and marked seedlings were taken. The seedlings were examined during the 2 years after final cutting. The study showed that removal of shelter trees increases the risk of severe damage by pine weevil and the variable that was most strongly correlated with the risk was the seedling root collar diameter. Both Scots pine and Norway spruce seedlings were severely damaged by pine weevil, and most of the feeding occurred during the first year after cutting. The amount of debarked area was significantly larger for Scots pine than for Norway spruce seedlings. Vitality (growth of the leading shoot before final cutting) of the seedlings also affected the probability of damage. Seedlings with high vitality were less damaged by pine weevil than seedlings with low vitality. For Scots pine the shelterwood density before final cutting was correlated to the intensity of pine weevil feeding after cutting. In conclusion, after the final cutting of a pine or spruce shelterwood, pine weevils will probably invade the area. To avoid serious damage, Norway spruce and Scots pine seedlings should have reached a diameter of at least 10–12 mm.     

Effects of silvicultural cleaning in mixed pine‐deciduous stands on moose damage to scots pine (Pinus sylvestris)

Silvicultural cleaning is commonly carried out in young stands to control competition between conifers and deciduous tree species. However, it has been questioned whether this practice affects moose (Alces alces L.) browsing on Scots pine (Pinus sylvestris L.) with respect to damage at the stand level. In this study, moose winter browsing was examined in relation to food availability in 19 Scots pine stands divided into silviculturally cleaned and non‐cleaned blocks. Cleaning had a negative effect on moose foraging in terms of reduced density, biomass availability, and height of the deciduous tree species. The total biomass consumed by moose was significantly lower on the cleaned blocks than on the non‐cleaned ones. There were no differences between the treatments in the amounts of pine consumed and in moose damage to pines. The density or biomass available of different deciduous tree species did not explain the variation in moose browsing on pine. In conclusion, timing of silvicultural cleaning with reference to moose browsing should be taken into account. If pines are not overtopped by deciduous trees, as in the present study, silvicultural cleaning is not necessary to prevent moose damage.     

Stem damage of lodgepole pine clonal cuttings in relation to wood and fiber traits,acoustic velocity,and spiral grain

Eight clones from a 16-year-old field trial of clonal cuttings of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were analyzed for growth, growth pattern, and stem damage in the field. In addition, wood and fiber traits (acoustic velocity [AcVel] and spiral grain) were analyzed and wood density, microfibril angle, modulus of elasticity, and radial fiber diameter (FibDR) determined from SilviScan analyzes. Two clones with considerably more bent, broken, and leaning stems differed from the other clones in terms of microfibril angle and modulus of elasticity (MOE) in the outermost annual rings. FibDR and, to some extent, MOE in the outermost annual rings were negatively correlated with the frequency of bent, leaning, or broken stems, while microfibril angle (MFA) was positively correlated. AcVel was negatively correlated with both MFA and the frequency of bent, broken, and leaning stems. We conclude that AcVel could be used as an effective tool to predict severe stem damage and determine stem strength in the field instead of using costly lab-based SilviScan measurements of microfibril angle. If developed further, this approach could be used for large-scale screening of progeny tests when selecting for stem strength.     

Long-term trends in height growth of Picea obovata and Pinus sylvestris during the past 100 years in Komi Republic (north-western Russia)

Abstract

Adapting forest management practices to the changing environment of Komi Republic requires an understanding of the response of unmanaged natural forests to climatic changes. Komi Republic is a region of north-western Russia where large areas of natural boreal forest still exist. Apical growth of Scots pine (Pinus sylvestris L.) (108 trees, 529 discs) and Siberian spruce (Picea obovata Ledeb.) (88 trees, 423 discs) was analysed using stem analysis techniques. Mean apical growth curves were calculated for four zones of boreal forests in two subsequent 50 year periods starting from 1900. A statistically significant increase in height increment of 40% for Siberian spruce and 30% for Scots pine was identified from samples representing the Komi Republic. Within this region statistically significant height increment increases were found in the middle taiga zone for Siberian spruce of 240% and Scots pine of 140%, while northern taiga Siberian spruce increased by 164%. Taking into account that trees were samples in remote untouched pristine forests, the main causes of increased height increment are suggested to be climatic, which shows a large increase in temperature (0.43°C during the past 30 years) and a modest decrease in precipitation (2.2% over the past 30 years).     

Conifer leader browsing by roe deer in English upland forests: Effects of deer density and understorey vegetation

At moderate to high densities ungulates can impact negatively on forest crops and these may be managed by lethal control. In production forestry an understanding of the relationship between ungulate density, habitat-related factors and the incidence of tree damage may promote more efficient ungulate damage management than by lethal control alone. In plantation forests in the north east of England, the incidence of conifer leader browsing by roe deer (Capreolus capreolus) was positively associated with an index of deer density (at the site scale) and planted crop tree density (at the feeding patch scale) and was negatively associated with the relative abundance of palatable understorey vegetation (at the site scale). An interaction between the deer density index and palatable understorey browse abundance was positively associated with leader browsing. Coefficients from the optimal model were used to construct a browse probability surface across a matrix of values of deer dung density and palatable understorey vegetation abundance. This illustrated a very different relationship between dung density and conifer leader browsing probability across the various levels of palatable understorey vegetation abundance. From this we hypothesise that in areas of limited palatable understorey vegetation abundance, higher levels of culling may be required to achieve reductions in the incidence of conifer leader browsing than would be necessary in areas with moderate to high palatable understorey vegetation abundance. Improvements to understorey vegetation in concert with roe deer population control may enhance the efficiency of deer damage management in upland areas with nutrient-poor soils.     

Stand and site characteristics in the decline of pinus sylvestris caused by gremmeniella abietina shoot disease in a severely damaged 50‐year‐old plantation in se lapland

The role of stand and site characteristics in a 50‐year‐old, sowed Scots pine (Pinus sylvestris L.) stand on the decline of Scots pine caused by Gremmeniella abietina was studied. Treewise damage of Scots pine was modelled using stand and site variables and stepwise regression analysis. The significant variables included in the model were stand elevation from the main cold air centre and the pH of the humus layer, while the other less significant variables were the number of stems per hectare of Scots pine and Norway spruce, content of Cu and Ni in the humus layer, and the thickness of the humus layer and the A₂ horizon. The studied variables excluded from the model were the number of broad‐leaved trees per hectare, Al and Pb contents in the humus layer, and Al, Cu, Pb and Ni contents in the A₂ horizon. The results strongly suggest that the vicinity of water as well as local depressions act as vulnerable sites for Scots pine and the said vulnerability is enhanced by increased pH of the humus layer.     

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.     

Damage caused by Lygus rugulipennis Popp. (Heteroptera,Miridae), to Pinus sylvestris L. seedlings

The tarnished plant bug (Lygus rugulipennis) and occasionally L. punctatus were found to feed on pine seedlings in central Finland. Both the nymphs and adults of Lygus bugs injured the apical meristem of the seedlings. This led to the death of the apex, and the opening of the lateral buds, resulting in a seedling with multiple leaders. L. rugulipennis may also oviposit on pine seedlings and the development from egg to adult on pine alone is possible. In laboratory experiments it was shown that the main factor in the apical meristem injury is the mechanical damage caused by the bug's stylet. The feeding damage and artificial mechanical damage caused by needles to the apical meristem of pine seedlings resulted in increased numbers of multiple‐leader seedlings and reduced shoot length and dry weight of the shoot and root.     

Leader Browsing by Red and Roe Deer on Young Sitka Spruce Trees in Western Scotland I. Damage Rates and the Influence of Habitat Factors

Leader browsing was monitored for several years on some 2000trees at 14 sites in Glenbranter Forest, Argyll. We recordedtrees individually to obtain cumulative totals for browsingand other damage, and to relate incidence to height and state(i.e. whether the trees had single or multiple leaders, oldor new leaders). Rates of leader browsing peaked in late winter and also fora few weeks during the spring flush of growth; they were leastfrom mid June to September. Incidence was closely related toheight, trees from 30 to 50 cm tall suffering the most damage,while trees taller than 80 cm rarely incurred leader browsing. Annual rates of leader browsing were greatest in the secondand third year after planting but varied considerably amongsites. Newly established crops were no more damaged than second-rotationrestocked crops. Multiple regression showed that the incidenceof leader browsing was significantly negatively related to thedensity of trees <60 cm tall and to percentage cover of ericoidplants, and significantly positively related to deer presence,as measured by the accumulation of pellet groups of both deerspecies. Individual trees were browsed two to three times on averagebefore reaching a safe height, but a few trees experienced upto eight leader browsings. In recovery from browsing, treesoften produced several leaders; we found that trees with multipleleaders or new leaders were more susceptible to leader browsingthan trees with single or old leaders. So once a tree has beenbrowsed the likelihood of future browsing is increased. Received 5 December 1989.     

Seedling shoot,needle and bud development in three provenances of Pinus sylvestris and Pinus contorta cultivated in northern Sweden

The patterns of current‐year shoot, needle and terminal bud elongation in seedlings of three Scots pine (Pinus sylvestris L.) and three lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) provenances were compared during the third and fourth growing seasons after planting. Lodgepole pine produced longer shoots and buds than did Scots pine, mainly because lodgepole pine formed more stem units and elongated at a faster rate. Stem unit length and the duration of shoot and bud elongation differed relatively little between species and provenances. Lammas or polycyclic growth occurred in some lodgepole pine provenances, but not in any Scots pine provenance, and was associated with enhanced shoot elongation. Needle elongation commenced earlier, proceeded at a faster rate, and was greater in lodgepole pine than in Scots pine, but ceased about the same time in all species and provenances. The heat sum required to attain 50% of final length was lower for shoots and needles in lodgepole pine than in Scots pine, and for shoots in northern provenances than in southern ones. Mitotic activity in the apical meristem of the terminal bud, which occurred less than one week after the seedlings were free from snow, started and ceased about the same time in each species, but was higher in lodgepole pine than in Scots pine early in the shoot elongation period.     

Relationship of site and stand characteristics to Armillaria root disease incidence on ponderosa pine in the Black Hills,South Dakota

Ponderosa pine (Pinus ponderosa) in the Black Hills National Forest, SD, USA, was surveyed for Armillaria root disease (ARD). The root pathogen Armillaria ostoyae occurred on ponderosa pine seedlings, saplings, pole‐size trees and large‐diameter trees. The mean incidence of aboveground disease symptoms by stem count was low (0.2%), but in certain areas, the incidence was higher, affecting the regeneration success and tree longevity. Symptomatic ponderosa pine were in areas characterized by having higher elevation, greater annual precipitation, more seedlings, bigger large‐diameter trees and greater odds of past harvesting activity than in areas without root disease. Stump density was positively spatially correlated with root disease incidence. No particular soil type was related to disease occurrence; though, in areas with symptomatic trees, soil available water holding capacity (AWC) was greater and soil permeability was less where root disease was present. Spatial analysis confirmed the relationships found in linear correlations, with soil AWC and stump density positively and soil permeability negatively correlated with per cent infected stems ha^?1 and basal area infected.     

Functions for Biomass Estimation of Young Pinus sylvestris,Picea abies and Betula spp. from Stands in Northern Sweden with High Stand Densities

New silvicultural regimes with high within-stand competition require new functions for estimation of standing stock and growth of biomass components, since the allometry of trees is changed by light competition. This paper presents functions for estimation of the aboveground biomass dry weights for stem wood, stem bark, branches and leaves of young (diameter at breast height <10 cm) Scots pine (Pinus sylvestris L.), Norway spruce [Picea abies (L.) Karst.] and birch (Betula pendula Roth. and Betula pubescens Ehrh.) trees growing in dense mixed stands. The functions were derived from a sample consisting of 84 Scots pine, 43 Norway spruce and 66 birch trees from six stands in northern Sweden with high stand densities (>10000 st ha^-1). The logarithmically transformed power function displayed a good ability to stabilize the variance of dry weights and showed a good fit to the material (0.37< R ² <0.99). A comparison with the most commonly used biomass functions in Sweden today showed that they overestimated the weight of stem wood and branches, while the weight of foliage was underestimated. The nature of these discrepancies suggested that the precision of biomass estimations might also be improved for young trees at wider spacing.