Bark Stripping Research Articles

The Effectiveness of Tannin on the Amount of Damage to Forest Trees and Stands Caused by Red Deer in the Western Carpathians

Damage caused by cloven-hoofed game and wild animals is a serious problem in Slovakia and neighboring countries. In 2022, the damage to forests in Slovakia was estimated at a level of almost EUR 2.9 million. Despite several implemented measures, the situation is so severe that successfully restoring some trees in some heavily attacked stands is impossible. This paper deals with the preventive elimination of damage caused by red deer in forest stands by the biological method of applying tannin-based mineral licks. Specifically, licks containing tannin obtained from the edible chestnut were used for testing. Several positive effects are attributed to tannins in developing livestock and animal fitness status. To date, however, the question of using tannins as biological agents for the possible protection of forest stands has not been addressed. Therefore, red deer damage was assessed at two localities with similar natural conditions in the central part of the Western Carpathians to explore such a possibility. After the initial sample measurement of the bark-stripping damage caused by the red deer in the autumn, mineral licks with tannin were placed in one selected study area over the winter. The levels of and differences in forest damage by deer between areas with the application of licks with tannin and without tannin were detected in spring of the following year. In the location treated with tannin, the number of damaged sample plots decreased, and the mean plot damage did not increase (no statistically significant differences were registered in mean plot damage between autumn and spring). Meanwhile, in the control location, the total amount of bark-stripped area doubled, mainly due to a statistically significant increase in mean plot damage between autumn and spring. Based on this, we conclude that tannin had a significant preventive effect and considerably reduced the extent of bark stripping. Such promising results indicate that tannin licks can effectively mitigate the problem of bark-stripping damage in areas heavily attacked by red deer.

Bite Me: Bark Stripping Showed Negligible Effect on Volume Growth of Norway Spruce in Latvia.

Over the past few decades, increasing populations of cervid species in the Baltic region have reduced the quality and vitality of cultivated Norway spruce (Picea abies (L.) Karst.) stands. This study evaluated the effect of bark stripping on the volume growth of spruce trees in Latvia. Data collection took place in two forest stands. In each stand, 20 Norway spruce trees were sampled, 10 with visible bark damage scars and 10 control trees. Stem discs were collected from control trees at specified heights (0 m, 0.5 m, 1 m, 1.3 m, and 2 m, and then at one-metre intervals up to the top) and from damaged trees at additional specific points relative to the damage. Each disc was sanded and scanned; tree ring widths were measured in 16 radial directions using WinDendro 2012a software. Annual volume growth reconstruction was performed for each tree. Changes in relative volume growth were analysed in interaction with scar parameters, tree type (damaged/control), and pre-damage volume using linear regression models. The significance of parameter interactions was assessed using analysis of variance (ANOVA). Pairwise comparisons of estimated marginal means (EMMs) were conducted using Tukey's HSD post hoc test. No significant effect of bark stripping on the total stem volume increment was detected. However, the length of bark stripping scars had a significant impact on relative volume growth in the lower parts of the stems. These findings underscore the importance of further research examining a broader spectrum of cervid damage intensity and the effects of repeated damage on tree survival and growth.

Stand-level sampling designs for bark stripping caused by red deer (Cervus elaphus L.): simulation studies based on nine fully censused stands

AbstractPrecise assessment of bark stripping damage is of high economic importance, since bark stripping makes wood unusable for saw timber and it is important for compensation payments for game damage. Bark stripping is clustered and decreases with increasing tree diameter, so that common forest inventories, optimized for assessing timber production variables such as standing timber volume, do not provide adequately precise estimates of bark stripping damage. In this study we analysed different sampling designs (random sampling, systematic sampling), tree selection methods (fixed radius plot, angle count sampling) and number of plots and plot sizes (plot radius: 2–20 m; basal area factor: 1–6m2/ha) for bark stripping assessment. The analysis is based on simulation studies in 9 fully censused stands (9026 trees). Simulations were done for actually assessed damage and randomly distributed damage and each scenario was repeated 100 times with different random points or different random grid locations. Systematic sampling was considerably more precise than random sampling in both scenarios. Sampling intensities to attain a standard error of 10% ranged between 12 and 18% dependent on the plot size. For a given sampling intensity, precision increased with decreasing plot size or increasing basal area factor. This implies, however, a large number of plots to be measured, which is expensive, when travel costs are high. Differences between tree selection by fixed radius plots or angle count sampling were minor. For bark stripping damage, we recommend sampling with fixed radius plots with a radius of 4–6 m and the measurement of approximately 230 or 150 plots, respectively.

Fungal Presence and Changes of Wood Structure in Bark Stripping Wounds Made by Red Deer (Cervus elaphus L.) on Stems of Fraxinus angustifolia (Vahl)

Narrow-leaved ash (Fraxinus angustifolia Vahl), a highly valued European forest tree species, has been severely affected by a large-scale decline, which is most probably driven by a complex of multiple interacting factors including fungi, which contribute to and accelerate this process. Red deer (Cervus elaphus L.) can be considered as one of the contributing factors, as they inflict damage on the stems of young trees by stripping the bark. These wounds not only represent suitable entry points for fungi which can cause tissue necroses and decomposition, they can lead to changes in the wood structure as well. The aims of this research were to analyze chosen parameters of bark stripping wounds in narrow-leaved ash stands, identify fungi present in the tissue exposed by wounding, and inspect the effect of wounding on the wood structure. Bark stripping was observed on ash trees from 2 cm up to 18 cm of DBH and between 0.1 m and 1.9 m of stem height. The most susceptible trees were those with an average DBH of 5 ± 2.5 cm. On most of the ash trees (51%), one-third to two-thirds of the circumference was damaged. In wounded tissue, 174 fungal isolates were found, most of which belonged to known endophytic fungi from the genera Trichoderma, Fusarium, and Clonostachys. It was observed that earlywood cells in the wounding zone had narrower lumens compared to ones in adjacent healthy zone with regard to different trees and stem heights.

How to recognise a healthy forest: Perspectives from private forest managers in Britain

The managers of private forests have critical roles in responding to forest health challenges. Basic knowledge of how they interpret and understand the health of their trees is, however, very sparse. Via an online survey of private forest managers in Britain, we reveal the basic characteristics of this group's understandings of tree and forest health both in general and, more specifically, in relation to the health (and ill health) of oak species. The survey generated 441 valid responses – from forest owners, forestry agents and other professionals. The majority of our respondents believe the forest(s) they manage to be healthy or very healthy, although vulnerable to future threats. We identify key themes within managers' understandings of the factors that promote tree health, and describe the visual signs of good- and ill-health used by them as indicators. Oak trees and oak woodlands were similarly judged to be healthy currently, but again this positivity was set against a sense of vulnerability and potential future decline. The biggest threat to oaks was considered to be browsing and bark stripping by mammals – a very long standing concern – rather than more recently emergent threats. Through this research we provide a clear sense of how forest managers think about, and make judgements on, the health of their trees and forests. This understanding needs to inform the increasing efforts by the forestry sector in engaging private forest managers in forest protection.

Predicting forest damage using relative abundance of multiple deer species and national forest inventory data

Deer, both native and non-native, can damage forest ecosystems when occurring at high densities, impacting biodiversity and ecological functioning at multiple levels. The ecological drivers of forest damage and the roles of single and multiple co-occurring deer species are not well understood due to a scarcity of simultaneous high resolution multi-species deer distribution and forest damage data. Here, we aimed to disentangle the relationship between forest damage, forest characteristics and the roles deer play in damaging forest ecosystems. To achieve this, we integrated novel high resolution deer distribution data for multiple deer species (native and non-native) with forest inventory data collected in 1,681 sampling stations across Ireland to (i) understand environmental drivers of damage, and (ii) demonstrate the utility of this approach in providing predicted damage scenarios based on the relative abundance of different co-occurring deer species. We found that forest characteristics played a key role in the severity and type of damage risk that deer posed. All damage types were more prevalent in forests with greater tree densities where deer are more likely to find refuge from human disturbance. Bark stripping damage was more prevalent in mature forests with high tree diversity and ground level flora (e.g., bryophytes, herbs, and shrubs). Similarly, browsing damage was more prevalent in forests with greater tree richness but with understorey vegetation dominated by grass and ferns. Fraying damage was more common in mixed woodlands with understories dominated by bryophytes and grass. Crucially, we found that type and severity of forest damage were shaped by the interaction of multiple deer species occurring simultaneously, particularly at high densities, suggesting subtle inter-species competition and exclusion/partition dynamics that require further investigation to understand the ecological mechanism. Finally, we developed predicted damage scenarios to precisely predict where damage is likely to occur based on relative densities of two co-occurring deer species. We predicted high levels of damage in sika and/or red deer hotspots, matching areas of highly concentrated deer distributions. Our study highlights the ecological drivers of deer-caused forest damage, the role that co-occurring native and non-native deer species may play on forest damage within a large spatial scale and describes an approach that can be replicated in other countries with similar datasets. By combining reliable species distribution models with the national forest inventory data, we can now provide a useful tool for practitioners to help alleviate and mitigate forest damage and human wildlife conflicts.

Fungi Inhabiting Stem Wounds of Quercus robur following Bark Stripping by Deer Animals

We investigated fungal communities in oak wounds to determine how fungal species richness and community composition changes depending on the age of wounds. The sampling of wood cores was carried out from 10-, 20-, 30-, 40-, and 50-year-old wounds. The fungal community was analyzed using high-throughput sequencing of ITS2 rDNA. Sequence analysis showed the presence of 534 fungal OTUs, which were 83.4% Ascomycota, 16.3% Basidiomycota, and 0.3% Mucoromycota. The fungal OTU richness changed over time: it increased as compared between 10- and 20-year-old wounds, remained similar in 20- to 40-year-old wounds, and decreased in 50-year-old wounds. The fungal community composition also changed over time with the largest differences detected between 10-year-old and older wounds (p < 0.001). The most common representatives of Basidiomycota were Laetiporus sulphureus (34.7%), Mycena galericulata (17.0%), and Cylindrobasidium evolvens (6.5%), and the most common of Ascomycota were Aposphaeria corallinolutea (13.6%), Sclerostagonospora cycadis (7.6%), and Cadophora malorum (5.8%). In conclusion, oak wounds of different ages were colonized by a high diversity of fungi including oak-associated species. Fungal communities in oak wounds underwent qualitative and quantitative changes over time, which led to the gradual shift from fungal generalists in young wounds to oak specialists in older wounds.

Bark stripping damage by red deer (Cervus elaphus L.): assessing the spatial distribution on the stand level using generalised additive models

Bark stripping damage by red deer (Cervus elaphus L.): assessing the spatial distribution on the stand level using generalised additive models

Bark Stripping by Deer Disturbs Regeneration in a Larix–Abies Subalpine Forest

Deer can slow the natural succession of forests from light-demanding to shade-tolerant species or even keep forests in an early successional stage. This study examined the effects of bark stripping by deer (Cervus nippon) on the stand dynamics in a Larix kaempferi–Abies veitchii subalpine forest in central Japan. Bark stripping by C. nippon was concentrated on smaller A. veitchii individuals, and the number of stems with stripped bark increased over the study period (2007–2019). Unlike other tree species in the study plot, the main mortality factor of A. veitchii was bark stripping. In addition, the mortality factors of A. veitchii clearly differed among tree sizes: smaller A. veitchii trees (diameter at breast height ≤ 15 cm) died owing mainly to bark stripping, whereas larger individuals died owing mainly to uprooting, snapping, and standing dead trees. At this forest site, bark-stripping deer preferred the late-successional species (A. veitchii) to the early-successional species (L. kaempferi), and consequently, the progress of succession was disturbed.

Development of a Monitoring Method Using UAVs That Can Detect the Occurrence of Bark Stripping by Deer

The occurrence of bark stripping associated with increased deer densities can severely damage forests. Identifying trends in bark stripping is crucial for forest management, but such data are often difficult to obtain through field surveys. Therefore, this study aimed to develop an efficient monitoring method using unmanned aerial vehicles (UAVs) that can detect the occurrence of bark stripping and enable long-term monitoring. The area around the Ochiai Pass in Higashi-Iya Ochiai, Miyoshi City, Tokushima Prefecture, Japan, was selected as the study area for the survey of Abies homolepis, which was found to be significantly bark-stripped by deer in the field. The location and root diameter of A. homolepis were measured, and the percentages of bark stripping and tree growth were visually determined. Simultaneously, normalized difference vegetation index (NDVI) and visible light orthomosaic images were produced using a UAV. A canopy polygon of A. homolepis was created, and the average value of the NDVI within the polygon was calculated. Where the bark stripping rate at the root edge was greater than 75%, the number of “partially dead” and “dead” trees increased significantly, indicating that bark stripping by deer was the primary cause of the death of A. homolepis in Ochiai Pass. In addition, the mean value of the NDVI was significantly lower, with a bark stripping rate of 75% or higher, indicating that the NDVI of the canopy of A. homolepis can be used to estimate individuals with a high bark stripping rate at the root tips, that is, those with a high probability of mortality. Furthermore, by extrapolating the results of the tree-by-tree survey to the nontarget A. homolepis, we detected 46 (8%) A. homolepis with an average NDVI value of 0.8 or less (i.e., those with a bark stripping ratio of 75% or higher and a high probability of mortality). Therefore, the utilization of remote sensing technology via UAVs, as demonstrated in this study, proves to be a potent means for monitoring the incidence of bark stripping.

The sustainability of timber and biomass harvest in perspective of forest nutrient uptake and nutrient stocks

The sustainability of tree harvest is questioned since harvest results in increased nutrient losses which may reduce nutrient stocks in forest soils, particularly in forests on acidified and poor soils with low base saturation. We used a new forest experiment to quantify nutrient stocks and nutrient uptake rates in mature forest stands, and to assess the forest nutrient balance in relation to different forest management scenarios: clearcutting, shelterwood and thinning; and whole-tree harvest (WTH), stem-only harvest (SOH) and wood only harvest (WOH, with on-site bark stripping). Forests were dominated by trees of Fagus sylvatica, Pseudotsuga Menziesii or Pinus sylvestris, all situated on poor, acidified soils.We measured forest biomass and nutrient stocks based on destructive sampling of fifteen mature trees per species and by using new, calibrated allometric relationships. Aboveground stocks of N, P, S, K, Ca, Mg, Mn, Cu, Fe and Zn were calculated for foliage, branches, stem bark and stem wood. Annual forest growth and nutrient uptake were determined using tree ring measures and allometric relationships. Organic layer nutrient stocks and available nutrients in the mineral soil were determined following intensive soil sampling.Stands of beech, Douglas fir and Scots pine differed in aboveground biomass and nutrient stocks, with highest biomass stocks in Douglas fir. However, beech stands had the highest aboveground nutrient stocks, nutrient uptake rates and nutrient losses following harvest, followed by Scots pine. Organic layer nutrient stocks generally exceeded aboveground nutrient stocks, except for the base cations and Mn. Compared to SOH, WTH increased nutrient export between 66% (Douglas fir) up to 100% (Scots pine), while WOH decreased the nutrient export between 23% (beech) up to 41% (Douglas fir).High aboveground base cation and Mn stocks indicate potential long-term threats to forest nutrition if trees are harvested. However, in Douglas fir stands, nutrient losses through SOH may fully recover when using rotation periods of 80 years. Contrary, negative Ca balances are predicted when applying SOH in beech and Scots pine, since Ca stocks are potentially depleted within 2 final fellings. WTH poses, regardless of the species, potential threats for sustainable biomass harvest as nutrients cannot be recovered using common rotation periods. WOH conserves nutrients within the forest posing opportunities for sustainable biomass harvest. For similar temperate forest on acidified, sandy soils, we therefore recommend to limit tree harvest depending on the tree species, and to avoid WTH and consider WOH to better conserve critical nutrients required for long-term forest recovery.

Do Large Herbivores Have an Important Role in Initiating Tree Cavities Used by Hole-Nesting Birds in European Forests?

Tree cavities are an essential resource for cavity-dwelling mammals, birds, invertebrates and fungi, and so are important for maintaining forest biodiversity. In North American forests, woodpeckers (Picidae) play a keystone role in cavity creation by excavating holes. However, in European forests many hole-nesting songbirds rely on non-excavated cavities that are formed by fungal decay and compartmentalization after tree damage. Several factors are recognised in initiating non-excavated cavities that are used by hole-nesting birds, including loss of a tree branch or stem breakage, but this topic is poorly studied. Here, we propose that bark stripping by large herbivores (e.g. Red Deer Cervus elaphus and European Bison Bison bonasus) could be another important, and previously overlooked, mechanism for initiating tree cavities that are used by hole-nesting birds. We suggest that, after the initial damage from herbivore bark-stripping, fungal decay can create specific elongated, slit-like cavities, which are particularly important as nest sites for some common forest songbirds. We outline this idea using original observations and evidence from the literature, primarily from the primeval forest in Poland's Białowieża National Park. We also use studies from elsewhere in Europe to show a generally low usage of slit cavities by birds where large herbivores are scarce or absent. We suggest that restoring such animals in European forests could help to restore the abundance and diversity of the tree cavity resource for hole-dwelling species. We encourage future research to investigate this proposal of large herbivores being important agents of tree cavity formation that could enhance biodiversity.

Assessing the damage caused by deer on young trees in a Sugi (Cryptomeria japonica) plantation based on field signs

ABSTRACT Predicting the level of damage by deer browsing in young plantations is important for considering damage control measures. In this study, we examined a method for assessing the level of deer damage in young Sugi (Cryptomeria japonica) plantations with deer-proof fences by observing field signs of deer. First, a questionnaire survey was conducted to obtain information about the damage by deer browsing on planted trees and the extent of field signs, such as browsing marks and deer fecal pellets around the young plantations. The extent of field signs was recorded as qualitative data (i.e. “None”, “A few”, and “Many”). A multiple correspondence analysis (MCA) revealed a relationship between the extent of deer damage in young plantations and the presence of five field signs (browsing marks, bark stripping marks, fecal pellets, trails and tracks) around the young plantations. Based on coordinate values of each field sign obtained using the MCA, the extent of each field sign was scored, and the total value was calculated as the deer impact score (DISco). When the relationship between the DISco and the extent of deer damage to planted trees was subjected to a logistic regression analysis (LRA), the DISco was found to be a significant explanatory variable and the LRA was an effective model (AUC of 0.7809 and 0.7048, respectively) for predicting the probability of stand damage and High stand damage. Therefore, the DISco was shown to be an effective tool for assessing the damage risk of deer in young Sugi plantations with deer-proof fences.

Monitoring reintroduciranog jelena običnog na području Tare (Zapadna Srbija)

The modern approach in the development of programs for the reintroduction of red deer was applied for the first time in Serbia. We compared the most important planned and implemented activities in the period 2018-2021, and assessed the results achieved in the Mt. Tara area. The plan was to hold the red deer (5♂ + 15♀) in the acclimatisation enclosure for several months and release them into the selected favourable area (150 km<sup>2</sup>) during three consecutive years. Bark stripping occurred mainly on thinner common hazel stems of coppice origin (≤ 9.9 cm). Total mortality among the 72 red deer that were transported to the acclimatisation enclosure was 8.3%. The longest movement of a 4-year-old female (held for 15 weeks) was 24 km. During the study period, no bark stripping was observed outside the acclimatization enclosure, nor were any deaths of the released red deer registered. In the period 2019-2021, 74 red deer were released from the acclimatization enclosure into the Mt. Tara area, which is about 60% of the estimated capacity of the selected favourable area.

Bark stripping behaviour by a large-sized rodent, the crested porcupine, as an adaptation to climate change

Bark stripping behaviour by a large-sized rodent, the crested porcupine, as an adaptation to climate change

Genomic selection for resistance to mammalian bark stripping and associated chemical compounds in radiata pine.

The integration of genomic data into genetic evaluations can facilitate the rapid selection of superior genotypes and accelerate the breeding cycle in trees. In this study, 390 trees from 74 control-pollinated families were genotyped using a 36K Axiom SNP array. A total of 15,624 high-quality SNPs were used to develop genomic prediction models for mammalian bark stripping, tree height, and selected primary and secondary chemical compounds in the bark. Genetic parameters from different genomic prediction methods-single-trait best linear unbiased prediction based on a marker-based relationship matrix (genomic best linear unbiased prediction), multitrait single-step genomic best linear unbiased prediction, which integrated the marker-based and pedigree-based relationship matrices (single-step genomic best linear unbiased prediction) and the single-trait generalized ridge regression-were compared to equivalent single- or multitrait pedigree-based approaches (ABLUP). The influence of the statistical distribution of data on the genetic parameters was assessed. Results indicated that the heritability estimates were increased nearly 2-fold with genomic models compared to the equivalent pedigree-based models. Predictive accuracy of the single-step genomic best linear unbiased prediction was higher than the ABLUP for most traits. Allowing for heterogeneity in marker effects through the use of generalized ridge regression did not markedly improve predictive ability over genomic best linear unbiased prediction, arguing that most of the chemical traits are modulated by many genes with small effects. Overall, the traits with low pedigree-based heritability benefited more from genomic models compared to the traits with high pedigree-based heritability. There was no evidence that data skewness or the presence of outliers affected the genomic or pedigree-based genetic estimates.

African Elephant (Loxodonta africana) Impact on Selected Tree Species and Assessment of PiosphereGradients in Venetia-limpopo Nature Reserve

Trees utilised by elephants often undergo a significant amount of damage compared to trees utilised byother browsers. Woody plants play a crucial role in plant community dynamics, species composition, andthe savannah system’s functioning. As drivers ofecosystems, elephants are capable of transforming habitatsin terms of structure and species composition. In this paper, the damage caused by elephants on differentselected tree species in Venetia-Limpopo Nature Reserve was studied following a field-based approach.Field data collected for trees included the species name, GPS location, tree height class, extent, and type ofdamage resulting from elephant foraging. The Normalized Difference Vegetation Index (NDVI) was usedto evaluate vegetation’s vigour using Landsat-5 imagery. A Multiple Ring Buffer Tool was used to extractmean NDVI values of buffer rings spread around waterholes at 400-metre intervals. The impact on woodyvegetation along the vegetation gradient, ‘Piosphere’, was evaluated. NDVI values extracted for the differentyears indicate that the impact on woody vegetationdegradation along the Piosphere gradient is negligible.There was no statistically significant relationship (Pearson correlation r3= –0.500, P = 0.391), trend or patternbetween the number of damaged trees and the type of damage. Different trees at different height classeswere utilised inconsistently by elephants. The dominant (45%) type of damage was for Broken Main Stem(BMS), with the lowest (1%) damage being for BarkStripping (BS). Overall, there was a statistically significantdifference (Pearson correlation r3= 0.973, P = 0.146) between the number of trees selected by elephants inthe various height classes. Trees between 3 m and 4 mwere the most selected and the impact seemed to bestabilising at these tree heights. Additional studies need to be focused on the recruitment rates of elephantforaged trees in the reserve to prevent local extirpation of these species in the future.

The Effect of Bark Stripping by Deer (Cervus elaphus L.) on Biometric Parameters of the Scots Pine (Pinus sylvestris L.)

Bark stripping by red deer (Cervus elaphus L.) is one of the most acute instances of damage wrought by these animals in a forest. Because of its location, bark stripping causes damage to the thickest and most valuable part of the tree trunk, which lowers the quality of the wood due to technical flaws. The research was conducted in 25 sampling sites of pine stands aged 35 years in a mixed, fresh forest habitat in south-western Poland. The study was aimed at assessing the influence of bark damage by deer on biometric parameters of pine stands (Pinus sylvestris L.). The assessment involved the diameter at breast height, height, basal area and volume of the tree stands. The results revealed a strong deer-specific pressure on the analysed pine stands. The share of bark stripped trees ranged from 65% to 96%. The number of bark damage instances (NBDI) on a given tree was found to significantly affect its diameter at breast height. The strip-damaged trees had breast height diameters lower by 23% on average, and their mean height was lower by 8.7% as compared with the trees without damage. The mean reduction in basal area increments (G1.3) of the trees was identified at 39%. In a similar way to the diameter at breast height and the basal area, the losses in tree stand volume growth caused by deer stripping were significant and oscillated at 41%.

The Effect of Beech (Fagus sylvatica L.) Bark Stripping by Deer on Depreciation of Wood

The aim of the study was to analyse the changes in the infection rate development inside the beech stem as a result of browsing by deer (Cervus elaphus). The research materials were collected from three research plots located in the Polanów Forest Inspectorate from March to April 2020. For the study, 80 beech trees were selected, for which the size of the fallow tree, the percentage of the section taken from its centre infected with rot, and the number of years passed since the tree was wounded were determined. The study shows that the infection affects only the rings formed before the tree was injured. The average size of stem rot was 7.75% of its area, and it spread at the rate of 2.52% of the cross-sectional area per year. The analysis of the obtained results proved that both the size of the wound (splits) and the time elapsed since the tree was damaged are significantly correlated with each other. It is also possible to build a model for estimating the size of decay in stunted beech trees based on easy-to-determine predictors, such as maximum wound width and elapsed time since tree damage.

Nutrient balancing or spring flush – What determines spruce bark stripping level by red deer?

The distribution and population density of red deer (Cervus elaphus) are increasing in several regions of Europe. The deer may cause severe damage in commercial forestry and agriculture. Bark stripping is the main problem in forests, especially on Norway spruce (Picea abies), and is thought to mostly occur during winter when other forage is scarce. It has been suggested that an imbalance in the nutrient intake, and especially a diet including high amounts of easily-digestible macronutrients, such as agricultural crops, can lead to an increased urge to consume bark. Feeding on brassicas, for example rapeseed (Brassica napus) might have this effect. The aim with this study was to investigate the relationship between intake of rapeseed and bark stripping on Norway spruce by red deer during early spring. We did this by a controlled feeding experiment with four groups of captive red deer in southern Sweden. All groups were given spruce logs every week, while only two groups had access to freshly harvested rapeseed plants. In addition, influence of air temperature and forage nutritional composition was taken into account. Our results show that red deer bark stripping can be considerable not only during winter but also during spring green-up. We found no significant influence of rapeseed on bark stripping performed by the deer. However, at a threshold temperature, deer suddenly started to ingest large amounts of bark biomass, coinciding with a significant change in the bark’s concentration of starch. We suggest that the lack of effect of rapeseed feeding can partly be explained by overshadowing effects caused by such seasonal changes of bark characteristics, and partly by the fact that the rapeseed plants in our study contained lower than expected concentrations of easily-digestible macronutrients (apart from protein). We conclude that the risk of damage on spruce can be especially high during certain periods, something that is important to consider when mitigating bark stripping. However, several interactive effects are involved and must be considered in order to more efficiently mitigate damage.