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Intensity of red deer browsing on young rowans differs between freshly-felled and standing individuals
Forest Ecology and Management 429 (2018) 511–519
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Intensity of red deer browsing on young rowans differs between freshlyfelled and standing individuals
T
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Bohdan Konôpkaa,b, , Jozef Pajtíka, Lisa A. Shipleyc a
National Forest Centre, Forest Research Institute, T.G. Masaryka 2175/22, 960 92 Zvolen, Slovakia Czech University of Life Science, Faculty of Forestry and Wood Sciences, Kamýcká 129, 165 00 Praha – Suchdol, Czech Republic c Washington State University, School of the Environment, Pullman 99164-2812, USA b
A R T I C LE I N FO
A B S T R A C T
Keywords: Cervus elaphus Sorbus aucuparia Herbivory Bark stripping Stand cleaning Slovakia
Because red deer (Cervus elaphus) forage extensively on woody plants, browsing is a serious problem in forest stands especially in initial growth stages. In Slovakia, rowans (Sorbus aucuparia) are the most attractive tree species for red deer, and when present, they may serve to divert the attention of foraging red deer from commercial forest stands. In this study we compared the extent of herbivory by red deer on standing and freshlyfelled rowans within a mixed conifer forest. We quantified the biomass of stem bark, branch bark and whole branches consumed by red deer on 60 rowans between 200 and 600 cm tall within young stands that regenerated after a large scale windstorm in the Tatra National Park, Northern Slovakia. We calculated the dry biomass of browsed branches using allometric relationships with branch diameter and browsed bark biomass from the product of the area of consumed bark and specific surface mass of bark. We found that the extent and intensity of browsing was much higher on felled than standing rowans. The number of patches of stripped bark on stems was twice as high (12 ± 6 bites/stem) on felled than on standing trees (6 ± 2 bites/stem). Similarly, red deer consumed more total biomass (i.e., bark stripping on both stem and branches and browsed whole branches) from felled (45 ± 41 g) than standing (28 ± 22 g) rowans. Red deer consumed more mass from stem bark than branches. Total browsed mass on trees (especially on felled ones) increased with their height. Based on our findings, we recommend cutting rowans after most trees exceed 500 cm in height and leaving them in the site. However, if rowans have been intensively damaged by browsing and the forage potential of the stem bark and branches is reduced, trees can be felled before they reach 500 cm. We concluded that cut timing and after-cut arrangement of rowans, and likely other non-commercial tree species attractive to red deer, may substantially mitigate red deer browsing on commercial tree species in young stands.
1. Introduction Although classified as mixed feeders because they are able to consume large amounts of both graminoids and woody plants (i.e., browse), red deer (Cervus elaphus) consume diets of predominately browse within many European forests (e.g., up to 90% seasonally, Finďo and Petráš, 2007; Jamrozy, 1980; Homolka, 1990). Because of their large size (males often weigh > 200 kg; Červený et al., 2013) and high densities in many areas (Holá et al., 2016; Konôpka et al., 2014), browsing by red deer on young trees can have a substantial effect on forest regeneration (Latham et al., 1999; Čermák et al., 2009), with damage exceeding that of other wild herbivores such as roe deer (Capreolus capreolus; Prokešová, 2004) and fallow deer (Dama dama; Moore et al., 2000). Red deer damage young trees by browsing shoots, foliage, and small branches, whereas larger trees are damaged mainly through ⁎
bark stripping (e.g., Konôpka et al., 2012). In Slovakia, data from the National Forest Inventory collected in 2015–2016 (Šebeň, 2017) showed that approximately one third of all trees up to 10 years old were affected by browsing by wild herbivores. In general, these effects are greatest in young even-aged and often post-disturbance forests, and can seriously reduce the economic feasibility of tree planting (Gill, 1992; Barančeková et al., 2007). In Slovakia, forest managers have attempted to mitigate damage by red deer and other wild herbivores using techniques such as protecting individual trees using olfactory repellents or placing plastic caps on the tree terminus and protecting groups of trees using fencing (Finďo and Petráš, 2007). However, these techniques are expensive and time-consuming to build and maintain, thus the use of fencing and barriers has declined over the last two decades (Ministry of Agriculture and Rural Development of the Slovak Republic, 2017). During the same time
Corresponding author at: National Forest Centre, Forest Research Institute, T.G. Masaryka 2175/22, 960 92 Zvolen, Slovakia. E-mail address: [email protected] (B. Konôpka).
https://doi.org/10.1016/j.foreco.2018.07.048 Received 23 May 2018; Received in revised form 23 July 2018; Accepted 27 July 2018 0378-1127/ © 2018 Elsevier B.V. All rights reserved.
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Calamagrostis sp., Avenella flexuosa, Luzula luzuloides), forbs (e.g., Epilobium angustifolium, Senecio nemorensis, Rubus idaeus) and shrubs (mostly Vaccinium myrtillus, Sambucus racemosa). The population density of red deer in the TNP in 2015 was estimated at 21 individuals per 1000 ha, a 75% increase in estimates made in a before the wind disaster episode (i.e., 12 individuals per 1000 ha in the reference year 2000; Headquarters of the TNP, pers comm.).
period, red deer populations have increased forest management and game management (Konôpka et al., 2015a), as has been reported in other European countries (Burbaite and Csányi, 2010; Schulze et al., 2014; Holá et al., 2016). Although reducing red deer populations has the potential to reduce tree damage in some forests, this measure is not equally supported by different interest groups (e.g., hunters, environmentalists, forest owners, farmers) in many countries such as Slovakia (Finďo and Petráš, 2007). Therefore, alternative methods for reducing forest damage by red deer are needed. One possibility is to purposely boost alternative desirable food to lure red deer away from commercially-valuable tree species. This might be accomplished by promoting mixed stands containing both commercially-valuable tree species and tree species attractive to herbivores but with low economic value (Čermák et al., 2009). On such attractive but low value species is rowan (Sorbus aucuparia), a deciduous tree that is a highly preferred forage by red deer and other large herbivores (e.g., Heroldová et al., 2003; Motta, 2003; Myking et al., 2013). Rowan naturally regenerates in post-disturbance areas within Slovakian forests (Konôpka et al., 2015b; Pajtík et al., 2015). In managed forests, rowan trees are usually cut down within the cleaning (i.e., removal of less desirable individuals during the sapling stage to prevent them from over-topping favoured saplings) at around 10 years post-regeneration or in the first thinning at about 20 years post-regeneration and left in the stands. Therefore, the standing or felled rowans (∼1 year post-felling) may provide a temporary attractive alternative to the commercial species, allowing the commercial species to grow past their most vulnerable stage (i.e., stand rotation time is about 90 years for coniferous species and 110 years for hardwood broadleaved species). However, as yet the relative accessibility and attractiveness of standing and felled rowans as deer forage has not been evaluated. In this study we compared consumption of felled and live standing rowans by free-ranging red deer recorded 11 years after a windstorm disturbance (i.e., trees were < 11 years old). We hypothesized that red deer would browse more intensely on felled rowan trees than live standing trees because they would take less effort to acquire bark and branch biomass and a greater proportion of the tree would be accessible to red deer. Moreover, we expected that differences in intensity of damage on stems and crowns between standing and felled individuals would be positively related to tree height because the taller the tree, the greater proportion of unreachable mass to total tree mass in standing but not in felled individuals. Understanding the value of standing and felled rowans to red deer will allow us to frame recommendations on timing of cut and after cut arrangement of rowans.
2.2. Estimation of basic stand characteristics To describe stand condition on the site (49° 08′ N and 20° 13′ E) located close to the Starý Smokovec village, we established a research transect in the early spring 2015. The site belongs to the Smokovce Protective Unit managed by the State Forests of the TNP. Orientation of the belt transect was from Northwest to Southeast at elevations between 925 and 970 m. The transect was 4 m wide and 300 m long. Along the transect, we established 25 plots of 4 × 4 m spaced 8 m apart to increase independence of plots. We measured height, stem diameter at 130 cm from the ground (DBH, hereafter) and stem diameter at ground level (d0 hereafter) of all trees inside the plots (approximately 600 total). We repeated these measurements in the early spring 2016, following a cleaning procedure performed by forest managers the previous summer. This cleaning targeted large rowans and goat willow which were cut with a chainsaw. Felled trees were left in the stands. 2.3. Measurement of browsing on rowan trees Browsing by red deer on the stem bark (stem bark browsing; hereafter SBB), on the branch bark (branch bark browsing; hereafter BBB), and on small branches cropped completely off and eaten (whole-branch browsing; hereafter WBB, see Fig. 1 for explanation) occurred during the winter of 2015–2016. In the early spring of 2016 we measured 60 rowan trees within the belt transect, including 30 lying (felled) and 30 standing (live) trees. Selected trees were ≥200 cm tall because most smaller trees were not browsed by red deer. For each felled tree selected we measured its height using a measure pole (precision ± 10 mm) and d0 and DBH (precision ± 0.1 mm) by digital calipers. The stem was divided into 20-cm long segments starting from the stem base, which were marked by chalk on the stem surface. We calculated the area of bark removed by red deer by measuring the length and width of all bark patches (SBB, an area of continuous debarking by red deer) on the stem using digital calipers (precision ± 0.1 mm) and recorded SBB by stem segment based on distance from the stem base (e.g., 0–50 cm, 50–100 cm, 100–150 cm etc.). In addition, in the middle of each stem segment, we measured the stem diameter in two perpendicular directions using digital calipers ( ± 1.0 mm). The same measurements were performed for BBB. Then, all branches
2. Material and methods 2.1. Site and forest description Our research was conducted in the central part of a post-disturbance area that arose after a large-scale windstorm that occurred on 19 November 2004 in the Tatra National Park (TNP) in northern Slovakia. The storm damaged spruce-dominated forests located mainly in elevations ranging from 700 to 1,400 m in a relatively continuous belt oriented in a West-East direction, nearly 35 km long and 5 km wide (Šebeň, 2010). The forest soils consit mainly of cambisols, the bedrock is granodiorit. The climate is continental with mean annual temperature of about 4.0° C. Precipitation averages 800–1,200 mm annually with nearly 140 days of snow cover (Vološčuk et al., 1994). During our study in 2015, 11 years post-disturbance, the area was covered mostly by young forest stands originating from both natural regeneration predominately of rowan, a variety of birches (primarily silver birch (B. pendula)), goat willow (Salix caprea) and trembling aspen (Populus tremula), and from planting mainly Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and European larch (Larix decidua). Scattered open areas among the young forest stands were covered by grasses (e.g.,
SBB
WBB
BBB Fig. 1. Example of bark browsing on stem (SBB), on branch (BBB), and browsing of whole branches (i.e. both wood and bark were consumed; WBB). 512
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Fig. 2. Dry mass of branches without foliage expressed on branch base diameter used for estimation of mass for WBB (plate a; after Pajtík et al., 2015) and specific surface mass of bark expressed on tree stem or branch base used for estimation of masses for SBB and BBB (plate b; after Pajtík et al., 2015). Table 1 Characteristics of the post-disturbance forest (average values and standard deviations) measured in spring 2015 before cleaning (e.g., removal of rowans (Sorbus aucuparia) and goat willow (Salix caprea)) and spring 2016 after cleaning in the High Tatra Mts., Slovakia. Season Before cleaning After cleaning
Tree density (trees/ha) 14,200 ± 12,700 7,900 ± 6,800
Mean diameter at the base d0 (mm) 38 ± 33 52 ± 45
Mean Lorey's height (cm) 329 ± 150 381 ± 143
Basal area (cm2·m−2) 11.1 ± 10.0 9.6 ± 7.6
0.05 for all tests. All statistical analyses were performed in Statistica 10.0.
cropped by red deer (WBB) in the tree crowns were identified and their base diameters ( ± 0.1 mm) measured in two perpendicular directions. We used the same protocol to measure browsing on standing rowans as for felled ones, except measurements were made only to the maximum height at which red deer could reach to browse, which was 200 cm for SBB and BBB and 250 cm for WBB.
3. Results Initial stand density for all tree species in spring 2015 was 14,200 ± 12,700 trees/ha, which was reduced by cleaning by almost half to 7,900 ± 6,800 trees/ha by spring 2016 (Table 1). During this period, both the mean diameter (d0) and mean tree height increased by 15–25%, whereas basal area declined by about 15% (Table 1). During that period, tree species composition also changed, with increases in Norway spruce, silver birch, and Scots pine, and decreases in rowan and goat willow (Table 2). The 60 rowans on which we measured red deer browsing ranged from 10 mm to 65 mm in DBH and from 200 cm to 580 cm tall (Fig. 3). On these trees, we recorded 557 patches of bark browsing (both SBB and BBB) and 1257 incidences of WBB. As expected, red deer consumed more of the felled than the standing rowans (Table 3, 4), and this difference increased with tree height.
2.4. Calculation of browsed biomass and statistical analysis Biomass (expressed in oven-dry matter) of individual branches used to estimate WBB was calculated by first developing an allometric relationship between the diameter at which the branches were cropped by red deer (db, mm) and the mass of woody material above that point (Fig. 2a; more detailed description is given in Pajtík et al., 2015). Values of BBB and SBB (dry matter) for each segment was calculated as:
Bbark = S. ws where S is the area of browsed bark and ws is the specific surface mass of bark. Because the specific surface mass of bark depends on tree size, we incorporated the model by Pajtík et al. (2015), where tree size is represented by diameter at the stem base; Fig. 2b). Then, the biomass removed from all types of browsing, SBB, BBB and WBB, was summed by the whole tree, and the area and biomass removed by SBB was summed by each 20-cm segment using the formula for a truncated cone. Finally, we calculated the percentage of total bark that was consumed (consumed stem bark portion; hereafter CSBP) by section. We compared differences in the number and mass of SBB, BBB and WBB between felled and standing rowans using a two-way ANOVA, with tree status (i.e., felled vs. standing) and tree size category (i.e., ≤400 cm, 401–500 cm, and > 500 cm) and their interaction. We also used a two-way ANOVA to compare CSBP by tree status and stem section (i.e., 20-cm segments). We followed all significant main effects with a post-hoc comparison of means (LSD), and used an alpha-level of
Table 2 Contribution of the individual tree species (% basal area; average values and standard deviations) in spring 2015 before cleaning (e.g., removal of rowans (Sorbus aucuparia) and goat willow (Salix caprea)) and spring 2016 after cleaning in the High Tatra Mts., Slovakia.
513
Tree species
Before cleaning
After cleaning
Betula pendula Larix decidua Picea abies Pinus sylvestris Salix caprea Sorbus aucuparia Others
25.1 ± 26.7 3.3 ± 3.5 27.1 ± 23.8 3.8 ± 4.2 10.9 ± 10.5 28.7 ± 26.9 1.1 ± 1.5
35.5 ± 24.3. 3.3 ± 3.2 34.3 ± 22.4 5.7 ± 4.3 3.8 ± 3.0 15.5 ± 14.1 1.9 ± 1.4
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(number: F = 11.41, P < 0.001, mass: F = 15.91, P < 0.001), but only the number of incidences had a significant interaction (F = 5.32, P < 0.001, Fig. 4, 5). Therefore, the total number of browsing incidences (F = 68.26, P < 0.001) and mass removed (F = 16.80, P < 0.001), regardless of browsing type, was also higher in felled than standing live rowans and increased with tree height (number: F = 19.90, P < 0.001, mass: F = 22.61, P < 0.001), with significant interactions (number: F = 9.36, P < 0.001, mass: F = 4.08, P < 0.001). Most patches of bark stripping (SBB) were < 60 cm2, and the patch size distribution was similar between felled and standing rowans (Fig. 6a). Most incidences of whole stem browsing (WBB) occurred on branches that were 2.1–4.0 mm in diameter in both felled and standing rowans, but more branches were cropped at diameters > 6.1 mm on felled than standing rowans (Fig. 6b). The intensity of browsing by red deer varied by the section of the stem and this pattern was different between felled and standing rowans (significant interaction of tree status and stem section; F = 10.479, P < 0.001). Overall, we found that CSBP was highest in stem sections between 100 and 200 cm from the stem base, and peaked at 15–25% (Fig. 7). CSBP did not vary between felled and standing trees from the base to about 150 cm, but felled trees had greater CSBP at distances > 150 cm from the base.
Fig. 3. The relationship between tree height and diameter at breast height (DBH, 130 cm) for 60 individuals of rowan (Sorbus aucuparia) 11 years after disturbance in the High Tatra Mts., Slovakia. Table 3 Mean ( ± standard deviation) of the number of recorded patches of stem bark browsing (SBB) and branch bark browsing (BBB) by red deer (Cervus elaphus), their total area and consumed dry mass per tree for felled and live standing rowans (Sorbus aucuparia) in a post-disturbance stand in cleaning in the High Tatra Mts., Slovakia. Status of rowans
Type of browsing
Number of recorded patches (patches/tree)
Total area of stripped bark (cm2/tree)
Mass of consumed bark (g/tree)
Felled Standing Felled Standing
SBB SBB BBB BBB
12.3 ± 5.9 6.1 ± 2.0 1.9 ± 2.8 0.6 ± 0.9
487.8 ± 430.6 249.8 ± 146.2 29.5 ± 29.3 8.7 ± 15.1
29.5 ± 29.3 16.3 ± 11.2 1.2 ± 1.9 0.4 ± 0.6
4. Discussion We found extensive browsing by red deer on rowans within a young mixed forest in the TNP in Slovakia that arose following a wind disturbance 11 years before. Rowan trees composed the greatest proportion of trees within the post-disturbance forest before cleaning (almost 30%), and each standing rowan tree lost an average of 29 g dry mass of tissue from red deer browsing during one winter season. However, felled rowan trees received twice the incidences of both SBB and WBB than did standing live rowan trees. At the same time, the quantity of consumed biomass (MACC) was about 1.6 times greater on felled than standing rowans. These results indicated that felling of rowans temporary stimulated red deer to consume more tree biomass in the form of SBB (82% more on felled than standing trees) than in the form of WBB (21% more on felled than standing trees). As for BBB, the amount of biomass consumed by red deer was negligible in comparison with those of SBB and WBB in both felled and standing rowans. In addition, the pattern of SBB intensity along the trunk differed between felled and standing rowans. Our findings, like those of other studies, emphasize the value of rowans as forage for red deer. For example, Šebeň (2010) showed that nearly 21% of natural regeneration, expressed as the number of trees, in the post-disturbance area of the TNP was comprised of rowan. In addition, Kaštier and Bučko (2011) surveyed damage by red deer browsing (specifically leader shoots and branches) in young post-disturbance stands in this region, and found a higher percentage of browsed rowan trees (72.9%) than goat willow (50.7%) and silver fir (50.6%). All other species were much less frequently damaged by red deer browsing. Our results showed remarkable differences in browsing (i.e., MACC) between felled and standing rowans, which can likely be attributed to both accessibility of tree components for deer consumption and ease or efficiency of browsing. The fact that the red deer consumed so much more mass on felled trees is in part a consequence of the entire length of the stem being within the reach of the red deer. However, unlike in standing trees, red deer might have more trouble accessing the underside of the stem and branches of felled trees lying on the ground. How accessible the underside of felled trees are to red deer likely depends on crown density and how close the felled tree is to the ground. Ground vegetation, slope, and other aspects of the stand may influence the position of felled trees. However, because felled trees were browsed more intensely that standing trees even where the stem was completely
Table 4 Mean ( ± standard deviation) of the number of recorded incidences of whole branch browsing (WBB) by red deer (Cervus elaphus), the diameter of the branch at browsing, and the dry mass of consumed branches per tree for felled and live standing rowans (Sorbus aucuparia) in a post-disturbance stand in the High Tatra Mts., Slovakia. Status of rowans
Number of recorded cases (pieces)
Felled Standing
27.4 ± 14.6 14.5 ± 7.1
Diameter of browsed branches (cm2) 3.2 ± 1.0 3.3 ± 1.4
Mass of consumed branches (g) 13.9 ± 9.7 11.5 ± 8.5
Felled trees had about twice as many patches (F = 66.55, P < 0.001) and mass (F = 17.15, P < 0.001) of SBB as did standing trees, and SBB increased with tree height for number of patches (F = 15.27, P < 0.001) and mass (F = 17.26, P < 0.001 (Figs. 4, 5). Significant interaction terms indicated that the difference in SBB between felled and standing trees increased with tree height (number: F = 7.26, P = 0.002, mass: = 4.99, P = 0.010). Similarly, felled trees had about three times more patches (F = 17.04, P < 0.001) and biomass (F = 12.91, P = < 0.001) of BBB than did standing trees, and number of patches (F = 11.09, P < 0.001) and mass (F = 8.36, P < 0.001) all increased with tree height, with a significant interaction (number: F = 5.58, P = 0.006, mass: F = 4.27, P = 0.019, Figs. 4, 5). Like bark stripping, WBB was higher on felled than standing rowans, in terms of number of incidences (F = 39.19, P < 0.001) and mass removed (F = 3.88, P = 0.054), both of which increased with tree height 514
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Fig. 4. The mean ( ± standard error) number of incidences of different types of browsing by red deer (Cervus elaphus), including stem bark browsing (SBB; plate a), branch bark browsing (BBB; plate b), whole branch browsing (WBB; plate c) and all three types of browsing together (i.e., SBB + BBB + WBB; plate d), for felled and standing live rowans (Sorbus aucuparia) in relation to height class in a post-disturbance mixed forest in the High Tatra Mts., Slovakia. Different letters indicates statistically significant differences (two-way ANOVA followed by LSD test, α = 0.05).
previously accessible. Large diameters on standing trees might also represent repetitive cropping on the same branch during that season or previous seasons, as has been reported for large ruminants (e.g., Welch et al., 1988; Faber and Lavsund, 1999). Our experiment suggests that rowans can provide a substantial amount of winter food for red deer that might provide natural protection for conifers, especially larch and spruce, even when deer are at high density. For example, in our study area, red deer consumed an average of 93 g of dry mass from felled and 44 g from standing live rowans between 500 and 580 cm tall. Because red deer require about 3 kg of dry mass per day when consuming woody forage in winter (Hell et al., 2000), if rowans provided the sole forage for deer in a winter with high snow cover, each deer would need to browse about 30 felled or over 60 standing rowans per day to satisfy its daily intake. Therefore, 1 ha could feed a theoretical maximum of 100–300 red deer per day in our system with 7900 rowan trees/ha or 1–3 deer per ha over a 90-day winter season. Previous studies suggest that in mixed stands the bulk of winter browsing by red deer occurs on rowans and willows, with very little on pine and larch, and none on spruce (see also Kaštier and Bučko,
accessible to red deer (i.e., in a comparable stem section), we suggest that red deer prefer to strip bark and crop branches of trees positioned horizontally than vertically. This position might make stripping and cropping more efficient, although future experiments observing deer behaviour are needed to test this hypothesis. Alternatively, felled rowans may differ from standing live rowans in their texture (e.g., softness, moisture content) or nutritional or chemical composition, which could be an area of further research. We also found differences in WBB between felled and standing rowans. Red deer cropped larger branch diameters, often as large as 6–10 mm, on standing rowans, whereas they rarely cropped branches this large on felled trees. One reason for these differences might be the fact that fewer branches were available to deer on the standing trees because many were out of reach or had been previously browsed, thus red deer consumed more from each branch. Other studies with large browsing herbivores have shown that they crop large stem diameters and more bites per tree when fewer bites are available or trees are spaced further apart (Vivås and Sæther, 1987; Shipley and Spalinger, 1995). Felled trees would provide new resources that were not 515
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Fig. 5. The mean ( ± standard error) mass of different types of browsing by red deer (Cervus elaphus), including stem bark browsing (SBB; plate a), branch bark browsing (BBB; plate b), whole branch browsing (WBB; plate c) and all three types of browsing combined (i.e., SBB + BBB + WBB; plate d), for felled and standing live rowans (Sorbus aucuparia) in relation to height class in a post-disturbance conifer forest in the High Tatra Mts., Slovakia. Different letters indicates statistically significant differences (two-way ANOVA followed by LSD test, α = 0.05).
1994), may also change. On the other hand, red deer seem to avoid standing rowans that have been heavily browsed in past seasons, because the more accessible bark and branches have been already removed. In addition, we observed that red deer seem to avoid browsing near the scars from previous bark stripping (personal observation and photo- documentary). Some woody plants respond to browsing by inducing plant secondary metabolites (Bryant et al., 1991) and bark peeling may disrupt flow of carbohydrates through the cambium in that area, although Saint-Andrieux et al. (2009) measured a slightly higher carbohydrates in stripped than non-stripped beech (Fagus sylvatica) near wounds. Not only does felling reduce the lifespan of rowans as browse, it could also temporarily reduce forage potential in forest stands because rowans typically reproduce by seeds. However, regeneration of rowans can also occur by epicormic shoots Raspé et al. (2000). Therefore, rowans can display intensive vegetative regeneration at high elevation or in response to browsing (Myking et al., 2013), thus could provide a sustainable source of browse even where felling is used. Our results showed that SBB on the standing rowans occurred up to the maximum distance of 200 cm from the ground level, peaking at
2011). In principle, there may be a trade off between retaining rowans to reduce browsing on conifers and removing rowans to improve growth of conifers. However, in areas such as the TNP region that have high red deer populations, the threat to commercial tree species by browsing by red deer exceeds the consequences of reduced growth rate caused by interspecific competition stress that might occur when retaining more rowans in the stands. Although red deer browsed felled rowan trees more intensely than standing trees, felled trees have a shorter lifespan as browse for deer. Standing live trees can provide forage for a couple of seasons depending on the intensity of browsing, but felled trees seem to be edible for only the few months of one winter season. Thereafter, as the wood tissue dries and hardens, its attractiveness as forage seems to decline, likely because thicker, dryer bark is more difficult for herbivores to strip (Kuiters et al., 2006; Saint-Andrieux et al., 2009). Drying reduces the elasticity of parenchyma cells, which become more lignified (Klich, 2017). During this process, the nutritional properties that herbivores seek, such as carbohydrates (Saint-Andrieux et al., 2009), and those that they avoid, such as monoterpenes and phenolics (Duncan et al., 516
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80 felled
70
standing
Contribution to total number (%)
Contribution to total number (%)
80
60 50 40 30 20 10
70 60 50 40 30 20 10
0 20
21-40
41-60
61-80
0
81-100 101-120
2.0
2
Area class (cm )
2.1-4.0 4.1-6.0 6.1-8.0 Diameter class (mm)
8.1-10.0
Fig. 6. Histogram of area classes of browsed bark on stems (n = 451) and diameter classes of branches (n = 1257) cropped by red deer (Cervus elaphus) for felled and standing rowans in a post-disturbance stand in the High Tatra Mts., Slovakia. Fig. 7. Mean ( ± standard errors) of percentage of total bark that was consumed (consumed stem bark portion; CSBP in %) by red deer (Cervus elaphus) over vertical stem profile by 50-cm-long sections for felled and standing rowans (Sorbus aucuparia) in a post-disturbance mixed stand in in the High Tatra Mts., Slovakia. Only rowans > 400 cm were included. Different letters indicates statistically significant differences (two-way ANOVA followed by LSD test, α = 0.05).
have good growth, reproductive and regenerative properties. Furthermore, rowans tolerate mechanical damage such as heavy browsing (Miller et al., 1982). The response to superficial wounding, with the formation of a wound periderm structurally similar to the original intact one, is completed within 28 days (Woodward and Pocock, 1996). The deposition of suberin is detectable within about 7 days after wounding. This process protects compromised tissues from desiccation and markedly reduces the likelihood of pathogen invasion (Woodward and Pocock, 1996). A third of the shoots can be browsed during winter with no serious effects on sapling survival or regeneration. In areas with higher light levels it takes an average of 7–8 years for a saplings terminal shoots to be out of range of browsing deer (Homolka and Heroldová, 2003). To prolong the sustainable availability of rowan within a growing and vulnerable conifer stand, we suggest foresters retain some rowan trees within stands during their repeated cleanings and other interventions such as thinning and tending. Until rowan are mature (i.e., life
101–150 cm. However, WBB occasionally occurred between 200 and 250 cm above the ground. Similarly, the highest intensity of SBB in young ash (Fraxinus excelsior) occurred between 71 and 170 cm (Konôpka et al., 2012). In Scotland, Welch et al. (1988) showed that most wounds on stems caused by red deer were situated in the heights from 50 to 150 cm. In general, heights of the most frequent browsing correspond with height of the red deer’s shoulder (Renaud et al., 2003). These browsing patterns for felled rowans differed from standing rowans in our study. Although red deer had access to the entire length of the tree, the highest CSBP was found in the middle part of stem, between about 100 cm from the base and about 150 cm from the crown top. Although information about patterns of browsing on felled trees is scarce, we suggest that the bottommost part of stem might be less stable, and may move under pressure caused by red deer teeth. Similarly, the uppermost part of stem is more flexible, thin and often covered by a many branches that may impede browsing. Not only are rowans a preferred winter forage for red deer, they also 517
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felled rowans within a commercially-valuable conifer forest in Slovakia that we measured in our study suggests that rowan and other fastgrowing deciduous species could provide a mechanism for mitigating forest damage by red deer at some levels of population density. However, we offer the caveat that we did not directly measure the effects of rowan density or status (live standing or felled) on conifer damage, deer movements, or deer density. Although we expect that our recommendations for forest management that includes rowans will provide an efficient and socially acceptable method for mitigating some conflicts between timber and wildlife production, other methods for reducing browsing damage will need to be considered in some instances, such as when populations increase rapidly after mass tree recruitment following extensive timber harvest or natural disasters (e.g., Moser et al., 2008; Krojerová-Prokešová et al., 2010; Kuijper, 2011). These could include non-lethal methods such as protective barriers (fencing, plastic caps on terminals), chemical deterrents, and lethal methods such as gradual reductions of large herbivores, especially red deer (see also Konôpka et al. (2015b)). This may require changes in legislation, such as the Hunting Law in Slovakia.
expectancy of about 60 years; Raspé et al., 2000), foresters could leave enough rowans to provide sustainable forage and regeneration without undue competition with economically important tree species. This density would likely differ across sites and depend on management goals (e.g., the balance between productive and other ecosystem services of the forest), but we suggest about approximately 30–50 rowan trees per ha for our study area. Although these trees could be left scattered across the stand, foresters might find it more efficient to leave smaller groups at the edge of stands, along skidding lines and roads, or on the naturally occurring stand gaps. These groupings could also focus dispersion of red deer in more disturbed areas. Regardless, total extinction of rowan can be expected in mature stands with high rates of felling and extremely exposed to red deer browsing (Lindner et al., 1997). An alternative to maintaining and managing attractive browse species within conifer stands would be to plant or manage these species on dedicated browse plots with for the primary goal of providing forage supply for red deer. These plantings have the advantage of luring deer further away from valuable sites and reduce competition between rowans and conifers within a stand, but also result in several disadvantages, including concentrating deer and taking land out of timber production. If browse plots are desired, they should be established in areas with a naturally high concentration of red deer (e.g. south-facing slopes, stands near meadows and agricultural crops) and areas that have actual potential to naturally regenerate rowan and other preferred species. Because red deer are attracted to concentration of browse (Royo et al., 2017) browse plots should be placed as far as possible from high-quality commercial forests (see also Mansson et al. (2015)) Browse plots are normally between 0.1 and 0.3 ha, and forest owners must realize that these plots cannot produce wood production for several decades, but could reduce damage to economically important stands grown in the vicinity (Finďo and Petráš, 2007). For maximum value to red deer, these plots should be managed for recruitment and sustainable production of browse. However, we would like to stress that managers will generally receive higher economical and ecological value from managing deciduous trees that are valuable for browse but not for timber production that naturally regenerate within a commercial forest than by planting and managing dedicated browse plots. Our findings lead to several recommendations for managing young rowans in mixed forests facing browsing by red deer. Many of these suggestions would apply similarly to other preferred deciduous trees such as trembling aspen and a variety of willows.
Acknowledgements The research was supported by the projects APVV-14-0086 from the Slovak Research and Development Agency and also by grant “EVA4.0”, No. CZ.02.1.01/0.0/0.0/16_019/0000803 financed by OP RDE and project ITMS: 26220220025 supported by the ERDF-funded operational program, Research and Development“. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.foreco.2018.07.048. References Barančeková, M., Krojerová-Prokešová, J., Homolka, M., 2007. Impact of deer browsing on natural and artificial regeneration in foodplain forest. Folia Zool. 56, 354–364. Bryant, J.P., Provenza, F.D., Pastor, J., Reichardt, P.B., Clausent, T.P., Du Toit, J.T., 1991. Interactions between woody plants and browsing mammals mediated by secondary metabolites. Annu. Rev. Ecol. Evol. Syst. 22, 431–446. Burbaite, L., Csányi, S., 2010. Red deer population and harvest changes in Europe. Acta Zool. Lit. 20, 179–188. Čermák, P., Horsák, P., Spiřík, M., Mrkva, V., 2009. Relationship between browsing damage and woody species dominance. J. For. Sci. 55, 23–31. Cervený, J., Hell, P., Slamecka, J., 2013. Otto's Encyclopedia. Game Management. Otto's Publisher, Praha, pp. 591 (in Czech). Duncan, A.J., Hartley, S.E., Iason, G.R., 1994. The effect of monoterpene concentrations oin Sikkaspruce (Picea sitchensis) on the browsing behavior of red deer (Cervus elaphus). Can. J. Zool. 72, 715–1720. Faber, W.E., Lavsund, S., 1999. Summer foraging on Scots pine (Pinus sylvestris) by moose (Alces alces) in Sweden - Patterns and mechanisms. Wildlife Biol. 5, 93–106. Find’o, S., Petráš, R., 2007. Ecological Principals of Forest Protection to Game Damage. National Forest Centre, Zvolen, pp. 186 (in Slovak). Gill, R.M.A., 1992. A review of damage by mammals in north temperate forests. 1. Deer. Forestry 65, 145–169. Hell, P., Gašparík, J., Kartusek, V., Paule, L., Slamecka, J., 2000. Special Animal Husbandry. Technical University, Zvolen, pp. 228 (in Slovak). Heroldová, M., Homolka, M., Kamler, J., 2003. Breakage of rowan caused by red deer – an important factor for Sorbeto-Piceetum stand regeneration? For. Ecol. Manag. 181, 131–138. Holá, M., Ježek, M., Kušta, T., Červený, J., 2016. Evaluation of winter food quality and its variability for red deer in forest environment: overwintering enclosures vs. freeranging areas. Lesn. Cas. For. J. 62, 139–145. Homolka, M., 1990. Food of Cervus elaphus in the course of the year in the mixed forest habitat of the Drahanská vrchovina Highlands. Folia Zool. 39, 1–13. Homolka, M., Heroldová, M., 2003. Impact of large herbivores on mountain forest stands in the Beskydy Mountains. For. Ecol. Manag. 181, 119–129. Jamrozy, G., 1980. Winter food resources and food preferences of red deer in Carpathian forests. Acta Theriol. 25, 221–238. Kaštier, P., Bucko, J., 2011. Influence of ungulate game to the Tatra forest ecosystems damaged by the windstorm. In: Proceedings of International conference held on April 28th and 29th 2011 in Nový Smokovec. National Forest Centre, Zvolen, pp. 114–118 (in Slovak). Klich, D., 2017. Selective bark stripping of various tree species by Polish horses in relation to bark detachability. For. Ecol. Manag. 384, 65–71.
(1) Wait to fell rowans until most trees exceed 500 cm in height. (2) If rowans have been intensively damaged by browsing and the forage potential of the stem bark and branches is reduced, trees can be felled before they reach 500 cm. The ideal time would be when red deer have consumed branches with thickness of 1 cm above 250 cm from the ground level and most of the stem bark up to the height of 200 cm. (3) Rowans should be felled at the end of the growing season or in the early part of the winter season so that the trees do not become too dry to be attractive to red deer. (4) When possible, felling of rowans within a stand should be done in several applications over 2–3 subsequent years, treating only a part of each stand area each year and retaining some rowans within each stand for regeneration and future use by red deer. (5) Felled rowans should not be piled, which reduces access by red deer. Instead, felled rowans should be leaned against uncut trees, stumps or mounds so that most of the tree remains above the snow and red deer can access all sides of the tree. (6) If birch is being felled at the same time as rowans, make sure that rowans are not covered by birch, which is a less attractive forage species for red deer. In summary, the patterns and intensity of browsing on standing and 518
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B. Konôpka et al. Konôpka, B., Pajtík, J., Kaštier, P., Šebeň, V., 2012. Estimates of young ash tree dendromass eaten by red deer using allometric models. Rep. For. Res. 57, 283–294 (in Slovak with English Summary). Konôpka, B., Pajtík, J., Šebeň, V., Bošeľa, 2015a. Aboveground net primary production of tree cover at the post-disturbance area in the Tatra national park. Slovakia. Lesn. Cas. For. J. 61, 167–174. Konôpka, J., Galko, J., Kaštier, P., Konôpka, B., Kunca, A., Leontovyc, R., Longauerová, V., Mal’ová, M., Pajtík, J., Šeben, V., 2014. Forest regeneration. Progressive Technologies of Forest Tree Protection in Initial Growth Stages. National Forest Centre, Zvolen, pp. 181 (in Slovak with English summary). Konôpka, J., Kaštier, P., Konôpka, B., 2015b. Theoretical bases and practical measures to harmonise the interests of forestry and game management in Slovakia. Lesn. Cas. For. J. 61, 114–123. Krojerová-Prokešová, J., Barančeková, M., Šustr, P., Heurich, M., 2010. Feeding patterns of red deer Cervus elaphus along an altitudinal gradient in the Bohemian Forest: effect of habitat and season. Wildl. Biol. 16, 173–184. Kuijper, D.P.J., 2011. Lack of natural control mechanisms increases wildlife-forestry conflict in managed temperate European forest systems. Eur. J. Forest Res. 130, 895–909. Kuiters, A.T., van der Sluijs, L.A.M., Wytema, G.A., 2006. Selective bark-stripping of beech, Fagus sylvatica, by free-ranging horses. For. Ecol. Manag. 222, 1–8. Latham, J., Staines, B.W., Gorman, M.L., 1999. Comparative feeding ecology of red deer (Cervus elaphus) and roe (Capreolus capreolus) in Scottish plantation forests. J. Zool. 247, 409–418. Lindner, P., Elfving, B., Zackrisson, O., 1997. Stand structure and successional trends in virgin boreal forest reserves in Sweden. For. Ecol. Manag. 98, 17–33. Mansson, J., Roberge, J.M., Edenius, L., Bergström, R., Nilsson, L., Lidberg, M., Komstedt, K., Ericsson, G., 2015. Food plots as a habitat management tool: forage production and ungulate browsing in adjacent forest. Wildl. Biol. 21, 246–253. Miller, G.R., Kinnaird, J.W., Cummins, R.P., 1982. Liability of saplings to browsing on a red deer range in the Scottish Highlands. J. Appl. Ecol. 19, 941–951. Ministry of Agriculture and Rural Development of the Slovak Republic, 2017. Report on the Forest Sector of the Slovak Republic – Green Report. National Forest Centre, Zvolen, pp. 68. Moore, N.P., Hart, J.D., Kelly, P.F., Langton, S.D., 2000. Browsing by fallow deer (Dama dama) in young broadleaved plantations: seasonality, and the effects of previous browsing and bud eruption. Forestry 73, 437–445. Moser, B., Schütz, M., Hindenlang, K.E., 2008. Resource selection by roe deer: are windthrow gaps attractive feeding places? For. Ecol. Manag. 255, 1179–1185. Motta, R., 2003. Ungulate impact on rowan (Sorbus aucuparia L.) and Norway spruce (Picea abies (L.) Karst.) height structure in mountain forests in the Eastern Italian Alps. For. Ecol. Manag. 181, 139–150.
Myking, T., Solberg, E.J., Austrheim, G., Speed, J.D.M., Bohler, F., Astrup, R., Eriksen, R., 2013. Browsing of sallow (Salix caprea L.) and rowan (Sorbus aucuparia L.) in the context of life history strategies: a literature review. Eur. J. For. Res. 132, 399–409. Pajtík, J., Konôpka, B., Bošeľa, M., Šebeň, V., Kaštier, P., 2015. Modelling forage potential for red deer: a case study in post-disturbance young stands of rowan. Ann. For. Res. 58, 91–107. Prokešová, J., 2004. Red deer in the floodplain forests: the browse specialist? Folia Zool. 53, 293–302. Raspé, O., Findlay, C., Jacquemart, A.L., 2000. Sorbus aucuparia L. J. Ecol. 88, 910–930. Renaud, P.C., Verheyden-Tixier, H., Dumont, B., 2003. Damage to saplings by red deer (Cervus elaphus): effect of foliage height and structure. For. Ecol. Manag. 181, 31–37. Royo, A., Kramer, D.W., Miller, K.V., Nibbelink, N.P., Stout, S.I., 2017. Spatio-temporal variation in foodscapes modifies deer browsing impact on vegetation. Landscape Ecol. 32, 2281–2295. Saint-Andrieux, C., Bonenfant, C., Toïgo, C., Basille, M., Klein, F., 2009. Factors affecting beech Fagus sylvatica bark stripping by red deer Cervus elaphus in a mixed forest. Wildlife Biol. 15, 187–196. Schulze, E.D., Bouriad, O., Wäldchen, J., Eisenhauer, N., Walentowski, H., Seele, C., Heinze, E., Pruschitzki, G., Danila, G., Marin, D., Hessenmöller, L., Bouriaud, L., Teodosiu, M., 2014. Ungulate browsing causes species loss in deciduous forests independent of community dynamics and silviculture management in Central and Southern Europe. Ann. For. Res. 57, 267–288. Šebeň, V., 2010. Natural regeneration after the disaster on November 2004 in the High Tatra Mountains. In: Research on Spruce Stands Destabilised by Harmful Agents. National Forest Centre, Zvolen, pp. 297–308 (In Slovak). Šebeň, V., 2017. The National Forest Inventory in the Slovak Republic 2015-2016. Forestry Studies 63. National Forest Centre, Zvolen, pp. 255 (In Slovak with English Summary). Shipley, L.A., Spalinger, D.E., 1995. Influence of size and density of browse patches on intake rates and foraging decisions of young moose and white-tailed deer. Oecologia 104, 112–121. Vivås, H.J., Sæther, B.E., 1987. Interactions between a generalist herbivore, the moose Alces alces, and its food resources: an experimental study of winter foraging behaviour in relation to browse availability. J. Anim. Ecol. 56, 509–520. Vološčuk, I., et al., 1994. The Tatra National Park. Gradus Publisher, Martin, pp. 557. Welch, D., Staines, B.W., Scott, D., Catt, D.C., 1988. Bark stripping damage by red deer in Sitka spruce forest in Western Scotland II. Wound size and position. Forestry 61, 245–254. Woodward, S., Pocock, S., 1996. Formation of the ligno–suberized barrier zone and wound periderm in four species of European broad-leaved trees. Eur. J. For. Pathol 26, 97–105.
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Intensity of red deer browsing on young rowans differs between freshlyfelled and standing individuals
T
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Bohdan Konôpkaa,b, , Jozef Pajtíka, Lisa A. Shipleyc a
National Forest Centre, Forest Research Institute, T.G. Masaryka 2175/22, 960 92 Zvolen, Slovakia Czech University of Life Science, Faculty of Forestry and Wood Sciences, Kamýcká 129, 165 00 Praha – Suchdol, Czech Republic c Washington State University, School of the Environment, Pullman 99164-2812, USA b
A R T I C LE I N FO
A B S T R A C T
Keywords: Cervus elaphus Sorbus aucuparia Herbivory Bark stripping Stand cleaning Slovakia
Because red deer (Cervus elaphus) forage extensively on woody plants, browsing is a serious problem in forest stands especially in initial growth stages. In Slovakia, rowans (Sorbus aucuparia) are the most attractive tree species for red deer, and when present, they may serve to divert the attention of foraging red deer from commercial forest stands. In this study we compared the extent of herbivory by red deer on standing and freshlyfelled rowans within a mixed conifer forest. We quantified the biomass of stem bark, branch bark and whole branches consumed by red deer on 60 rowans between 200 and 600 cm tall within young stands that regenerated after a large scale windstorm in the Tatra National Park, Northern Slovakia. We calculated the dry biomass of browsed branches using allometric relationships with branch diameter and browsed bark biomass from the product of the area of consumed bark and specific surface mass of bark. We found that the extent and intensity of browsing was much higher on felled than standing rowans. The number of patches of stripped bark on stems was twice as high (12 ± 6 bites/stem) on felled than on standing trees (6 ± 2 bites/stem). Similarly, red deer consumed more total biomass (i.e., bark stripping on both stem and branches and browsed whole branches) from felled (45 ± 41 g) than standing (28 ± 22 g) rowans. Red deer consumed more mass from stem bark than branches. Total browsed mass on trees (especially on felled ones) increased with their height. Based on our findings, we recommend cutting rowans after most trees exceed 500 cm in height and leaving them in the site. However, if rowans have been intensively damaged by browsing and the forage potential of the stem bark and branches is reduced, trees can be felled before they reach 500 cm. We concluded that cut timing and after-cut arrangement of rowans, and likely other non-commercial tree species attractive to red deer, may substantially mitigate red deer browsing on commercial tree species in young stands.
1. Introduction Although classified as mixed feeders because they are able to consume large amounts of both graminoids and woody plants (i.e., browse), red deer (Cervus elaphus) consume diets of predominately browse within many European forests (e.g., up to 90% seasonally, Finďo and Petráš, 2007; Jamrozy, 1980; Homolka, 1990). Because of their large size (males often weigh > 200 kg; Červený et al., 2013) and high densities in many areas (Holá et al., 2016; Konôpka et al., 2014), browsing by red deer on young trees can have a substantial effect on forest regeneration (Latham et al., 1999; Čermák et al., 2009), with damage exceeding that of other wild herbivores such as roe deer (Capreolus capreolus; Prokešová, 2004) and fallow deer (Dama dama; Moore et al., 2000). Red deer damage young trees by browsing shoots, foliage, and small branches, whereas larger trees are damaged mainly through ⁎
bark stripping (e.g., Konôpka et al., 2012). In Slovakia, data from the National Forest Inventory collected in 2015–2016 (Šebeň, 2017) showed that approximately one third of all trees up to 10 years old were affected by browsing by wild herbivores. In general, these effects are greatest in young even-aged and often post-disturbance forests, and can seriously reduce the economic feasibility of tree planting (Gill, 1992; Barančeková et al., 2007). In Slovakia, forest managers have attempted to mitigate damage by red deer and other wild herbivores using techniques such as protecting individual trees using olfactory repellents or placing plastic caps on the tree terminus and protecting groups of trees using fencing (Finďo and Petráš, 2007). However, these techniques are expensive and time-consuming to build and maintain, thus the use of fencing and barriers has declined over the last two decades (Ministry of Agriculture and Rural Development of the Slovak Republic, 2017). During the same time
Corresponding author at: National Forest Centre, Forest Research Institute, T.G. Masaryka 2175/22, 960 92 Zvolen, Slovakia. E-mail address: [email protected] (B. Konôpka).
https://doi.org/10.1016/j.foreco.2018.07.048 Received 23 May 2018; Received in revised form 23 July 2018; Accepted 27 July 2018 0378-1127/ © 2018 Elsevier B.V. All rights reserved.
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Calamagrostis sp., Avenella flexuosa, Luzula luzuloides), forbs (e.g., Epilobium angustifolium, Senecio nemorensis, Rubus idaeus) and shrubs (mostly Vaccinium myrtillus, Sambucus racemosa). The population density of red deer in the TNP in 2015 was estimated at 21 individuals per 1000 ha, a 75% increase in estimates made in a before the wind disaster episode (i.e., 12 individuals per 1000 ha in the reference year 2000; Headquarters of the TNP, pers comm.).
period, red deer populations have increased forest management and game management (Konôpka et al., 2015a), as has been reported in other European countries (Burbaite and Csányi, 2010; Schulze et al., 2014; Holá et al., 2016). Although reducing red deer populations has the potential to reduce tree damage in some forests, this measure is not equally supported by different interest groups (e.g., hunters, environmentalists, forest owners, farmers) in many countries such as Slovakia (Finďo and Petráš, 2007). Therefore, alternative methods for reducing forest damage by red deer are needed. One possibility is to purposely boost alternative desirable food to lure red deer away from commercially-valuable tree species. This might be accomplished by promoting mixed stands containing both commercially-valuable tree species and tree species attractive to herbivores but with low economic value (Čermák et al., 2009). On such attractive but low value species is rowan (Sorbus aucuparia), a deciduous tree that is a highly preferred forage by red deer and other large herbivores (e.g., Heroldová et al., 2003; Motta, 2003; Myking et al., 2013). Rowan naturally regenerates in post-disturbance areas within Slovakian forests (Konôpka et al., 2015b; Pajtík et al., 2015). In managed forests, rowan trees are usually cut down within the cleaning (i.e., removal of less desirable individuals during the sapling stage to prevent them from over-topping favoured saplings) at around 10 years post-regeneration or in the first thinning at about 20 years post-regeneration and left in the stands. Therefore, the standing or felled rowans (∼1 year post-felling) may provide a temporary attractive alternative to the commercial species, allowing the commercial species to grow past their most vulnerable stage (i.e., stand rotation time is about 90 years for coniferous species and 110 years for hardwood broadleaved species). However, as yet the relative accessibility and attractiveness of standing and felled rowans as deer forage has not been evaluated. In this study we compared consumption of felled and live standing rowans by free-ranging red deer recorded 11 years after a windstorm disturbance (i.e., trees were < 11 years old). We hypothesized that red deer would browse more intensely on felled rowan trees than live standing trees because they would take less effort to acquire bark and branch biomass and a greater proportion of the tree would be accessible to red deer. Moreover, we expected that differences in intensity of damage on stems and crowns between standing and felled individuals would be positively related to tree height because the taller the tree, the greater proportion of unreachable mass to total tree mass in standing but not in felled individuals. Understanding the value of standing and felled rowans to red deer will allow us to frame recommendations on timing of cut and after cut arrangement of rowans.
2.2. Estimation of basic stand characteristics To describe stand condition on the site (49° 08′ N and 20° 13′ E) located close to the Starý Smokovec village, we established a research transect in the early spring 2015. The site belongs to the Smokovce Protective Unit managed by the State Forests of the TNP. Orientation of the belt transect was from Northwest to Southeast at elevations between 925 and 970 m. The transect was 4 m wide and 300 m long. Along the transect, we established 25 plots of 4 × 4 m spaced 8 m apart to increase independence of plots. We measured height, stem diameter at 130 cm from the ground (DBH, hereafter) and stem diameter at ground level (d0 hereafter) of all trees inside the plots (approximately 600 total). We repeated these measurements in the early spring 2016, following a cleaning procedure performed by forest managers the previous summer. This cleaning targeted large rowans and goat willow which were cut with a chainsaw. Felled trees were left in the stands. 2.3. Measurement of browsing on rowan trees Browsing by red deer on the stem bark (stem bark browsing; hereafter SBB), on the branch bark (branch bark browsing; hereafter BBB), and on small branches cropped completely off and eaten (whole-branch browsing; hereafter WBB, see Fig. 1 for explanation) occurred during the winter of 2015–2016. In the early spring of 2016 we measured 60 rowan trees within the belt transect, including 30 lying (felled) and 30 standing (live) trees. Selected trees were ≥200 cm tall because most smaller trees were not browsed by red deer. For each felled tree selected we measured its height using a measure pole (precision ± 10 mm) and d0 and DBH (precision ± 0.1 mm) by digital calipers. The stem was divided into 20-cm long segments starting from the stem base, which were marked by chalk on the stem surface. We calculated the area of bark removed by red deer by measuring the length and width of all bark patches (SBB, an area of continuous debarking by red deer) on the stem using digital calipers (precision ± 0.1 mm) and recorded SBB by stem segment based on distance from the stem base (e.g., 0–50 cm, 50–100 cm, 100–150 cm etc.). In addition, in the middle of each stem segment, we measured the stem diameter in two perpendicular directions using digital calipers ( ± 1.0 mm). The same measurements were performed for BBB. Then, all branches
2. Material and methods 2.1. Site and forest description Our research was conducted in the central part of a post-disturbance area that arose after a large-scale windstorm that occurred on 19 November 2004 in the Tatra National Park (TNP) in northern Slovakia. The storm damaged spruce-dominated forests located mainly in elevations ranging from 700 to 1,400 m in a relatively continuous belt oriented in a West-East direction, nearly 35 km long and 5 km wide (Šebeň, 2010). The forest soils consit mainly of cambisols, the bedrock is granodiorit. The climate is continental with mean annual temperature of about 4.0° C. Precipitation averages 800–1,200 mm annually with nearly 140 days of snow cover (Vološčuk et al., 1994). During our study in 2015, 11 years post-disturbance, the area was covered mostly by young forest stands originating from both natural regeneration predominately of rowan, a variety of birches (primarily silver birch (B. pendula)), goat willow (Salix caprea) and trembling aspen (Populus tremula), and from planting mainly Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and European larch (Larix decidua). Scattered open areas among the young forest stands were covered by grasses (e.g.,
SBB
WBB
BBB Fig. 1. Example of bark browsing on stem (SBB), on branch (BBB), and browsing of whole branches (i.e. both wood and bark were consumed; WBB). 512
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Fig. 2. Dry mass of branches without foliage expressed on branch base diameter used for estimation of mass for WBB (plate a; after Pajtík et al., 2015) and specific surface mass of bark expressed on tree stem or branch base used for estimation of masses for SBB and BBB (plate b; after Pajtík et al., 2015). Table 1 Characteristics of the post-disturbance forest (average values and standard deviations) measured in spring 2015 before cleaning (e.g., removal of rowans (Sorbus aucuparia) and goat willow (Salix caprea)) and spring 2016 after cleaning in the High Tatra Mts., Slovakia. Season Before cleaning After cleaning
Tree density (trees/ha) 14,200 ± 12,700 7,900 ± 6,800
Mean diameter at the base d0 (mm) 38 ± 33 52 ± 45
Mean Lorey's height (cm) 329 ± 150 381 ± 143
Basal area (cm2·m−2) 11.1 ± 10.0 9.6 ± 7.6
0.05 for all tests. All statistical analyses were performed in Statistica 10.0.
cropped by red deer (WBB) in the tree crowns were identified and their base diameters ( ± 0.1 mm) measured in two perpendicular directions. We used the same protocol to measure browsing on standing rowans as for felled ones, except measurements were made only to the maximum height at which red deer could reach to browse, which was 200 cm for SBB and BBB and 250 cm for WBB.
3. Results Initial stand density for all tree species in spring 2015 was 14,200 ± 12,700 trees/ha, which was reduced by cleaning by almost half to 7,900 ± 6,800 trees/ha by spring 2016 (Table 1). During this period, both the mean diameter (d0) and mean tree height increased by 15–25%, whereas basal area declined by about 15% (Table 1). During that period, tree species composition also changed, with increases in Norway spruce, silver birch, and Scots pine, and decreases in rowan and goat willow (Table 2). The 60 rowans on which we measured red deer browsing ranged from 10 mm to 65 mm in DBH and from 200 cm to 580 cm tall (Fig. 3). On these trees, we recorded 557 patches of bark browsing (both SBB and BBB) and 1257 incidences of WBB. As expected, red deer consumed more of the felled than the standing rowans (Table 3, 4), and this difference increased with tree height.
2.4. Calculation of browsed biomass and statistical analysis Biomass (expressed in oven-dry matter) of individual branches used to estimate WBB was calculated by first developing an allometric relationship between the diameter at which the branches were cropped by red deer (db, mm) and the mass of woody material above that point (Fig. 2a; more detailed description is given in Pajtík et al., 2015). Values of BBB and SBB (dry matter) for each segment was calculated as:
Bbark = S. ws where S is the area of browsed bark and ws is the specific surface mass of bark. Because the specific surface mass of bark depends on tree size, we incorporated the model by Pajtík et al. (2015), where tree size is represented by diameter at the stem base; Fig. 2b). Then, the biomass removed from all types of browsing, SBB, BBB and WBB, was summed by the whole tree, and the area and biomass removed by SBB was summed by each 20-cm segment using the formula for a truncated cone. Finally, we calculated the percentage of total bark that was consumed (consumed stem bark portion; hereafter CSBP) by section. We compared differences in the number and mass of SBB, BBB and WBB between felled and standing rowans using a two-way ANOVA, with tree status (i.e., felled vs. standing) and tree size category (i.e., ≤400 cm, 401–500 cm, and > 500 cm) and their interaction. We also used a two-way ANOVA to compare CSBP by tree status and stem section (i.e., 20-cm segments). We followed all significant main effects with a post-hoc comparison of means (LSD), and used an alpha-level of
Table 2 Contribution of the individual tree species (% basal area; average values and standard deviations) in spring 2015 before cleaning (e.g., removal of rowans (Sorbus aucuparia) and goat willow (Salix caprea)) and spring 2016 after cleaning in the High Tatra Mts., Slovakia.
513
Tree species
Before cleaning
After cleaning
Betula pendula Larix decidua Picea abies Pinus sylvestris Salix caprea Sorbus aucuparia Others
25.1 ± 26.7 3.3 ± 3.5 27.1 ± 23.8 3.8 ± 4.2 10.9 ± 10.5 28.7 ± 26.9 1.1 ± 1.5
35.5 ± 24.3. 3.3 ± 3.2 34.3 ± 22.4 5.7 ± 4.3 3.8 ± 3.0 15.5 ± 14.1 1.9 ± 1.4
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(number: F = 11.41, P < 0.001, mass: F = 15.91, P < 0.001), but only the number of incidences had a significant interaction (F = 5.32, P < 0.001, Fig. 4, 5). Therefore, the total number of browsing incidences (F = 68.26, P < 0.001) and mass removed (F = 16.80, P < 0.001), regardless of browsing type, was also higher in felled than standing live rowans and increased with tree height (number: F = 19.90, P < 0.001, mass: F = 22.61, P < 0.001), with significant interactions (number: F = 9.36, P < 0.001, mass: F = 4.08, P < 0.001). Most patches of bark stripping (SBB) were < 60 cm2, and the patch size distribution was similar between felled and standing rowans (Fig. 6a). Most incidences of whole stem browsing (WBB) occurred on branches that were 2.1–4.0 mm in diameter in both felled and standing rowans, but more branches were cropped at diameters > 6.1 mm on felled than standing rowans (Fig. 6b). The intensity of browsing by red deer varied by the section of the stem and this pattern was different between felled and standing rowans (significant interaction of tree status and stem section; F = 10.479, P < 0.001). Overall, we found that CSBP was highest in stem sections between 100 and 200 cm from the stem base, and peaked at 15–25% (Fig. 7). CSBP did not vary between felled and standing trees from the base to about 150 cm, but felled trees had greater CSBP at distances > 150 cm from the base.
Fig. 3. The relationship between tree height and diameter at breast height (DBH, 130 cm) for 60 individuals of rowan (Sorbus aucuparia) 11 years after disturbance in the High Tatra Mts., Slovakia. Table 3 Mean ( ± standard deviation) of the number of recorded patches of stem bark browsing (SBB) and branch bark browsing (BBB) by red deer (Cervus elaphus), their total area and consumed dry mass per tree for felled and live standing rowans (Sorbus aucuparia) in a post-disturbance stand in cleaning in the High Tatra Mts., Slovakia. Status of rowans
Type of browsing
Number of recorded patches (patches/tree)
Total area of stripped bark (cm2/tree)
Mass of consumed bark (g/tree)
Felled Standing Felled Standing
SBB SBB BBB BBB
12.3 ± 5.9 6.1 ± 2.0 1.9 ± 2.8 0.6 ± 0.9
487.8 ± 430.6 249.8 ± 146.2 29.5 ± 29.3 8.7 ± 15.1
29.5 ± 29.3 16.3 ± 11.2 1.2 ± 1.9 0.4 ± 0.6
4. Discussion We found extensive browsing by red deer on rowans within a young mixed forest in the TNP in Slovakia that arose following a wind disturbance 11 years before. Rowan trees composed the greatest proportion of trees within the post-disturbance forest before cleaning (almost 30%), and each standing rowan tree lost an average of 29 g dry mass of tissue from red deer browsing during one winter season. However, felled rowan trees received twice the incidences of both SBB and WBB than did standing live rowan trees. At the same time, the quantity of consumed biomass (MACC) was about 1.6 times greater on felled than standing rowans. These results indicated that felling of rowans temporary stimulated red deer to consume more tree biomass in the form of SBB (82% more on felled than standing trees) than in the form of WBB (21% more on felled than standing trees). As for BBB, the amount of biomass consumed by red deer was negligible in comparison with those of SBB and WBB in both felled and standing rowans. In addition, the pattern of SBB intensity along the trunk differed between felled and standing rowans. Our findings, like those of other studies, emphasize the value of rowans as forage for red deer. For example, Šebeň (2010) showed that nearly 21% of natural regeneration, expressed as the number of trees, in the post-disturbance area of the TNP was comprised of rowan. In addition, Kaštier and Bučko (2011) surveyed damage by red deer browsing (specifically leader shoots and branches) in young post-disturbance stands in this region, and found a higher percentage of browsed rowan trees (72.9%) than goat willow (50.7%) and silver fir (50.6%). All other species were much less frequently damaged by red deer browsing. Our results showed remarkable differences in browsing (i.e., MACC) between felled and standing rowans, which can likely be attributed to both accessibility of tree components for deer consumption and ease or efficiency of browsing. The fact that the red deer consumed so much more mass on felled trees is in part a consequence of the entire length of the stem being within the reach of the red deer. However, unlike in standing trees, red deer might have more trouble accessing the underside of the stem and branches of felled trees lying on the ground. How accessible the underside of felled trees are to red deer likely depends on crown density and how close the felled tree is to the ground. Ground vegetation, slope, and other aspects of the stand may influence the position of felled trees. However, because felled trees were browsed more intensely that standing trees even where the stem was completely
Table 4 Mean ( ± standard deviation) of the number of recorded incidences of whole branch browsing (WBB) by red deer (Cervus elaphus), the diameter of the branch at browsing, and the dry mass of consumed branches per tree for felled and live standing rowans (Sorbus aucuparia) in a post-disturbance stand in the High Tatra Mts., Slovakia. Status of rowans
Number of recorded cases (pieces)
Felled Standing
27.4 ± 14.6 14.5 ± 7.1
Diameter of browsed branches (cm2) 3.2 ± 1.0 3.3 ± 1.4
Mass of consumed branches (g) 13.9 ± 9.7 11.5 ± 8.5
Felled trees had about twice as many patches (F = 66.55, P < 0.001) and mass (F = 17.15, P < 0.001) of SBB as did standing trees, and SBB increased with tree height for number of patches (F = 15.27, P < 0.001) and mass (F = 17.26, P < 0.001 (Figs. 4, 5). Significant interaction terms indicated that the difference in SBB between felled and standing trees increased with tree height (number: F = 7.26, P = 0.002, mass: = 4.99, P = 0.010). Similarly, felled trees had about three times more patches (F = 17.04, P < 0.001) and biomass (F = 12.91, P = < 0.001) of BBB than did standing trees, and number of patches (F = 11.09, P < 0.001) and mass (F = 8.36, P < 0.001) all increased with tree height, with a significant interaction (number: F = 5.58, P = 0.006, mass: F = 4.27, P = 0.019, Figs. 4, 5). Like bark stripping, WBB was higher on felled than standing rowans, in terms of number of incidences (F = 39.19, P < 0.001) and mass removed (F = 3.88, P = 0.054), both of which increased with tree height 514
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Fig. 4. The mean ( ± standard error) number of incidences of different types of browsing by red deer (Cervus elaphus), including stem bark browsing (SBB; plate a), branch bark browsing (BBB; plate b), whole branch browsing (WBB; plate c) and all three types of browsing together (i.e., SBB + BBB + WBB; plate d), for felled and standing live rowans (Sorbus aucuparia) in relation to height class in a post-disturbance mixed forest in the High Tatra Mts., Slovakia. Different letters indicates statistically significant differences (two-way ANOVA followed by LSD test, α = 0.05).
previously accessible. Large diameters on standing trees might also represent repetitive cropping on the same branch during that season or previous seasons, as has been reported for large ruminants (e.g., Welch et al., 1988; Faber and Lavsund, 1999). Our experiment suggests that rowans can provide a substantial amount of winter food for red deer that might provide natural protection for conifers, especially larch and spruce, even when deer are at high density. For example, in our study area, red deer consumed an average of 93 g of dry mass from felled and 44 g from standing live rowans between 500 and 580 cm tall. Because red deer require about 3 kg of dry mass per day when consuming woody forage in winter (Hell et al., 2000), if rowans provided the sole forage for deer in a winter with high snow cover, each deer would need to browse about 30 felled or over 60 standing rowans per day to satisfy its daily intake. Therefore, 1 ha could feed a theoretical maximum of 100–300 red deer per day in our system with 7900 rowan trees/ha or 1–3 deer per ha over a 90-day winter season. Previous studies suggest that in mixed stands the bulk of winter browsing by red deer occurs on rowans and willows, with very little on pine and larch, and none on spruce (see also Kaštier and Bučko,
accessible to red deer (i.e., in a comparable stem section), we suggest that red deer prefer to strip bark and crop branches of trees positioned horizontally than vertically. This position might make stripping and cropping more efficient, although future experiments observing deer behaviour are needed to test this hypothesis. Alternatively, felled rowans may differ from standing live rowans in their texture (e.g., softness, moisture content) or nutritional or chemical composition, which could be an area of further research. We also found differences in WBB between felled and standing rowans. Red deer cropped larger branch diameters, often as large as 6–10 mm, on standing rowans, whereas they rarely cropped branches this large on felled trees. One reason for these differences might be the fact that fewer branches were available to deer on the standing trees because many were out of reach or had been previously browsed, thus red deer consumed more from each branch. Other studies with large browsing herbivores have shown that they crop large stem diameters and more bites per tree when fewer bites are available or trees are spaced further apart (Vivås and Sæther, 1987; Shipley and Spalinger, 1995). Felled trees would provide new resources that were not 515
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Fig. 5. The mean ( ± standard error) mass of different types of browsing by red deer (Cervus elaphus), including stem bark browsing (SBB; plate a), branch bark browsing (BBB; plate b), whole branch browsing (WBB; plate c) and all three types of browsing combined (i.e., SBB + BBB + WBB; plate d), for felled and standing live rowans (Sorbus aucuparia) in relation to height class in a post-disturbance conifer forest in the High Tatra Mts., Slovakia. Different letters indicates statistically significant differences (two-way ANOVA followed by LSD test, α = 0.05).
1994), may also change. On the other hand, red deer seem to avoid standing rowans that have been heavily browsed in past seasons, because the more accessible bark and branches have been already removed. In addition, we observed that red deer seem to avoid browsing near the scars from previous bark stripping (personal observation and photo- documentary). Some woody plants respond to browsing by inducing plant secondary metabolites (Bryant et al., 1991) and bark peeling may disrupt flow of carbohydrates through the cambium in that area, although Saint-Andrieux et al. (2009) measured a slightly higher carbohydrates in stripped than non-stripped beech (Fagus sylvatica) near wounds. Not only does felling reduce the lifespan of rowans as browse, it could also temporarily reduce forage potential in forest stands because rowans typically reproduce by seeds. However, regeneration of rowans can also occur by epicormic shoots Raspé et al. (2000). Therefore, rowans can display intensive vegetative regeneration at high elevation or in response to browsing (Myking et al., 2013), thus could provide a sustainable source of browse even where felling is used. Our results showed that SBB on the standing rowans occurred up to the maximum distance of 200 cm from the ground level, peaking at
2011). In principle, there may be a trade off between retaining rowans to reduce browsing on conifers and removing rowans to improve growth of conifers. However, in areas such as the TNP region that have high red deer populations, the threat to commercial tree species by browsing by red deer exceeds the consequences of reduced growth rate caused by interspecific competition stress that might occur when retaining more rowans in the stands. Although red deer browsed felled rowan trees more intensely than standing trees, felled trees have a shorter lifespan as browse for deer. Standing live trees can provide forage for a couple of seasons depending on the intensity of browsing, but felled trees seem to be edible for only the few months of one winter season. Thereafter, as the wood tissue dries and hardens, its attractiveness as forage seems to decline, likely because thicker, dryer bark is more difficult for herbivores to strip (Kuiters et al., 2006; Saint-Andrieux et al., 2009). Drying reduces the elasticity of parenchyma cells, which become more lignified (Klich, 2017). During this process, the nutritional properties that herbivores seek, such as carbohydrates (Saint-Andrieux et al., 2009), and those that they avoid, such as monoterpenes and phenolics (Duncan et al., 516
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80 felled
70
standing
Contribution to total number (%)
Contribution to total number (%)
80
60 50 40 30 20 10
70 60 50 40 30 20 10
0 20
21-40
41-60
61-80
0
81-100 101-120
2.0
2
Area class (cm )
2.1-4.0 4.1-6.0 6.1-8.0 Diameter class (mm)
8.1-10.0
Fig. 6. Histogram of area classes of browsed bark on stems (n = 451) and diameter classes of branches (n = 1257) cropped by red deer (Cervus elaphus) for felled and standing rowans in a post-disturbance stand in the High Tatra Mts., Slovakia. Fig. 7. Mean ( ± standard errors) of percentage of total bark that was consumed (consumed stem bark portion; CSBP in %) by red deer (Cervus elaphus) over vertical stem profile by 50-cm-long sections for felled and standing rowans (Sorbus aucuparia) in a post-disturbance mixed stand in in the High Tatra Mts., Slovakia. Only rowans > 400 cm were included. Different letters indicates statistically significant differences (two-way ANOVA followed by LSD test, α = 0.05).
have good growth, reproductive and regenerative properties. Furthermore, rowans tolerate mechanical damage such as heavy browsing (Miller et al., 1982). The response to superficial wounding, with the formation of a wound periderm structurally similar to the original intact one, is completed within 28 days (Woodward and Pocock, 1996). The deposition of suberin is detectable within about 7 days after wounding. This process protects compromised tissues from desiccation and markedly reduces the likelihood of pathogen invasion (Woodward and Pocock, 1996). A third of the shoots can be browsed during winter with no serious effects on sapling survival or regeneration. In areas with higher light levels it takes an average of 7–8 years for a saplings terminal shoots to be out of range of browsing deer (Homolka and Heroldová, 2003). To prolong the sustainable availability of rowan within a growing and vulnerable conifer stand, we suggest foresters retain some rowan trees within stands during their repeated cleanings and other interventions such as thinning and tending. Until rowan are mature (i.e., life
101–150 cm. However, WBB occasionally occurred between 200 and 250 cm above the ground. Similarly, the highest intensity of SBB in young ash (Fraxinus excelsior) occurred between 71 and 170 cm (Konôpka et al., 2012). In Scotland, Welch et al. (1988) showed that most wounds on stems caused by red deer were situated in the heights from 50 to 150 cm. In general, heights of the most frequent browsing correspond with height of the red deer’s shoulder (Renaud et al., 2003). These browsing patterns for felled rowans differed from standing rowans in our study. Although red deer had access to the entire length of the tree, the highest CSBP was found in the middle part of stem, between about 100 cm from the base and about 150 cm from the crown top. Although information about patterns of browsing on felled trees is scarce, we suggest that the bottommost part of stem might be less stable, and may move under pressure caused by red deer teeth. Similarly, the uppermost part of stem is more flexible, thin and often covered by a many branches that may impede browsing. Not only are rowans a preferred winter forage for red deer, they also 517
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felled rowans within a commercially-valuable conifer forest in Slovakia that we measured in our study suggests that rowan and other fastgrowing deciduous species could provide a mechanism for mitigating forest damage by red deer at some levels of population density. However, we offer the caveat that we did not directly measure the effects of rowan density or status (live standing or felled) on conifer damage, deer movements, or deer density. Although we expect that our recommendations for forest management that includes rowans will provide an efficient and socially acceptable method for mitigating some conflicts between timber and wildlife production, other methods for reducing browsing damage will need to be considered in some instances, such as when populations increase rapidly after mass tree recruitment following extensive timber harvest or natural disasters (e.g., Moser et al., 2008; Krojerová-Prokešová et al., 2010; Kuijper, 2011). These could include non-lethal methods such as protective barriers (fencing, plastic caps on terminals), chemical deterrents, and lethal methods such as gradual reductions of large herbivores, especially red deer (see also Konôpka et al. (2015b)). This may require changes in legislation, such as the Hunting Law in Slovakia.
expectancy of about 60 years; Raspé et al., 2000), foresters could leave enough rowans to provide sustainable forage and regeneration without undue competition with economically important tree species. This density would likely differ across sites and depend on management goals (e.g., the balance between productive and other ecosystem services of the forest), but we suggest about approximately 30–50 rowan trees per ha for our study area. Although these trees could be left scattered across the stand, foresters might find it more efficient to leave smaller groups at the edge of stands, along skidding lines and roads, or on the naturally occurring stand gaps. These groupings could also focus dispersion of red deer in more disturbed areas. Regardless, total extinction of rowan can be expected in mature stands with high rates of felling and extremely exposed to red deer browsing (Lindner et al., 1997). An alternative to maintaining and managing attractive browse species within conifer stands would be to plant or manage these species on dedicated browse plots with for the primary goal of providing forage supply for red deer. These plantings have the advantage of luring deer further away from valuable sites and reduce competition between rowans and conifers within a stand, but also result in several disadvantages, including concentrating deer and taking land out of timber production. If browse plots are desired, they should be established in areas with a naturally high concentration of red deer (e.g. south-facing slopes, stands near meadows and agricultural crops) and areas that have actual potential to naturally regenerate rowan and other preferred species. Because red deer are attracted to concentration of browse (Royo et al., 2017) browse plots should be placed as far as possible from high-quality commercial forests (see also Mansson et al. (2015)) Browse plots are normally between 0.1 and 0.3 ha, and forest owners must realize that these plots cannot produce wood production for several decades, but could reduce damage to economically important stands grown in the vicinity (Finďo and Petráš, 2007). For maximum value to red deer, these plots should be managed for recruitment and sustainable production of browse. However, we would like to stress that managers will generally receive higher economical and ecological value from managing deciduous trees that are valuable for browse but not for timber production that naturally regenerate within a commercial forest than by planting and managing dedicated browse plots. Our findings lead to several recommendations for managing young rowans in mixed forests facing browsing by red deer. Many of these suggestions would apply similarly to other preferred deciduous trees such as trembling aspen and a variety of willows.
Acknowledgements The research was supported by the projects APVV-14-0086 from the Slovak Research and Development Agency and also by grant “EVA4.0”, No. CZ.02.1.01/0.0/0.0/16_019/0000803 financed by OP RDE and project ITMS: 26220220025 supported by the ERDF-funded operational program, Research and Development“. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.foreco.2018.07.048. References Barančeková, M., Krojerová-Prokešová, J., Homolka, M., 2007. Impact of deer browsing on natural and artificial regeneration in foodplain forest. Folia Zool. 56, 354–364. Bryant, J.P., Provenza, F.D., Pastor, J., Reichardt, P.B., Clausent, T.P., Du Toit, J.T., 1991. Interactions between woody plants and browsing mammals mediated by secondary metabolites. Annu. Rev. Ecol. Evol. Syst. 22, 431–446. Burbaite, L., Csányi, S., 2010. Red deer population and harvest changes in Europe. Acta Zool. Lit. 20, 179–188. Čermák, P., Horsák, P., Spiřík, M., Mrkva, V., 2009. Relationship between browsing damage and woody species dominance. J. For. Sci. 55, 23–31. Cervený, J., Hell, P., Slamecka, J., 2013. Otto's Encyclopedia. Game Management. Otto's Publisher, Praha, pp. 591 (in Czech). Duncan, A.J., Hartley, S.E., Iason, G.R., 1994. The effect of monoterpene concentrations oin Sikkaspruce (Picea sitchensis) on the browsing behavior of red deer (Cervus elaphus). Can. J. Zool. 72, 715–1720. Faber, W.E., Lavsund, S., 1999. Summer foraging on Scots pine (Pinus sylvestris) by moose (Alces alces) in Sweden - Patterns and mechanisms. Wildlife Biol. 5, 93–106. Find’o, S., Petráš, R., 2007. Ecological Principals of Forest Protection to Game Damage. National Forest Centre, Zvolen, pp. 186 (in Slovak). Gill, R.M.A., 1992. A review of damage by mammals in north temperate forests. 1. Deer. Forestry 65, 145–169. Hell, P., Gašparík, J., Kartusek, V., Paule, L., Slamecka, J., 2000. Special Animal Husbandry. Technical University, Zvolen, pp. 228 (in Slovak). Heroldová, M., Homolka, M., Kamler, J., 2003. Breakage of rowan caused by red deer – an important factor for Sorbeto-Piceetum stand regeneration? For. Ecol. Manag. 181, 131–138. Holá, M., Ježek, M., Kušta, T., Červený, J., 2016. Evaluation of winter food quality and its variability for red deer in forest environment: overwintering enclosures vs. freeranging areas. Lesn. Cas. For. J. 62, 139–145. Homolka, M., 1990. Food of Cervus elaphus in the course of the year in the mixed forest habitat of the Drahanská vrchovina Highlands. Folia Zool. 39, 1–13. Homolka, M., Heroldová, M., 2003. Impact of large herbivores on mountain forest stands in the Beskydy Mountains. For. Ecol. Manag. 181, 119–129. Jamrozy, G., 1980. Winter food resources and food preferences of red deer in Carpathian forests. Acta Theriol. 25, 221–238. Kaštier, P., Bucko, J., 2011. Influence of ungulate game to the Tatra forest ecosystems damaged by the windstorm. In: Proceedings of International conference held on April 28th and 29th 2011 in Nový Smokovec. National Forest Centre, Zvolen, pp. 114–118 (in Slovak). Klich, D., 2017. Selective bark stripping of various tree species by Polish horses in relation to bark detachability. For. Ecol. Manag. 384, 65–71.
(1) Wait to fell rowans until most trees exceed 500 cm in height. (2) If rowans have been intensively damaged by browsing and the forage potential of the stem bark and branches is reduced, trees can be felled before they reach 500 cm. The ideal time would be when red deer have consumed branches with thickness of 1 cm above 250 cm from the ground level and most of the stem bark up to the height of 200 cm. (3) Rowans should be felled at the end of the growing season or in the early part of the winter season so that the trees do not become too dry to be attractive to red deer. (4) When possible, felling of rowans within a stand should be done in several applications over 2–3 subsequent years, treating only a part of each stand area each year and retaining some rowans within each stand for regeneration and future use by red deer. (5) Felled rowans should not be piled, which reduces access by red deer. Instead, felled rowans should be leaned against uncut trees, stumps or mounds so that most of the tree remains above the snow and red deer can access all sides of the tree. (6) If birch is being felled at the same time as rowans, make sure that rowans are not covered by birch, which is a less attractive forage species for red deer. In summary, the patterns and intensity of browsing on standing and 518
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