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Winter habitat use by red and roe deer in pine-dominated forest
Forest Ecology and Management 255 (2008) 468–475 www.elsevier.com/locate/foreco
Winter habitat use by red and roe deer in pine-dominated forest J. Borkowski a,*, J. Ukalska b,1 b
a Department of Forest Ecology and Wildlife Management, Forest Research Institute, Se˛kocin-Las, 05-090 Raszyn, Poland Department of Biometry, Faculty of Agriculture and Biology, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776 Warsaw, Poland
Received 31 October 2006; received in revised form 23 May 2007; accepted 5 September 2007
Abstract Although pines (Pinus spp.) represent the main tree genus in Europe, most studies of habitat use by European deer (Cervidae) have been conducted in spruce-dominated forests. This neglects the fact that the two forest types are quite different. Ground vegetation is much more abundant in pine stands, especially when they are mature. In this study, red and roe deer pellet groups were counted in approximately 12,500 ha of pine forests during the early spring over 4 years. Combinations of food and cover determined habitat attractiveness. Those habitat types which offered both food and cover were used most intensely. The role of forage was important only where cover was sufficient, suggesting that cover plays a primary role in influencing winter habitat use by deer. Habitat use by red and roe deer was similar both among habitats and within them, but the smaller species, roe deer seemed able to satisfy their cover requirements more easily than the larger red deer. No evidence of interspecific influence of red on roe deer (as suggested by Latham et al., 1997) was found in this study. As predicted, mature pine stands were an attractive habitat for deer. It was concluded that, in hunted deer populations, the presence of cover is important even in areas lacking large predators. Introduction of forest understories into mature pine forests should thus be promoted in big game management. # 2007 Elsevier B.V. All rights reserved. Keywords: Central Europe; Cover; Winter; Habitat use; Pine forest; Poland; Red deer; Roe deer
1. Introduction Red deer (Cervus elaphus) and roe deer (Capreolus capreolus) are the most numerous and widespread deer in Europe, and are the most extensively studied ungulates (CluttonBrock et al., 1982; Andersen et al., 1998). There are many studies of habitat use by these two species in European forests (e.g. Staines and Welch, 1984; Catt and Staines, 1987; Thirgood and Staines, 1989; Aulak and Babin´ska-Werka, 1990a; Welch et al., 1990; Latham et al., 1996; Tufto et al., 1996; Palmer and Truscott, 2003). However, most studies have been conducted in spruce-dominated (Picea) forests, even though the most abundant trees in Europe are pines (Pinus spp.; UN-ECE/ FAO, 1992). There are distinct differences between pine and spruce, especially in mature forests. Due to different crown structure and light conditions (Robakowski et al., 2004), the
* Corresponding author. Tel.: +48 22 7150412; fax: +48 22 7150417. E-mail addresses: [email protected] (J. Borkowski), [email protected] (J. Ukalska). 1 Tel.: +48 22 5932730; fax: +48 22 5932722. 0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2007.09.013
ground vegetation in pine stands is generally much richer than under the spruce canopy. Since old stands are among the most food-abundant age classes in pine-dominated forests (Borkowski, 2003), the question arises as to how deer use old pine stands in comparison with younger stands. Old growth pine forests are expected to be more attractive to deer than their spruce counterparts. Moreover, most studies on red and roe deer habitat use come from Scotland. Only a few were conducted in winter, which is a period of physiological stress, affecting important processes such as population dynamics (among others). Winter is also the season damage caused by deer in forests is most concentrated (Gill, 1992). Thus, a better understanding of factors affecting winter habitat use by deer is important for both game and forest management. In general, habitat use by deer is determined by the presence of both food and cover. The role of cover in habitat use may be especially important in winter, when cervids reduce their food intake and live to a remarkable extent off fat reserves (Putman, 1988). Two recognized cover types are thermal cover, in which a forest overstorey protects against weather and sun, and hiding (security) cover used in escape and as protection against predators and humans (Peek et al., 1982). Although many
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studies have documented the role of thermal cover (see Mysterud and Østbye, 1999, for references), recent experimental study demonstrated no positive effect of thermal cover on elk (C. elaphus nelsoni; Cook et al., 1998). On the contrary, the authors found that thermal cover resulted in greater over winter mass loss, fat catabolism and mortality. Less information is available on hiding cover, which is generally presumed to be associated with predation risk (Mysterud and Østbye, 1999). In fact, it is often people who influence deer behaviour and habitat use most. Hunting, as the extreme manifestation of human influence, is obviously an important factor. While animals in unhunted populations are usually tolerant of human presence (Schultz and Bailey, 1978; Borkowski, 2001), hunting tends to promote flight behaviour (Altman, 1958; Behrend and Lubeck, 1968). Moreover, as hunting is ‘‘human predation,’’ it ensures that hiding cover will be an important determinant of forest habitat use by deer, even where natural enemies are absent. This has been demonstrated for red deer by Bonenfant et al. (2004). Kufeld et al. (1988), found that mule deer (Odocoileus hemionus) used habitats with increasingly better cover as the hunting season progressed. A reasonable assumption, is that use of old pine forest (a relatively open habitat) during the hunting season would be positively influenced by understorey cover conditions. To date, the role of cover in habitat use among European deer, has mostly been studied in roe deer (Mysterud and Østbye, 1995), with much less attention given to red deer. Being much larger than roe deer, red deer may experience greater difficulty finding cover under the same habitat conditions. For instance, habitat use by red deer in young pine stands depends much more on tree height than is the case with roe deer (Borkowski, 2004). Similar phenomena may also apply in older forests. In spite of the numerous studies on both deer species, relatively little information is available on comparisons of habitat use and potential competition. However, Latham et al. (1996) compared red and roe deer densities in 20 localities and found a negative correlation between them. In the same 20 forests, the authors also found that red deer density had a negative influence on roe deer density, while the reverse was not the case (Latham et al., 1997). Both these studies are from Scotland and there is little information available from other places. If there is an interspecific influence of red on roe deer, spatial distribution of both species may be negatively related, not only between areas but also within them. The objective of this study was to examine patterns of winter habitat use by red and roe deer in pine-dominated forests. It was predicted that in pine-dominated forests, deer would use mature stands more frequently as compared to deer in spruce forests. Another prediction was that a hunted population would use habitats with security cover more intensely than habitats with less security cover, even in predator-free environments. It was also predicted that security cover would influence habitat use more in large deer species (red deer) than in small ones (roe deer). The final prediction was that, if interspecific competition between them is a factor, than deer densities in different habitats within one area would be negatively correlated.
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2. Study area The study was carried out near Rudy Raciborskie, in a Forest District of ca. 17,500 ha in southwestern Poland. As a large stand-replacement fire burned about 5000 ha of the District in 1992, data referred to here are from unburned forest only. Coniferous habitat types accounted for approximately 65% of the study area, with Scots pine (Pinus silvestris), the main tree species in the canopy (up to 85% of cover). As there was almost no management in the unburned forest for several years after the fire, the proportion of new plantations, and especially of pre-thickets, was minor. All of the forest is managed for timber with artificial regeneration accounting for the greatest part of it. Brown podzolic soils, together with podzols, make up 73% of the soils in the study area. About 20 years ago, foresters in this area began to introduce understories as part of a nationwide strategy to enrich homogenous pine stands. The main species used for this purpose were Norway spruce (Picea abies), common beech (Fagus sylvatica), black dogwood (Frangula alnus) and black cherry (Prunus serotina). The winter climate of the study area is very mild. The average temperature between December and March is 0.2 8C, with January being the coldest month (2.1 8C). The number of days with snow covers between December and February is usually around 45, and average snow depth rarely exceeds 5 cm. The area is flat with an elevation range between 180 and 307 m above sea level. At the time of the study, red and roe deer population densities (as estimated by drive counts) were of 4–6 and 6–10 individuals/100 ha of forest area, respectively (P. Nasiadka, unpubl. data). Other ungulates in the area were wild boar (Sus scrofa) and the less-common fallow deer (Dama dama). All the species were hunted by both individuals and groups. The hunting season varied with the species, but was most intense between October and February. There are no large predators in the area, except for occasional occurrences of single wolves (Canis lupus). The study area is located in Silesia, a densely populated, industrial region of Poland, and is commonly used for recreation. 3. Methods The study was conducted between 1997 and 2000, using standing crop counts of faecal pellet groups (Neff, 1968; Collins and Urness, 1981; Mayle et al., 1999). Pellet groups were counted every year in March along 2 m wide transects. Because the disappearance rate of summer and autumn pellets is relatively rapid in Poland (Aulak and Babin´ska-Werka, 1990b), all data refer to patterns of winter habitat use by red and roe deer. The transects were drawn on a 1:50000 map, so that their spatial distribution in the study area was more or less even. Each transect started at a characteristic point (e.g. a crossroads), which could be easily found in the field. The bearing of each transect was measured on the map and then walked with a compass. In total there were eight transects. Transects walked in 1997 differed slightly from subsequent years, when transects were drawn such that they could be reached by car (using forest and not the main
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Table 1 The length of transect units (km) in different habitat types in year 2000
T PS MF De P0 P1 P2 P3
Total
Palatable
Unpalatable
Pal/Unpal
2.7 3.3 26.0 2.2 2.1 4.0 9.0 8.7
– – – – 0.8 1.2 3.0 2.7
– – – – 0.9 2.4 3.1 2.5
– – – – 0.4 0.4 2.9 3.5
T: thicket; PS: pole size forest; MF: mature forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; Palatable: patches dominated by palatable plants; Unpalatable: patches dominated by unpalatable plants; Pal/Unpal: patches with both palatable and unpalatable plants.
roads). Total transect length was about 32 km. Each year transect length could differ slightly, for reasons such as recent forest work in a given sub-compartment (e.g. tree cutting and young plantation fencing) or high groundwater level. Pellet groups were counted separately for each part of the transect crossing an area of similar habitat characteristics (stand age class, tree species, understorey and ground vegetation condition). Each such part of the transect was considered a sampling unit, hereafter called a transect section. The length of each section was measured from the map or estimated by pacing. The total number of sections in different study years ranged from 108 to 184. Table 1 shows the length of sections in different habitats. Average section length was 220 m, while the average number of sections per transect was 18.4. Beside the numbers of red and roe deer pellets alongside transects, section data were collected on habitat characteristics with regards to dominant tree species (pine, deciduous), forest age class (thickets: 16–25; pole stage forests: 26–50; mature forests: >50-year-old stands) and understorey or ground vegetation conditions. Understorey and ground vegetation conditions were recorded in mature pine stands only, since both were scarce or absent in the other habitats. Understorey (woody and shrubby vegetation up to 4 m in height) tree/shrub species data (spruce, deciduous) was augmented by density information. The understorey in each transect section was assigned to one of four classes: no understorey (P0), sparse – composed of single trees or shrubs (P1), medium-density – visibility distance longer than 100 m (P2) and dense – visibility distance below 100 m (P3). Thus, the term ‘understorey density’ in this study refers to visibility rather than to shrub/tree stem density. In addition, understorey was classified as deciduous or spruce, depending on composition. Although the classification of understorey density was in this sense somewhat arbitrary, the fact that a single observer collected most data (with only limited help from another person) assured consistency. Data on ground vegetation (herbaceous vegetation and dwarf shrubs such as berries) was also collected within each transect section. Based on food preferences of red and roe deer (Dzie˛ciołowski, 1969; Ge˛bczyn´ska, 1980), the ground vegetation was classified as palatable (dominated by plants known to
be preferred, e.g. grasses, raspberry (Rubus ideus), bramble (R. caesius) and bilberry (Vaccinium myrtillus) or unpalatable (dominated by plants which are usually avoided or seldom consumed, e.g. small-reed (Calamagrostis sp.) and sedges (Carex sp.)). For clarity, analysis was confined to those sections in which the ground vegetation could be clearly classified as dominated by palatable or unpalatable plants (more than 50% of ground cover as estimated visually). 4. Statistical methods Generalized linear mixed models GLMM (Breslow and Clayton, 1993; Littel et al., 1996) were applied to the data for each species separately. Two mixed models were used. The first basic model (Model 1) was used to examine whether habitat type, year and their interaction, influence forest use in red and roe deer (habitat is defined as transect sections with similar stand age and species, understorey and ground vegetation). The second model (Model 2) analysed whether deer utilization of mature forest with various understorey densities depends on ground vegetation and its interaction with the understorey. Pellet group count data per section was a linear combination of fixed and random effects described by the generalized linear mixed Model 1: hi jk ¼ logðli jk Þ ¼ logðsÞ þ m þ yi þ h j þ ðyhÞi j þ tk
(1)
where hijk is the log link function log(lijk) with a Poisson error term, lijk the conditional mean (Littel et al., 1996) for the ijkth year–habitat–transect combination, m the intercept, yi the ith year fixed effect, hj the jth habitat type fixed effect, (yh)ij the year–habitat interaction and tk is the random effect of the kth transect. The logarithm of the section area, log(s), is an offset term to allow for the different lengths of the transect sections. Model 2 exclusively used data from mature pine forest where ground vegetation was observed. The form of this model was hi jkl ¼ logðli jkl Þ ¼ logðsÞ þ m þ yi þ u j þ gl þ ðugÞ jl þ tk (2) where lijkl is the conditional mean for the ijklth year–understorey–ground vegetation–transect combination, uj the jth understorey fixed effect, gl the lth ground vegetation fixed effect and (ug)jl is the understorey–ground vegetation interaction and the other effects are the same as in Model 1. Because empirical count data are typically over-dispersed, (i.e., the variance is greater than the mean; Littel et al., 1996), the significance of fixed effects of both models was based on the F-statistics adjusted for over-dispersion. Degrees of freedom were estimated using the Satterthwaite approximation, which could give non-integer values. Differences between factorial combinations were tested using Tukey–Kramer adjustment for unbalanced data (Kramer, 1956). In order to check if cover was equally important in habitat used by the two deer species, index of selectivity was calculated. Index of selectivity was defined as the ratio of mean pellet group count values per area unit in examined habitats to the general mean pellet group count value per area
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unit. The assumption was that the species with more pronounced cover requirements will ‘‘prefer more’’ covered habitats and ‘‘avoid more’’ open ones, while the species with less pronounced cover requirements will not show these preferences. As a result, the range of the index will be larger for the former than for the latter. Correlation between pellet group count data of the two deer species was checked using the Spearman rank correlation. For each species, transect residuals from Model 1 were compared by Pearson’s correlation to see if there was any unexplained variation correlated in the same way for red and roe deer. Both correlations were done on the scale of the study area (sections from all the transects together) and on the habitat scale (separately for each habitat type). Both GLMM models were fitted using the GLIMMIX macro-implement in the SAS System for Windows 9.1.3 (SAS Institute, 2002). Pearson’s correlation was assessed using the CORR procedure of the SAS System.
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Fig. 1. Pellet group density means for red (closed bars) and roe (open bars) deer per 100 m2 in different habitats. T: thicket; PS: pole stage forest; D: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey. Error bars show 1 S.E.
For both species, the rankings were nearly identical and the score of given habitat type depended very much on its cover conditions. More meaningful however, are the comparisons of specific pairs of habitats (Table 2). For both deer species, pellet group densities were higher in mature pine stands with dense deciduous and spruce understorey (P3d and P3s), and to some extent in mature pine stands with medium density spruce understorey (P2s; p < 0.05 or less), than in most other habitat types (thickets, pole-sized and deciduous stands). In general, there were no differences in either red or roe deer pellet group densities among mature pine stands with sparse or no understorey. Pellet group densities of both species were not dependent on the kind of understorey (deciduous vs. spruce) in any of understorey density classes ( p > 0.05 in all cases, Table 2). In mature pine stands, in all understorey density classes except for the sparse understorey, there were significantly more red deer pellet groups in transect sections with the ground vegetation dominated by palatable plants then in those dominated by unpalatable plants ( p < 0.05 or less, Fig. 2). In the case of roe deer, more pellet groups were recorded in sections with palatable plants than in unpalatable ones only in P0, P2s and P3d ( p < 0.05 or less, Fig. 2).
5. Results In total, 2890 red deer and 3101 roe deer pellet groups were recorded. Red deer pellet group density differed significantly among the habitats (F = 16.14; d.f. = 9, 540.4; p < 0.001) and years of the study (F = 2.74; d.f. = 3, 543.7; p = 0.04), but was not influenced by the interaction habitat year (F = 0.71; d.f. = 27, 538.6; p > 0.05). Similarly, habitat type was an important factor influencing roe deer pellet group density (F = 9.27; d.f. = 9, 545.3; p < 0.001). Roe deer pellet group density was similar among the years (F = 1.46; d.f. = 3, 541.4; p > 0.05); interaction habitat year (F = 1.31; d.f. = 27, 542; p > 0.05). It was possible to rank the habitats based on mean pellet group density (Fig. 1): red deer : D PS P1d P0 P1s T P2d P2s P3d P3s red deer : D P1d P0 PS T P1s P2s P2d P3d P3s
Table 2 Significance of comparisons of red (bold font) and roe deer (underlined font) pellet group densities recorded in different habitats
T PS D P0 P1d P1s P2d P2s P3d P3s
T
PS
D
P0
P1d
P1s
P2d
P2s
P3d
P3s
– ns ns ns ns ns ns ns ** ***
ns – ns ns ns ns ns * *** ***
ns ns – ns ns * * ** *** ***
ns ns ns – ns ns ns ns ** ***
ns ns ns ns – ns ns ns ns ns
ns ns ns ns ns – ns ns ns/* *
ns ns ns/* ns ns ns – ns ns ns
ns *** * * ns *** ns – ns *
* *** *** *** ns *** ns ns – ns
*** *** *** *** ns *** ns *** ns –
T: thicket; PS: pole stage forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; ns: not significant; ns/*: 0.05 < p < 0.1, *p < 0.05, **p < 0.01, ***p<0.001.
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J. Borkowski, J. Ukalska / Forest Ecology and Management 255 (2008) 468–475 Table 4 Correlation between red and roe deer pellet group densities in different habitats Habitat type
RS
P
T PS De P0 P1d P1s P2d P2s P3d P3s
0.45 0.46 0.51 0.27 0.22 0.51 0.41 0.29 0.71 0.52
* * * ns ns * ns ns * *
All habitats
0.57
*
T: thicket; PS: pole stage forest; MF: mature forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; RS: Spearman correlation coefficient; P: probability; ns: not significant; *p < 0.05.
Fig. 2. Pellet group density means and standard errors for red and roe deer per 100 m2 in transect sections dominated by palatale (closed bars) and unpalatable plants (open bars) in mature pine forest: P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; ns: not significant. *p < 0.05, **p < 0.01 and ***p<0.001.
positive but insignificant ( p > 0.05). Similarly, there was a positive correlation between the two sets of GLMM residuals on the scale of the study area (r = 0.44 and p < 0.001, Table 5). Significant ( p < 0.05 or less) positive correlations between the residuals were recorded in 7 out of 10 habitats (Table 5). 6. Discussion 6.1. Pellet count credibility
The index of selectivity (Table 3) for red was more than one and half times larger than for roe deer (1.88 and 1.17, respectively). Similarly, the coefficient of variation of the index for red deer was nearly twice as large as the one recorded for roe deer (39% and 65%, respectively, Table 3). On the scale of the study area, red and roe deer pellet groups were similarly distributed (RS = 0.57 and p < 0.05, Table 4). Pellet groups of both species were positively correlated in 6 out of 10 habitats (Table 4), while in 4 remaining ones RS were
Dissimilarities in structural characteristics among habitats in this study may have influenced deer pellet group density in different habitats. Pellet decomposition rates may depend on habitat conditions (Aulak and Babin´ska-Werka, 1990b), particularly openness (Welch et al., 1990; Lehmkuhl et al., 1994; Massei et al., 1998). However, in each of the cited studies, habitat-related differences in decomposition rates were minor in winter. Thus, it is unlikely that this factor exerted an
Table 3 Index of selectivity (see Section 3 for details) in red and roe deer habitat use
Table 5 Correlation between the two sets of GLMM residuals (Model 1) for red and roe deer in different habitats
Habitat
Habitat type
RS
P
T PS D P0 P1d P1s P2d P2s P3d P3s
0.47 0.52 0.41 0.47 0.02 0.18 0.35 0.35 0.65 0.47
*** *** * ** ns ns ns *** *** ***
0.44
***
T PS D P0 P1d P1s P2d P2s P3d P3s Range CV (%)
Red deer
Roe deer
0.94 0.49 0.25 0.54 0.50 0.61 1.29 1.32 1.93 2.13
0.83 0.75 0.41 0.72 0.68 1.02 1.29 1.15 1.58 1.58
1.88 65
1.17 39
T: thicket; PS: pole stage forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; CV: coefficient of variation.
All habitats
T: thicket; PS: pole stage forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; R: Pearson correlation coefficient; P: probability; ns: not significant; *p < 0.05, **p < 0.01 and ***p<0.001.
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important effect. Similarly, ground vegetation is scarce at the end of winter and should not have much influence on the ability to detect pellet groups. Ground vegetation therefore, was assumed not to influence the results of this study. 6.2. Mature pine stand use Our results suggest that mature pine forests (especially some patches within them), were much more attractive to deer, than has been reported for mature stands with spruce (Staines and Welch, 1984; Catt and Staines, 1987; Latham et al., 1996). The reason for this is probably poorer food conditions under the spruce canopy, due to the presence of much less favourable light conditions than in mature pine stands (Robakowski et al., 2004). Mature spruce forests with ground vegetation have been shown to sustain greater use on the part of red, and especially roe, deer, than those lacking ground vegetation (Welch et al., 1990). However, in this study, reference to the ground vegetation alone could not account for the use deer made of mature stands. For instance, use of deciduous stands offering little food was similar to that of mature pine stands with little or no understorey, that had much more abundant food resources. 6.3. Influence of security cover and ground vegetation As predicted, cover seemed to be a very important determinant of winter habitat use by the red and roe deer in Rudy Raciborskie. General habitat rankings for both species very much reflected a gradient of hiding cover conditions offered by various habitats. Deciduous mature stands received very little use, pole stage stands and mature pine stands without or with sparse understorey received moderate use, and mature pine stands with dense understorey were used most intensely. When the number of visitors to an area is high, deer seek dense cover (Jeppesen, 1987) even in populations generally tolerant of human presence (Borkowski, 2001). As already mentioned, this study area is commonly used, not only by people for recreation, but also for hunting. Hunting promotes intensive cover use by deer (Lovaas, 1958; Skolvin, 1982; Kufeld et al., 1988). However, cover alone was not able to explain habitat use pattern by deer in this study. For instance, there was no significant difference in habitat use intensity between thickets offering favourable cover conditions, pole stage stands with neither food nor cover, or mature pine stands without understorey which had abundant food but no cover. Thus, the combination of food and cover seemed to determine habitat attractiveness. Mature pine stands with a dense understorey were the habitat type most preferred by both deer species. No other habitat within the study area could have offered both abundant food and good cover conditions. It has been documented that simultaneous access to food and cover can influence home range size. That is, the more fine-grained a habitat mosaic, the smaller the home range that can encompass all required resources (Moe and Wegge, 1994; Borkowski and Furubayashi, 1998). Henry (1981) concluded that forest rides were the habitat type most used by roe deer because of high food availability and proximity to cover.
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Although a dense understorey offering cover could also attract deer through its abundant browse, this probably was not the main reason for the use of such patches. Spruce twigs are usually avoided by deer in Poland (Dzie˛ciołowski, 1969; Borowski and Kossak, 1975), but the sites with a deciduous understorey of higher quality browse were used as often as those with spruce-dominated understories. Although Borowski and Kossak (1975) found spruce bark to be important in winter diets, in our study area we observed no spruce de-barking. 6.4. Comparison of habitat use between red and roe deer 6.4.1. Importance of ground vegetation Ground vegetation was an important factor modifying deer habitat use in Rudy Raciborskie. In case of red deer, this trend was recorded in nearly every understorey density class and use intensity was positively related to understorey density. Thus, the cover seems to be a necessary primary condition for preferred winter habitat of the studied deer species. Only when cover is sufficient will food availability influence deer distribution within this habitat. Although we do not have data on animal activity in the studied habitats, these results suggest that cover is important not only for resting but also for foraging animals. The use of mature pine stands by roe deer seemed to be less influenced by ground vegetation than was found for red deer. However, this is probably a result of the coarse classification of patches with palatable or unpalatable plants. Roe deer is a concentrate selector (Hofmann, 1985). The classification of the patches in the present study probably better reflected the conditions for an intermediate or roughage eater such as red deer (Hofmann, 1985). Contrary to roe deer, red deer depends more on food biomass than on its quality. In addition, unlike red deer, roe deer winter fat reserves are relatively small and the principal source of winter energy is food supply (Holand et al., 1998). Therefore, winter habitat use by roe deer should have been more influenced by food resources than was the case for red deer. 6.4.2. Importance of security cover In spite of similar habitat use patterns, roe deer (the smaller species) seemed to find it easier to satisfy its cover requirements than did the larger red deer. The idea of the more pronounced cover requirements for red deer than for roe deer was supported by wider ranges of the selectivity index and higher coefficient of variation for red than for roe deer. A similar conclusion was drawn by Lyon and Jensen (1980), who found that habitat use among the smaller mule deer was less influenced by security cover than was that of the larger elk. An especially clear relationship between species size and the need for cover was found in the relatively open post-burn area of young pine stands at Rudy Raciborskie (Borkowski, 2004). 6.4.3. Interspecific relations Latham et al. (1996) found that the densities of both deer species in different forests of Scotland were negatively correlated. In a subsequent study, Latham et al. (1997) pointed
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out that there were several climatic factors (such as temperature, snow depth, windspeed and rainfall), shaping the negative relation between red and roe deer densities. Moreover, within individual forests studied by Latham et al. (1997), red and roe deer used their habitats in different ways. In this study, densities of red and roe deer pellet groups were positively correlated on the scale of the study area and within many among available habitats. In winter especially, this should not come as a surprise, since major differences in the feeding habits of the two species observed in summer are likely to disappear in winter (Staines et al., 1985; Latham et al., 1999). Therefore, winter habitat use by both species may differ less than in the other seasons. Similar habitat use patterns between both species were also found in other studies (Staines and Welch, 1984; Welch et al., 1990). Latham et al. (1997) suggested that there may be an interspecific influence of red on roe deer. In the present study, red and roe deer pellet group densities were not negatively correlated, either on the study area or the habitat scale. Nevertheless, there may be negative effect of red on roe deer performance (body mass, survival and reproduction), even with similar habitat preferences. As a result, temporal exclusion or declining body mass of roe deer could have occurred. During last decade however, no decline in roe deer population number (Nasiadka, unpubl. data) or body mass (Borkowski, in prep.) has been observed. In addition, transect section residuals from the fitted models were positively correlated for red and roe deer. This suggests that untested factors were affecting both species in the same way. In combination with similar habitat preferences, these results suggest that interspecific competition was not an important factor in this study. Nevertheless, the relations between the two main and largely sympatric European deer species should receive more attention from the researchers. 7. Conclusions In hunted areas, security cover is an important factor determining habitat use by deer, even though large predators are absent. This study suggests that food also plays an important role, but only where cover requirements are already met. Where managers are interested in high densities of deer, it is important to make sure that security cover is available. This is especially true in habitats with abundant food and probably in areas where people hunt in groups using beaters. Under such circumstances, dense cover not only impedes shooting, but also allows some deer to remain undriven. This issue should be considered, especially in regions inhabited by larger deer species, since cover requirements in smaller deer seem to be less pronounced. Mature pine forests can serve as high-quality winter habitat for deer, but only when they offer abundant understories. The precise species composition of these understories is less important in central Europe. The introduction of such understories by foresters would thus seem important, not only for general biocenotic reasons, but also on account of the ‘‘side effect’’ of improved deer habitat. Such work can be seen as an integrated forest and game management practice worthy of promotion. However, in areas where large deer species cause
remarkable damage to forests, young plantations near forest patches offering security cover may be under higher pressure than those surrounded by poor cover stands. Acknowledgements We are grateful to the Headquarters of the Rudy Raciborskie Forest District for assistance and the friendly atmosphere. Thanks also to Dr. Pawel Nasiadka for his help and suggestions. Prof. Rory Putman kindly commented on an earlier draft of the manuscript. References Altman, M., 1958. The flight distance in free-ranging big game. J. Wildl. Manage. 22, 207–209. Andersen, R., Duncan, P., Linnel, J.D.C., 1998. The European Roe Deer: Biology of Success. Scandinavian University Press, Oslo. Aulak, W., Babin´ska-Werka, J., 1990a. Preference of different habitats and age classes of forest by roe deer. Acta Theriol. 35, 289–298. Aulak, W., Babin´ska-Werka, J., 1990b. Estimation of roe deer density based on the abundance and rate of disappearance of their faeces in the forest. Acta Theriol. 35, 111–120. Behrend, D.F., Lubeck, R.A., 1968. Summer flight behaviour of white-tailed deer in two Adirondack forests. J. For. 48, 118–126. Bonenfant, C., Leif, E.L., Mysterud, A., Langvatn, R., Stenseth, N.C., Gaillard, J.-M., Klein, F., 2004. Multiple causes of sexual segregation in European red deer: enlightenments from varying breeding phenology at high and low latitude. Proc. Roy. Soc. Lond. B 271, 883–892. Borkowski, J., 2001. Flight behaviour and observability in human-disturbed sika deer. Acta Theriol. 46, 195–206. Borkowski, J., 2003. Influence of forest age on fallow deer food availability. Sylwan 1, 88–95 (in polish with English summary). Borkowski, J., 2004. Distribution and habitat use by red and roe deer following a large forest fire in South-western Poland. For. Ecol. Manage. 201, 287–293. Borkowski, J., Furubayashi, K., 1998. Home range size and habitat use in radiocollared female sika deer at high altitudes of Tanzawa Muntains. Jpn. Ann. Zool. Fenn. 35, 181–186. Borowski, S., Kossak, S., 1975. The food habits of deer in the Bialowiez˙a primeval forest. Acta Theriol. 20, 463–506. Breslow, N.E., Clayton, D.G., 1993. Approximate inference in generalized linear mixed models. J. Am. Stat. Assoc. 88, 9–25. Catt, D.C., Staines, B.W., 1987. Home range use and habitat selection by red deer (Cervus elaphus) in a Sitka spruce plantation as determined by radiotracking. J. Zool. Lond. 211, 681–693. Clutton-Brock, T.H., Guinness, F.E., Albon, S.D., 1982. Red Deer: Behaviour and Ecology of Two Sexes. University of Chicago Press, Chicago. Collins, W.B., Urness, P.J., 1981. Habitat preferences of mule deer as rated by pellet-group distributions. J. Wildl. Manage. 45, 969–972. Cook, J.G., Irwin, L.L., Bryant, L.D., Riggs, R.A., Thomas, J.W., 1998. Relations of forest cover and condition of elk: a test of the thermal cover hypothesis in summer and winter. Wildl. Monogr. 141 (1), 1–61. Dzie˛ciołowski, R., 1969. The Quantity, Quality and Seasonal Variation of Food Resources Available to Red Deer in Various Environmental Conditions of Forest Management. Forest Research Institute, Warsaw. Ge˛bczyn´ska, Z., 1980. Food of the roe deer and red deer in the Białowiez˙a primeval forest. Acta Theriol. 25, 487–500. Gill, R.M.A., 1992. A review of damage by mammals in north temperate forests. 1. Deer. Forestry 65, 145–169. Henry, B.A.M., 1981. Dstribution patterns of roe deer (Capreolus capreolus) related to the availability of food and cover. J. Zool. Lond. 194, 271–275. Hofmann, R.R., 1985. Digestive physiology of the deer—their morphological specialisation and adaptation. In: Fennessy, P.F., Drew, K.R. (Eds.), Biology of Deer Production. Royal Society of New Zeland, pp. 393–407. Holand, Ø., Mysterud, A., Wannag, A., Linnell, J.D.C., 1998. Roe deer in northern environments: physiology and behaviour. In: Andersen, R.,
J. Borkowski, J. Ukalska / Forest Ecology and Management 255 (2008) 468–475 Duncan, P., Linnell, J.D.C. (Eds.), The European Roe Deer: The Bioogy of Success. Scandinavian University Press, Oslo, pp. 117–137. Jeppesen, J.L., 1987. Impact of human disturbance on home range, movements and activity of red deer (Cervus elaphus) in a Danish environment. Dan. Rev. Game Biol. 13, 1–38. Kramer, C.Y., 1956. Extension of multiple range tests to group means with unequal numbers of replications. Biometrics 12, 309–310. Kufeld, R.C., Bowden, D.C., Scrupp, D.L., 1988. Influence of hunting on movements of female mule deer. J. Range Manage. 41, 70–72. Latham, J., Staines, B.W., Gorman, M.L., 1996. The relative densities of red (Cervus elaphus) and roe (Capreolus capreolus) deer and their relationship in Scottish plantation forest. J. Zool. Lond. 240, 285–299. Latham, J., Staines, B.W., Gorman, M.L., 1997. Correlations of red (Cervus elaphus) and roe (Capreolus capreolus) deer densities in Scottish forests with environmental variables. J. Zool. Lond. 242, 681–704. Latham, J., Staines, B.W., Gorman, M.L., 1999. Comparative feeding ecology of red (Cervus elaphus) and roe deer (Capreolus capreolus) in Scottish plantation forest. J. Zool. Lond. 247, 409–418. Lehmkuhl, J.F., Hansen, C.A., Sloan, K., 1994. Elk pellet-group decomposition and detectability in coastal forests of Washington. J. Wildl. Manage. 58, 664–669. Littel, R.C., Milliken, G.A., Stroup, W.W., Wolfinger, R.D., 1996. SAS System for Mixed Models. SAS Institute Inc., Cary. Lovaas, A.L., 1958. Mule deer food habits and range use, Little Belt Mtns., Montana. J. Wildl. Manage. 22, 275–283. Lyon, L.J., Jensen, C.E., 1980. Management implications of elk and deer use of clear-cuts in Montana. J. Wildl. Manage. 44, 352–362. Massei, G., Bacon, P., Genov, P.V., 1998. Fallow deer and wild boar pellet group disappearance in a Mediterranean area. J. Wildl. Manage. 62, 1086–1094. Mayle, B.A., Peace, A.J., Gill, R.M.A., 1999. How Many Deer? A Field Guide to Estimating Deer Population Size. Forestry Commission, Edinburgh. Moe, S.R., Wegge, P., 1994. Spacing behaviour and habitat use of axis deer (Axis axis) in lowland Nepal. Can. J. Zool. 72, 1735–1744. Mysterud, A., Østbye, E., 1995. Bed-site selection by European roe deer (Capreolus capreolus) in southern Norway during winter. Can. J. Zool. 73, 924–932.
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Mysterud, A., Østbye, E., 1999. Cover as a habitat element for temperate ungulates: effects on habitat selection and demography. Wildl. Soc. Bull. 27, 385–394. Neff, D.J., 1968. The pellet-group count technique for big game trend, census, and distribution: a review. J. Wildl. Manage. 32, 597–614. Palmer, S.C.F., Truscott, A.M., 2003. Seasonal habitat use and browsing by deer in Caledonian pinewoods. For. Ecol. Manage. 174, 149–166. Peek, J.M., Scott, M.D., Nelson, L.J., Pierce, J.D., 1982. Role of cover in habitat management for big game in northwestern United States. Trans. North Am. Wildl. Nat. Res. Conf. 47, 363–373. Putman, R., 1988. The Natural History of Deer. Christopher Helm, London. Robakowski, P., Wyka, T., Samardakiewicz, S., Kierzkowski, D., 2004. Growth, photosynthesis, and needle structure of silver fir (Abies alba Mill.) seedlings under different canopies. For. Ecol. Manage. 201, 211–227. SAS Institute, 2002. SAS 9.1.3. SAS Institute Inc., Cary. Schultz, R.D., Bailey, J.A., 1978. Responses of national park elk to human activity. J. Wildl. Manage. 42, 91–100. Skolvin, J.M., 1982. Habitat requirements and evaluation. In: Thomas, J.W., Toweill, D.E. (Eds.), Elk of North America: Ecology and Management. Stackpole Books, Harrisburg, pp. 219–278. Staines, B.W., Welch, D., 1984. Habitat selection of red (Cervus elaphus L.) and Roe (Capreolus capreolus) deer in a Sitka spruce plantation. Proc. Roy. Soc. Edinb. 82B, 303–319. Staines, B.W., Welch, D., Catt, D.C., Hinge, M.D.C., 1985. Habitat use and feeding by deer in Sitka spruce plantations. Institute of Terrestrial Ecology Annual Report. ITE, Abbots Ripton, pp. 12–16. Thirgood, S.J., Staines, B.W., 1989. Summer use of young stands of restocked sitka spruce by red and roe deer. Scot. For. 43, 183–191. Tufto, J., Andersen, R., Linnel, J., 1996. Habitat use and ecological correlates of home range size in a small cervid: the roe deer. J. Anim. Ecol. 65, 715– 724. UN-ECE/FAO, 1992. The Forest Resources of the Temperate Zone. General Forest Resource Information, vol. 1. United Nations, New York. Welch, D., Staines, B.W., Catt, D.C., Scott, D., 1990. Habitat usage by red (Cervus elaphus) and roe (Capreolus capreolus) deer in a Scottish Sitka spruce plantation. J. Zool. Lond. 221, 453–476.
Winter habitat use by red and roe deer in pine-dominated forest J. Borkowski a,*, J. Ukalska b,1 b
a Department of Forest Ecology and Wildlife Management, Forest Research Institute, Se˛kocin-Las, 05-090 Raszyn, Poland Department of Biometry, Faculty of Agriculture and Biology, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776 Warsaw, Poland
Received 31 October 2006; received in revised form 23 May 2007; accepted 5 September 2007
Abstract Although pines (Pinus spp.) represent the main tree genus in Europe, most studies of habitat use by European deer (Cervidae) have been conducted in spruce-dominated forests. This neglects the fact that the two forest types are quite different. Ground vegetation is much more abundant in pine stands, especially when they are mature. In this study, red and roe deer pellet groups were counted in approximately 12,500 ha of pine forests during the early spring over 4 years. Combinations of food and cover determined habitat attractiveness. Those habitat types which offered both food and cover were used most intensely. The role of forage was important only where cover was sufficient, suggesting that cover plays a primary role in influencing winter habitat use by deer. Habitat use by red and roe deer was similar both among habitats and within them, but the smaller species, roe deer seemed able to satisfy their cover requirements more easily than the larger red deer. No evidence of interspecific influence of red on roe deer (as suggested by Latham et al., 1997) was found in this study. As predicted, mature pine stands were an attractive habitat for deer. It was concluded that, in hunted deer populations, the presence of cover is important even in areas lacking large predators. Introduction of forest understories into mature pine forests should thus be promoted in big game management. # 2007 Elsevier B.V. All rights reserved. Keywords: Central Europe; Cover; Winter; Habitat use; Pine forest; Poland; Red deer; Roe deer
1. Introduction Red deer (Cervus elaphus) and roe deer (Capreolus capreolus) are the most numerous and widespread deer in Europe, and are the most extensively studied ungulates (CluttonBrock et al., 1982; Andersen et al., 1998). There are many studies of habitat use by these two species in European forests (e.g. Staines and Welch, 1984; Catt and Staines, 1987; Thirgood and Staines, 1989; Aulak and Babin´ska-Werka, 1990a; Welch et al., 1990; Latham et al., 1996; Tufto et al., 1996; Palmer and Truscott, 2003). However, most studies have been conducted in spruce-dominated (Picea) forests, even though the most abundant trees in Europe are pines (Pinus spp.; UN-ECE/ FAO, 1992). There are distinct differences between pine and spruce, especially in mature forests. Due to different crown structure and light conditions (Robakowski et al., 2004), the
* Corresponding author. Tel.: +48 22 7150412; fax: +48 22 7150417. E-mail addresses: [email protected] (J. Borkowski), [email protected] (J. Ukalska). 1 Tel.: +48 22 5932730; fax: +48 22 5932722. 0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2007.09.013
ground vegetation in pine stands is generally much richer than under the spruce canopy. Since old stands are among the most food-abundant age classes in pine-dominated forests (Borkowski, 2003), the question arises as to how deer use old pine stands in comparison with younger stands. Old growth pine forests are expected to be more attractive to deer than their spruce counterparts. Moreover, most studies on red and roe deer habitat use come from Scotland. Only a few were conducted in winter, which is a period of physiological stress, affecting important processes such as population dynamics (among others). Winter is also the season damage caused by deer in forests is most concentrated (Gill, 1992). Thus, a better understanding of factors affecting winter habitat use by deer is important for both game and forest management. In general, habitat use by deer is determined by the presence of both food and cover. The role of cover in habitat use may be especially important in winter, when cervids reduce their food intake and live to a remarkable extent off fat reserves (Putman, 1988). Two recognized cover types are thermal cover, in which a forest overstorey protects against weather and sun, and hiding (security) cover used in escape and as protection against predators and humans (Peek et al., 1982). Although many
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studies have documented the role of thermal cover (see Mysterud and Østbye, 1999, for references), recent experimental study demonstrated no positive effect of thermal cover on elk (C. elaphus nelsoni; Cook et al., 1998). On the contrary, the authors found that thermal cover resulted in greater over winter mass loss, fat catabolism and mortality. Less information is available on hiding cover, which is generally presumed to be associated with predation risk (Mysterud and Østbye, 1999). In fact, it is often people who influence deer behaviour and habitat use most. Hunting, as the extreme manifestation of human influence, is obviously an important factor. While animals in unhunted populations are usually tolerant of human presence (Schultz and Bailey, 1978; Borkowski, 2001), hunting tends to promote flight behaviour (Altman, 1958; Behrend and Lubeck, 1968). Moreover, as hunting is ‘‘human predation,’’ it ensures that hiding cover will be an important determinant of forest habitat use by deer, even where natural enemies are absent. This has been demonstrated for red deer by Bonenfant et al. (2004). Kufeld et al. (1988), found that mule deer (Odocoileus hemionus) used habitats with increasingly better cover as the hunting season progressed. A reasonable assumption, is that use of old pine forest (a relatively open habitat) during the hunting season would be positively influenced by understorey cover conditions. To date, the role of cover in habitat use among European deer, has mostly been studied in roe deer (Mysterud and Østbye, 1995), with much less attention given to red deer. Being much larger than roe deer, red deer may experience greater difficulty finding cover under the same habitat conditions. For instance, habitat use by red deer in young pine stands depends much more on tree height than is the case with roe deer (Borkowski, 2004). Similar phenomena may also apply in older forests. In spite of the numerous studies on both deer species, relatively little information is available on comparisons of habitat use and potential competition. However, Latham et al. (1996) compared red and roe deer densities in 20 localities and found a negative correlation between them. In the same 20 forests, the authors also found that red deer density had a negative influence on roe deer density, while the reverse was not the case (Latham et al., 1997). Both these studies are from Scotland and there is little information available from other places. If there is an interspecific influence of red on roe deer, spatial distribution of both species may be negatively related, not only between areas but also within them. The objective of this study was to examine patterns of winter habitat use by red and roe deer in pine-dominated forests. It was predicted that in pine-dominated forests, deer would use mature stands more frequently as compared to deer in spruce forests. Another prediction was that a hunted population would use habitats with security cover more intensely than habitats with less security cover, even in predator-free environments. It was also predicted that security cover would influence habitat use more in large deer species (red deer) than in small ones (roe deer). The final prediction was that, if interspecific competition between them is a factor, than deer densities in different habitats within one area would be negatively correlated.
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2. Study area The study was carried out near Rudy Raciborskie, in a Forest District of ca. 17,500 ha in southwestern Poland. As a large stand-replacement fire burned about 5000 ha of the District in 1992, data referred to here are from unburned forest only. Coniferous habitat types accounted for approximately 65% of the study area, with Scots pine (Pinus silvestris), the main tree species in the canopy (up to 85% of cover). As there was almost no management in the unburned forest for several years after the fire, the proportion of new plantations, and especially of pre-thickets, was minor. All of the forest is managed for timber with artificial regeneration accounting for the greatest part of it. Brown podzolic soils, together with podzols, make up 73% of the soils in the study area. About 20 years ago, foresters in this area began to introduce understories as part of a nationwide strategy to enrich homogenous pine stands. The main species used for this purpose were Norway spruce (Picea abies), common beech (Fagus sylvatica), black dogwood (Frangula alnus) and black cherry (Prunus serotina). The winter climate of the study area is very mild. The average temperature between December and March is 0.2 8C, with January being the coldest month (2.1 8C). The number of days with snow covers between December and February is usually around 45, and average snow depth rarely exceeds 5 cm. The area is flat with an elevation range between 180 and 307 m above sea level. At the time of the study, red and roe deer population densities (as estimated by drive counts) were of 4–6 and 6–10 individuals/100 ha of forest area, respectively (P. Nasiadka, unpubl. data). Other ungulates in the area were wild boar (Sus scrofa) and the less-common fallow deer (Dama dama). All the species were hunted by both individuals and groups. The hunting season varied with the species, but was most intense between October and February. There are no large predators in the area, except for occasional occurrences of single wolves (Canis lupus). The study area is located in Silesia, a densely populated, industrial region of Poland, and is commonly used for recreation. 3. Methods The study was conducted between 1997 and 2000, using standing crop counts of faecal pellet groups (Neff, 1968; Collins and Urness, 1981; Mayle et al., 1999). Pellet groups were counted every year in March along 2 m wide transects. Because the disappearance rate of summer and autumn pellets is relatively rapid in Poland (Aulak and Babin´ska-Werka, 1990b), all data refer to patterns of winter habitat use by red and roe deer. The transects were drawn on a 1:50000 map, so that their spatial distribution in the study area was more or less even. Each transect started at a characteristic point (e.g. a crossroads), which could be easily found in the field. The bearing of each transect was measured on the map and then walked with a compass. In total there were eight transects. Transects walked in 1997 differed slightly from subsequent years, when transects were drawn such that they could be reached by car (using forest and not the main
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Table 1 The length of transect units (km) in different habitat types in year 2000
T PS MF De P0 P1 P2 P3
Total
Palatable
Unpalatable
Pal/Unpal
2.7 3.3 26.0 2.2 2.1 4.0 9.0 8.7
– – – – 0.8 1.2 3.0 2.7
– – – – 0.9 2.4 3.1 2.5
– – – – 0.4 0.4 2.9 3.5
T: thicket; PS: pole size forest; MF: mature forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; Palatable: patches dominated by palatable plants; Unpalatable: patches dominated by unpalatable plants; Pal/Unpal: patches with both palatable and unpalatable plants.
roads). Total transect length was about 32 km. Each year transect length could differ slightly, for reasons such as recent forest work in a given sub-compartment (e.g. tree cutting and young plantation fencing) or high groundwater level. Pellet groups were counted separately for each part of the transect crossing an area of similar habitat characteristics (stand age class, tree species, understorey and ground vegetation condition). Each such part of the transect was considered a sampling unit, hereafter called a transect section. The length of each section was measured from the map or estimated by pacing. The total number of sections in different study years ranged from 108 to 184. Table 1 shows the length of sections in different habitats. Average section length was 220 m, while the average number of sections per transect was 18.4. Beside the numbers of red and roe deer pellets alongside transects, section data were collected on habitat characteristics with regards to dominant tree species (pine, deciduous), forest age class (thickets: 16–25; pole stage forests: 26–50; mature forests: >50-year-old stands) and understorey or ground vegetation conditions. Understorey and ground vegetation conditions were recorded in mature pine stands only, since both were scarce or absent in the other habitats. Understorey (woody and shrubby vegetation up to 4 m in height) tree/shrub species data (spruce, deciduous) was augmented by density information. The understorey in each transect section was assigned to one of four classes: no understorey (P0), sparse – composed of single trees or shrubs (P1), medium-density – visibility distance longer than 100 m (P2) and dense – visibility distance below 100 m (P3). Thus, the term ‘understorey density’ in this study refers to visibility rather than to shrub/tree stem density. In addition, understorey was classified as deciduous or spruce, depending on composition. Although the classification of understorey density was in this sense somewhat arbitrary, the fact that a single observer collected most data (with only limited help from another person) assured consistency. Data on ground vegetation (herbaceous vegetation and dwarf shrubs such as berries) was also collected within each transect section. Based on food preferences of red and roe deer (Dzie˛ciołowski, 1969; Ge˛bczyn´ska, 1980), the ground vegetation was classified as palatable (dominated by plants known to
be preferred, e.g. grasses, raspberry (Rubus ideus), bramble (R. caesius) and bilberry (Vaccinium myrtillus) or unpalatable (dominated by plants which are usually avoided or seldom consumed, e.g. small-reed (Calamagrostis sp.) and sedges (Carex sp.)). For clarity, analysis was confined to those sections in which the ground vegetation could be clearly classified as dominated by palatable or unpalatable plants (more than 50% of ground cover as estimated visually). 4. Statistical methods Generalized linear mixed models GLMM (Breslow and Clayton, 1993; Littel et al., 1996) were applied to the data for each species separately. Two mixed models were used. The first basic model (Model 1) was used to examine whether habitat type, year and their interaction, influence forest use in red and roe deer (habitat is defined as transect sections with similar stand age and species, understorey and ground vegetation). The second model (Model 2) analysed whether deer utilization of mature forest with various understorey densities depends on ground vegetation and its interaction with the understorey. Pellet group count data per section was a linear combination of fixed and random effects described by the generalized linear mixed Model 1: hi jk ¼ logðli jk Þ ¼ logðsÞ þ m þ yi þ h j þ ðyhÞi j þ tk
(1)
where hijk is the log link function log(lijk) with a Poisson error term, lijk the conditional mean (Littel et al., 1996) for the ijkth year–habitat–transect combination, m the intercept, yi the ith year fixed effect, hj the jth habitat type fixed effect, (yh)ij the year–habitat interaction and tk is the random effect of the kth transect. The logarithm of the section area, log(s), is an offset term to allow for the different lengths of the transect sections. Model 2 exclusively used data from mature pine forest where ground vegetation was observed. The form of this model was hi jkl ¼ logðli jkl Þ ¼ logðsÞ þ m þ yi þ u j þ gl þ ðugÞ jl þ tk (2) where lijkl is the conditional mean for the ijklth year–understorey–ground vegetation–transect combination, uj the jth understorey fixed effect, gl the lth ground vegetation fixed effect and (ug)jl is the understorey–ground vegetation interaction and the other effects are the same as in Model 1. Because empirical count data are typically over-dispersed, (i.e., the variance is greater than the mean; Littel et al., 1996), the significance of fixed effects of both models was based on the F-statistics adjusted for over-dispersion. Degrees of freedom were estimated using the Satterthwaite approximation, which could give non-integer values. Differences between factorial combinations were tested using Tukey–Kramer adjustment for unbalanced data (Kramer, 1956). In order to check if cover was equally important in habitat used by the two deer species, index of selectivity was calculated. Index of selectivity was defined as the ratio of mean pellet group count values per area unit in examined habitats to the general mean pellet group count value per area
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unit. The assumption was that the species with more pronounced cover requirements will ‘‘prefer more’’ covered habitats and ‘‘avoid more’’ open ones, while the species with less pronounced cover requirements will not show these preferences. As a result, the range of the index will be larger for the former than for the latter. Correlation between pellet group count data of the two deer species was checked using the Spearman rank correlation. For each species, transect residuals from Model 1 were compared by Pearson’s correlation to see if there was any unexplained variation correlated in the same way for red and roe deer. Both correlations were done on the scale of the study area (sections from all the transects together) and on the habitat scale (separately for each habitat type). Both GLMM models were fitted using the GLIMMIX macro-implement in the SAS System for Windows 9.1.3 (SAS Institute, 2002). Pearson’s correlation was assessed using the CORR procedure of the SAS System.
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Fig. 1. Pellet group density means for red (closed bars) and roe (open bars) deer per 100 m2 in different habitats. T: thicket; PS: pole stage forest; D: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey. Error bars show 1 S.E.
For both species, the rankings were nearly identical and the score of given habitat type depended very much on its cover conditions. More meaningful however, are the comparisons of specific pairs of habitats (Table 2). For both deer species, pellet group densities were higher in mature pine stands with dense deciduous and spruce understorey (P3d and P3s), and to some extent in mature pine stands with medium density spruce understorey (P2s; p < 0.05 or less), than in most other habitat types (thickets, pole-sized and deciduous stands). In general, there were no differences in either red or roe deer pellet group densities among mature pine stands with sparse or no understorey. Pellet group densities of both species were not dependent on the kind of understorey (deciduous vs. spruce) in any of understorey density classes ( p > 0.05 in all cases, Table 2). In mature pine stands, in all understorey density classes except for the sparse understorey, there were significantly more red deer pellet groups in transect sections with the ground vegetation dominated by palatable plants then in those dominated by unpalatable plants ( p < 0.05 or less, Fig. 2). In the case of roe deer, more pellet groups were recorded in sections with palatable plants than in unpalatable ones only in P0, P2s and P3d ( p < 0.05 or less, Fig. 2).
5. Results In total, 2890 red deer and 3101 roe deer pellet groups were recorded. Red deer pellet group density differed significantly among the habitats (F = 16.14; d.f. = 9, 540.4; p < 0.001) and years of the study (F = 2.74; d.f. = 3, 543.7; p = 0.04), but was not influenced by the interaction habitat year (F = 0.71; d.f. = 27, 538.6; p > 0.05). Similarly, habitat type was an important factor influencing roe deer pellet group density (F = 9.27; d.f. = 9, 545.3; p < 0.001). Roe deer pellet group density was similar among the years (F = 1.46; d.f. = 3, 541.4; p > 0.05); interaction habitat year (F = 1.31; d.f. = 27, 542; p > 0.05). It was possible to rank the habitats based on mean pellet group density (Fig. 1): red deer : D PS P1d P0 P1s T P2d P2s P3d P3s red deer : D P1d P0 PS T P1s P2s P2d P3d P3s
Table 2 Significance of comparisons of red (bold font) and roe deer (underlined font) pellet group densities recorded in different habitats
T PS D P0 P1d P1s P2d P2s P3d P3s
T
PS
D
P0
P1d
P1s
P2d
P2s
P3d
P3s
– ns ns ns ns ns ns ns ** ***
ns – ns ns ns ns ns * *** ***
ns ns – ns ns * * ** *** ***
ns ns ns – ns ns ns ns ** ***
ns ns ns ns – ns ns ns ns ns
ns ns ns ns ns – ns ns ns/* *
ns ns ns/* ns ns ns – ns ns ns
ns *** * * ns *** ns – ns *
* *** *** *** ns *** ns ns – ns
*** *** *** *** ns *** ns *** ns –
T: thicket; PS: pole stage forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; ns: not significant; ns/*: 0.05 < p < 0.1, *p < 0.05, **p < 0.01, ***p<0.001.
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J. Borkowski, J. Ukalska / Forest Ecology and Management 255 (2008) 468–475 Table 4 Correlation between red and roe deer pellet group densities in different habitats Habitat type
RS
P
T PS De P0 P1d P1s P2d P2s P3d P3s
0.45 0.46 0.51 0.27 0.22 0.51 0.41 0.29 0.71 0.52
* * * ns ns * ns ns * *
All habitats
0.57
*
T: thicket; PS: pole stage forest; MF: mature forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; RS: Spearman correlation coefficient; P: probability; ns: not significant; *p < 0.05.
Fig. 2. Pellet group density means and standard errors for red and roe deer per 100 m2 in transect sections dominated by palatale (closed bars) and unpalatable plants (open bars) in mature pine forest: P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; ns: not significant. *p < 0.05, **p < 0.01 and ***p<0.001.
positive but insignificant ( p > 0.05). Similarly, there was a positive correlation between the two sets of GLMM residuals on the scale of the study area (r = 0.44 and p < 0.001, Table 5). Significant ( p < 0.05 or less) positive correlations between the residuals were recorded in 7 out of 10 habitats (Table 5). 6. Discussion 6.1. Pellet count credibility
The index of selectivity (Table 3) for red was more than one and half times larger than for roe deer (1.88 and 1.17, respectively). Similarly, the coefficient of variation of the index for red deer was nearly twice as large as the one recorded for roe deer (39% and 65%, respectively, Table 3). On the scale of the study area, red and roe deer pellet groups were similarly distributed (RS = 0.57 and p < 0.05, Table 4). Pellet groups of both species were positively correlated in 6 out of 10 habitats (Table 4), while in 4 remaining ones RS were
Dissimilarities in structural characteristics among habitats in this study may have influenced deer pellet group density in different habitats. Pellet decomposition rates may depend on habitat conditions (Aulak and Babin´ska-Werka, 1990b), particularly openness (Welch et al., 1990; Lehmkuhl et al., 1994; Massei et al., 1998). However, in each of the cited studies, habitat-related differences in decomposition rates were minor in winter. Thus, it is unlikely that this factor exerted an
Table 3 Index of selectivity (see Section 3 for details) in red and roe deer habitat use
Table 5 Correlation between the two sets of GLMM residuals (Model 1) for red and roe deer in different habitats
Habitat
Habitat type
RS
P
T PS D P0 P1d P1s P2d P2s P3d P3s
0.47 0.52 0.41 0.47 0.02 0.18 0.35 0.35 0.65 0.47
*** *** * ** ns ns ns *** *** ***
0.44
***
T PS D P0 P1d P1s P2d P2s P3d P3s Range CV (%)
Red deer
Roe deer
0.94 0.49 0.25 0.54 0.50 0.61 1.29 1.32 1.93 2.13
0.83 0.75 0.41 0.72 0.68 1.02 1.29 1.15 1.58 1.58
1.88 65
1.17 39
T: thicket; PS: pole stage forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; CV: coefficient of variation.
All habitats
T: thicket; PS: pole stage forest; De: deciduous forest; P0: pine forest with no understorey; P1: pine forest with sparse understorey; P2: pine forest with medium understorey; P3: pine forest with dense understorey; s: spruce understorey; d: deciduous understorey; R: Pearson correlation coefficient; P: probability; ns: not significant; *p < 0.05, **p < 0.01 and ***p<0.001.
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important effect. Similarly, ground vegetation is scarce at the end of winter and should not have much influence on the ability to detect pellet groups. Ground vegetation therefore, was assumed not to influence the results of this study. 6.2. Mature pine stand use Our results suggest that mature pine forests (especially some patches within them), were much more attractive to deer, than has been reported for mature stands with spruce (Staines and Welch, 1984; Catt and Staines, 1987; Latham et al., 1996). The reason for this is probably poorer food conditions under the spruce canopy, due to the presence of much less favourable light conditions than in mature pine stands (Robakowski et al., 2004). Mature spruce forests with ground vegetation have been shown to sustain greater use on the part of red, and especially roe, deer, than those lacking ground vegetation (Welch et al., 1990). However, in this study, reference to the ground vegetation alone could not account for the use deer made of mature stands. For instance, use of deciduous stands offering little food was similar to that of mature pine stands with little or no understorey, that had much more abundant food resources. 6.3. Influence of security cover and ground vegetation As predicted, cover seemed to be a very important determinant of winter habitat use by the red and roe deer in Rudy Raciborskie. General habitat rankings for both species very much reflected a gradient of hiding cover conditions offered by various habitats. Deciduous mature stands received very little use, pole stage stands and mature pine stands without or with sparse understorey received moderate use, and mature pine stands with dense understorey were used most intensely. When the number of visitors to an area is high, deer seek dense cover (Jeppesen, 1987) even in populations generally tolerant of human presence (Borkowski, 2001). As already mentioned, this study area is commonly used, not only by people for recreation, but also for hunting. Hunting promotes intensive cover use by deer (Lovaas, 1958; Skolvin, 1982; Kufeld et al., 1988). However, cover alone was not able to explain habitat use pattern by deer in this study. For instance, there was no significant difference in habitat use intensity between thickets offering favourable cover conditions, pole stage stands with neither food nor cover, or mature pine stands without understorey which had abundant food but no cover. Thus, the combination of food and cover seemed to determine habitat attractiveness. Mature pine stands with a dense understorey were the habitat type most preferred by both deer species. No other habitat within the study area could have offered both abundant food and good cover conditions. It has been documented that simultaneous access to food and cover can influence home range size. That is, the more fine-grained a habitat mosaic, the smaller the home range that can encompass all required resources (Moe and Wegge, 1994; Borkowski and Furubayashi, 1998). Henry (1981) concluded that forest rides were the habitat type most used by roe deer because of high food availability and proximity to cover.
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Although a dense understorey offering cover could also attract deer through its abundant browse, this probably was not the main reason for the use of such patches. Spruce twigs are usually avoided by deer in Poland (Dzie˛ciołowski, 1969; Borowski and Kossak, 1975), but the sites with a deciduous understorey of higher quality browse were used as often as those with spruce-dominated understories. Although Borowski and Kossak (1975) found spruce bark to be important in winter diets, in our study area we observed no spruce de-barking. 6.4. Comparison of habitat use between red and roe deer 6.4.1. Importance of ground vegetation Ground vegetation was an important factor modifying deer habitat use in Rudy Raciborskie. In case of red deer, this trend was recorded in nearly every understorey density class and use intensity was positively related to understorey density. Thus, the cover seems to be a necessary primary condition for preferred winter habitat of the studied deer species. Only when cover is sufficient will food availability influence deer distribution within this habitat. Although we do not have data on animal activity in the studied habitats, these results suggest that cover is important not only for resting but also for foraging animals. The use of mature pine stands by roe deer seemed to be less influenced by ground vegetation than was found for red deer. However, this is probably a result of the coarse classification of patches with palatable or unpalatable plants. Roe deer is a concentrate selector (Hofmann, 1985). The classification of the patches in the present study probably better reflected the conditions for an intermediate or roughage eater such as red deer (Hofmann, 1985). Contrary to roe deer, red deer depends more on food biomass than on its quality. In addition, unlike red deer, roe deer winter fat reserves are relatively small and the principal source of winter energy is food supply (Holand et al., 1998). Therefore, winter habitat use by roe deer should have been more influenced by food resources than was the case for red deer. 6.4.2. Importance of security cover In spite of similar habitat use patterns, roe deer (the smaller species) seemed to find it easier to satisfy its cover requirements than did the larger red deer. The idea of the more pronounced cover requirements for red deer than for roe deer was supported by wider ranges of the selectivity index and higher coefficient of variation for red than for roe deer. A similar conclusion was drawn by Lyon and Jensen (1980), who found that habitat use among the smaller mule deer was less influenced by security cover than was that of the larger elk. An especially clear relationship between species size and the need for cover was found in the relatively open post-burn area of young pine stands at Rudy Raciborskie (Borkowski, 2004). 6.4.3. Interspecific relations Latham et al. (1996) found that the densities of both deer species in different forests of Scotland were negatively correlated. In a subsequent study, Latham et al. (1997) pointed
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out that there were several climatic factors (such as temperature, snow depth, windspeed and rainfall), shaping the negative relation between red and roe deer densities. Moreover, within individual forests studied by Latham et al. (1997), red and roe deer used their habitats in different ways. In this study, densities of red and roe deer pellet groups were positively correlated on the scale of the study area and within many among available habitats. In winter especially, this should not come as a surprise, since major differences in the feeding habits of the two species observed in summer are likely to disappear in winter (Staines et al., 1985; Latham et al., 1999). Therefore, winter habitat use by both species may differ less than in the other seasons. Similar habitat use patterns between both species were also found in other studies (Staines and Welch, 1984; Welch et al., 1990). Latham et al. (1997) suggested that there may be an interspecific influence of red on roe deer. In the present study, red and roe deer pellet group densities were not negatively correlated, either on the study area or the habitat scale. Nevertheless, there may be negative effect of red on roe deer performance (body mass, survival and reproduction), even with similar habitat preferences. As a result, temporal exclusion or declining body mass of roe deer could have occurred. During last decade however, no decline in roe deer population number (Nasiadka, unpubl. data) or body mass (Borkowski, in prep.) has been observed. In addition, transect section residuals from the fitted models were positively correlated for red and roe deer. This suggests that untested factors were affecting both species in the same way. In combination with similar habitat preferences, these results suggest that interspecific competition was not an important factor in this study. Nevertheless, the relations between the two main and largely sympatric European deer species should receive more attention from the researchers. 7. Conclusions In hunted areas, security cover is an important factor determining habitat use by deer, even though large predators are absent. This study suggests that food also plays an important role, but only where cover requirements are already met. Where managers are interested in high densities of deer, it is important to make sure that security cover is available. This is especially true in habitats with abundant food and probably in areas where people hunt in groups using beaters. Under such circumstances, dense cover not only impedes shooting, but also allows some deer to remain undriven. This issue should be considered, especially in regions inhabited by larger deer species, since cover requirements in smaller deer seem to be less pronounced. Mature pine forests can serve as high-quality winter habitat for deer, but only when they offer abundant understories. The precise species composition of these understories is less important in central Europe. The introduction of such understories by foresters would thus seem important, not only for general biocenotic reasons, but also on account of the ‘‘side effect’’ of improved deer habitat. Such work can be seen as an integrated forest and game management practice worthy of promotion. However, in areas where large deer species cause
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