Habitat separation by sympatric forest grouse in

Habitat separation by sympatric forest grouse in Fennoscandia in relation to boreal forest succession JON E. SWENSON~ A N D PER ANGELSTAM Grimso Wildlife Research Station, Department of Wildlife Ecology, Swedish University of Agricultural Sciences, S-730 91 Riddarhyttan, Sweden

Can. J. Zool. Downloaded from www.nrcresearchpress.com by Harbin Industrial University on 06/03/13 For personal use only.

Received November 4, 1992 Accepted March 3, 1993 SWENSON, J.E., and ANGELSTAM, P. 1993. Habitat separation by sympatric forest grouse in Fennoscandia in relation to boreal forest succession. Can. J. Zool. 71: 1303- 1310. Sympatric forest grouse in intensively managed conifer-dominated forests of the southern boreal zone in Sweden occupied different forest successional stages. Black grouse (Tetrao tetrix) selected forest stands 0 -20 years old, hazel grouse (Bonasa bonasia) selected those 20-50 years old, and capercaillie (Tetrao urogallus) selected those 2 9 0 years old. Moreover, hazel grouse also selected stands with 1 - 10% deciduous trees, whereas capercaillie selected stands with no deciduous trees. The relative numbers of each grouse species were similar in two areas of intensively managed industrial forest, but differed in an area where forestry was less intensive and where forests had old-growth characteristics, i.e., they were old and multilayered. Black grouse dominated in the intensively managed areas, whereas hazel grouse dominated in the less intensively managed area. We suggest that under natural conditions, black grouse inhabited the early-successional stages of forest following burns, hazel grouse inhabited the next, denser, successional stage and also old-growth spruce-dominated forests in fire refugia, and capercaillie inhabited stands of open, old, pine-dominated forest maintained by forest fire. The black grouse appears to be preadapted to the modern system of clearcut forest management. However, this system is clearly detrimental to the hazel grouse and capercaillie. To maintain all three species in a managed landscape, forest managers must strive to mimic more closely the natural variation in types and sizes of forest stands. SWENSON, J.E., et ANGELSTAM, P. 1993. Habitat separation by sympatric forest grouse in Fennoscandia in relation to boreal forest succession. Can. J. Zool. 71 : 1303- 1310. Les Tetraoninae qui vivent en sympatrie dans les forCts trks exploitees, dominkes par les conifkres, dans le sud de la zone boreale de la Sukde, se partagent les differents stades de succession de la for&. Les TCtras lyres (Tetrao tetrix) habitent les bois de 0 -20 ans, les Gelinottes des bois (Bonasa bonasia), les bois de 20 -50 ans, et les Grands Tetras (Tetrao urogallus), les bois de 90 ans et plus. En outre, les Gelinottes des bois habitent surtout les forCts qui comptent 1- 10% d'arbres decidus, alors que les Grands Tetras prefkrent les bois sans arbres dkcidus. Les nombres relatifs de chaque espkce se sont avCrCs semblables en deux zones de for& industrielle trks exploitees, mais differents dans une zone moins exploitee oh les forCts ont les caractkristiques de vieilles forCts, i.e., que les arbres sont vieux et de toutes les hauteurs. Les TCtras lyres dominent dans les zones trks exploitees, alors que ce sont les Gelinottes des bois qui dominent dans les zones les moins exploitees. Nous croyons que, dans des conditions naturelles, les TCtras lyres habitent les premiers stades de la succession qui apparaissent h la suite des incendies, que les Gelinottes des bois occupent le stade suivant, plus dense, de mCme que les vieilles forCts h dominance d'epinettes dans les refuges non incendiks et que les Grands Tetras habitent les bois clairsemks, vieux, domines par les pins, et qui ont survecu aux incendies. Le TCtras lyre semble preadapt6 au systkme moderne de coupe A blanc des forCts. Cependant, ce systkme est visiblement nuisible A la GClinotte des bois et au Grand TCtras. Pour assurer la survie des trois espkces dans un environnement amenage, les responsables doivent s'efforcer d'imiter le plus possible les variations de dimensions et de compositions qui prevalent dans les forCts naturelles. [Traduit par la redaction]

Introduction In a forest environment, habitat patches consisting of different stages of secondary succession form a mosaic. In this patchy environment, many animal species are confined to a certain successional stage (e.g ., Grange 1948; Johnston and Odum 1956; Haapanen 1965, 1966; Ferry and Frochot 1970; LeResche et al. 1974; Meslow and Wight 1975; Fox 1982; Boag 1991; Schroeder and Boag 1991). If the habitat preference of a given species is fairly narrow, populations may "track' ' the amount of preferred habitat (Roughgarden 1974; Wiens 1976; Boyce and Daley 1980; Cody 1981), which is likely to change as succession proceeds. As a consequence, forest landscape composition should greatly influence the local occurrence as well as densities of breeding populations (Hansson 1979). Fire was a major factor in the destruction or disturbance of mature primeval boreal forests on the local scale, in both 'Present address: Norwegian Institute of Nature Research, Tungasletta 2, N-7005 Trondheim, Norway. Printed in Canada 1 lrnprirne au Canada

Fennoscandia (Seiskari 1962; Zackrisson 1977) and North America (Wright 1974; Viereck and Schandelmeier 1980). These disturbances resulted in a patchy distribution of different successional stages within the forest (Heinselman 1981). In Fennoscandia, forest fires have been suppressed almost totally during the last century (Zackrisson 1977), but commercial logging has created a patchy pattern of different successional stages (Andersson and Hultman 1980; Gamlin 1988). Both today's commercial forests and the primeval forests thus can be characterized as mosaics of stands, although today's stands seem to be considerably and consistently smaller, based on comparisons of Rowe (1979, cited in Heinselman 1981) and Tenow (1974) with Eriksson and Janz (1975) and Andersson and Hultman (1980). Fennoscandian boreal forests therefore provide a good opportunity to study if and how animal assemblages respond to horizontal patchiness. Boreal forest grouse species (Phasianidae; Tetraoninae) are relatively sedentary birds with a strong potential for population growih. ~orphological~haracters suggest that the grouse family evolved in a boreal environ-

CAN. J. ZOOL. VOL. 71, 1993


1304

ment (Hjorth 1970). Hence, we argue that boreal grouse species ought to have evolved adaptions to track the local changes of patches in different successional stages in a dynamic landscape. All four Fennoscandian forest-dwelling grouse tend to use forest stands of different ages (Seiskari 1962; SGrensen 1979; Marcstrom et al. 1982). Seiskari (1962) hypothesized that after mature coniferous forest disappears as a result of fire or of man's activities, these species colonize and leave patches of different successional stages in the following order: first willow ptarmigan (Lagopus lagopus), then both black grouse (Tetrao tetrix) and hazel grouse (Bonasa bonasia), and lastly capercaillie (Tetrao urogallus). In this paper we test Seiskari's (1962) hypothesis by analyzing if and how the latter three species, when found in sympatry in the southern part of the boreal zone, divide the successional sere in a horizontally structured environment. We also speculate about the effects on forest grouse of the change from natural to man-made processes in the Fennoscandian boreal forest.

Study areas The study was carried out in southern boreal type forests in southcentral Sweden (Ahti et al. 1968). The northern part of the area near Hallefors (59"50rN, 14"40rE) and the Grimso Wildlife Research Area (59"42 'N, 15"30rE) are covered with commercially managed coniferous forest. Logging consists of clear-cutting large patches of forest. Management is intensive and includes planting and several thinnings during a rotational period of about 100 years. Individual clearcuts are usually (61 %) 11- 30 ha in size (WidCn 1989). However, the cleared patches are effectively over twice as large, because clearcuts are often located adjacent to recently cut stands. In the southern part of the region (Fellingsbro; 59"27'N, 15'35'E) the boreal forest is broken up into islands surrounded by farmland. Here land holdings are small and owned by the farmers. Forests are managed mainly by cutting single trees or small groups of trees; only a minor proportion (ca. 4 % ) has been clear-cut. Clearcuts were small, usually about 1.5 ha. In all forests there are two coniferous tree species, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). The three main deciduous tree species are birch (Betula pubescens and B. pendula) and aspen (Populus tremula) .

Methods The data base for the detailed habitat analyses was the wildlife observation file at Grimso Wildlife Research Station (grouse observation data set). Everyone working at the station records their observations of selected species on a map (scale 1 : 50 000) of the area (130 km2). These maps are changed weekly. Data for all three sympatric species of grouse in the Grimso Wildlife Research Area were summarized by location (25-ha blocks) and season (winter and summer, with separating dates of approximately 1 May and approximately 1 November) for the period 1977- 1988. All portions of the Grimso Wildlife Research Area were not covered evenly during a season, and we have no measure of the intensity of searching effort within the area. Therefore, we analyzed the data in 3-year periods, and recorded only whether a species had been observed within a given block during the period. To analyze forest succession data within blocks as large as 25 ha, we required relatively even-aged stands. Thus, we chose only those 25-ha blocks that were covered by at least 75 % of one of the four following successional classes (based on the terminology of the Swedish Forest Service): (1) clearcuts without ensured reforestation (logging class 10); (2) plantations with or without the need for thinning (logging classes 21 and 22); (3) young forests with two or more future thinnings (logging classes 23, 3 1, and 32); and (4) older forests with

at most one thinning before the final cutting (logging classes 33 and 40). However, if agricultural areas or lakes covered more than 25 % of the block and it was otherwise homogeneous, we included it. The age of the forest (the average age if several stands were included) was determined for each block in 1978, 1981, 1984, and 1987. Clearcutting during this period was taken into account, with respect to both the age in the block and whether the block met the requirements stated above. Within each of the blocks that met these requirements, we determined the proportion of deciduous trees (expressed as the percentage of stems), using an average, corrected for the sizes of different stands when necessary. All forestry data were obtained from forest maps and stand descriptions provided by the Swedish Forest Service. Originally we attempted to separate forests into pinedominated, spruce-dominated, and mixed forests, but we did not continue to do this because most of stands were mixed forest. A total of 751 data points was available (one block during one 3-year period), and 3557 grouse were observed on these suitable blocks (1075 capercaillie, 23 11 black grouse, and 17 1 hazel grouse). Capercaillie were observed on 38% of the blocks, black grouse on 40 % , and hazel grouse on 10% . Data were analyzed with X 2 tests, using either contingency tables or one-way tests against expected values, first in 10-year forest age categories. If the samples were too small in any class, adjacent classes were combined to meet or exceed minimum sample size requirements (Zar 1974). Two-by-two tests were corrected for continuity using Yates' correction (Zar 1974). The X 2 goodness-of-fit test and the Bonferroni family of simultaneous confidence intervals were used to test use versus availability of specific age or deciduous classes (Neu et al. 1974). We chose a probability level of 0.05 to reject null hypotheses, but we present the actual probability level for each test. We also conducted transect censuses in three areas, Grimso, Hallefors, and Fellingsbro, during 1984 - 1986 to gather data on the composition of forest grouse species in forests subject to different types of management (grouse census data set). The transects followed the Finnish method (Rajala 1974), i.e., all grouse were counted within a transect 60 m wide. Two or three walkers were used and the area was covered at 500-m intervals during July and August. Transects measured 160 km per year at Grimso and 125 km per year at both Hallefors and Fellingsbro. All birds, both adult and juveniles, were included in the comparison of grouse species composition among areas.

Results Grouse species in relation to forest succession at Grimso (observational data) Black grouse showed no differences in use of forest ageclasses between the sexes in summer (x2 = 13.94, df = 8, P = 0.08) or winter (x2 = 8.32, df = 7, P = 0.31), nor between summer and winter for males (x2 = 4.06, df = 8, P = 0.85) or females (x2 = 12.94, df = 7, P = 0.07). Data for both sexes and seasons were therefore combined. The use of forest age-classes was very different from the available distribution (x2 = 33.22, df = 10, P < 0.0003). Black grouse used forests 0-49 years old more than expected, but only the 0 - 19 year class was selected (Fig. 1). Forests 50 - 89 years old were avoided (Fig. 1). Hazel grouse were rarely identified to sex, and there was no difference in use of forest age-classes between summer and winter (x2 = 2.17, df = 4, P = 0.70), so all data were combined. The use of forest age-classes was different from expected (x2 = 52.24, df = 9, P < 0.0001). Hazel grouse used forests 20-69 years old more than expected, selecting those 20-49 years old (Fig. 1). They used forests 0- 19 and >70 years old less than expected, avoiding those over 90 years old (Fig. 1). Capercaillie showed no differences in use of age-classes of

SWENSON AND ANGELSTAM

Black

Grouse Black

Grouse


I

u Z

w

a a

0

z w

H a z e l Grouse

0.6-

P: P:

0.4-

0 0.2-

W

cn

3

s 5

-0.2

-

-0.4

-

-0.6

-

a

(3

S

0 W

0.2-

3

0.0-

cn

0.0-

LL

0

H a z e l Grouse

0.4-

0

0

0.6-

LL

-0.2

-

a

-0.4

-

(3

-0.6

.

O

2 F P:

9

1

HI

Capercai 11 ie

1

Capercai 11 ie

I

AGE CATEGORY (YEARS)

PROPORTION OF DECIDUOUS TREES (Yo)

FIG. 1 . Occurrence (log,, of ratio) of sympatric forest grouse in relation to forest age on the Grimso Wildlife Research Area. A star indicates use of a category significantly more or less than expected (P < 0.05). Of a total of 751 available blocks, sample sizes were 287 blocks with capercaillie, 298 blocks with black grouse, and 75 blocks with hazel grouse.

FIG.2. Occurrence (log,, of ratio) of sympatric forest grouse in relation to the proportion of deciduous trees on the Grimso Wildlife Research Area. A star indicates use of a category significantly more or less than expected (P < 0.05). Of a total of 585 available blocks, sample sizes are 245 blocks with capercaillie, 21 1 blocks with black grouse, and 56 blocks with hazel grouse.

forests between the sexes in summer (x2 = 9.02, df = 9, P = 0.44) or winter (x2 = 1.57, df = 7, P = 0.98), nor between summer and winter for males (x2 = 11.00, df = 8, P = 0.20) or females (x2 = 8.48, df = 6, P = 0.21). Data for both sexes and seasons were therefore combined. The ages of forests in which capercaillie were observed differed clearly from those available (x2 = 40.72, df = 10, P < 0.0001). Capercaillie showed a preference for forests 2 9 0 years old, but used all forests over 70 years old more than expected (Fig. I). Forests less than 70 years old were used less than expected, and forests 0- 19 years old were avoided (Fig. I). The use of forest age-classes was different among the three species (x2 = 70.37, df = 8, P < 0.0001). Moreover, each pair of species also differed: capercaillie and black grouse (x2 = 30.82, df = 4, P < 0.0001), capercaillie and hazel grouse (x2 = 44.49, df = 4, P < 0.0001), and black grouse and hazel grouse (x2 = 29.69, df = 4, P < 0.0001).

Proportion of deciduous trees (observational data) Black grouse did not differ according to sex in their use of the deciduous classes in winter (x2 = 3.02, df = 3, P = 0.39) or in summer (x2 = 7.62, df = 3, P = 0.054). Combined data for both sexes showed no difference between winter and summer (x2 = 5.53, df = 4, P = 0.24), so all data were combined for the following test. Black grouse used forest stands as expected, based on the availability of dedicuous trees in the forest (x2 = 2.22, df = 4, P = 0.70, Fig. 2). However, the age-classes preferred by black grouse contained a relatively high proportion of deciduous trees (Fig. 3). Hazel grouse showed no difference between seasons in use of the deciduous classes (x2 = 3.82, df = 2, P = 0.15), so all data were combined. Their use of deciduous classes was different from expected, (x2 = 38.692, df = 4, P < 0.0001). Hazel grouse used forests with 1 -20% deciduous trees more than expected on the basis of availability, and

CAN. J. ZOOL. VOL. 71. 1993

TABLE1. Composition of forest grouse species during 1984- 1986 in three areas subject to two forms of forest management

Clear-cutting


Hallefors

Grimso

Combined

Selective cutting (Fellingsbro)

Black grouse % No.1100 km Hazel grouse % No.1100 km Capercaillie % No.1100 km No. of observations Length of transects (km)

a

.

W W

.

K I-

20-

-

a

-

W

-

0

.

Q

K

-

W

m -

m N

m m

m U

u

m ,

m c

m n

C

W

I

m O

O N

O m

O U

O u

O ,

O ~

O C

AGE CATEGORY (YEARS)

O

m

I

o -

-

O O

-

m o

I

O -

I

m m

-

m

-

A

I o

a

FIG. 3. Relationships beween forest age and proportion of deciduous trees (mean f SE) on 25-ha plots within the Grimso Wildlife Research Area.

selected forests with 1 - 10% (Fig. 2). They avoided forests with no deciduous trees (Fig. 2). Capercaillie did not differ according to sex in their use of abundance classes of deciduous trees in either summer (x2 = 1.242, df = 3, P = 0.74) or winter (x2 = 0.427, df = 3, P = 0.43), so data from the two sexes were combined. Nor was there a difference between summer and winter in use of deciduous forests (x2 = 8.56, df = 4, P = 0.07), so all data were combined for the following test. The use of deciduous trees in the forest by capercaillie was different from expected (x2 = 16.76, df = 4, P = 0.002). Capercaillie used forests with 0 % deciduous trees more than expected, but avoided forests with > 11% deciduous trees (Fig. 2). The three species differed from each other in use of forest stands containing deciduous trees (x2 = 47.5, df = 8, P < 0.0001). Two comparisons of pairs of species showed differences: capercaillie - hazel grouse (x2 = 45.17, df = 4, P < 0.0001), and black grouse - hazel grouse (X2= 28.58, df = 4, P < 0.0001). Surprisingly, no significant difference was found between capercaillie and black grouse (x2 = 6.64, df = 4, P = 0.16) in their annual use of stands with different proportions of deciduous trees.

Composition of grouse species in two types of forests (census data) The two industrial forests managed intensively by large-scale clear-cutting, Grimso and Hallefors, showed no difference in grouse species composition (x2 = 0.15, df = 2, P = 0.93). Black grouse was the dominant species in these forests, constituting 61 % of the grouse observed in the two areas (Table 1). The capercaillie was next in abundance, and the hazel grouse last (only 10%). The composition of grouse species in the Fellingsbro area was very different (comparison of Fellingsbro with Grimso and Hallefors combined: X2 = 129.5, df = 2, P < 0.0001). There, hazel grouse was the most abundant species, composing 59 % of the grouse censused, and black grouse and capercaillie were similar in abundance (Table 1). The same pattern was obtained when using sightings of birds per 100 krn of transect (Table 1). Hazel grouse were 5 times more common at Fellingsbro than in the industrial forests, and black grouse were 3.5 times more common in the industrial forest than at Fellingsbro. At Fellingsbro, forests were managed by making few small clearcuts; 95% of the forest was older than clearcuts and young plantations. In contrast, only 38 and 44% were in this older category in the industrial forests at Grimso and Hallefors, respectively. Within the old forest stands at Fellingsbro, more vegetation was left below the canopies of large trees and the deciduous component of the forest was greater than in old forest stands in the industrial forests.

Discussion Our observational data from Grimso were based on a conservative measure of use, because one observation of one bird over a 3-year period determined "use" of that block by that species. However, this was the only practical way to analyze the data without a measure of observer effort. The vast majority of the blocks were visited by station personnel many times over a 3-year period, so the time span was long enough to ensure adequate coverage. This means that our tests were also conservative, tending not to reveal differences in habitat use among the three species. However, the tests usually revealed highly significant differences, which we believe are real.


2W

20

f

v

7

a

U)

; o

Black Grouse Hazel

k W

s cW>


100

FOREST AGE (YEARS)

FIG. 4. Two-dimensional niches of three forest grouse species within managed forests on the Grimso Wildlife Research Area. Darkly shaded areas indicate areas significantly selected on both axes (P < 0.05); lightly shaded areas indicate areas significantly selected on one axis and used more than expected, but not significantly so, on the other axis. The black area represents niche space not present in the study area, i.e., greater than the maximum amount of deciduous trees available within each age-class.

Forest grouse niches in managed boreal forest Seiskari (1962) proposed two-dimensional niches of the three forest grouse in winter, based on forest type and age under pristine conditions, where a fire or storm removed the mature forest. He predicted that both hazel grouse and black grouse would prefer stands 20-60 years old, female capercaillie would prefer those 40 - 80 years, and male capercaillie would prefer those over 40 years. Our results also showed that, in a forest landscape created by man, with a mosaic of patches of different age, this simple model describes the main structuring force behind the different patterns of occurrence of black grouse, hazel grouse, and capercaillie. However, our results differed from Seiskari's (1962) predictions in terms of the specific ages of forest used by these species (Fig. 1). We found no difference between the sexes in use of forest of different ages by capercaillie, perhaps because of the conservative nature of our data base; more intensive studies have documented a difference (Rolstad and Wegge 1987; Gjerde 1991). We also found that capercaillie preferred older forest and black grouse younger forest than was predicted by Seiskari (1962). Our results from the industrial forest agreed well with his predictions for hazel grouse, but our results from the private forests indicated that hazel grouse also inhabit forest with an old-growth structure, i.e., with a vegetation layer below the canopy. Two factors that may have influenced the differences between our results and Seiskari's (1962) predictions are the types of forestry practised in the two areas and the inclusion of the willow ptarmigan in the youngest age-classes of forest in Seiskari's (1962) model. Willow ptarmigan were not found in our study areas. In the industrial forest at Grimso the three species showed significant differences with respect to both forest age and proportion of deciduous trees preferred. We were therefore able to define niches on the basis of these two dimensions (Fig. 4). The black grouse was the bird of the pioneer stage, selecting forests 90 years old but avoided those with deciduous trees. The old forests at Grimso are on generally poorer sites because the old forests on the richer sites were cut first. Deciduous trees are rare in these old pine forests, a feature apparently of no importance to capercaillie, as they feed exclusively on pine in winter (Klaus et al. 1989). The results from grouse censuses in the two types of managed forests added another aspect to these results. Hazel grouse was the most common grouse in private forests, where forests were old and cutting units were small (Table 1). These forests had a structure similar to old-growth forests, with unevenly aged successional stages occurring as very small patches in a generally old forest with a relatively high deciduous component. This indicated that the hazel grouse niche also occurs in spruce-dominated old forests which have a second layer of younger trees below the canopy layer (Fig. 5A). This forest structure is not common in old stands of intensively managed industrial forest (Fig. 5A). Capercaillie were not more abundant than black grouse in these latter forests with an old-growth character, perhaps because the forests are generally quite dense. Within the industrial forests managed by large-scale clearcutting, the black grouse was the most common species (Table 1). This was consistent with our findings from Grimso that black grouse prefer young forests. Both industrial forests had a relatively high proportion of clearcuts and young forests. Also, the capercaillie was more common in the industrial forests than the hazel grouse, perhaps because the repeated thinning of the industrial forests results in very open forests in the older age-classes, a condition that is preferred by capercaillie and avoided by hazel grouse (Bergmann et al. 1982; Rolstad and Wegge 1987). This study shows that in boreal forest the local distribution of tetraonids is strongly related to the local distribution of suitable habitats. Within each successional stage, habitat qualities such as cover and deciduous trees also may influence habitat preferences. Sedentary passerine bird species that prefer old

CAN. J. ZOOL. VOL. 71, 1993

-


+ BLACK GROUSE + HAZEL + GROUSE

+BLACK

-

GROUSE

CAPERCAILLIE

HAZEL GROUSE

-

-

- CAPERCAILLIE

HAZEL GROUSE

-

HAZEL GROUSE

CAPERCAlLLlE

t

FIG. 5 . (A) Graphic portrayal of the forest structures studied; intensively managed forest on the left, farmer's forests on the right. (B) Hypothesized structure of primeval forest. The age-classes found or hypothesized to be used by the three forest grouse species are indicated.

boreal forest stands seem to track the amount of such habitats (Helle and Jarvinen 1986). Helle and Jarvinen (1986) raised the possibility that species less abundant than those that they studied could be less vulnerable to habitat changes. This caution appears to be unwarranted, since the grouse in our study had population densities at least one order of magnitude less than those of the passerines they studied, but nevertheless showed a strong tracking ability. Other examples of habitat tracking by bird populations on a local or regional scale are given by Cody (1985). Forest grouse niches in relation to natural boreal forest succession Black grouse were characteristic of younger successional stages, which contain a large deciduous component, as shown by our study and others (Sorensen 1979; Seiskari 1962; Klaus et al. 1990). Thus, the niche of the black grouse under natural conditions appeared to be the birch-rich early successional stages following forest fires (Fig. 5B) or bogs (Angelstam and Martinsson 1990). The dominant fire regime in the main boreal forest was large, intense fires (Heinselman 1981). Hazel grouse inhabit two successional stages: the early secondary successional stage following fire (though somewhat later than black grouse), and old-growth forest (Fig. 5B). Within both habitats, hazel grouse in most of the western Palearctic boreal forest are closely tied to spruce (see the review by Bergmann et al. 1982). Hazel grouse have been reported to inhabit younger successional stages (Teidoff 1951; Rajala 1966; Sorensen 1979; Bergmann et al. 1982) and oldgrowth spruce forests (Haapanen 1966; Sevast'yanov 1974;

Wiesner et al. 1977; Helle 1986). Also, hazel grouse are common in spruce forests where small-scale clear-cutting is performed, which results in an old forest wi.th stratified layering and a high deciduous component (Teidoff 195 1; Tomek 1965; Eiberle and Koch 1975; Wiesner et al. 1977; this study), similar to that found in natural old-growth forests (Falinski 1986). Old-growth spruce was relatively rare in the boreal forest, but did occur as patches in moist areas that were infrequently burned either because of their concave topography or because they were surrounded by bog (Zackrisson 1977; Engelmark 1987). Capercaillie are dependent upon old forests, as was found in our study (Fig. 5B) and numerous others (see the review by Rolstad and Wegge 1987). Capercaillie prefer relatively dry, open pine forests, particularly in winter (Seiskari 1962; Sorensen 1979; Gjerde 1991; Klaus et al. 1989). This habitat type was formerly subjected to, and apparently maintained by, repeated fires (Zackrisson 1977; Engelmark 1987). The change from natural to managed forest systems: consequences for forest grouse The forest management system used in state and large private forest company lands throughout Fennoscandia is intensive and highly mechanized. It is based on clear-cutting areas of 10-60 ha (in central Sweden) that have very little internal structural diversity. Some pine trees are left temporarily to provide seed for natural reproduction, or spruce are planted. This results in even-aged coniferous monocultures that undergo several thinnings, removal of undergrowth, and selective


0

100

200


FOREST AGE (YEARS)

FIG.6. Age-class distributions of forest in a managed and a natural, fire-dominated landscape with the same rotation period, 100 years (from Van Wagner 1978). The block represents managed forest and the negative logarithmic line represents natural forest. The ageclasses selected by the three grouse species within the managed forest are indicated by shading, and age-classes hypothesized to be selected in natural, but not managed,.forest are indicated by arrows. Light shading denotes black grouse, medium shading denotes hazel grouse, and the black area denotes capercaillie.

removal of deciduous trees in several stages starting soon after the young trees are established. Wet areas are drained also. Clear-cutting removes blocks of old forest, creating an early successional stage of forest, which in most forest types in Fennoscandia is dominated by birches. Our data suggest that black grouse did well in these habitats. Although forest management caused a reduction in the proportion of deciduous trees, we did not document that the proportion of dedicuous trees in the study area influenced black grouse distribution. There is also a somewhat greater proportion of the youngest age-classes of forest, i.e., black grouse habitat, in an intensively managed landscape than in a natural forest with the same rotation period (Van Wagner 1978; Fig. 6), and the black grouse was the most common grouse in the two industrial forests we studied. Therefore, we conclude that black grouse habitat has been positively affected by modern forestry. As the young forests grow and become dense, they still contain deciduous trees and become habitat for hazel grouse (Fig. 5A). The future decline of deciduous trees in the ageclasses used by hazel grouse (Fig. 3) will have a negative impact on hazel grouse habitat. As the young forest grows older, it is thinned repeatedly. Because hazel grouse depend on dense vegetation, particularly if it is close to the ground, for cover (Eiberle and Koch 1975; Weisner et al. 1977; Scherzinger 1979), the opening up of the lower forest layer by means of these thinnings is probably an important reason for the rapid decline in hazel grouse use after the 20- to 50-year period (Fig. 2). Natural thinning also occurs (Haapanen 1965; Heinselman 1981), but this is certainly more gradual. Therefore, we hypothesize that modern forestry has caused a shortening of the period during which young forests are suitable for hazel grouse (Fig. 5). The second habitat used by hazel grouse, old-growth spruce forest with a layered structure, does not exist in intensively managed forests (Figs. 5 and 6). We conclude that modern forestry has eliminated stable, long-term hazel grouse habitat in the natural landscape, and has reduced the quality of the transient habitat in younger forests by removing deciduous trees and shortening the time period during which it is suitable. On the other hand, the proportion of these younger habitats is probably greater in the managed landscape than in the natural landscape (Fig. 6). However, our

1309

comparison of censuses among areas indicated that industrial forestry is detrimental to hazel grouse (Table 1). Capercaillie used forests >70 years old more than expected, and selected forests >90 years old. Forest management in this area is based on an average rotation period of 100 years. Consequently, the vast majority of the fire-maintained old pine forest, to which the capercaillie is adapted, disappears under modern forest management (Fig. 6). All grouse may be negatively affected by other factors associated with modern forestry that were not incorporated into this study. These include the increase in small and mediumsized predators that has accompanied the appearance of modern forest landscapes (Hansson 1977, 1979; Rolstad and Wegge 1989) and the draining of wet spruce forests, which are important chick-rearing areas (Sjoberg and Ericson 1992). In addition, industrial forestry may also cause habitat fragmentation resulting in a reduction of habitat patch sizes and (or) habitat patch isolation (Rolstad and Wegge 1989; Angelstam and Martinsson 1990). We conclude that the black grouse is preadapted to the system of modern forestry and will do well with relatively few changes in forest management. Hazel grouse can survive in managed forest landscapes in the early successional stage if adequate cover and the deciduous tree component are maintained. The maintenance of capercaillie in the managed landscape presents the greatest challenge to forestry, on both the habitat and landscape scales. To maintain all three species in a landscape, forest managers must strive to mimic more closely the natural variation in structure and size of forest stands.

Acknowledgements We are thankful to our colleagues at Grimso Wildlife Research Station for conscientiously recording their observations of grouse on weekly maps. Trevor Wiens helped to summarize the data from these maps and Ingemar Jonsson extracted data from forestry maps. We thank David Boag, Henrik AndrCn, Jorund Rolstad, and two anonymous reviewers for their helpful comments on the manuscript. This study was financed by a grant from the Swedish Environmental Protection Agency. Ahti, T., Hamet-Ahti, L., and Salas, J. 1968. Vegetation zones and their sections in western Europe. Ann. Bot. Fenn. 5: 169-21 1. Andersson, B., and Hultman, S.-G. 1980. Skogens varden, skogsbrukets roll. [The forest's world, the role of forestry.] LT:s Forlag, Kristianstad, Sweden. Angelstam, P., and Martinsson, B. 1990. The importance of appropriate spatial and temporal scales in population studies-conservation lessons based on the population dynamics of black grouse in boreal forest in Sweden. In Symposium Proceedings: De toekomst van de wilde hoenderachtigen in Nederland, Wageningen, Netherlands, February 23 and 24, 1990. Edited by J.T. Lumeij and Y.R. Hoogeveen. Organisatiecommissie Nederlandse Wilde Hoenders, Amersfoort, the Netherlands. pp. 82-96. Bergmann, H.-H., Klaus, S., Miiller, F., and Wiesner, J. 1982. Das Haselhuhn Bonasa bonasia. 2. Auflage. A. Ziemsen Verlag , Wittenberg Lutherstadt, Germany. Boag, D.A. 1991. Spring population density of Spruce Grouse and pine forest maturation. Ornis Scand. 22: 181- 185. Boyce, M.S., and Daley, D. J. 1980. Population tracking of fluctuating environments and natural selection for tracking ability. Am. Nat. 115: 480-491. Cody, M.L. 1981. Habitat selection in birds: the roles of vegetation structure, competitors and productivity. BioScience, 31: 107 113.


1310

CAN. J . ZOOL. VOL. 71, 1993

Cody, M.L. 1985. Habitat selection in birds. Academic Press, Orlando, Fla. Eiberle, K., and Koch, N. 1975. Die Bedeutung der Waldstruktur fiir die Erhaltung des Haselhuhnes (Tetrastes bonasia L.). Schweiz. Z. Forstwes. 126: 876-888. Engelmark. 0 . 1987. Fire history correlations to forest type and topography in northern Sweden. Ann. Bot. Fenn. 24: 317-324. Eriksson, A., and Janz, K. 1975. Results from the National Forest Survey in 1968-1972. Res. Notes No. 21. Royal College of Forestry, Department of Forest Survey, Stockholm, Sweden. Falinski, J.B. 1986. Vegetation dynamics in temperate lowland primeval forests; ecological studies in Bialowieza forest. Dr. W. Junk bv Publishers, Dordrecht, the Netherlands. Ferry, C., and Frochot, B. 1970. L'avifaune nidificatrice d'une for& de ch6nes pCdonculCs en Bourgogne : Ctude de deux successions Ccologiques. Terre Vie, 1970: 153-250. Fox, B.J. 1982. Fire and mammalian secondary succession in an Australian coastal heath. Ecology, 63: 1332- 1341. Gamlin, L. 1988. Sweden's factory forest. New Sci. 117: 41 -47. Gjerde, I. 1991. Cues in winter habitat selection by capercaillie. I. Habitat characteristics. Ornis Scand. 22: 197 -204. Grange, W .B. 1948. Wisconsin grouse problems. Wisconsin Conservation Department, Madison. Haapanen, A. 1965. Bird fauna of the Finnish forests in relation to forest succession. I. Ann. Zool. Fenn. 2: 153- 196. Haapanen, A. 1966. Bird fauna of the Finnish Forests in relation to forest succession. 11. Ann. Zool. Fenn. 3: 176 -200. Hansson, L. 1977. Landscape ecology and stability of populations. Landscape Plann. 4: 85 - 93. Hansson, L. 1979. On the importance of landscape heterogeneity in northern regions for the breeding population densities of homeotherms: a general hypothesis. Oikos, 33: 162 - 189. Heinselman, M. L. 1981. Fire and succession in the conifer forests of northern North America. In Forest succession-concepts and application. Edited by D.C. West, H.H. Shugart, and D.B. Botkin. Springer-Verlag, New York. pp. 374 -405. Helle, P. 1986. Bird community dynamics in a boreal forest reserve: the importance of large-scale regional trends. Ann. Zool. Fenn. 23: 157- 166. Helle, P., and Jarvinen, 0 . 1986. Population trends of North Finnish land birds in relation to their habitat selection and changes in forest structure. Oikos, 46: 107 - 115. Hjorth, I. 1970. Reproductive behaviour in Tetraonidae with special reference to males. Viltrevy , 7: 183 -596. Johnston, D.W., and Odum, E.P. 1956. Breeding bird populations in relation to plant succession on the Piedmont of Georgia. Ecology, 37: 50 -62. Klaus, S., Andreev, A.V., Bergmann, H.-H., Miiller, F., Porkert, J., and Wiesner, J. 1989. Die Auerhiihner. A. Ziemsen Verlag, Wittenberg Lutherstadt, Germany. Klaus, S., Bergmann, H.-H., Marti, C., Miiller, F., Vitovic, O.A., and Wiesner, J. 1990. Die Birkhiihner. A. Ziemsen Verlag, Wittenberg Lutherstadt, Germany. Leresche, R.E., Bishop, R.H., and Coady, J.W. 1974. Distribution and habitats of moose in Alaska. Nat. Can. 101: 143- 178. Marcstrom, V., Brittas, R., and Engen, E. 1982. Habitat use by tetraonids during summer-a pilot study. In Proceedings of the 2nd International Grouse Symposium, Edinburgh, Scotland, March 1981. Edited by T.W.I. Lovel. World Pheasant Association, Reading, England. pp. 148-153. Meslow, E.C., and Wight, H.M. 1975. Avifauna and succession in Douglas-fir forests of the Pacific Northwest. USDA For. Serv. Gen. Tech. Rep. WO-1, pp. 266-271. Neu, C.W., Byers, C.R., and Peek, J.M. 1974. A technique for analysis of utilization-availability data. J. Wild. Manage. 38: 541 -545. Rajala, P. 1966. The number of tetraonid birds and their occurrence in various habitat types in the Oulu District according to compass line census, 1966. Suom. Riista, 19: 130- 144.

Rajala, P. 1974. The structure and reproduction of Finnish populations of capercaillie Tetrao urogallus and black grouse Lyrurus tetrix, on the basis of late summer census data from 1963-66. Finn. Game Res. 35: 1 -5 1. Rolstad, J., and Wegge, P. 1987. Capercaillie habitat: a critical assessment of the role of old forest. In Proceedings of the 4th International Grouse Symposium, Lam, Germany, September 1987. Edited by T. Lovel and P. Hudson. World Pheasant Association, Reading, England. pp. 235-250. Rolstad, J., and Wegge, P. 1989. Capercaillie Tetrao urogallus populations and modern forestry-a case for landscape ecological studies. Finn. Game Res. 46: 43 -52. Roughgarden, J. 1974. Population dynamics in a spatially varying environment: how population size "tracks" spatial variation in carrying capacity. Am. Nat. 108: 649-664. Rowe, J.S. 1979. Large fires in the large landscapes of the north. In Proceedings of the Symposium of Fire Management in the Northern Environment. USDI Bureau of Land Management, Anchorage, Alaska. Scherzinger, W. 1979. Zum Feindverhalten des Haselhuhnes (Bonasa bonasia). Vogelwelt, 100: 205 -2 17. Schroeder, M .A., and Boag, D. A. 1991. Spruce grouse populations in successional lodgepole pine. Ornis Scand. 22: 186 - 191. Seiskari, P. 1962. On the winter ecology of the capercaillie, Tetrao urogallus, and the black grouse, Lyrurus tetrix, in Finland. Pap. Game Res. 22: 1- 119. Sevast'yanov, G.N. 1974. Uchet teterevinykh v podzone srednei taigi Komi ASSR. [Census of grouse in middle taiga subzone of the Komi ASSR.] Ornithologiya, 11: 339 - 346. Sjoberg, K., and Ericson, L. 1992. Forested and open wetland complexes. In Ecological principles of nature conservation, applications in temperate and boreal environments. Edited by L. Hansson. Elsevier, London. pp. 326 - 35 1. Sqrensen, 0 .J . 1979. Skogsfuglbiotoper og skogsbruk. [Forest grouse habitats and forestry.] Tidskr. Skogbruk, 87(3): 129- 141. Swenson, J.E. 1993. The importance of alder to hazel grouse in Fennoscandian boreal forest: evidence from four levels of scale. Ecography, 16: 37:46. Teidoff, E. 1951. Zur Okologie, Biologie und Psychologie des Haselhuhns (Testrates [sic] bonasia). Bonn. Zool. Beitr. 2: 99 - 108. Tenow, 0 . 1974. Development of forested landscape and forest use in Fennoscandia up to the 20th century-an outline. Internal Rep. No. 2, Swedish Coniferous Forest Project, Swedish Agricultural University, Uppsala. Tomek, W. 1965. Hazel hen in Ciezkowice Highlands, southern Poland. Przegl. Zool. 9: 395 -404. Van Wagner, C.E. 1978. Age-class distribution and the forest fire cycle. Can. J. For. Res. 8: 220-227. Viereck, L.A., and Schandelmeier, L.A. 1980. Effects on fire in Alaska and adjacent Canada-a literature review. Bureau of Land Management Alaska Tech. Rep. No. 6. U.S. Department of the Interior, Alaska. Widen, P. 1989. The hunting habitats of goshawks Accipiter gentilis in boreal forests of central Sweden. Ibis, 131: 205 -23 1. Wiens, J.A. 1976. Population responses to patchy environments. Annu. Rev. Ecol. Syst. 7: 81 - 120. Wiesner, J., Bergmann, H.-H., Klaus, S., and Miiller, F. 1977. Siedlungsdichte und Habitatstruktur des Haselhuhns (Bonasa bonasia) im Waldgebiet von Bialowieza (Polen). J. Ornithol. 118: 1-20. Wright, E.E. 1974. Landscape development, forest fires, and wilderness management. Science (Washington, D.C .), 186: 487 -495. Zackrisson, 0 . 1977. Influence of forest fires on the north Swedish boreal forest. Oikos, 29: 22-32. Zar, J.H. 1974. Biostatistical analysis. Prentice-Hall, Inc., Englewood, Cliffs, N.J.