 Responses
of Wildlife to Clearcutting and Associated Treatments in the Eastern
United States intro
table of contents |
| Responses
of Wildlife to Clearcutting and Associated Treatments in the Eastern
United States intro
table of contents |
 Effects
of Clearcutting on Birds1. Clearcutting a. Seral Stages, Nesting Season Studies b. Winter Study c. Nest Predation and Parasitism d. Edge Effects e. Size of Clearcuts f. Harvesting Methods 2. Associated Treatments a. Site Preparations (Including Post Treatments) b. Thinning c. Planting (Including Site Conversion to Other Timber Types) d. Streamside Management Zones (SMZs) e. Snags
It is impossible to generalize about the needs of forest birds because each species has different requirements. As a result, each forest cover type, including the forest edge, has a somewhat different community of bird species at each phase in the stand’s development, from the seedling stage to a mature stand (Hooper 1981). a.
Seral Stages, Nesting Season Studies
The compatibility of even-aged timber management and red-cockaded woodpecker conservation was studied year round over a 6-year period in South Carolina by Wood et al. (1985). Treatments of 6 clan home ranges included early winter clearcuts on 0, 7, 11, 20, 22, and 37% of the annual territory. No relationships between level of cutting and changes in movements or habitat use were suggested. In addition, there was no effect on numbers of nestlings surviving to the immediate prefledgling period. Hooper and Lennartz (1995) studied the effect of removal of foraging habitat on group size and reproductive success of a dense aggregation of red-cockaded woodpeckers on the Francis Marion National Forest, South Carolina from 1979 to 1989. In the core zone, 448 acres (32%) of the foraging habitat in pines ³ 30 years old were clearcut. Including the trees removed in thinnings, 43% of the pines ³ 10 inches DBH were removed from the core zone. The removal had no discernible negative impact on the study groups. The results suggest that red-cockaded wood- peckers are not sensitive to loss of foraging habitat except at low densities. b. Winter
Study c.
Nest Predation and Parasitism Some studies have shown that clearcutting can affect predation rates in older, adjacent stands that are not harvested. Studies of nest predation in riparian buffer strips created by commercial clearcutting and in unharvested control areas in eastern Maine were conducted by Vander Haegen and DeGraaf (1996). Wide (792 ft) buffer strips along riparian zones reduced edge-related nest predation. A related study of predation on artificial ground and arboreal (5 ft above ground) nests was done in mature (uncut) forests with 0, 25, and 50% of the surrounding forest harvested by clearcutting (Yahner and Scott 1988). Nest depredation was highest in the 50% zone and least in the zero percent zone; more arboreal nests than ground nests were disturbed. American crows and blue jays were the major predators. Thus, clearcutting adversely impacts avian nesting success in the surrounding mature forest, particularly for shrub- and canopy-nesting birds. While predation is elevated in the
remaining mature forest, it actually is lower in young successional
stages. Depredation on artificial arboreal nests was studied in 2.5-ac
clearcut aspen plots in central Pennsylvania. Fewer nests were disturbed
in 4year-old plots than in 8yearold or mature
plots (Yahner and Cypher 1987). The shrubby vegetation in young
clearcuts provided well-concealed nest sites for birds that constructed
nests near ground level. Rates of predation on artificial ground and
shrub nests in clearcuts and remnant patches of mature forest were
studied in eastern Maine by Rudnicky and Hunter (1993). Predation rates
were higher for forest nests than for clearcut nests. Neither clearcut
size nor forest tract size exhibited a consistent relationship with
predation intensity. Distance to edge had no apparent effect on
predation of ground nests. However, the predation rate of shrub nests on
the edge was significantly higher than for ground nests in the edge and
ground and Forest-interior birds are vulnerable to brood parasitism by the brown-headed cowbird, particularly in fragmented forest landscapes. Stribley (1993) evaluated cowbird distributions relative to landscape-level patterns as well as site specific habitat conditions in northern Michigan hardwood forest stands. The probability that cowbirds would occur at any given site was 3-3.5 times greater when agricultural lands were present within 1.86 miles of a study site. Results indicated that intra- stand structural diversity and surrounding habitat heterogeneity were also important. Studies in the Midwest also suggest parasitism rates by cowbirds may be dependent on the landscape context and levels of permanent forest fragmentation by agriculture, housing, industry, etc.; more so than on the distribution of temporary openings created by regulated timber harvest (Thompson 1992). d. Edge
Effects Some species, however, may be adversely affected by the presence of stand edges. Ovenbird habitat use and reproductive success were examined in northern New Hampshire to determine the effect of edge in predominantly forested landscapes (King et al. 1995). The proportion of nests that failed from all causes, including predation, was higher along edges in 1992 but not in 1993. The number of young fledged per female and the proportion of pairs fledging at least one young did not differ between edge and interior in either year. They concluded that the effects of clearcutting are moderated by the abundance of mature forest cover in the region and by the tendency of ovenbirds to renest after initial nest failure. The degree of contrast along edges appears to be an important consideration. In even-aged northern hardwood stands in the White Mountain National Forest, New Hampshire, DeGraaf (1992), found the proportion of edge-associated species was higher in the younger stands in all edge-contrasts studied except the most subtle edge between mature and nearly mature stands. Only across seedling-sawlog and sapling-large sawlog edges were bird assemblages more different than similar. Edge “avoidance” was most pronounced when stands were most different. Edges between even-aged northern hardwood stands, even of greatly contrasting age or height, were found to be used by birds differently than field-forest edges. e. Size
of Clearcuts f.
Harvesting Methods In the Monongahela National Forest of
West Virginia, Wood and Nichols (1995) studied the effects of two-age
timber management vs clearcutting on songbird density and reproductive
success in 19 forest stands, 9 to 14 years after cutting. They concluded
that "silvicultural practices cannot be categorized as always
beneficial or detrimental to all birds." Two-age management and
clearcutting have similar effects, changing the habitat to the extent
that some birds, particularly some forest interior species, disappear
from these areas for a short period of time immediately following The effects of group selection vs clearcutting on breeding birds were compared in the Southern Appalachian hardwood forests of Virginia by Kerpez and Stauffer (1995). Clearcuts and large group selection cuts (>2.7 ac) provided breeding habitat for the same bird species. Both methods negatively impacted forest-interior species in the adjacent forest. However, the net negative effect was substantially less for clearcuts than for an equivalent area harvested by group selection. Costello et al. (1995) compared conventional clearcutting with group selection cutting in northern hardwood stands in New Hampshire. Group selection appears to retain much of the mature forest bird community while providing benefits for only a small number of early successional species. a.
Site Preparation (Including Post-Treatments) Perkins (1973) found in a study of the effects of clearcutting and site preparation on vegetation and wildlife in the flatwoods in Mississippi that numerous raptors, principally marsh hawks and barred owls were attracted to the bedded areas by the high populations of small rodents. He also found that the first year following herbicidal treatments the areas provided many different micro- habitats attractive to a variety of avifaunal species. Bird communities of undisturbed mature sand pine-scrub oak habitat of central Florida were compared to 5- to 7-year-old stands that had been burned and salvage logged to improve regeneration (Greenberg et al. 1995). Bird communities of the undisturbed stands were more species rich and diverse than those of stands disturbed in spring; whereas winter residents did not differ among treatments. Canopy and cavity nesters and canopy- and bark-foraging species were virtually restricted to mature forests. The threatened and endemic Florida scrub jay, however, occurred only in disturbance treatments. Two- to 6-year-old pine plantations in east Texas that were chopped, KG bladed and burned most benefitted indigo buntings, blue grosbeaks, bobwhite quail, and prairie warblers (Dickson et al. 1984). Shrubs that developed in areas with little or no site preparation most benefitted yellow-breasted chats, northern cardinals, white-eyed vireos, Carolina vireos, and field sparrows. b. Thinning In northern Florida, Repenning and Labisky (1985) compared bird communities in slash pine plantations and older longleaf pine stands. In summer, many species of birds inhabited both types; however, young plantations provided some habitat features (i.e., a shrub layer) that attracted several species of birds not found in the natural longleaf pine forest. A comparison of these types in winter produced a slightly different result. Although 1-year-old plantations had the highest winter bird density, this community had little in common with that of longleaf pine. Nevertheless, 40-year-old slash pine plantations provided habitat for a wintering bird community that was reasonably similar in composition to that of the longleaf pine forest. However, short-rotation slash pine stands may not support all birds associated with older longleaf pine forests. Bachman’s sparrow has declined over much of its range in the last 40 years (Dunning and Watts 1990). The authors examined patterns of habitat occupancy by this species in 2 areas of South Carolina. Relatively high densities of breeding sparrows were found in mature (>80 yr old) pine stands, and relatively low densities were found in young pine stands. Sparrows characteristically used areas with open understories and a dense ground cover of grasses and forbs. When stands become older, timber management practices such as burning and thinning will produce suitable habitat conditions for the sparrow. Avifauna was sampled by Childers et al. (1986) in 8 developmental stages of loblolly pine plantations and in second growth pine-hardwood forests during spring, summer, and winter seasons in the central Piedmont of Virginia. Number of birds, number of species per stand, and total number of species in all stands were significantly lower in second-growth forests and 7- to 24-year-old plantations than in 2- to 5-year-old plantations during spring and summer. Birds using second-growth forests were also comparable to those in the 7- to 24-year-old plantations in winter. Karriker (1993) studied the effects of intensive silviculture on breeding and winter birds in North Carolina pocosins. During the breeding season, unmanaged short pocosins and open pine plantations supported low diversity bird communities, while unmanaged tall pocosins and thinned pine plantations supported more diverse breeding bird communities. During winter, thinned pine plantations supported a diverse community of forest birds, while unmanaged tall pocosins supported a community of forest birds intermediate in diversity. Closed pine plantations supported a low diversity of birds, characteristic of all dense forest stands. d.
Streamside Management Zones (SMZs) There are many variables associated with SMZs that influence their use by birds. The most studied and seemingly most important variable is width, a factor found to be strongly related to bird species richness by Stauffer and Best (1980), Tassone (1981), Keller et al. (1993), Darveau et al. (1995), and Dickson et al. (1995) but only weakly related by Thurmond et al. (1995). Predation on artificial nests was studied by Vander Haegen and DeGraaf (1996), who found a higher predation rate in narrow SMZs than in wider ones, or in the more mature natural forest. They attributed this predation on the diversity of predators associated with narrow, linear forest stands. Red squirrels and blue jays were responsible for more than 50% of the identified predation. Tappe et al. (1994) found that “Increasing width of SMZs does not necessarily result in greater abundance, more species, or increased diversity.” Even though species richness generally increases with width, the differences are most pronounced between the more narrow width classes. Stauffer and Best (1980) found that 70 to 80% of the breeding bird species occurred in SMZs that were only 17% of the maximum width sampled (820 ft). Hodges and Krementz (1996) found that the bird response to increasing corridor width was most pronounced between 164-328 feet. Applying results of studies across regions, forest types, or landscape conditions may be inappropriate (Wigley 1995). For example, the Acadian flycatcher, a riparian associate, was found by Keller et al. (1993) to increase in abundance as riparian corridor width increased. In contrast, Hodges and Krementz (1996) found the opposite trend, and speculated that the response to corridors may be related to variables other than width, such as snag size, number of canopy layers, and tree size. Wigley and Melchiors (1994) found that stand structure, species composition, and adjacent habitats effect habitat quality in SMZs. The relationship of bird use to SMZs width also is not pro- nounced where there is no sharp contrast between vegetation in the riparian and adjoining habitats (Murray and Stauffer 1995). Another variable that may cause conflicting study results is the amount of time since the adjoining areas were cut. Darveau et al. (1995) found that the largest response occurred the first year following cutting; bird use declined thereafter to approximately pretreatment levels. While it is not surprising that Louisiana
water thrushes as well as Acadian flycatchers are found in SMZs, Tassone
(1981) also found red-eyed vireos and scarlet tanagers there, both
normally associated with forest interiors.
Marcot (1983) recorded bird species richness in Douglas-fir clearcuts in northwestern California. He found that mean detection rates and percent occurrence of five primary and four secondary cavity nesters were significantly greater in clearcuts with snags compared to clearcuts without snags during breeding and post-breeding seasons. While the study was not conducted in the east, we feel the findings are applicable here.
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Bird
abundance, richness, and diversity are sometimes inconsistent between
clearcuts and the mature forest. In Eastern Maine, Derleth et al. (1989)
studied the response of birds to small clearcuts (3 to 20 ac) in
conifer, hardwood, and mixed growth stands. Species richness and
diversity increased following clearcutting in the treated hardwood and
mixed stands but not in the conifer stands. Bird communities were
studied for equitability, richness, and diversity in a northern hardwood
area of Kentucky by Triquet et al. (1990). Bird abundance was higher,
but diversity and richness were lower on the clearcuts compared to the
mature forest during the second season after cutting. Thompson and
Fritzell (1990) compared breeding bird density in clearcuts and mature
oak-hickory stands in southern Missouri. Bird density was nearly 2 times
greater in clearcuts than in the mature forest. However, the mature
forest had more species present. Regarding the affects of clearcutting
on forest interior birds in the Missouri Ozark forest type, Thompson et
al. (1992) found that some species were dependent on mature forest
habitat. Other forest interior species, in contrast, made extensive use
of early and mid-successional even-aged stands and occurred in greater
numbers on stands derived by clearcutting. Hamel (1989) compared bird
populations in undisturbed old-growth, clearcuts, and selectively cut
stands in a bottomland hardwood forest in South Carolina. More species
achieved their highest densities in old-growth than in the other two
types. However, several bird species typical of open areas had highest
densities in clearcuts and others were highest in selectively-cut areas.
Several
studies have compared clearcut stands of different ages. In a bald
cypress-tupelo wetland in the Coastal Plain of South Carolina, bird
abundance and diversity were assessed by Mitchell et al. (1991) in
naturally regenerated stands 5, 12, 24, 31, and 127 years of age.
Species richness and diversity were high in the 5-year-old cut, lower in
the sapling and poletimber stages, and high in the 127-year-old stand.
The 31-year-old stand exhibited the lowest richness and diversity and
the 127-year-old stand supported the greatest number of birds. Whiting
and Fleet (1987) counted birds in loblolly-shortleaf pine stands in east
Texas. The study areas included stands in the seedling, sapling, pole,
and sawtimber stages. Generally, the highest number of species and
individuals were found in seedling stands. Bird numbers gradually
decreased as stand age and tree size increased.
e.
Snags