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
Many bird species, including neotropical migrants, are found in early successional habitat created by clearcutting. Thompson and Fritzell (1990) found that several supposedly area-sensitive forest birds in mature oak-hickory stands in southern Missouri bred in clearcuts even though the stands were <12 acres in size and only 3 years old. A more recent study was completed by Annand and Thompson (1997) in the same region of breeding bird populations in a predominantly forested landscape, portions of which had been clearcut, shelterwood cut, group selection cut, and single-tree selection cut. The clearcut and shelterwood treatments were inhabited predominantly by bird species associated with shrub or young forest habitats. These two treatments also had the greatest species richness and total detections. In an industrial forest in northern Maine, early successional habitats (£20 years old) contained 16 abundant neotropical migrant species while late successional habitats (60+ years old) hosted 13 species (Hagan et al. 1995). In a study of bird species diversity on clearcut vs uncut areas conducted by Welsh and Healy (1993) in the hardwoods of northern New Hampshire, clearcuts contained 53 bird species compared to 33 on the uncut areas. All 33 species on the uncut areas also were present in the clearcuts. In New England’s hardwood forests, mature even-aged and uneven-aged stands were found to support many of the same bird species, but the younger even-aged stands provided habitat for species not found in uneven-aged stands (DeGraaf 1987, 1993). The reverse was not true. The author concluded that clearcut harvesting is decidedly beneficial to bird populations.
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.
As even-aged forests progress through clearcutting to a mature state, each type and age-class supports a unique set of bird species. Songbird numbers were censused by Titterington et al. (1979) in clearcut stands of a spruce-fir forest in northern Maine, in a northern hardwood forest in Vermont by Thompson and Capen (1988), and in aspen and mixed oak forests of Pennsylvania by Yahner (1986). All three studies found that each seral stage (clearcuts, pole, and mature stands) was dominated by a characteristic group of birds. They concluded that managers can encourage the presence of a variety of bird communities by maintaining a mixture of forest age classes. In recently clearcut stands in the hardwoods of north-central Pennsylvania, insectivorous foliage gleaners and omnivorous ground foragers, such as chestnutsided warblers, mourning warblers, common yellowthroats, eastern towhees, and song sparrows, were the predominant species (Yahner 1986, Yahner et al. 1987, Dessecker and Yahner 1988). Bird species richness and diversity were highest in the intermediate-stocked (³70%), hardwood clearcut stands. In mixed oak stands in southwestern Virginia, diversity of birds was lowest in 1-year-old clearcuts and highest in 7-year-old clearcuts (Conner and Adkisson 1975). Forest-interior birds first appeared in 12-year-old clearcuts. Clearcutting provided nesting habitat for a greater diversity of birds than no cutting.
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
Studies of winter birds in stands regenerated through clearcutting are limited and reveal mixed results. Clearcutting hardwood and softwood stands in Pennsylvania had no significant effect on the winter abundance of 11 trunk-bark foraging bird species (Yahner 1992). In pitch pine-oak stands of southwestern Virginia, Conner et al. (1979) found that winter bird species richness and density were lowest in 3-year-old clearcuts and highest in mature stands.
c. Nest Predation and Parasitism
Several studies suggest that predation in largely forested landscapes is not influenced by even-aged management. Depredation on artificial ground and cup nests in even-aged seedling/ sapling, pole, and mature stands of northern hardwood forest was investigated by DeGraaf and Angelstam (1993) in the White Mountains National Forest, New Hampshire. No increase in nest predation rate occurred in the early stages of stand growth, nor was rate of predation related to stand area. A further study in the same forest type by DeGraaf (1995) compared predation rates in large blocks of managed vs remote reserved areas. No differences in nest predation rates were found for either ground or shrub nests between the even-aged clearcut regenerated areas and the reserved forest blocks. A study by Yahner (1991) examined abundance, location, and success of avian nests in small 2.5 ac even-aged stands. Nesting success was independent of stand age and distance from an edge but was inversely related to height of nests. Higher nests (>15 ft above ground) were more susceptible than lower nests to predators.
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
shrub nests in the interior of the uncut forest. Analysis of vegetation surrounding nests suggests cover was negatively associated with predation rates in forests, and positively associated in clearcuts.
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
Because some birds preferentially use edges, young successional stages within older forests can enhance diversity. Breeding bird communities of tidally-influenced bald cypress-tupelo swamps in Alabama were studied by Mitchell and Lancia (1990). Sixteen of 45 species detected in first-year clearcuts, forest-clearcut edges, and 70-year-old reference stands differed significantly in abundance among habitat types. Three species preferred forest interior, 5 preferred edge, 7 preferred interior and edge over clearcut, and 1 preferred clearcut and edge. Species richness from a standard sample size decreased from edge (36) to forest interior (27) to clearcut (21). Brooks (1987) censused populations of Bachman’s sparrow and prairie warblers in clearcuts in east Texas and found the sparrow primarily along habitat edges. The prairie warbler, in contrast, preferred clearcuts which were more dense, brushy, and larger in size. Yahner (1987) found that species richness was higher along edges than interiors of stands in both seasons. Edges of clearcut stands were avoided by winter birds but were used extensively by spring birds.
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
The size of clearcuts is also an important variable in determining their use by birds. The effects of clearcut and forest patch size on bird species richness in 45 clearcuts 5 to 378 ac in size in a forest-dominated landscape in eastern Maine were examined by Rudnicky and Hunter (1992). Of the 15 most common species present in both years, most (10 in 1989 and 12 in 1990) occurred in greater abundance in clearcuts between 5 and 49 ac, while four species were more abundant in the larger cuttings, up to 247 ac in size. Bird locations in clearcuts were largely independent of distance from forest edge. The effects of different-sized forest cuttings were studied on 3 songbird species in northern hardwoods of Michigan (DellaSala 1986). Fewer breeding red-eyed vireos were detected in medium (2-10 ac) and large (240 ac) forest openings. Shifts in distribution away from forest openings were evident for flycatchers, but ovenbirds did not avoid forest openings.
f. Harvesting Methods
Harvest methods used during clearcutting can effect some of the remaining habitat features (e.g., slash). In 5 study areas in Tennessee, clearcuts ranging in size up to 40 ac were cleared without removing felled, nonmerchantable timber (Ambrose 1975). Overall, breeding bird populations were 3.0 to 3.6 times more dense in the clearcuts than in an adjacent forest. In the boreal hardwoods of Michigan, Eaton (1986) compared songbird populations between 8 whole-tree harvested aspen clearcuts and 8 aspen clearcuts harvested by conventional pulpwood methods, where more slash remains. Half the bird species preferred the conventional harvest sites and the other half the whole-tree sites. Therefore, in large forest tracts, a mix of both methods was recommended.
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 cutting. Early successional species will then colonize these areas.
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)
Site preparation treatments temporarily alter the vegetative community and habitat for birds. However, the nature and duration of resulting alterations differ according to the site preparation method used and other ecological considerations (e.g., soils, climate). Treatments of clearcuts with glyphosate herbicide reduced the complexity of vegetation through 3 years post-treatment compared to untreated clearcuts in northcentral Maine (Santillo et al. 1989). Total numbers of birds (mainly common yellowthroats, Lincoln’s sparrows, and alder flycatchers) were less abundant on treated than on untreated clearcuts. Leaving untreated patches of vegetation and staggering herbicide treatments on large clearcuts maintained bird populations similar to those on untreated clearcuts.
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.
In central Massachusetts oak forests, DeGraaf et al. (1991) evaluated the effect that thinning and whitetailed deer browsing in even-aged stands have on breeding birds. Unthinned stands with few deer had moderately dense woody understories and moderate ground cover, while unthinned stands with many deer had sparse woody understories and little ground cover. Thinned stands with many deer had sparse woody understories and lush ground cover. Understory changes associated with high deer densities were apparently offset by the effects of thinning, so that thinned stands
supported more breeding bird species than unthinned stands.
c. Planting (Including Site Conversions to Other Timber Species)
Clearcutting and planting creates stands that differ in character from surrounding, unmanaged habitats. Depending on the landscape context, however, intensively managed stands contribute to diversity by providing habitat for some birds not found elsewhere in the landscape. In a study of oak, oak-pine, and pine forest types and associated bird populations in the Missouri Ozarks, Briggs et al. (1982) found that each forest type provided habitat for some bird species not present in the other types. They concluded that bird communities would not be devastated by conversion of hardwood sites to pine but would change species composition. Pure oak and pure pine stands supported the greatest number of bird species during the winter. Mixed stands had the greatest number during the summer.
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)
The retention of SMZs can enhance bird diversity within a managed landscape. Where SMZs are retained following clearcutting, habitat is provided for some bird species typical of mature forests and forest interiors that clearcutting without SMZs does not (Triquet et al. 1990).
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.
Although SMZs or riparian buffer strips can be important habitat, there is presently little technical basis for fixed-width SMZs. Few studies have examined relationships between wildlife communities and SMZ characteristics and much more data are needed before sound policy or management recommendations can be devised (Wigley 1995).
Snags retained during clearcutting appear to enhance the diversity of bird communities. Mitchell and Lancia (1990) detected twice as many bird species in a clearcut where snags were retained compared to a more complete clearcut. Dickson et al. (1983) counted birds during the breeding season in young successional stages with and without snags in an east Texas clearcut. After 4 years, 44 of the original 75 snags remained. Species richness, abundance, diversity, and equitability of birds were all significantly higher in plots with snags than in snagless plots. Snag users included loggerhead shrike, northern flicker, Carolina chickadee, red-bellied woodpecker, and red-tailed hawk.
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.Next page...Effects of Clearcutting on Amphibians and Reptiles