Action: Clear or open patches in forests
- Of nine studies, seven from the UK and the USA found that early-successional species increased in clearcut areas or opened forests, compared to control areas, areas before management, or other management techniques. One study found that population increases only occurred in clearcuts up to 20 ha in size. Two studies report that mature-forest species declined in cut/opened areas of forest.
- A replicated, randomised, controlled study from the USA found no differences in species richness between clearcuts of different sizes, whilst another American study found that a mosaic of cut and uncut areas supported a variety of species. A long-term study from the USA of a landscape with opened patches found that there were no consistent differences between clearcut and controlled areas, although some species were only seen in clearcuts.
Forests naturally undergo disturbances, from storms, lightning and even large animals. These disturbances can create a mix of different habitats, with open clearings allowing a greater range of species to survive in a forest. Deliberately creating open patches may, therefore, encourage woodland edge and ‘early-successional’ species.
Supporting evidence from individual studies
A replicated study between December 1981 and June 1984 in a mosaic of aspen Populus spp. and oak Quercus spp. managed for ruffed grouse Bonasa umbellus at Barrens Grouse Management Area, Pennsylvania, USA (Yahner 1987), found that 13 species in winter and 69 species in spring were recorded. In winter, birds were significantly more abundant in the interior of mature aspen (>60 years old) stands than in young (1-3 years since clear-cutting) aspen stands and the edge of intermediate (4-8 years since clear-cutting) aspen stands. In spring, birds were significantly more abundant in intermediate aspen and oak stands (interior and edge) and the interior of mature aspen, than in the interior of mature oak stands and the edge of mature and young aspen stands.
A before-and-after study at Minsmere reserve (151 ha), Suffolk, UK, in 1978-1988 (Burgess et al. 1990), found that the number of churring (calling) male European nightjars Caprimulgus europaeus increased significantly from eight to 23 following a series of management interventions, including the creation of woodland ‘glades’. Other interventions included increasing the length of woodland edge habitat; creating potential nesting sites (10-50/ha), mainly by clearing 1 m square patches of heather Calluna vulgaris at the base of small (1-3 m tall) birch Betula spp. trees (previously shown to be the most frequently-used nest sites); planting windbreaks; coppicing birch trees and the opening of areas of heath.
A replicated study in 1989-1990 at three mixed forest sites in Maine, USA (Rudnicky & Hunter 1993), found some evidence of increased bird species richness in clearcuts from 2 ha up to 20 ha in area: of the 15 most common clearcut species in both years, ten (in 1989) and 12 ( in 1990) were more abundant in larger clearcuts, up to 20 ha, beyond which no preference for clearcut size was apparent, however, average species richness showed no trend amongst the range of clearcut sizes. Study sites comprised 45 clearcuts (2 to 112 ha in area) from 3-10 years post-cut age. These were surveyed in May-June 1989 and 1990; 69 bird species were recorded.
A replicated study in 1993-4 in mixed forests in the Missouri Ozarks, Missouri, USA (Annand & Thompson 1997), found that eight species (brown-headed cowbird Molothrus ater, blue-winged warbler Vermivora pinus, prairie warbler Dendroica discolor, rufous-sided towhee Pipilo erythrophthalmus, white-eyed vireo Vireo griseus and yellow-breasted chat Icteria virens) were more abundant in 12 clearcuts than in 12 shelterwood stands (see ‘Use shelterwood cutting instead of clearcutting’), 22 stands under selective logging (see ‘Use selective harvesting/logging instead of clearcutting’) or 12 mature stands. Six species were more abundant in selectively-logged or mature forest than in clearcuts.
In oak-hickory forest in the Missouri Ozarks, USA, in 1991-2000, a replicated, randomised, controlled study (Gram et al. 2003) found that early successional species increased in response to even- (i.e. clearcutting) and uneven-aged (i.e. selection cutting) management, whereas mature forest species declined. Mature forest bird abundance declined as trees were removed, with harvest disturbance affecting densities of some species in adjacent forest for three years or more. Nest success (average of 29% for all species) did not change after treatment. Each of nine sites was randomly assigned even- or uneven-aged treatment (undertaken May 1996 to May 1997) with a patch of about 10% of each site left uncut. The two treatments are compared in ‘Use selective harvesting/logging instead of clearcutting’.
A before-and-after study in mixed woodlands in Pennsylvania, USA (Yahner 2003), at the same study site as (Yahner 1987) found that three early successional species (indigo bunting Passerina cyanea, eastern towhee Pipilo erythrophthalmus and field sparrow Spizella pusilla) were more abundant and three woodland species (red-eyed vireo Vireo olivaceus, ovenbird Seiurus aurocapilla and American redstart Setophaga ruticilla) were less abundant on test plots in 2001-2002, compared with 1998-1999, following the completion of a cutting cycle. Across the entire site (both test and control plots) total bird abundance and species richness increased over the study period, with several species showing significant population increases. The authors suggest this is because the cutting management increased the heterogeneity of habitats across the site.
In Ouachita National Forest, Arkansas and Oklahoma, USA, a replicated study (Alterman et al. 2005) found that three species of songbird known to favour early-successional habitats were all more abundant in three ‘seed-tree’ stands (10-25 mature trees left/ha), compared to in the openings made by group-selection harvesting (typically 10% of stand cut every 10 years in patches of 0.8 ha or less): indigo bunting (54 nests and 31% success in seed-tree stands vs. 28 and 42% in group-selection stands); yellow-breasted chat (50 nests and 31% success vs. two and 0%) and prairie warbler (14 nests with 45% success, all in seed-tree stands). The authors conclude that group-selection openings appeared too small to support nesting yellow-breasted chat and prairie warbler. Nests were monitored in May-August 2000-2001, within three-, six- and seven-year-old openings created by the two management techniques.
A replicated controlled before-and-after study in oak and hickory Carya spp. forests in the Missouri Ozarks, USA (Wallendorf et al. 2007), found that densities of early-successional species (indigo bunting, prairie warbler and yellow-breasted chat) increased after even-aged forest management (clearcutting), compared to control (no harvest) stands, whilst some mature forest species (Acadian flycatcher Empidonax virescens, ovenbird, and worm-eating warbler Helmitheros vermivorus) declined. Bird territories were recorded during before (1991-1995) and after cutting (1997-2000) in six sites (312-512 ha), three randomly assigned to even-aged management. Each even-aged site was partitioned into: clearcut (average 5.4 ha), buffer (0-100 m from clearcut), and interior (>100 m from clearcut) bird. No effects of cutting were found >100 m from clearcuts.
A study from mixed woods in Pennsylvania, USA (Yahner 2008), at the same site as Yahner (2003), compared the results from Yahner (2003) with bird surveys in 2005-7. Species composition and abundance differed but early successional species did not decline (despite forest maturation). Overall habitat management for ruffed grouse did not affect other bird populations since the last cutting cycle. During 2005-2007, 46 species were recorded. Of the 17 species recorded 10 or more times, six were observed only in managed area plots (grey catbird Dumetella carolinensis, chestnut-sided warbler Dendroica pensylvanica, common yellowthroat Geothlypis trichas, indigo bunting, field sparrow Spizella pusilla and chipping sparrow S. passerina). No species were observed only within unmanaged plots.
- Yahner R.H. (1987) Use of even-aged stands by winter and spring bird communities. Wilson Bulletin, 99, 218-232
- Burgess N.D., Evans C.E. & Sorensen J. (1990) The management of lowland heath for nightjars at Minsmere, Suffolk, Great Britain. Journal of Environmental Management, 31, 351-359
- Rudnicky T.C. & Hunter M.L. (1993) Reversing the fragmentation perspective: effects of clearcut size on bird species richness in Maine. Ecological Applications, 3, 357-366
- Annand E.M. & Thompson F.R. (1997) Forest bird response to regeneration practices in central hardwood forests. The Journal of Wildlife Management, 61
- Gram W.K., Porneluzi P.A., Clawson R.L. & Richter S.C. (2003) Effects of experimental forest management on density and nesting success of bird species in Missouri Ozark forests. Conservation Biology, 17, 1324-1337
- Yahner R.H. (2003) Responses of bird communities to early successional habitat in a managed landscape. Wilson Bulletin, 115, 292-298
- Alterman L.E., Bednarz J.C. & Thill R.E. (2005) Use of group-selection and seed-tree cuts by three early-successional migratory species in Arkansas. The Wilson Bulletin, 117, 353-363
- Wallendorf M.J., Porneluzi P.A., Gram W.K., Clawson R.L. & Faaborg J. (2007) Bird response to clear cutting in Missouri Ozark Forests. The Journal of Wildlife Management, 71, 1899-1905
- Yahner R.H. (2008) Bird responses to a managed forested landscape. Wilson Journal of Ornithology, 120, 897-900