State of the Greater Fundy Ecosystem - Effects of forestry on breeding birds

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Effects of Forestry on Breeding Bird
Communities in the Vicinity of
Fundy National Park

Greg Johnson and Bill Freedman
Dept. of Biology, Dalhousie University
Halifax, N.S. B3H 4J1

Various studies have related changes in the structure and quality of habitats in temperate forests to variations of the diversity and abundance of avian communities. However, knowledge and understanding have not yet progressed to the state where accurate predictions can be made of the effects of forest harvesting and intensive plantation management on bird communities. This deficiency is due to geographical variations in bird species and communities, and in their responses to changes in habitat structure and quality caused by forestry activities. A few studies in Europe and the southern United States have identified that intensively managed conifer monocultures are deficient in bird life (Moss, 1978; Repenning and Labisky, 1985), although another in New Brunswick found less-drastic changes (Parker et al., 1994). Other relevant studies have examined the effects of clear-cutting and other harvesting practices on bird communities, including some work in Nova Scotia (Freedman et al., 1981; Morgan & Freedman, 1986), and studies in the central and northeastern U.S. (Crawford & Titterington, 1979; Titterington et al., 1979; Niemi & Hanowski, 1984).

GOALS

The present research has investigated the responses of breeding-bird communities to the clear-cutting of natural, mixed-species forests in the vicinity of Fundy National Park (Fundy NP) and their conversion into intensively managed conifer plantations. The objectives were to determine the effects of forest conversion on breeding birds at the species, guild, and community levels, and to recommend additional areas of research needs and management strategies.

METHODS

Breeding birds were censussed at six sites during the 1992 field season, and at an additional 10 sites in 1993, for a total of 11 plantations and five reference sites. Plantations outside of Fundy NP were compared to adjacent or nearby natural stands (reference sites) located inside of the park. The plantations were chosen to represent the full range of plantation ages located in the Greater Fundy Ecosystem (GFE), and they ranged in age from 3-21 years old. The spot-mapping technique was used to census birds, and all plots were at least 10 hectares in area. Vegetation and structural attributes of the habitat were quantitatively surveyed following the breeding season. The plantations represent a chronosequence of stands of various age, originating after a similar type of disturbance, while the natural forests provide a reference for the avian communities and habitats that were present prior to clear-cutting and plantation establishment. Both univariate and multivariate tests were performed on the avian and habitat data.

RESULTS

Bird density reached pre-cutting levels within five years of plantation establishment, and peaked at 15 years (Figure 1). The avian community of younger plantations was strongly dominated by ground-nesting species, particularly Common Yellowthroat, Lincoln's Sparrow, Song Sparrow, and White-throated Sparrow. The density of ground-nesting species increased quickly, leveled off by five years, and then decreased to lower levels in the oldest plantations and the reference stands. The density of canopy-nesting species was zero or very low until tree-sized plants (defined as having a diameter at breast height greater than or equal to 5 cm) became established, after a plantation age of about 13 years. These species included Magnolia Warbler, Ruby-crowned Kinglet, Yellow-bellied Flycatcher, and Yellow-rumped Warbler. Plantations aged 13 to 15 years were suitable for high populations of both ground- and canopy-nesting birds. Cavity-nesting species only occurred in significant numbers in reference forests (the only two exceptions were single pairs of Bluebird and Flicker in a 5-year-old plantation; these nested in the only two snags that remained in the census plot after clear-cutting). The most abundant cavity-nesters in reference forests were Black-capped Chickadee, Downy Woodpecker, Hairy Woodpecker, and Yellow-bellied Sapsucker.

Although plantations start out with a significant component of herbaceous ground vegetation and angiosperm shrubs, they become dominated by the planted conifers within a decade or so, and therefore become unsuitable for bird species that require mixed-species forest to meet their habitat needs. Snags and cavity trees are rare or absent in all plantations, making these habitats effectively unusable for nesting by cavity-nesting birds, although they may forage in the plantations. A more detailed study of cavity-nesting birds is reported by Woodley et al. (this volume).

A total of 16 species that bred in natural forest sites in the present study were not found in the plantations, including three species of cavity nesters, and five species that prefer or require forest with a significant component of angiosperm trees. However, clear-cutting and subsequent plantation establishment do provide temporary site opportunities for many open-canopy species of birds, and later on, species of conifer-dominated forest. If the plantations are adjacent to natural forest, they are also utilized by many forest species for foraging.

Multivariate analyses are not presented here in detail. However, it is notable that an ordination of a matrix of bird species densities in the various stands grouped the 21-year-old plantation closer to the reference sites than to the younger plantations.

IMPLICATIONS FOR MANAGEMENT

We recommend that forest managers should ensure that adequate areas of closed-canopy, mixedwood and angiosperm-dominated forest remain available in the GFE. In large part, this can be achieved by allowing clear-cut or otherwise harvested stands to regenerate naturally after logging. This is necessary to sustain the indigenous species of birds that require those relatively natural kinds of forest, and that are potentially threatened by the extensive development of conifer plantations.

Areas converted to plantations should be allowed to retain or regenerate a substantial component of deciduous trees, and actions should be undertaken to ensure the availability of snags, cavity trees, and coarse woody debris as critical habitat for dependent species. More detailed recommendations about these dead-wood elements of habitat are in Chapter 7 (this volume).

ACKNOWLEDGEMENTS

We would like to thank Fulton Lavender, Greg's indispensable field assistant and preacher of all things that tweet. Also, we gratefully acknowledge the field assistance or other support of Wolfgang Maass, Jonathan Freedman, Kathleen O'Sullivan, Cindy Stacier, and fellow graduate students Tracy Fleming, Ruth Waldick, Minga O'Brien, Cam Veinotte, and Jill Adams. Additional thanks go to the help and patience of park wardens, biologists and administrative staff of Fundy NP. This study was funded by grants or contracts from the Canadian Wildlife Service University Research Support Fund, the Fundy Model Forest, the Greater Fundy Ecosystem Research Group, and the Natural Sciences Engineering and Research Council. A Dalhousie University Graduate Fellowship to Greg Johnson is also greatly appreciated.

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