Bird Habitat Relationships in Natural and Managed Forests in the West Cascades of Oregon

Abstract

Ecologists have advocated retaining various densities of canopy trees in harvest units in Pacific Northwest forests. In contrast to clear‐cutting, this practice may better emulate the patterns of disturbance and structural complexity typical of natural forests in the region. Several ecological attributes, including vertebrate habitat diversity, are thought to be associated with stands of complex structure. The goal of this study was to determine bird abundance in canopy retention sites relative to other common stand types in the Pacific Northwest and to develop habitat functions for extrapolating bird abundance across current and future landscapes. We used data from five previous studies in the west central Cascades of Oregon to compare bird abundance and to develop habitat functions for forest birds across a wide range of natural and managed stand structures and ages. The 67 stands included clearcuts, retention sites, young closed‐canopy plantations, mature stands, and old‐growth stands. ANOVA revealed that 18 of the 23 species included in the analysis differed significantly in abundance among the stand types, with some species being primarily associated with each of the stand types. The habitat variables used to build habitat functions included tree density by size class, mean tree diameter, and variation in tree diameter. Linear, polynomial, and various nonlinear regression models were evaluated for each bird species. Significant habitat functions were generated for 17 of the 23 bird species. The analyses identified four habitat‐use guilds among the 17 bird species: open‐canopy; open‐canopy with dispersed large trees; structurally complex closed‐canopy; and structurally simple closed‐canopy guilds. This study is the first in the Pacific Northwest to compare bird abundances across natural stands, traditionally managed plantations, and stands managed under ecological forestry approaches. The results suggested that canopy tree retention benefits many, but not all, of the bird species we studied, Moreover, the nonlinear responses of bird abundance revealed thresholds in tree density at which bird abundance changed dramatically. Knowledge of these thresholds allow managers to design stands for specific biodiversity objectives. The habitat functions presented here can be used to predict bird abundance based on habitat measurements derived from field data, remotely sensed data, or output from computer models of forest dynamics.

Effects of Timber Harvesting and Plantation Development on Cavity-nesting Birds in New Brunswick

“…Of the plantations, those with relatively abundant and species-rich cavitynesting birds clustered together (i.e., P7, P15, P19, and P17), while the most depauperate ones formed another cluster (i.e., P5b, P8, P9a, P9b, P5a). The observation that cavity-nesters are more abundant in mature mixedwood forest than in harvested stands or plantations is consistent with research elsewhere, although the specifics vary depending on the forest region and species of birds present (e.g., Raphael and White 1984;DeGraaf and Shigo 1985;Zarnowitz and Manuwal 1985;Hansen et al 1995;Kirk and Naylor 1995;Niemi et al 1998;Hobson and Bayne 2000).…”

Nonlinear dynamics in ecosystem response to climatic change: Case studies and policy implications

“…Their findings suggested that the failure to account for nonlinear, threshold effects in an ecosystem's future progression alters preservation decisions and ignores important information that will influence the outcome of management actions intended to enhance avian diversity. In Pacific Northwest forests, Jansen et al (1995) compared avian density across natural stands, traditionally managed plantations, and stands managed under ecological forestry approaches. Their results suggested that, although canopy tree retention generally benefited many species, the nonlinear responses of bird abundance revealed thresholds in tree density at which bird abundance changed dramatically.…”

Response of small mammals and birds to partial cutting and clearcutting in northwest British Columbia

“…Had the clearcuts been larger with less edge relative to area, or no scattered mature trees left unharvested, we expect that the bird community similarity of the clearcuts to the other treatments would have been lower. Hansen et al (1995b) using bird abundance data from several studies in the U.S. Pacific Northwest, suggested that most forest birds can be placed in four guilds in terms of overstory tree canopy density: open canopy species (e.g., Dark-eyed Junco and American Robin); open canopy with dispersed large trees (e.g., MacGillivray7s Warbler, Hammond's Flycatcher, and Western Tanager); structurally complex closed-canopy (e.g., Brown Creeper, Chestnut-backed Chickadee and Winter Wren); and structurally simple closedcanopy species (e.g., Golden-crowned Kinglet and Swainson's Thrush). Our results, and those of Mannan and Meslow (1984), Adam et al (1996), andHagar et al (1996) in the northwestern U.S.A., and Annand and Thompson (1997) in hardwood forests of Missouri, supported that conceptualization.…”