Temporal trends in bird abundance in response to thinning of lodgepole pine (Pinus contorta)

Abstract

Forest managers are continually seeking methods of extracting more timber from the land base while maintaining appropriate wildlife habitat. A 7-year before–after control–impact (BACI) experiment was conducted in 60-year-old lodgepole pine (Pinus contorta Douglas ex Loudon) to determine the effects of thinning on forest birds. One year of pretreatment data was compared with 6 years of posttreatment data. Using linear trend analysis corrected for detection error, we found that Chipping Sparrow (Spizella passerina (Bechstein, 1798)), Dark-eyed Junco (Junco hyemalis (Linnaeus, 1758)), and Red-eyed Vireo (Vireo olivaceus (Linnaeus, 1766)) increased over time in thinned stands and declined in control stands. Alder Flycatcher (Empidonax alnorum Brewster, 1895), Hermit Thrush (Catharus guttatus (Pallas, 1811)), Rose-breasted Grosbeak (Pheucticus ludovicianus (Linnaeus, 1766)), and Blue-headed Vireo (Vireo solitarius (Wilson, 1810)) decreased in control and thinned stands but declined more in controls. Varied Thrush (Ixoreus naevius (J. F. Gemlin, 1789)) and White-winged Crossbill (Loxia leucoptera Gemlin, 1789) increased in control stands relative to thinned areas, where they were stable or declined. A significant interaction between treatment and year was observed for 24 species when year was categorical. Of these, species more likely found in control stands were Boreal Chickadee (Poecile hudsonicus (J.R. Forster, 1772)), Golden-crowned Kinglet (Regulus satrapa Lichtenstein, 1823), and Least Flycatcher (Empidonax minimus (W.M. Baird & S.F. Baird, 1843)), whereas Ruffed Grouse (Bonasa umbellus (Linnaeus, 1766)), Tennessee Warbler (Vermivora peregrina (A. Wilson, 1811)), and Warbling Vireo (Vireo gilvus (Vieillot, 1808)) were more likely in thinned stands. Total bird abundance was higher in thinned stands, which is consistent with 83% of thinning studies in western coniferous forests. Thinning can be a useful tool for achieving wildlife management goals and increasing timber yields.