Multi-scale responses of breeding birds to experimental forest management in Indiana, USA

Abstract

Forest managers frequently must balance timber production and wildlife conservation goals when choosing management approaches. We studied the response of the breeding bird community to silvicultural treatments at multiple spatial scales over a 10-year period in 60–90year old oak-hickory forests of Indiana, USA. We conducted point count surveys in a 3603-ha study area both before (n=3years) and after (n=6years) application of silvicultural treatments. Bird responses were analyzed at two spatial scales: management units and individual harvests. At the multi-stand management unit scale, treatments were even-aged management, uneven-aged management, and a no-harvest control. We also analyzed the responses of birds at the spatial scale of individual timber harvests (clearcuts, patch cuts, shelterwood harvests, and single-tree selection). Multi-species N-mixture models were used to estimate bird species density and richness at both spatial scales. At the management unit scale, 4 species increased in density following even-aged management (relative to the control), while 1 species (Red-eyed Vireo [Vireo olivaceus]) declined. A larger number of species responded both positively (n=9) and negatively (n=3) to uneven-aged management. Overall richness was significantly greater in the even- and uneven-aged treatments than in the control. At the harvest scale, only the clearcuts and patch cuts resulted in changes in the density of any species, but a larger number of species were impacted and effect sizes were generally larger in these harvests than at the management unit scale. In the clearcuts, 13 species increased in density relative to the no-harvest control, while 5 species declined. A larger number of species were impacted by patch cut harvests (18 species increasing and 6 decreasing). Overall richness was greatest in the clearcut harvests. At both scales, species that increased were generally those associated with early successional habitat, including the Eastern Towhee (Pipilo erythrophthalmus) and Indigo Bunting (Passerina cyanea), while species that declined were typically associated with mature forest habitat (e.g., Red-eyed Vireo [Vireo olivaceus] and Ovenbird [Seiurus aurocapilla]). Harvesting appeared to benefit several species of conservation concern in Indiana, including the Cerulean Warbler (Setophaga cerulea) and Black-and-white Warbler (Mniotilta varia). Both management treatments appear to be good options for simultaneously conserving bird species diversity (particularly of early-successional specialist species) while meeting other forest management goals. However, the impact of the next phases of the shelterwood harvests remains to be evaluated.