Initial experimental effects of intensive forest management on avian abundance

Abstract

Components of biodiversity in intensively managed forest stands may be reduced in comparison to naturally regenerated stands. Use of herbicides to suppress herbaceous and woody plant species that compete with planted seedlings has been implicated in negative impacts. We designed a large-scale experimental study to test the influence of intensive forest management on the abundance of early seral bird species in the Oregon Coast Range, US. Experimental applications consisted of ‘Intensive’ (i.e., heavy use of herbicides), ‘Moderate’ and ‘Light’ treatments, as well as controls with no herbicide application. In relation to the control, abundance of six out of thirteen bird species was significantly reduced in at least one of the three treatments. Leaf-gleaning insectivorous birds were more negatively affected by heavier herbicide treatments in general than bird species with other foraging behavior. Long-term bird population trends, derived from the Breeding Bird Survey, were correlated with the effect of intensive treatment; species more negatively associated with intensive treatments at the stand scale, were more likely to be in decline across the Pacific Northwest, US. Our results also indicate that reducing intensity of herbicide applications has positive effects on early seral bird abundance during the first 2years of stand growth – particularly those species exhibiting negative population trends. To balance biodiversity conservation and timber production, research examining the tradeoffs between reduced application of herbicide and tree growth is required.