Response of wildlife to forest herbicide applications in northern coniferous ecosystems

Abstract

Reviewed studies of the effects of forest herbicide applications on wildlife often lacked replication, pretreatment information, and (or) were conducted for only one or two growing seasons after treatment. Because of these problems, as well as the use of dissimilar sampling techniques, study conclusions have sometimes been contradictory. A review of eight studies of the effects of herbicide treatments on northern songbird populations in regenerating clearcuts indicates that total songbird populations are seldom reduced during the growing season after treatment. Densities of species that use early successional brushy, deciduous cover are sometimes reduced, while densities of species which commonly use more open areas, sometimes increase. A review of 14 studies of the effects of herbicide treatments on small mammals indicates that like songbirds, small mammal responses are species specific. Some species are unaffected, while some select and others avoid herbicide-treated areas. Only studies that use kill or removal trapping to study small mammal responses show density reductions associated with herbicide treatment. It seems that some small mammal species may be reluctant to venture into disturbed areas, although residents in those areas are apparently not affected by the disturbance. Fourteen relevant studies examined the effects of conifer release treatments on moose and deer foods and habitat use. Conifer release treatments reduce the availability of moose browse for as long as four growing seasons after treatment. The degree of reduction during the growing season after treatment varies with the herbicide and rate used. Deer use of treated areas remains unchanged or increases during the first growing season after treatment. Eight years after treating a naturally regenerated spruce–fir stand browse was three to seven times more abundant on treated than on control plots (depending on the chemical and rate used). Forage quality (nitrogen, ash, and moisture) of crop trees increased one growing season after the soil-active herbicide simazine was applied to control competition around outplanted 3-year-old balsam fir seedlings.