Effects of herbicide treatments on biotic components in regenerating northern forests

We reviewed literature, primarily since 1990, that documents effects of herbicide treatments on major biotic components in northern forested ecosystems. Vegetation changes are responsible for changes in all other biotic components. Non-conifer vegetation is commonly reduced for two to five years following broadcast herbicide treatments. Fungal components, however, seem relatively unaffected. Short-term vegetation reductions in cover, density, and related biomass, if they occur, are species and/or vegetation group specific; longer-term changes are linked to conifer stocking, site quality, and the ability of conifers to dominate treated sites. Herbicide treatments do not reduce, and may increase, stand- and landscape-level plant species richness. Those treatments seldom produce mono-cultures when used by foresters for boreal or boreal mixedwood management. The active ingredients in the herbicide products used in forestry in northern ecosystems have no direct effect on the general health (survival, growth, reproduction) of animals in treated areas. Specific, stand-level forest management practices, particularly effects of site preparation and conifer release, must be examined in relation to the landscape mosaic and the desired future forest conditions. At broad scales, across boreal and boreal mixedwood ecosystems, conifers have been consistently replaced by hardwoods since Europeans began harvesting timber from those ecosystems. Herbicides provide a safe, effective tool for restoring conifers in previously conifer-dominated ecosystems. Forest scientists presently have a reasonable understanding of effects of a variety of herbicide treatments on conifer growth and a variety of environmental components. However, they need to continually update that understanding relative to treatments (replicates, chemicals, combinations, or timing) that may be used in the future.