Streamside Management Zone
The maintenance of water quality is becoming increasingly important. Streamside management zones are strips of land adjacent to a stream or river that are managed to maintain riparian functions to meet water quality, fish habitat, wildlife, productivity, and other goals. Functions can be maintained by a number of management restrictions including limits on: timber harvesting, soil disturbance, disturbance to understory vegetation, storage or application of chemicals, and disposal of slash or sediment. Riparian buffers are a simple type of management zone consisting of an unharvested and undisturbed forest or other vegetative strip adjacent to the stream. Further down the management spectrum is the equipment (or animal) exclusion zone which allows harvesting of trees or grass but limits the amount of understory and soil disturbance. Streamside management zones are often somewhere in between, allowing some recovery of merchantable timber (or grass, in the case of animal grazing) but restricting harvest and disturbance to prescribed limits.
Streamside management zones and buffers have been shown to effectively trap sediments, fertilizers, and pollutants before they reach a stream. Buffers are commonly used in agriculture that includes two or three zones moving away from the stream including an unharvested forest or prairie grassland immediately adjacent to the stream, a managed forest zone, and then a grass zone (to maximize trapping of sediment). In addition to trapping sediment, fertilizer, animal manure and pesticides, a SMZ may be managed for timber or other plant biomass, though usually with a minimum residual basal area requirement in the case of trees. Some SMZs are managed for wildlife benefits, as well. Depending on the region, SMZs may be managed so that large trees of desired species will fall into the stream when they die to provide critical fish habitat. A narrow SMZ may be adequate for protecting many water quality functions, but wider SMZs may be desired for wildlife benefits. A “best” width depends on management objectives and costs, and the management limits in the SMZ. Where sediment trapping is a goal (filter strip), slightly wider buffers may be needed in steeper terrain. Other terms used to describe SMZs include riparian management zones, riparian management areas, and water and lake protection zones (WLPZ). An alternative use of the word "buffer" in forestry refers to the distance between an application of a forest chemical (e.g., herbicide, fungicide or insecticide) and a stream or other location of concern (e.g., residence) where no chemical is directly applied. During aerial applications operators may shift their application lines upwind to account for swath displacement by the wind in order to maintain an adequate buffer around a stream.