Riparian forests provide many benefits to streams, including filtering overland flow, decreasing soil erosion and peak sediment loads, recycling organic matter and nutrients, moderating stream temperatures, and influencing channel morphology. Utilizing forestry BMPs such as riparian buffer zones and soil erosion protection techniques can significantly mitigate negative impacts often associated with forestry activities.
Studies have shown mean maximum temperatures to be 1-2.4°C cooler in shaded riparian buffer zones compared to completely harvested areas. RBZs also moderate how much stream temperature fluctuates during the day. Elevated stream temperatures result in a shift toward warm water fish species.
In addition to elevating temperatures, clearcutting along streams has been shown to increase and accelerate the delivery of sediment to streams. Increases in suspended sediment and turbidity have a range of physical and behavioral effects on fish ranging from delays in migration to reduced feeding and even death at very high concentrations. The effects of increased suspended sediment on instream may be even more important, causing loss of spawning habitat, stream widening, and loss of pools. Riparian buffer zones can effectively filter sediment from upland sources and have been shown to significantly reduce stream bank erosion, runoff volume, and sediment transport.
Clearcutting can significantly increase nutrients in forest streams. Increased Nitrogen, in the form of nitrate and organic nitrogen bound to sediments, is a concern following forestry activities. Fewer plants in the riparian zone generally correlates to increased nutrients entering the stream. Excess nutrients, coupled with the increased light reaching the stream, can often result in increased plant and algal growth resulting in low dissolved oxygen and pH fluctuations.
While there is no way to completely avoid these issues, there are many proven tools that have been developed over time and across the globe to minimize the negative impacts of forestry projects. These tools are collectively known as Best Management Practices, or BMPs for short. BMPs are practices, physical structures, and processes that can be used individually or in combination to protect water quality and promote soil conservation. BMPs are chosen based on the goals of your project, legal requirements, and applicability of techniques based on the physical surroundings (land use, soil type, slope/elevation, and pollutant of concern). While some BMPs may be voluntary, there are many instances where they are required by local, state, or federal statutes. Forest certification programs, like those from Sustainable Forestry Initiative, Inc. and the Forest Stewardship Council, may also require the use of BMPs. All Michigan forest landowners, managers and loggers are strongly encouraged to implement BMPs whenever forestry activities are conducted. The BMP manual may be found online through the MI DNR at: www.mi.gov/documents/dnr/IC4011_SustainableSoilAndWaterQualityPracticesOn ForestLand_268417_7.pdf
By effectively using BMPs you can prevent and control negative impacts (nonpoint source pollution) of your forestry activities, protect water quality of adjacent streams, lakes, or wetlands, and remain in compliance with the various water quality regulations your project may be subject to.
Forestry BMPs and how they protect streams and fish
There have been many BMPs developed that deal with protection of aquatic resources and forest soils but determining which ones are applicable to your specific harvest operation can be difficult. An important first step in the timber harvest process is developing a Pre-Harvest Plan. A Pre-Harvest Plan will help the land owner and logging contractors understand the area and its resources and allow them to choose BMPs that are applicable to the site. A harvest site map, for example, can help guide the landowner or contractor in choosing which permits need to be obtained and the BMPs necessary to protect soils and water quality. Developing a harvest site map including property boundaries; existing roads; proposed roads, trails, and landings; and aquatic resources such as streams, wetlands, or vernal pools is a useful tool in a Pre-Harvest Plan. The plan may also include a narrative describing details of the harvest and may include road and trail specifications, timber products to be removed, riparian management zone specifications, timing of the harvest, as well as site-specific health and safety considerations.
Riparian Management Zones (RMZs)
A riparian zone is an ecologically significant and dynamic transitional area between aquatic and terrestrial habitats. Riparian Management Zones, also known as riparian buffer zones or filter strips, occur on both sides of a stream or around the perimeter of a pond, lake, or wetland. RMZs serve to protect water quality by providing an area of mostly undisturbed vegetation to maintain shade, filter and slow overland water flow, and provide large woody debris and litter fall to adjacent water bodies.
Michigan’s standard RMZ minimum width is 100 feet measured from the top of the bank or the ordinary high water mark. The RMZ width should be increased with increasing slope (see MDNR guidance document, “SUSTAINABLE SOIL AND WATER QUALITY PRACTICES ON FOREST LAND”. Additionally, RMZ width may have to be increased along a designated Natural River or a federally designated Wild and Scenic River.
The actual width of the RMZ for your project depends on a variety of site-specific factors including the type of waterbody (DNR designated trout stream, designated Natural River, wetland, etc.), topography, soil type, existing vegetation, and shade requirements to maintain water temperature, to name a few. A qualified forester or other natural resource professional should be consulted if you are unsure of the water quality impacts of your timber harvest.
Forest roads the major source of erosion and sedimentation to streams. Therefore, the road system in any forest operation where aquatic resources are a concern need to be carefully planned and implemented. When constructing new forest roads or upgrading existing roads several factors need to be considered to minimize erosion including soil type, grades/slopes, stream crossings, location and potential impact on wetlands, as well as the size, timing, and duration of the forestry activities.
The following BMPs have been developed to reduce the water volume and velocity coming from forest roads and thereby reduce the sediment load to nearby streams, lakes, and wetlands.
Road Grades, Slopes, and Crowning
The Michigan DNR recommends a road grade of 2% - 10% to promote proper drainage and avoid high velocity runoff and erosion. Grades of 15% to 20% may be used for short distances but may require special surfacing to avoid erosion and rutting. There are many road crowning and sloping techniques available for specific situations. Road crowning/sloping BMPs are designed to direct water and erosion to ditches and water diversion devices. Road slopes are also used for safety reasons on high gradient roads, sharp turns, or on clay/or slippery soil types.
Road Drainage and Water Diversion Devices
Water diversions device serve to slow the velocity of water runoff on roads and to direct that flow to culverts or downslope areas where water can be properly dispersed.
Road Closure and Retirement
Landowners should consider closing or retiring roads upon completing forestry activities. Road closure can be done seasonally or on a semi-permanent basis for prolonged but intermittent forestry activities. Roads should be retired, stabilized and re-vegetated if harvest has been concluded or if forest activities will not occur for several years. Eliminating or reducing vehicle traffic will significantly reduce erosion and sedimentation to nearby aquatic resources.
Skid Trails and Landings
A skid trail is a single lane trail or road used to transport a felled log from the stump to a landing. Landings are areas used for the temporary staging and handling of timber products and equipment during forestry activities. Although the use of skid trails and landings are temporary and generally of short duration there are environmental concerns such as soil erosion, sedimentation, soil compaction, damage to residual trees, and fuel/oil spills associated with equipment refueling and maintenance that should be addressed. Skid trails and landings should always be placed outside of RMZs on generally flat terrain with well-drained soils. Skidding operations should avoid bogs, fens, vernal pools, gullies, seeps, swales and other permanently wet areas. Upon completion of forestry activities skid trails and landings should be immediately stabilized and re-vegetated using appropriate seeding and mulching mixtures.
One of the most sensitive areas of a forest road system is where a stream crossing is required. This is the point where sedimentation from the road system is mostly likely to reach the stream and cause water quality issues. In Michigan, it is illegal to transport heavy machinery or felled logs through even a small, shallow, dry streambed. It should be noted that installing a new or upgrading an existing stream crossing requires a permit from the DEQ prior to installation. It is advisable to work with a local DEQ representative when developing your forest management plan to make sure permit requirements are met and to ensure proper BMPs are employed. While there are many stream crossing options available the two BMPs that are most recommended for stream crossings in Michigan are culverts and portable bridges.
The use of portable or temporary bridges have been shown to cause far less sedimentation than that caused by the installation of a culvert. These bridges are especially useful for temporary (in place less than 2 years) stream crossings. In addition to causing less sedimentation, portable bridges are reusable, do not impact the stream bottom, and do not impede fish passage.
Installing culverts is another option for crossing streams if portable/temporary bridges are not feasible. Culvert installation and placement requires more planning and expertise than portable bridges, increases the amount of sedimentation, and increases the likelihood of impeding fish passage. Culvert installation may also require addition permits or additional permit requirements.
Contact a Local Resource Professional
This bulletin is only an overview of forestry BMPs and how you can help protect water quality during a timber harvest on your property. The Michigan Department of Natural Resources, the Department of Environmental Quality, and your county Conservation District personnel can provide more detailed information specific to your project on where, when, and how to use BMPs.