The last few years have seen a strongly renewed interest in the subject of water quality across Minnesota. How we as a society treat and use our land to provide necessary resources while still maintaining environmental quality is a complex issue. While most of the water quality conversation is centered on agriculture and mining, responsible forest management is an important role to play as well.
In the northern part of the state, the Minnesota Department of Natural Resources’ Forestry Division manages public forests for many components of a sustainable forest. While harvesting trees supports a valuable forest products industry and provides materials we all use, that is really only one ingredient. Wildlife habitat, soil conservation, protecting cultural resources, recreation and visual quality are all part of the recipe too.
However, one of the most significant and often overlooked outputs of a healthy forest is clean water. We may be the land of 10,000 lakes, but consider all of the many rivers and streams that originate in Minnesota and either run into our lakes or travel the length of North America. Many of these begin in a forest. Providing clean water is something forests have always done and always will do, if they are managed right.
Every action we take in our forests has the potential to affect the water that people, fish, and wildlife depend on. Activities that expose soil near water bodies can cause more sediment to enter the water during rainfall which can cover rock and gravel beds that are important spawning areas. Loss of forest cover near the water’s edge can raise the water temperature and reduce the ability of the water to hold oxygen. Many species of amphibians that live in the riparian zone (the area where the forest and water meet) are very sensitive to UV light and depend on shade. Soil compaction from equipment can lead to increased runoff and higher peak streamflows during rain events. In fact, a healthy forest will produce four times less runoff than an agricultural area during a 4-inch rainfall.
Riparian areas deserve special considerations because they are distinctive habitats important to many fish and wildlife species. Starting in 1999, the forestry community adopted the Minnesota Forest Resource Council’s “Voluntary Site-level Forest Management Guidelines” as standard practice in our activities. A major focus of these guidelines is protecting water quality, and there are many ways we accomplish this in forestry.
For example, when harvesting timber near streams or lakes, a riparian management zone (RMZ) is put in place. This RMZ is of variable width depending on the stream or lake classification (trout lake, intermittent stream, etc.), and it dictates the amount of residual forest that is to be left. Generally, these RMZ’s are between 50’ and 200’ in width, and will have between 20%-80% of the forest remaining. Other guidelines restrict the amount of exposed soil that remains after a timber harvest on slopes near water bodies, which is a way to keep the vegetation on the forest floor intact. Keeping an undamaged vegetative buffer creates a filtering effect to minimize excess nutrients like phosphorus from entering waterways. We take special caution to not place any forest roads near water bodies where runoff could occur, and often place “slash”- leftover limbs from trees in areas of exposed soil to slow down rain and water running over the surface. This minimizes erosion and sedimentation into water bodies. Harvesting in winter when the ground is frozen is by far the most common technique used to reduce soil compaction and exposed mineral soil.
Combining these guidelines in our management allows us to provide the forest products that society needs without incurring negative impacts to high quality water resources. Adherence to these guidelines is monitored and results indicate a compliance rate of over 90%.
Troy Holcomb is a forester with the Minnesota DNR Division of Forestry based out of the Aitkin office.