Low Impact Logging Techniques


Logging can be a messy process. Forests are sensitive ecosystems, and if not careful, a poorly-managed logging operation can do substantial damage to soils and water, as well as the aesthetic quality of a forest. Fortunately, low impact logging exists to help landowners and loggers manage their land in the most sustainable, environmentally-sound way possible. Low impact logging techniques are timber harvesting strategies that account for the vulnerabilities of the forest ecosystems and work to mitigate or eliminate damage to them. While it is not possible to completely eliminate logging’s impact, careful design can prevent permanent alteration to hydrology, stream banks, and soils. By far the greatest impact logging has to the forest is the invasive trail system necessary to move wood from the forest to the road.

Low Impact Logging Equipment

By far the greatest impact logging has to the forest is the invasive trail system necessary to move wood from the forest to the road. Consequently, one of the most important considerations that can be made to limit logging’s impact is the equipment used. Not all machinery is created equal. Some machines like grapple skidders are heavy and put tremendous pressure on soils. If a site has poor drainage, a grapple skidder is likely to cause rutting, and ruts can permanently alter the hydrology of the forest as well as greatly damage the roots of residual standing timber and reduce future soil productivity. An optimum low impact logging system will utilize a small-scale operation or a cut-to-length system.

A small-scale system will use smaller equipment, putting less pressure on trails and thus reducing the risk of ruts. A cut-to-length system, however, has the unique advantage of being able to drop limbs and unmerchantable tops on the trail. the mat of woody debris creates buoyancy for the machines and protects the soil by better distributing weight. The two strategies can also be combined for ideal results. smaller harvesters, like those made by Vimek or the Komatsu below, are able to pile brush in trails with an overall lighter machine.

Brush placed on trails can be an important low impact logging technique.
Brush left on trails helps to give the machines buoyancy and to protect the soil and root systems.

If such systems simply cannot be used, and a whole tree system utilizing a feller-buncher and grapple skidder is all that is available, brush from the delimber can still be brought back into the woods and placed manually on sensitive spots along the trail. This, however, is best used when the overall site quality is good and there are only a few areas at risk of increased damage. If the entire block is wet, it will be difficult to concentrate brush on trails enough to make a difference.

Optimize Trail Systems For the Lowest Impact

Even with optimum equipment, trails can still be damaged by logging operations. After all, these are extremely heavy machines making countless passes on bare ground. It takes a multi-faceted approach to truly practice low impact logging. Part of the process is being meticulous in the overall design of a harvest, including in the design of the trail system itself.

Every landscape has natural micro-site features that determine sub-surface water flow and soil saturation. Low areas on a landscape are more likely to be saturated and sensitive to the pressure of forestry equipment. Trail systems should be designed to avoid these wet areas to the greatest extent possible. Trails that are built on high ground will be much better equipped to handle logging traffic, and they will be much easier to protect with brush and other low-impact strategies.

To find the highest and best-suited ground on a landscape, the first line of defense is always boots on the ground. Taking time to visit a site and thoroughly explore and analyze the landscape will help you find hidden water features and soft spots that you can avoid during harvest. However, even for trained foresters, certain topographic features can be imperceptible to the human eye, and it can pay to consult specialty geo-spatial data such as LiDAR.

LiDAR is a precision remote sensing technique that allows GIS professionals to create incredibly detailed and precise digital elevation models, as seen in the image below. Analyzing such data can further unveil hydrologic features and highlight areas best suited for trails. Contact your state or local GIS office to see if LiDAR data is available for your area, or you can find it here.

Lidar can help design trails to limit impact.
A LiDAR DEM shows astonishingly detailed topography, helping you design optimum trail systems.

Additionally, it may be impossible to eliminate stream crossings entirely, but they should be minimized to the greatest extent possible. When streams are crossed, use proper skidder bridges or corduroy crossings to protect banks and limit impact, and close them out once finished. Be sure to check your local regulations to see what is required for temporary stream crossings in your jurisdiction.

Logging in Optimal Weather Conditions

Even the highest and most well-drained soils will saturate if exposed to pouring rains for extended periods of time. Time your harvests for dryer periods to ensure soil stability. If unpredictable weather prevails, it may be necessary to shut down the harvest operation until the weather subsides. In some cases, this may be a legal necessity. Operating in heavy rains creates mud and erosion. If mud finds its way into the watershed, it is likely local regulations have been violated. Even if it isn’t illegal, it is something that should be avoided at all costs for the sake of preserving delicate ecosystems. As usual, be sure to check the regulations of your jurisdiction. Your local forest service or department of natural resources can be useful sources for legal information.

Harvesting during the winter is a great way to limit the impact of logging.
Frozen ground protected soils and root systems in this whole tree harvest perfectly.

In higher elevations and in the north, the only time to harvest more sensitive areas may be the winter. During the winter, ground is frozen, and frozen ground is extremely well-protected from damage. This is perhaps the ultimate tool for the best low impact logging outcomes. As a forester, I routinely harvested in bogs and swamps in the winter, and I would return in the summer to see the moss on the trails virtually undisturbed. If it is possible in your geographic area and economy (loggers tend to be busy in the winter), I recommend timing harvests for winter. If however, you are harvesting your own property, keep in mind smaller equipment may have a difficult time operating in heavy snow. Consider all the factors in your specific situation.

Leave Adequate Buffers Around Sensitive Ecosystems

Because of the impossibility of fully eliminating the impact of logging, there are some ecosystems that are too important or too delicate to risk damage, such as vernal pools and riparian zones. If a harvest runs adjacent to such an area, it can be prudent to leave a buffer in which machines cannot enter or harvest. In certain situations, these areas may be subject to regulation, so as always, consult with your local relevant authorities to understand the specifics for your area. Foresters are also trained in both the legalities and science of protecting these ecosystems, so it may be best to consult with a forester.

Close-Out the Logging Operation Properly to Fully Limit Impact.

To be honest, I am not a detail-oriented person myself (apologies for any typos you may find here), but when it comes to low impact logging, details matter. All stream crossings need to be properly removed. Rutting, if it occurred, should be repaired. Trails, even if relatively undisturbed, should be outfitted with properly-installed water bars and other BMPs. Yards should be cleaned to maintain visual aesthetics. If there are any remaining brush piles, have the equipment spread them in the woods or flatten them. By the time the equipment is loaded on the lowbed and moves out, the forest should look nice and relatively clean.

Beauty is in the eye of the beholder, and it can be difficult to discern good harvest practices from bad, particularly if you haven’t seen many harvests. However, if you follow these guidelines and follow your local laws, you can mitigate logging’s impact, not just to the ecosystem, but to its visual, aesthetic quality.

Zachary Lowry

Working as a professional forester in northern Maine, I quickly saw the opportunities within the forest industry for small-time investors and woodlot owners. I started The TImberland Investor to bring these insights and opportunities to you.

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