Soil,SnowandIce- Considerationsfor SpringandWinterHarvests

ByTomGilbert

WaterResourcesSpecialist

Frozen conditions are often the ideal time to begin a timber harvest, especially on sites that are wet or near sensitive resources such as lakes. However, there are a few negative impacts from winter harvests to keep in mind. Keep an eye on packed snow trails once thaw begins, as they can inhibit water movement, causing temporary ponding or flooding in some situations. This impact can be minimized by using cross-drain culverts or by cutting cross drainages in trails following harvest operations.

Another major consideration for winter harvesting is whether the ground has sufficiently frozen to allow access to wetter, or sensitive areas. There are a few factors to consider in determining this.

Ground frost occurs when the ground temperature goes below 0° C (32° F). Frost depth (or the frost line) is the deepest point to which ground water will freeze. Frost depths vary depending upon the climate and the length of time the air is cold. The longer the cold period, the deeper the ground will freeze. But the depth of frozen ground can be limited by more than just climate and the length of time a cold snap persists.

As the ground surface cools in the winter, the layers deep underground may stay warmer than the surface. Winter snowfalls will insulate the ground, preventing heat from the ground from escaping into the atmosphere and blocking cold air from moving into the soil. By trapping the ground’s heat, snow restricts the depth of the frost layer. In other words, soils with deep snow cover often have thinner frost layers than those without snow.

Harvesting in more sensitive areas during frozen conditions will expose snow-covered ground to the cold air and extend the frost layers in these areas. If you find that conditions are marginal, keep in mind that moving a single hitch through these areas will help to freeze up the ground for another day.

Also keep in mind that some soils freeze more easily than others. Dryer soils freeze sooner and stay frozen longer than wet soils. This is because drier (lighter) soils tend to be looser and contain sand particles which have more space for water and ice to form. Wetter (darker) soils are denser and have smaller particles with less space for water. Clay, for example, does not freeze as easily as sand. For more information on the use of forestry BMPs, please visit the Maine Forest Service website: https:// www.maine.gov/dacf/mfs/policy_management/ water_resources/index.html

For more information on fundamental forestry BMPs please see our field friendly BMP manual, Protecting Maine’s Water Quality, available on our website: https://www.maine.gov/dacf/mfs/ policy_management/water_resources/ bmps.html