Woodland wildfire and protecting your property

USFS photo of the Ham Lake Fire by Hans Martin. Click for larger.

Minnesota has two distinct wildfire seasons: springtime after winter snow cover leaves, and prior to vegetation green up and again in the fall. Typically, spring wildfire season occurs from mid-March through May. Minnesota’s fall fire season, when vegetation has cured after hard frosts, occurs from early September through November, or when snow cover returns. Wildfire season can be extended into summer during dry periods. Minnesota Wildfire Prevention Week is held during the peak of our wildfire season, encouraging us to take action. Homeowners can take action by reducing wildfire risk.

In Minnesota most wildfires are caused by people during activities such as debris burning, equipment usage, campfires, and smoking. In fact, Minnesota averages 2,200 wildfires each year, from quick moving grass fires that commonly occur in spring, persistent peatfires slowly burning through organic soils, and when conditions are prime, explosive crown fires can occur. However, the most dramatic crown fires are not necessarily responsible for most fire-related damage; all it takes is a spark or an ember igniting flammable fuels to create problems. Firewise, a program designed to protect dwellings from the ravages of wildfires, can help you and your neighbors be safe.

Forest fires are classified as surface, crown, or ground fires based on their manner of spread.  Most forest fires in the Midwest are surface fires. They burn only the litter and other small fuels on the forest floor. They may scar the base of large trees and kill small trees.

Crown fires

Crown fire
Crown fire. MNICS image.

Crown fires usually start as surface fires that reach into the canopy with the help of dry winds and fuel ladders. They occur most often in conifer stands and are very damaging and difficult to control. An intense crown fire will produce showers of sparks and glowing embers that easily jump firebreaks and set additional fires well in advance of the leading edge. Although conifer crowns frequently catch fire, true crown fires that spread through the air from one crown to the next are fairly rare.  They’re also very difficult to control.

Ground Fires

A ground fire burns and smolders below the surface sometimes going undetected for days or weeks. It consumes soil high in organic matter including dried peat and thick litter. It produces enough heat to kill most of the trees in its path through root damage. Such a fire may cross firebreaks through roots and dry organic matter. Ground fires are very difficult to control, but are likely to occur only in dry years.

Protecting your woodlands

MN DNR image: Firewise landscaping

Few woodland owners can afford their own fire suppression equipment. Instead, most rely on state and local agencies to control fires. While these organizations respond quickly, there may be some delay before the fire is reported and crews arrive on the scene. For this reason you need to maintain your land so wildfires cause minimal damage before they are suppressed. The following practices will help:

  • Maintain a cleared firebreak around your woodland. A firebreak might consist of a rough bulldozed road with a bare mineral soil surface that can be driven by a four-wheel drive fire truck. Although such a firebreak may stop a surface fire, it is more likely to be a good starting place for a fire suppression crew to build a fire line.
  • If the woodland is more than 20 acres, consider establishing a trail/road system within it to provide access to all areas and break it into smaller, more defensible units. The road system also may provide access for other management activities or recreation.
  • Create a pond. This will provide water for fire suppression and may benefit wildlife.
  • Thin and prune pine and spruce-fir stands to keep stands from building fuel ladders (a ladder fuel is a fuel that will carry a surface fire into the crowns) that permit a surface fire to climb into the tree crowns.
  • Create buffer strips of hardwoods around conifers for added protection. Hardwood stands are less flammable than conifer stands and also may diversify wildlife habitat.
  • After timber harvests, lop or chip slash so that it lies close to the ground and decays quickly. You can also pile and burn slash, but take care not to start a wildfire.
  • Cooperate with adjacent landowners in designing and establishing fire prevention measures.
  • Place fire prevention and suppression clauses in logging contracts.

Protecting your home or cabin

Defensible space: Firewise image

The following recommendations are from Minnesota’s Firewise program:

  • Maintain at least 30 feet of defensible space around your home or cabin.  Defensible space can contain trees, but they should be well pruned (to avoid ladder fuels) and widely spaced.
  • Maintain a driveway and turn area large enough to accommodate fire trucks and equipment.
  • Stack firewood at least 30 feet from any structure.
  • Install firebreaks and thin the surrounding woodlands to reduce the likelihood of a crown fire reaching the cabin.
  • Consider installing a sprinkler system around the home or cabin that can be turned on if a fire is imminent.

Controlled Burning

Prescribed burn - Flickr photo by devlandt
Flickr photo by devlandt. Click for original.

Controlled burns are fires set intentionally under specific fuel and weather conditions. They can be used in established stands to change the quantity and species of understory vegetation, thus enhancing the growth of overstory trees or benefiting wildlife. They can be used to reduce fuel loads that contribute to wildfire hazard. On recently harvested sites they are used to kill or set back the growth of undesirable trees and shrubs and to eliminate woody debris that hinders access for planting trees or that may harbor insect and disease pests.

The soil chemistry and physical processes on a burn site change temporarily, but will return to normal. However, a poorly planned or improperly controlled burn may kill crop trees. Consult a forester in regard to firebreak placement, weather requirements, tools needed, legal liabilities, and other important aspects. DNR foresters and wildlife managers will be able to assist you in determining if a burn plan is appropriate for the goals you have for your property. A controlled burn always poses some risk, but it should remain an option if it fits into your management plan.

For more information:

Many more suggestions to protect your woods and personal property are at the MN DNR’s Firewise site.

The University of Minnesota Extension Forestry team.

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