Restoration Activities

Controlled Burns

The term "prescribed burn" refers to a type of burn carried out based on a precisely written burn plan. A prescribed burn is a controlled burn. Background on prescribed burns. Pleasant Valley Conservancy conducts two types of controlled burns, in prairies and in oak savanna areas. Both are critical management activities, but they have to be managed in different ways. Most people involved in restoration ecology are familiar with prairie burns. We concentrate here on oak savanna burns, which are less well understood.

The most important management tool in oak savanna restoration is the controlled burn. Savanna burns kill invading brush, small trees, and brambles, keeping the woods open and encouraging the growth of grasses and forbs. These are low-intensity burns that have no effect on the oaks themselves.


History of controlled burns in wooded areas

Numerous early accounts of visitors and settlers in our area mention burns in the woods. Farmers knew the value of burning as a way of keeping the land open for pasture. Two factors led to elimination of fire in Wisconsin's oak savannas: 1) The Department of Natural Resources and its predecessor the Wisconsin Conservation Commission discouraged or actively campaigned against fire in the woods. 2) The contraction of agriculture activity in southern Wisconsin and increasing urbanization led to the elimination of farms, and hence, farmers.

The importance of fire in the maintenance of the oak forest is now well established. Oaks are less easily killed by fire than most of their associates, and are able to resprout as small saplings even when they are top-killed. Controlled fire in an oak savanna is not a high-intensity fire raging through the tree tops. It is a slowly moving, low-intensity ground fire, consuming the dry oak leaves as well as savanna grasses and forbs. (See photo above) It kills invasive shrubs and trees and keeps the savanna open.

Over thousands of years, Native Americans had used fire in the woods as an important part of their culture. Fire was used to encourage berry production, expose acorns for collection, prepare planting sites, control undesirable pests, fireproof villages, create and maintain open woodlands and savannas, concentrate game, and help maintain trails. Fires were ignited either in spring, before plants had started to grow, or in fall, after frosts had killed off above ground parts of plants. When European settlers displaced Native Americans, the use of fire continued, for many of the same reasons. However, by the late 19th century, widespread logging left vast acreages with dried slash that ignited easily and burned with unusual power, creating landscapes prone to high-intensity wildfire. State laws related to wildfires were enacted to prevent damage to the land and to humans. In the early 1900s, the newly established U.S. Forest Service began a major campaign to control forest fires. "Smoky the Bear" was created as an icon of fire suppression. All of these activities had unintended consequences, destroying the values that the oak forest provided, and replacing the oaks with undesirable trees and shrubs.

Since the early 1970s there has been a gradual reintroduction of the use of prescribed fire. Even the forest industry now realizes that in the oak forest fire plays a major role in removing many weedy trees and shrubs. Prescribed fire removes the thin-barked shrubs and trees from the midstory and understory of the forest without harming the dominant oaks. Fire also consumes the litter, thus promoting the growth of grasses and forbs, and encouraging the regeneration of oak. Long-term research studies have shown that annual burns over a number of years gradually restore the oak savanna to its original state.


Controlled burns in oak savannas at Pleasant Valley Conservancy

We have burned the oak savanna in both spring and fall, but the fall is often the best time. A lot depends upon rainfall and temperature, and since the leaf litter is the major fuel, on leaf fall. Bur oaks begin to lose their leaves in mid October and by the end of the month, or in early November, most of the leaves are on the ground. If conditions have not been too wet, this is an excellent time to do a controlled burn on our ridge-top savannas (units 8, 10, 11, and 19).

White oaks hang on to their leaves a lot longer than bur oaks, and some leaves stay on the tree through the winter. We have burned our white oak savannas in both spring and fall, but for the past several years we have had successful fall burns. Much depends upon the weather.

Savanna burns are much more difficult to do than prairie burns, because there is a lot more preparation necessary before a burn can begin, and "mop-up" after the burn takes more time. Once a prairie is burned, it takes very little time to ensure that the fire is out and it is safe to leave. A savanna almost always has standing dead trees which can easily catch on fire. A standing dead tree can act as a chimney, carrying the fire from the ground into the upper parts of the tree. Such a "smoker" cannot be left to burn, even if there is nothing around to catch fire, because changes in wind may blow sparks into distant parts. The best way to deal with a standing dead tree is to prevent it from catching fire in the first place. This means mowing or raking a wide vegetation- and stick-free zone around the tree. A satisfactory way is to mow the vegetation around each tree with a brush cutter and follow this with a leaf blower. It may take a whole day to "fire-proof" all such trees on a 20-30 acre savanna.

In mop-up, smoldering downed trees can be left if they are in the middle of a blackened area, but if they are near the edge they must be put out before the area can be called secure. If the fire is burning in a standing dead tree, the tree must be cut down and cut apart so that the fire can be reached with water. It sometimes takes a long time to secure the area.

Savannas often have a lot of dead branches or even whole logs on the ground. These logs can block the fire from moving through the area. If the fire does not carry well through the unit, because of dead logs or other reasons, it is essential to walk into the unburned area with a drip torch and restart the fire. Often one has to "strip" the unit, walking back and forth with the drip torch, igniting the unit over and over again.

 

A number of photos on this web site show various savanna burns in progress. For examples, see the following pages: spring 2004; fall 2004; spring 2005 ; spring 2006; Tom's Journal.

Equipment used in controlled burns at Pleasant Valley Conservancy.

Details on a major controlled burn of our wetland, conducted by the U.S. Fish and Wildlife Service.

Tutorial on prescribed burns.

 

For questions or comments regarding this web site please send email to info@savannaoak.org