Prescribed burning is a vital part of successful land management in grassland and shrubland landscapes. Restoring fire often results in increased vegetation productivity and diversity of species (both plants and wildlife). There is great interest in using prescribed burning to restore pastures that are overrun by invasive plant species, particularly with the rising cost of herbicides. Several factors are important when considering whether prescribed fire will be useful in controlling invasive species.
Successful control of invasive plant species often is determined by the type of plant that is targeted. Generally there are two broad categories used to characterize plants 1) resprouters and 2) non-resprouters. Resprouting plants are those that are capable of growing again from roots when the top is removed. Non-resprouting plants are incapable of growing again after the top is removed and die. Prescribed burning can be a very successful strategy when trying to control non-resprouting plants as it often will kill the plant. Resprouting plants can be much more difficult to control and fire is often used in tandem to other control methods such as grazing, herbicides and mechanical control.
Fire Return Interval
The fire return interval is how often a particular piece of land is burned. For example, if a pasture is burned every three years, then the fire return interval would be three years. Native plants evolved in regions with specific fire return intervals. For grasslands, research suggests that fire return intervals for tallgrass prairie were 3-5 years, 4-7 years for mix-grass prairie and 7-15 years for less productive short grass prairie. In western landscapes, return intervals can be much longer with sagebrush ecosystems burning every 50-100 years. Burning within these suggested return intervals will promote the plants native to that region. Burning more or less frequently may harm native plants and allow exotic and invasive plants to become more abundant.
Season of burn
Many regions have seasons when fire is more common than others. In landscapes where snow covers the vegetation during winter months, fire is limited to summer and fall months. Other regions where winters are mostly snow free, fire is common throughout the year. Plants that evolved with fire seem to be less affected by season of burn than those that evolved without fire. Burning plants when they are actively growing is a good strategy to suppress growth and reproduction of invasive plants. Over several burn cycles, this can greatly reduce the abundance of the target plant in pastures. Also, burning when plants are growing can be safer because fires are often slower and less intense.
Prescribed burning can be used to control invasive species, but a one-size fits all approach will not work and invasive species control must be included in a successful fire prescription.
Fire is one management tool that can be used to control the dominance of sericea lespedeza (Lespedeza cuneata). Data from Kansas and Oklahoma suggests growing-season fire can be more detrimental to sericea than dormant-season fire. Prescribed fire can limit sericea seed production if burned before the plant produces seed. Following fire, sericea is palatable to livestock as tannin levels are lower immediately following germination or resrouting as compared to a mature plant. Using a patch-burning system (e.g., burning a portion of a pasture each year) higher levels of sericea consumption by livestock have been demonstrated as cattle concentrate or continuously graze on the recently burned patch. Using patch-burning, coverage of sericea has increased at a lower rate as compared to more traditional fire and grazing applications where the entire pasture is burned. In some cases, a combination of burning, grazing and herbicide applications may be necessary to control sericea.
Japangrass (Microstegium vimineum) is a nonnative, invasive annual grass that is capable of overtaking forest understories in eastern U.S. forests. Fire is one tool that can be used to manage Japangrass. Fire prescriptions to control Japangrass include burning in early spring just after Japangrass germinates, but before overstory trees have leafed out, or burning during August and September before Japangrass has seeded. Burning during mid-summer is difficult because of high litter moisture as a result of overstory forest shading. Japangrass can also be managed using a variety of herbicides, including grass-selective herbicides at relatively low application rates.
Prescribed fire is the most economical method to control ash juniper and eastern redcedar in the Great Plains. But many times these trees are too large by the time land managers use fire to control them. In this case, the lower leaves will turn brown and eventually fall off with the remaining upper portion of the tree staying green and living. Shortly after a prescribed fire is conducted, when the lower leaves of these juniper trees become brown, is a good time to conduct individual tree ignition.
Individual scorched-tree ignition is a very economical follow-up to prescribed burning and can be done over a period of several weeks. Ignition of these trees can be accomplished with a propane weed burner torch, drip torch, hand held propane or MAP gas torch. It is best to do individual tree ignition when the wind is very light or calm so the heat and flames can draw straight up into the crown of the tree, killing the entire tree.
Remember to have fire fighting equipment on stand by in case embers from crowning trees drift into unburned areas. Also be sure to notify the local authorities and neighbors before re-burning trees. The the smoke and flames that this technique creates from crowning trees will be visible to neighbors. Always be sure to follow all local and state laws regarding the use of fire.
To watch a short video about individual tree cedar control using fire, go to the following video link: http://www.youtube.com/watch?v=am6yXl-paQ8&feature=player_detailpage
For more information about individual tree cedar control using fire, see the Oklahoma State University Extension fact sheet NREM-5053 Cedar Control by Individual Scorched-tree Ignition Following Fire http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-7936/NREM-5053.pdf
With proper conditions you can ignite a single point on smaller trees or several point on larger trees along the browned lower branches on the upwind side.
Re-igniting unburned cedars following a prescribed fire is a safe, effective and very economical method of controlling larger cedars.