Miller, James H.; Manning, Steven T.; Enloe, Stephen F. 2010. A management guide for invasive plants in southern forests. Gen. Tech. Rep. SRS–131. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 120 p.
Several cultural practices, including prescribed burning and water-level manipulation, can reduce or control nonnative invasive plant populations. However, such practices also may have undesirable impacts to soils, animal habitat, and native species, so care in planning and enactment must be exercised.
Prescribed Burning
Fire has played a critical and natural role in the development and maintenance of grasslands, forests, and wetlands throughout history. Prescribed burning is the deliberate use of fire under specified and controlled conditions to achieve a resource management goal. Most States train burn specialists through a certified prescribed burn managers program and require that those who contract burning have certification for providing liability protection. Like other invasive treatments, prescribed burning requires special skills and experience, including smoke management, for effective and safe implementation. A prescribed burning plan must include clearly stated objectives, the ignition approach, equipment and manpower needs, and mitigation measures. Additionally, a permit is required from State or local agencies before burning. Prescribed burning for invasive plant management has advantages and disadvantages.
Advantages of prescribed burning for invasive plant control
- Per acre, prescribed burning is one of the most inexpensive treatments.
- Top growth of herbaceous invasive plants can be consumed and small woody plants can be fire girdled, resulting in resprouts of lower heights. Resprouts of trees, shrubs, and vines then can be more easily treated with herbicide foliar sprays.
- Some seeds of invasive plants can be consumed in the burn.
- Prescribed burns improve access to the treatment site and expose hazards, such as stumps, sinkholes, old wells, and pits that might otherwise hinder or endanger further operations.
- Prescribed burns can clear thatch and shrubs for more effective herbicide applications.
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Disadvantages of prescribed burning for invasive plant control
- Prescribed burning requires special skills and experience, investments in time for training and certification, and purchase of special equipment.
- Results are variable and can be unexpected when fire escapes.
- Abundant resprouts and seedlings of invasives along with native regrowth can exacerbate conditions for subsequent treatments and jeopardize their success.
- Prescribed burns can stimulate flowering and seeding of some invasive plants, such as cogongrass, and scarify seeds of others, such as lespedezas (Lespedeza spp.), to promote enhanced germination.
- Some invasive plants can burn extremely hot and intense, with vines creating ladder fuels, placing fire crews in jeopardy, killing or injuring desirable plants, and increasing chances of fire escape.
- Litter clearing and loss of stand components like shrubs can make the site more prone for reinvasion or invasion by other species.
- Plowing fire lines can spread invasive plants and make soil susceptible to invasion and soil erosion.
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Prescribed burn effectiveness
The effectiveness of a prescribed burn depends on the intensity and timing relative to target plant size and development. Fire intensity is determined by the amount of fuel and its arrangement and dryness, along with weather, topography, and ignition source and pattern. Prescribed burns are usually ignited by drip torches, initially along plowed or disked fire lines to widen the fire break. Then the area is ignited as a ring-fire technique around the perimeter or as strip (or spot) headfires or backfires working with or against the wind direction.
The most effective time for weakening woody invasive plants is burning in the late spring after plants have initiated growth using root reserves. Burning in late winter or spring leaf-out can minimize the period of bare soil, while summer burns are the hottest and can maximize consumption of standing plants. Burning can predispose a forest stand or opening to invasion, even though prescribed burning increasingly is favored for native plant and longleaf pine ecosystem restoration as well as fuel reduction. A close evaluation of the benefits and risks is demanded before applying prescribed burning.
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Flamers or Spot Burners
Fire from a propane spot burner can be used to kill individual or small groups of invasive plants. Commercial kits are available for attaching propane cylinders to a backpack frame and fitting the cylinder with a flame nozzle. Additionally, tractor mounted units have also been developed. When plant and wet fuel conditions permit, the flame is directed at herbaceous and woody invasives. This operation can be convenient since it can be performed in wet conditions and when fuels are low. Best results are obtained under windless conditions as winds can prevent the heat from reaching the target weeds. For further details, refer to the The Nature Conservancy’s “Weed Control Methods Handbook” appendix at http://www.invasive.org/gist/products/handbook/23.Spotburn.pdf.
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