Prescribed Fire and Integrated Management Strategies
First, a word of caution: prescribed fire, even if it is done repeatedly to deplete the seed bank, is not effective on all invasive species and types of ecosystems. For example, repeated burnings can create shorter fire intervals that can be detrimental to some fire-sensitive native plants. Increasing fire frequencies can also alter an ecosystem’s rate of soil formation and erosion and patterns of nutrient cycling. Thus, the effects of fire on plant populations and communities must be considered; a fire regime that aims to reduce invasive species cover can create a disturbed environment that may encourage infestation of other invasive species. Repeated burnings that completely manage an invasive species population are rare. Therefore, other management strategies can be used with or without prescribed fire in an integrated approach.
In cases where fire alone cannot provide sufficient control, it can be used to dramatically enhance other control methods, such as chemical or mechanical control methods. The initial burn can be used to stimulate seed germination and thus deplete the seed bank faster than one control method alone. The new seedlings can then be killed with chemical or mechanical methods. Prescribed burning can also be used to clear away invasive species in areas of high density; this can provide more access for additional treatments. For example, litter or thatch removal can improve deposition of herbicide on a target surface. This method is also effective for dealing with vine species, such as kudzu and Japanese honeysuckle, but be careful that the fire does not spread into the tree canopy for vines wrapped around tree trunks.
For annuals, where the invasive infestation is heavy and there is not adequate fuel for ideal burn timing, an herbicide treatment the previous year can increase the grass population and facilitate a complete burn the second year. However, when using this strategy, it is important to use a third year control option since burning can stimulate germination of some invasive plants. A similar strategy can apply to woody species; top vegetation can be killed by herbicides and a subsequent burn can kill the root systems. Prescribed fire can also be used after mechanical or chemical methods to remove the dead biomass and stimulate recovery or re-vegetation of infested site with more desirable species.
Tools Used in an Integrated Control Strategy
1. Mechanical Control
Mechanical methods of control consist of removing or damaging above- or below-ground biomass, including stems, new shoots and roots. Mechanical control methods includes hand-pulling, mowing shredding, roller chopping, clipping (wood cutting) and chaining. These treatments increase the amount of dried and thus the effectiveness of burning. Mechanical control methods should be limited to fairly gentle terrain accessible to the equipment used, such as bulldozers and tillage equipment.
2. Chemical Control
Most integrated approaches that include prescribed burning also incorporate an herbicide treatment either before or after the burn. Before a burn, these treatments can increase fuel loads, and after a burn they can be used to control re-sprouting vegetation.
3. Biological Control
Biological control programs for invasive plants often do not eradicate the target plant but exert sufficient environmental stress to reduce invasive plant dominance and spread. Burn timing can be critical to the survival of biological control agents and should be carefully considered. Burning a site when the control agent is inactive (for example, burning in spring and fall for a summer-active control species) can increase the population of the control agent. However, in most situations, prescribed fire’s direct effect is damaging to biological control agents. Despite this, biological control and prescribed fire is still a sound integrated approach since insects and pathogens are mobile and can re-occupy a treated site. A combination of these methods can further stress the invasive species and reduce its dominance.