Prescribed Fire and Melaleuca

Prescribed fire managers, particularly in south Florida, must consider the effects of non-native, invasive species on their burn program and conversely the effect of their burn program on invasive species. Melaleuca poses several problems with regards to burning programs. Fire alone often aids the spread of Melaleuca by triggering massive seed release (Myers and Belles 1995, Laroche 1999). Land stewards managing lands infested with melaleuca often ask two questions: 1- How can my burn program designed to benefit and perpetuate native plant communities be carried forward without promoting the spread of melaleuca? 2- How can a burn program be used to aid the elimination of melaleuca? The answer to both questions involves active control measures in addition to fire.

The melaleuca management plan (Laroche 1999) has adopted a strategy of containment of infestations. The first course of action is to eliminate outlying individuals that may serve as foci for seed release and population spread. This is an important point in burn programs because fire triggers seed release. When managing areas with outlying individuals managers are advised to:

• Apply herbicides (see Laroche 1999 for recommendations and further details) to trigger seed release into an intact fuel bed. Germination will be less successful than in a newly burned area and fire may be applied at a later date to kill seedlings while in a fire susceptible stage. Monitor the site for germination, which is triggered by adequate moisture levels. Monitor the cohort(s) of seedlings for growth rate and apply fire before seedlings leave the fire-susceptible size classes. Virtually all seedlings less than 6 months old and 90% of seedlings less than 2 years old can be killed by fire. Growth rates vary greatly from site to site necessitating monitoring. The best kill rates of seedlings can be achieved before they reach 1 m in height (Myers and Belles 1995).
• If herbicide application is not possible prior to burning due to other management concerns or because of budgetary constraints (see the Florida Department of Environmental Protection invasive plant management program for funding assistance on public conservation lands), then there are several options:
  • Protect outlier trees from fire and exclude thickets of melaleuca from burn blocks to avoid seed release (Wade 1981).
  • If it is not possible to exclude all outlier trees, conduct burning at a time when seed will be released just prior to conditions unfavorable for seedling survival. For example:
    • Apply fire early in the wet season prior to rising water such that seedlings will germinate and then be flooded.
    • Apply fire prior to the onset of a lengthy drought period, at the end of the wet season such that seeds will germinate on a moist seedbed then the dry season ensues causing seedling mortality.
    • Chemically treat resprouting adults before they replenish seed and burn again as soon as fuel conditions warrant (Myers and Belles 1995).
    • This technique is ecologically risky and much less desirable because moisture regimes reliant on the weather cannot be controlled or predicted with accuracy.
    • Monitoring germination and seedling growth is important in the success of this method, but failure may occur because more than one episode of germination can occur depending on moisture conditions, germination may be delayed if normal rains fail to materialize, and if dry periods are interrupted with rainfall, seedlings may survive (Laroche 1999, Myers and Belles 1995).
    • In addition, without efforts to kill adult trees, they will resprout and will have replenished seed stores prior to the next fire cycle.
• Land stewards must be aware of other environmental factors that may trigger seed release from melaleuca such as frost, or herbicide treatments. In the case of frost, it is possible for managers to burn seedlings established within the intact fuel bed. Preferably, these tactics should be coupled with an integrated control strategy. Alternatively, the potential additional seed release stimulated by burning should be evaluated and the benefits weighed. Burning after herbicide treatments should be part of the integrated management plan.
• Control of the massive melaleuca regeneration following a wildfire will involve not only fire but also extensive chemical control efforts (See Myers and Belles 1995 or Laroche 1999 for details and recommendations).
• Fire is not a recommended management tool for dense stands of melaleuca. However, dense stands of melaleuca pose significant wildfire threats, particularly when they are in urban interface areas. Common control tactics utilized in the southeast are often unsuccessful in control of crown fires (Wade 1981).