Fire and Melaleuca Biology

Melaleuca is well adapted to fire and can recover after fire both vegetatively and sexually. Melaleuca often survives even intense fires. Melaleuca, common name paper bark, has white, flaky, spongy bark that can reach more than 3” thick at maturity. Like many other fire resistant trees, this bark insulates the vascular cambium from heat generated by fires. Melaleuca can sprout from any point below that killed by an intense fire: along the stem, at the root collar or from roots (Wade 1981, Bodle et al. 1994, Myers and Belles 1995). Production of epicormic branches along the bole in response to injury by fire can enhance reproductive potential by creating large numbers of new twigs and thus, many flowering sites.

Melaleuca has a very high reproductive potential in which fire plays a major role (Wade et al 1980). Seed release from serotinous capsules is triggered by fire. Melaleuca can flower within 3 years of germination and may flower up to 5 times per year (Meskimen 1962 in Laroche 1999). Minute seeds are held in persistent woody capsules along branches. Each capsule can hold 200 to 300 seeds (Meskimen 1962 in Laroche 1999) and each tree holds many thousands of capsules. Capsules open when they desiccate (often when the vascular connection with the parent tree is broken). This can be in response to radial growth, to shading and death of lower branches, to frost, to herbicides, and to fire (Myers and Belles 1995).

Neither seed capsules nor seeds are generally endangered by fire. Opening of capsules takes several days following desiccation and seed capsules are not usually consumed by fire because they are dense woody structures and because crown fires typically do not have long residence times (Wade 1981).

Seed rain after fire is affected by fire type and by the stand structure. Most seed (95%) is released within 5 weeks of a fire; however, several thousand seed per square meter continued to fall 5 weeks after fire (Myers and Belles 1995). Extremely dense stands tend to produce fewer seeds than scattered open- grown individuals or stands with mature emergent seed-baring trees (Myers and Belles 1995). It has been estimated that a 10m tall open-grown tree can release around 20 million seeds (Alexander and Hofstetter 1975 in Myers and Belles 1995). An intense crown fire that kills branches will release more seed than a surface fire that causes little vegetative mortality (Myers and Belles 1995, Wade 1981). Mature trees can replenish stored seed within 2 years (Myers and Belles 1995).

Seedling establishment and survival is affected by fire, flooding and drought. More germination occurs on burned sites than unburned sites, i.e., fire prepares a seed bed (Myers and Belles 1995) and episodes of germination tend to be triggered by the presence of adequate moisture levels. Seeds may remain dormant on a site for months. It appears that seed viability may be limited after 1 year. Prolonged periods of flooding and dry conditions cause seedling mortality. Fires kill 90% of seedlings less than 20cm tall. Some saplings are killed by fire until they reach 2-3 m tall at which point saplings survive fires (Myers and Belles 1995).

Fires may also aid melaleuca dispersal, establishment and persistence. Fire has been postulated to remove vegetation that hinders the transport of tiny seeds by water, thus increasing dispersal distances via water. Fire removes competing vegetation. Fire also creates a safe site for melaleuca seedlings because recent fires “fireproof” areas by removing fuels. Fire also liberates nutrients for use by plants (Wade 1981). Late dry season fires (April and May, when the most acreage is burned in the Everglades) allow Melaleuca to get its seed on the ground before most other dominant tree species.