More info for the terms: basal area
, fire management
, fire regime
, nonnative species
, prescribed burn
, prescribed fire
, seed tree
, stand-replacing fire
Impacts: Melaleuca has been called "the greatest exotic weed threat" to wetlands in southern Florida. Its impacts threaten natural areas such as Big Cypress National Preserve and the Everglades. Systematic reconnaissance flights indicated that by 1992 there were 119,000 acres (48,160 ha) of melaleuca-infested habitat in Big Cypress National Preserve . Everglades National Park is 1 of only 3 sites internationally listed by The International Biosphere Reserve, World Heritage, and Ramsar as critical reserves. The native flora of southern Florida represents a unique assemblage of communities. Southern Florida encompasses the only region of the continental United States where temperate, subtropical and tropical floral elements coexist. This unique area has produced approximately 65 endemic plant taxa, many of which are threatened due to habitat diminishment (reviewed by ).
Melaleuca's negative impacts in southern Florida largely stem from the species's interference with and displacement of native species . A review by Hofstetter  indicates that in the Everglades and southeastern Florida melaleuca may invade "essentially all types of communities, including those where vegetative components appear to be healthy and presumed" to be "comparable to historical vigor." Intact native communities may be more resistant to invasion in southwestern Florida but are still susceptible, particularly following unnatural disturbance or other human-caused environmental degradation.
Presence of melaleuca in fire-maintained sawgrass communities can promote conversion of these habitats to melaleuca forest. Everglades marshlands are comprised of fire-maintained communities of mostly sawgrass prairies. Natural fires periodically eliminate the native, fire-intolerant hardwoods that would otherwise colonize this habitat. However, because melaleuca is so well-adapted to fire it is able to persist and even thrive in this environment, eventually shading out the herbaceous community and transforming the site into a melaleuca forest . See Habitat Types and Plant Communities for more information about specific taxa and communities that are potentially impacted.
Conversion of native forest types to melaleuca forest may or may not impact understory species composition and density, depending on the community invaded. Where invaded and uninvaded forest overstory structure is similar, casual observation indicates that the understory may be relatively unchanged, such as in cypress swamps and pine flatwoods where melaleuca establishment is typically "not dense enough" to alter stand structure. Understory vegetation may be most severely impacted where melaleuca invasion increases forest overstory density or leads to conversion of prairie or savanna to melaleuca-dominated forest, such as in pine flatwoods depressions, sloughs, wet prairies, and the seasonally flooded ecotone surrounding cypress swamps .
Conversion of the dominant overstory species as a result of melaleuca invasion in forested habitats may be a more obvious impact. Geary and Woodall  indicate "mature" melaleuca stands in Florida "swamps" range from 7,000 to 20,000 stems/ha, and up to 133 mÂ²/ha of basal area. Stands growing on shallow or better-drained soils produce similar stem densities, although volume is "substantially" reduced. Myers  described how melaleuca "invades portions of fire-maintained pine and cypress forests in southern Florida, and in some cases appears to pre-empt sites where the native vegetation would normally regenerate following fire. Melaleuca accomplishes this by being the first woody species to get its seed on the ground following a late dry season fire. Once established it forms a dense canopy, shading out or preventing seedling establishment of other species. Melaleuca's shaggy bark and flammable leaves may facilitate burning at a greater frequency than normally took place. The result is the development of a new melaleuca-dominated community maintained by fire" .
Strong melaleuca competition in invaded communities may result from greater exploitation of soil resources. Results from Di Stefano and others [20,21] revealed that melaleuca-dominated stands (8-10 years old) contained significantly (p<0.05) more woody species root biomass in the upper 8 inches (20 cm) of soil than nearby grand eucalyptus (Eucalyptus grandis) (9 years old) or slash pine (20 years old) plantation stands, or palmetto prairie. The 3 forested sites contained similar levels of aboveground biomass.
One of the most important factors in the success of melaleuca in southern Florida may be its relationship to fire. Melaleuca is well-adapted to perpetuation in a fire-prone environment, perhaps more so than any dominant native plant species in southern Florida. As a result, Wade and others  suggested that if melaleuca is present in a burned stand, and postfire hydrologic conditions are conducive to germination and establishment of substantial numbers of melaleuca seedlings, native species in the new stand may be substantially reduced. Because of its many adaptations to fire, melaleuca may have an advantage over many native species in response to dry season fire, to which many native species are apparently not well adapted (reviewed by ). Melaleuca invasion may pose particular risk to fire-dependent communities in southern Florida. Myers and others  pointed out that marshes, wet prairies, cypress swamps, and pinelands, all habitats that are susceptible to melaleuca invasion, also are all common habitats in southern Florida that require fire for survival. For more information about melaleuca and fire, see Fire Ecology and Fire Effects.
Geary and Woodall  attributed the success of invasive melaleuca in Florida to altered hydrology, as well as altered fire regime. Lowered water tables as a result of drainage and excessive groundwater withdrawals in some areas of southern and central Florida have led to changes in the natural hydroperiod. In many areas shortening of flood duration may have led to increased size and severity of wildfires . In addition, sites experiencing stand-replacing fire are frequently subject to seed rain from established melaleuca trees that were planted as ornamentals. The combination of altered hydrology, altered fire regime, and available seed sources can lead to postfire sites that become fully-stocked melaleuca stands with much reduced native plant presence . Melaleuca invasion may itself alter FIRE REGIMES, as well as fuels .
South Florida Water Management District and the U.S. Army Corps of Engineers consider impacts of invasive melaleuca in the littoral zone of Lake Okeechobee when adjusting lake water levels. Lower lake levels may stimulate melaleuca growth and establishment, and prolonged periods of reduced water levels may lead to the expansion of established melaleuca populations (reviewed in ).
Ewel  has argued that southern Florida may be especially susceptible to invasion by nonnative plants because it is geologically young and not all ecological niches are fully occupied by its indigenous flora. In particular, pondcypress growing on sites that are too wet to support south Florida slash pine, but are drier than is optimal for pondcypress, may be unable to effectively compete with invading melaleuca [24,52]. Pondcypress stands in these ecotones are short, open-canopied, and subject to frequent fires . Myers  and Ewel  suggest pondcypress in southern Florida occupies sites for which it is not well adapted. Melaleuca invasion in "dwarf cypress" habitats, which are typically a mix of wet prairie and stunted south Florida slash pine and pondcypress, may represent displacement of native species that had occupied "suboptimal sites due to an absence of competition" (see Myers  for details). The ecotone between pondcypress and south Florida slash pine forest communities seems particularly susceptible to melaleuca invasion .
It is commonly asserted that one reason nonnative invasive plants are so successful is that they are largely unconstrained by the impacts of herbivory from coevolved pests in their native habitat (e.g. a review by Mack and others ). Balciunas and Burrows  demonstrated how ambient, nonoutbreak levels of insect herbivory significantly (p<0.05) suppressed height and diameter growth of melaleuca saplings in northern Queensland, Australia. They also suggested that reduced levels of herbivory on southern Florida melaleuca, compared with herbivory in Australia where the species is native, might explain part of melaleuca's strong competitiveness in southern Florida's plant communities . Comparative data from melaleuca populations in eastern Australia and southern Florida suggest that seed production is substantially greater in Florida melaleuca trees than those in Australia .
Indirect impacts may also result from presence of melaleuca in peninsular Florida. Melaleuca is a host to lobate lac scale (Paratachardina lobata), a nonnative invasive insect pest in southern Florida. Lobate lac scale has a broad host range, attacking well over 100 different woody plants including native species, ornamentals, and crop plants. Damage to melaleuca from lobate lac scale is apparently minimal, but melaleuca can serve as a reservoir for lobate lac scale's infestations of more desirable plants .
Although melaleuca has been blamed for human respiratory and allergic reactions , a study by Stablein and others  concluded that melaleuca is not a significant source of aeroallergen, and melaleuca odor is not a respiratory irritant.
As of this writing (2005), there is very little information indicating whether melaleuca is invasive in areas of North America outside Florida. Woodcock and others  described a melaleuca plantation established in the early 1930s on a mid-elevation (869-951 feet (265-290 m)) site on the island of Oahu, Hawaii. The relatively open character of the stand permitted native woody plants to establish in the understory, while excluding more light-demanding nonnative species. It was hypothesized that the melaleuca plantation may be fostering the regeneration of a native successional forest. According to Little and Skolmen , in Hawaii melaleuca is "naturalized, but not a pest as in Florida."
Control: The challenge of melaleuca control is influenced by an ever-changing, frequently ephemeral arrangement of environmental conditions, stand structures, seed sources, regeneration status, and fuel loads. Anticipating and identifying windows of opportunity in target susceptibility can enhance success. For instance, treatments for controlling seed-bearing melaleuca may be timed to minimize opportunities for successful seedling establishment resulting from the inevitable postdisturbance seed rain. Treatments that put seed on the ground in late fall or early winter, typically when the soil is still moist from seasonal rains, stimulate germination. Yet many, if not all of the delicate young seedlings are likely to die during the predictably dry months of March, April, and May . Van and others  suggested the best time for melaleuca control in southern Florida might be spring, when plants are most actively growing (see Seasonal Development).
Because treating seed-bearing adults inevitably leads to substantial seed release, follow-up treatment or multiple treatments of establishing seedlings will be required to prevent immediate reinvasion. Control activities minimizing disturbance to soil and surrounding desirable plants may help mitigate subsequent melaleuca seedling establishment [93,110] (see Site Characteristics). Myers and Belles  point out the importance of field monitoring for knowing a) when germination begins following major seed release, b) whether germination is complete, c) whether additional germination episodes occur following receding flood waters or cessation of drought, and d) size of the largest seedlings in a cohort relative to cohort age. This last point may be important for determining whether the largest seedlings are capable of sprouting in response to top-kill.
Woodall  recommended focusing control efforts first on outlying individuals that serve as seed sources for new infestations. Dense, well-established melaleuca stands are more difficult, time consuming, and expensive to eradicate, especially over large areas. Once outliers are eliminated and dense, well-established stands are contained, strategies for complete eradication can be implemented .
For areas with scattered, mature melaleuca seed trees that have not recently burned, Woodall  recommended killing trees and releasing seed from late October to late December. Moisture provided by occasional winter showers will stimulate germination. Lack of fire will promote plant "competition," resulting in slow-growing melaleuca seedlings. Typical spring drought conditions will kill most germinants. The ensuing summer wet season should stimulate germination of any ungerminated seeds left on the site. These and any remnant seedlings can be removed with prescribed fire during the following dry season .
In extremely dense melaleuca stands seed production may be substantially reduced within the dominant age cohort due to shading. However, these stands may also contain larger, older, canopy-emergent individuals that bear large numbers of capsules. It may be prudent to first focus control efforts in these stands on the emergents. Without these, extremely dense stands may pose a comparatively lessened threat of massive seed release .
A strategy utilized by resource managers at Big Cypress National Preserve is to delay follow-up treatments in melaleuca control units for 3 years, allowing seedlings an opportunity to reach a height that facilitates detection with a minimal chance of seed production ; however, some plants may produce seed at <3 years of age .
Prevention: Because melaleuca seed dispersal is typically distance-limited, treatment of outlier trees that occur far from established melaleuca populations may prevent establishment of new, invasive populations. If the outlier is eliminated in such a way that seeds are not released, then the probability of colonization in that habitat is substantially reduced . Woodall  describes how, "as one proceeds toward the central denser portion of a melaleuca population, the relative benefits from killing individual trees decline. The biggest payoff is from controlling the most isolated, most distant trees." Biennial inspections of uninvaded areas will help identify melaleuca outliers .
Integrated management: A combination of stressors, both natural and human-caused, might be integrated for more effective management and control of melaleuca: "A judiciously timed, integrated approach using chemicals, mechanical means, and fire can be effective. Present control efforts use mechanical cutting followed by a dose of herbicide. Little attention, on the other hand, has been given to the site susceptibility and timing of treatment. Sites should be treated when the seeds would be most unlikely to encounter favorable conditions for establishment. Full advantage should be taken of both fire and frost. Both occur naturally every few years. Fire can be prescribed at practically any time as long as fuel is available. Both destroy melaleuca biomass in leaves, branches, and small diameter stems, all of which are replaced by sprouts. To accomplish this, the tree uses and depletes stored food reserves. If the tree is cut and treated with herbicide while these reserves are low, the energy for sprouting would be lacking and follow-up treatment would be minimal. Due to the time of year, frost-released seed is likely to encounter unfavorable site conditions, and fuel for burning still remains. Treatment of seed trees following frost and prescribed burning should greatly reduce sprouting. A late wet or early dry season prescribed burn would put the seed on the ground at an unfavorable time" .
Biological control agents may further reduce melaleuca populations that have been damaged by other means, such as mechanical, chemical, or fire. Center and others  described a release site for melaleuca snout beetle where an estimated 51,360 cut stumps "had coppiced profusely." Snout beetles had fed upon an estimated 25% of coppices. Of those plants that were fed upon, damage on 53% was low (generally consisting of nibbling on one or a few tips), damage on 31% was moderate (extensive damage to several stem tips), and damage on the remaining 16% was high (almost all foliage destroyed) .
Physical/mechanical: Mechanical clearing or felling of mature melaleuca trees can be an effective means of control. However, to be most effective desirable vegetation should be subsequently established and maintained, and posttreatment seedling control undertaken. Follow-up treatment(s) are required to control stump sprouts . In a field experiment, 98% of melaleuca plants 2.3 to 3.9 feet (0.7-1.2 m) tall sprouted after a single cutting. The month in which stems were cut had no effect on biomass recovery after a single cutting. Following a 2nd cutting (2 years after the 1st cut), melaleuca mortality rates were still ≤27% for all but 3 months of the year. Mortality rates in June, July, and August were 72%, 55%, and 42%, respectively. High mortality in August may have been influenced by flooding during that month . Plants <3.3 feet (1 m) tall may be hand-pulled and should be stacked to prevent sprouting. Plants > 3.3 feet (1 m) tall are best cut with a machete or chainsaw and the cut surface treated with herbicide .
According to Timmer and Teague , mature trees that are mechanically cleared should be removed from the site and destroyed to reduce seed dispersal and sprouting. However, Myers and Belles  cut >5,000 melaleuca trees in the course of field research, and observed sprouting in "only a few" downed stems, all of which were lying on extremely wet soils or floating. In all cases, sprouts died during subsequent drought.
Fire: See Fire Management Considerations.
Biological: One reason frequently offered for the success of nonnative invasive plants is that in their new environment they are freed from the negative impacts of pests and parasites with which they coexisted in their native habitats (e.g. see the review by Mack and others ). Balciunas and Burrows  demonstrated how ambient, nonoutbreak levels of insect herbivory significantly (p<0.05) suppressed height and diameter growth of melaleuca saplings in northern Queensland, Australia. They speculated that a classical biological control program using Australian insect herbivores should also suppress melaleuca sapling growth in southern Florida, as well as reduce flowering and seed production, and perhaps lower fire tolerance. Several sources suggest that an integrated biological control program will reduce melaleuca's impact on native species [4,70,107].
Preliminary investigation indicates melaleuca has not acquired indigenous herbivores (or other pathogens) at sufficient densities to cause appreciable damage to trees in southern Florida . Yet several organisms, indigenous and introduced, have shown some potential for reducing melaleuca in southern Florida.
Botryosphaeria ribis is an indigenous fungus in southern Florida. It is pathenogenic to melaleuca but is not known to cause "large-scale epiphytotics" on melaleuca in the field. However, B. ribis canker development and tree mortality may be enhanced by stresses associated with drought, low temperatures, or complete defoliation, so B. ribis may enhance the efficacy of other control activities . Although compatibility between the herbicide chemical imazapyr and B. ribis has been demonstrated in-vitro , field studies demonstrated that stump regrowth following treatment with imazapyr and B. ribis mixtures were not significantly (p=0.05) different from regrowth of stumps treated with imazapyr alone . It is logical, though speculative, that defoliation by fire may enhance the pathogenic effect of B. ribis infection, suggesting inoculation prior to prescribed fire in melaleuca-infested areas may reduce postfire melaleuca survival. Further research is needed to establish the efficacy of purposeful B. ribis inoculation in concert with other control methods or natural melaleuca stressors.
Puccinia psidii is a rust fungus that occurs on a variety of Myrtaceae throughout the Caribbean islands and North (Florida), Central, and South America (reviewed in ). In 1997, P. psidii was discovered on new growth of about 70% of melaleuca trees and saplings over a 1.2-mile (2 km) strip in southern Florida. Trees were 10 to 16 feet (3-5 m) tall, top-killed, and bushy in appearance, with many new shoots . P. psidii can cause defoliation and twig dieback in infected melaleuca [66,67,68]. The P. psidii-melaleuca "pathosystem" may contribute to melaleuca control in southern Florida, especially if integrated into current control programs . Again, research is needed to establish if purposeful use of P. psidii could be useful for melaleuca control.
Lobate lac scale, an invasive exotic insect in southern Florida, is reported to feed on melaleuca, but as of this writing (2005) melaleuca damage has seemed inconsequential  (see Indirect impacts).
Balciunas  speculated that melaleuca snout beetle may reduce melaleuca's fire tolerance in Florida, especially of saplings, presumably by depleting energy reserves needed for postfire sprouting. The melaleuca snout beetle (Oxyops vitiosa), an Australian weevil, was released as a biological control agent at 13 sites throughout the range of established melaleuca in southern Florida in 1997 [15,16]. Melaleuca snout beetle establishment (as of May 1999) occurred at 10 of these sites  (for a comprehensive description of these sites, introduction methods, and establishment results, see [15,16]). Because of slow dispersal rates (≈ 0.6 mile/year (1 km/yr)), melaleuca snout beetle has been collected and redistributed to >150 locations in southern Florida . Both the adults and larvae prefer to feed on young melaleuca foliage. Although larvae develop best on new leaves, the long-lived (>1 year) adults can subsist on less nutritious, mature foliage and stems during quiescent periods of foliage production [60,106]. Eggs and larvae are most abundant in late fall and early winter when susceptible young foliage is most abundant, and are absent or uncommon in spring and summer unless regrowth from damaged trees is present. Females usually oviposit on the surface of young leaves and expanding buds during the flush of young foliage produced after flowering. The resulting larvae pass through 4 instars, each lasting about 5 days (in eastern Australia). Fourth instars crawl or drop from the host plant, burrow into the ground, and pupate for about 11 days (in eastern Australia) [60,64]. Establishment of beetle populations appears hindered on permanently flooded sites due to drowning of larvae when they drop to search for pupation sites [16,60]. Dispersal of newly released populations may be most rapid on sites with scattered melaleuca in open "savanna-like" areas. Open-grown trees with an abundance of new foliage support healthier snout beetle populations, compared to dense stands with a paucity of young foliage . Based on observations in its native range in eastern Australia, Balciunas and others  predicted that melaleuca snout beetle would have the greatest impact on sapling size trees in southern Florida. Feeding by larvae on new foliage causes tip dieback, and persistent damage causes loss of apical dominance. Subsequent branching and new growth provides a feedback of additional resources to sustain continual adult and larval populations. Tissue loss and diversion of photosynthetic resources associated with snout beetle feeding appears to limit flowering in mature melaleuca trees [60,62] and may delay reproductive maturity of saplings .
The melaleuca psyllid (Boreioglycaspis melaleucae), an Australian native, was released in southern Florida as a biocontrol agent in February 2002 [61,107]. It has established across a variety of melaleuca-invaded habitats in southern Florida, from permanently flooded wetlands to upland pine flatwood sites. Both adults and larvae feed on melaleuca sap, usually feeding at the tips of new twigs . Most damage is attributed to nymphs . "Tender, expanding buds and leaves as well as mature older leaves are destroyed by nymphs. When populations are large, damage may extend to somewhat woody stems" .
Eucerocoris suspectus, a Hemipteran native to Australia, was approved for quarantine testing in the U.S. in 1995. Adults and nymphs feed on young melaleuca leaves and shoots .
Chemical: Herbicides are among the most effective and widely used tools for controlling melaleuca in peninsular Florida . Herbicides are most effective when integrated within a suite of control measures and strategies. Cost and logistics can make chemical control difficult to implement over large areas of infestation. As Myers and Belles  explained, "for small administrative units, like Corkscrew Swamp Sanctuary, portions of Sanibel Island, and some state parks, existing control technologies focusing on herbicides have worked well. For larger units, like Loxahatchee National Wildlife Refuge, the Conservation Area, and Big Cypress Preserve, the sheer scale of the problem has limited control success" .
Damage to melaleuca trees from herbicide may induce the release of substantial numbers of canopy-held seeds. Aside from the cut-stump application method, herbicide treatments presumably result in longer periods of seed release, compared with postfire seed rain, because the herbicides act more slowly than fire . Burkhead  indicated melaleuca capsules opened within 6 months after stem injection treatment with either hexazinone or triclopyr. Woodall  observed differences in the rate of seed dispersal with different herbicides. Seedfall from trees injected with either picloram or dicamba accelerated rapidly following treatment, corresponding to the rapid effect these chemicals had on the health of treated trees, peaking at 2 weeks posttreatment and remaining above baseline level for 10 weeks to 3 months. In contrast, herbicides that cause gradual damage to trees may not affect seedfall as strongly or as rapidly . Although melaleuca capsules are retained in the tree canopy, mature seeds are not connected to the plant's vascular system so herbicide treatment will not impact seed viability . In some cases, control efforts may actually lead to greater spread due to posttreatment seedling establishment .
Herbicide treatments are also complicated by the necessity of retreating the trees that sprout [54,93]. While at least some fraction of mature melaleuca trees that are treated with herbicides can survive initial treatment, detailed information about subsequent sprouting is lacking. Herbicide treatments that leave trees standing (i.e. foliar spray, stem injection or soil-applied herbicide) may result in regrowth of canopy foliage and other aerial tissues . Initial application of chemicals to cut stumps (see below) may also be insufficient to prevent stump sprouting, requiring retreatment.
Timing of herbicide application may also be important. Stocker and Sanders  suggested that stem injection treatments administered near the beginning of the growing season only affected tissues above the cut line, since transport in the plant was primarily toward the growing shoots at that time of year. Myers and Belles  compared effectiveness of 3 foliar-applied herbicides, applied in January, March, May, June, or November, for controlling melaleuca stump sprouts. Imazapyr was generally more effective than hexazinone, and glyphosate was least effective. Imazapyr killed significantly (p<0.05) more trees when sprayed in November (83.1%) or January (79.3%), compared with March (47.8%), June (32.5%), and May (25.0%). Overall, control effectiveness was significantly (p<0.004) greater for larger (greater crown volume) trees. Reasons for variation in treatment effectiveness by month were unclear. Rather than considerations of seasonal effectiveness of herbicides at killing trees, Myers and Belles  recommended timing herbicide treatments to minimize the chances for successful post-treatment seedling establishment (see Control and Fire Management Considerations).
Foliar application of herbicides yields inconsistent results and may be ineffective compared with other methods. Foliar-applied herbicides are probably most effective for controlling stump sprouts, or aerial sprouts in dense and/or low-statured stands following disturbance (such as fire) . For dense stands, Myers and Belles  speculated that burning, followed by ground-based foliar herbicide application to sprouts at 3 to 9 postfire months, is more effective than spraying untreated or unburned stands from aircraft. They tested 3 foliar-applied herbicides for controlling postfire sprouting on melaleuca trees (1.3 to 8.5 feet (0.4-2.6 m) tall). Trees were sprayed either 3 months after fire (mortality sampled at postfire month 20) or 9 months after fire (mortality sampled at postfire month15). Sites were burned under prescription in March and January. Considering all treatment and burn periods, foliar-applied triclopyr produced significantly (p<0.01) greater mortality (81%) than imazapyr (55%), which in turn produced significantly (p<0.01) greater mortality than glyphosate (19%).
Use of soil-applied pelleted herbicide can control melaleuca and has less site impact than felling and stump treatment. Pelleted herbicide is best for nonseedbearing trees since subsequent seed release is protracted and slow to initiate . Stocker and Sanders  found that soil applied pellets of hexazinone and tebuthiuron resulted in 100% mortality of mature trees in periodically flooded habitat.
Stem injection of chemicals is an effective, relatively low-impact melaleuca control method. Injected seed trees purge their canopy-held seedbank relatively quickly. Ideally, most seeds are released within 1 month of injection . Burkhead  found injection had little adverse impact on nontarget plant species in experimental plots in Big Cypress National Preserve. Grasses within 1.6 feet (0.5 m) of hexazinone-treated trees were killed but reestablished within 1 year of treatment. Imazapyr, picloram + 2,4-D, triclopyr, and hexazinone have all shown good results when used in stem injection [13,54,90]. Myers and Belles  also successfully used stem injection (with Hexazinone) to treat postfire sprouting. Mortality was 96% at 5 months after fire and 98% at 9 months after fire, but this treatment was significantly (p<0.05) less effective when applied at 2 months after fire. See Fire Management Considerations for more information about fire and melaleuca control.
Felling melaleuca trees and applying herbicide to cut stumps is also an effective chemical control method. Woodall  recommended picloram + 2,4-D for cut-stump treatment. Laroche and others  tested several herbicides for effectiveness when applied to cut stumps. Imazapyr yielded 100% control, while application of triclopyr, glyphosate, or hexazinone resulted in >85% melaleuca mortality. Myers and Belles  and Stafford  also successfully used imazapyr applied to cut stumps. Stafford described moderate but temporary damage to nearby herbaceous plants. It was speculated that this damage was caused by herbicide uptake from soil or root grafts associated with treated melaleuca stumps, rather than from sloppy spraying. Myers and Belles  found that applying herbicide to cut stumps of melaleuca trees that had recently burned was also effective.
Regardless of the herbicide used, Myers and Belles  suggested the cut-stump method was "slightly more effective" in killing the target tree than stem injection. Also, standing trees are more likely to disperse seeds over a greater area compared with downed trees. Further, while downed trees can release their seed within 2 weeks after cutting, stem-injected trees may take substantially longer (up to 1 year was suggested) for all branches to die and release seed. Inducing rapid seed release by felling trees results in more rapid germination and establishment of closer (both temporally and spatially) cohorts of seedlings, permitting effective seedling control using a follow-up prescribed fire. With stem injection, seedling establishment may occur over a more extended time period, rendering seedling control using prescribed fire problematic. "If burning is conducted when the earliest established seedlings are still small enough to be killed, all seeds may not have been released from dying (or surviving) trees. Such a burn may also stimulate remaining seeds to be released. These seeds will encounter bare mineral soil, reduced competition, and fuel loads too low for a repeat burn. On the other hand, if the burn is conducted after all seeds are released, some early establishing seedlings may already be large enough to survive the burn.". Stump treatments may also be timed to take advantage of seasonal flooding and the suppressive effects of inundation on stump sprouting  (see Cultural control below).
However, Woodall  recommended against cut stump treatments for general purposes: "Large amounts of the chemical are needed because the circulation of fluids within the tree stops when the tree is cut. Any herbicide that can prevent stump sprouting can do a much more efficient job when injected into the stem of an otherwise undamaged tree. Stump treatment is advisable when: (1) the stem is too small for injection and the rooting medium is unsuitable for soil application, or (2) the need to remove all seeds is so critical as to require felling. A good example of (1) is a small sapling rooted on a cypress knee; an example of (2) is a large seed tree immediately adjacent to a prepared seed bed, such as the right-of-way of a powerline being constructed" .
Melaleuca seedlings can also be controlled with herbicides. According to Timmer and Teague  "herbicide treatments using either broadcast foliar sprays or soil treatment may prevent germination and/or establishment" of seedlings. In a greenhouse study, Woodall  attained complete kill of 45-day-old seedlings with bromacil, diuron, picloram + 2,4-D, and hexazinone, complete kill of 106-day-old seedlings with bromacil, diuron, and picloram + 2,4-D, and complete or near-complete kill of 106-day-old seedlings with hexazinone. Stocker and Sanders  achieved 100% mortality of seedlings between 8 and 24 inches (20-60 cm) tall after 6 weeks following broadcast applications of bromacil, tebuthiuron, and hexazinone, and after 44 weeks using glyphosate.
For more information, a review of specific control methods using herbicides is provided by Timmer and Teague .
Cultural: Timmer and Teague  indicated that, where water levels can be manipulated, seedlings can be controlled by flooding the treatment area. However, they did not indicate the optimum depth or duration of flooding for effective control. In addition, several studies have shown that melaleuca seedlings can survive complete submersion for several months, indicating that this approach may only be marginally effective unless conducted over a long time.
On the other hand, stump sprouting following felling of mature melaleuca trees may be reduced or even eliminated if stumps are subsequently submerged. Mechanical treatments conducted just prior to seasonal flooding may be particularly useful in dense melaleuca stands with access for large mechanized cutters. For best results, stumps should be submerged within at least 2 weeks of cutting and should be submerged for at least 40 days. If seasonal flooding is insufficient, stump sprouts can be treated with foliar-applied herbicides .
] described "forced succession," in which conditions are created that will induce the development of a shade tolerant native plant community, while gradually reducing melaleuca overstory and discouraging melaleuca regeneration. Gradually thinning melaleuca, perhaps over a 10-year period, increases light levels sufficiently to maintain a favorable microclimate, resulting in improved vigor of native seedlings that are likely already present in the understory of melaleuca-dominated stands. Simultaneously, care is taken to maintain a thick, undisturbed litter layer that inhibits establishment of melaleuca seedlings. Thinning may be carried out by felling or chemical stem injection, although felled trees should remain where they fall to prevent undue disturbance. Thinning should remove the largest, oldest trees first to minimize sprouting, since sprouting decreases with age of trees [110