Seed in M. deanei is produced in barrel shaped woody capsules that contain 500-600 seeds (Felton 1993). It is held in the canopy of the plant for several years (possibly up to 15 years) until dehydration allows the capsules to open (Benson & McDougall 1998). Seed release is triggered by fire, occasionally also by drought or frost (Virtue 1991; Felton 1993).
Melaleuca deanei seed is wind dispersed. Light winds are sufficient to empty most capsules of M. quinquenervia, which has similar sized seed (Virtue 1991). It is unknown whether M. deanei possesses a persistent soil seedbank. Itsseeds remain viable for at least nine weeks following release from the capsules, but their viability after this period is unknown (Felton 1993). Felton suggests that the species does not require a persistent soil seedbank as the requirements for germination are provided by fire, which also triggers the release of the seed from its capsule.
Under laboratory conditions, seeds germinated readily and had high levels of viability (Virtue 1991; Felton 1993). Germination seems to be greatest in seeds that are sourced from large populations (Virtue 1991). However, in the wild, no seedlings have been observed during the field work associated with the preparation of this recovery plan, or in previous studies (Travers Morgan 1990; Virtue 1991; Felton 1993). Doig (pers. comm.) notes that despite setting lots of potentially viable seed, germination in the wild is poor and many seedlings do not survive. Seedling establishment is most likely also dependent on prolonged moisture availability (Virtue 1991). It appears that overall, this species relies predominantly on clonal reproduction and produces seed infrequently.
Melaleuca deanei frequently produces coppiced growth and suckers from its roots, particularly after fire or the disturbance and death of a major stem (Travers Morgan 1990). The species has also been observed to regenerate from epicormic buds that are protected from fire by thick papery bark (Felton 1993).
It has been suggested that fire is required to provide the right conditions for germination and seedling growth and that seedlings very rarely establish at any time other than after fire (Felton 1993). It has also been suggested that fire may be required to stimulate flowering of M. deanei (L. McDougall pers. comm. cited in Benson & McDougall 1998), however Felton (1993) states that some populations flower annually regardless of time since the last fire.
Melaleuca deanei has been observed growing most commonly and vigorously in sites exposed to direct sunlight, or in places where light penetration has been increased by disturbance, such as the edge of fire trails (Travers Morgan 1990; S. Douglas, pers. comm.). The species’ preference for light may explain its habitat preference for open ridgetop vegetation (Felton 1993). Shaded plants seem to have fewer and shorter new stems and leaves, and a shorter internodal distance (Travers Morgan 1990).
It is therefore likely that fire, and possibly other physical disturbances that increase light levels without impacting upon the soil, play a role in providing for the recruitment and long term persistence of the species.
5Threats and Management Issues
6.1.1 Low fecundity and viability
Melaleuca deanei appears to have low fecundity levels as exhibited by infrequent flowering, poor seed production, and poor seedling vigour (Virtue 1991; Felton 1993; Travers Morgan 1990; R. Johnstone, pers. comm.). Also, larger populations seem to have greater seed viability and are more likely to produce fruit than smaller populations (Virtue 1991). A number of small populations (i.e. less than 10 ramets) have been lost or have suffered significant declines in population size in the last 10 years, even though habitat conditions at these sites do not appear to have changed (R. Doig, pers. comm.).
The causes of this low fecundity are not known and warrant further research, to determine both its exact cause and its implications for the viability of small M. deanei populations (see Table 7). Possible reasons could be inbreeding depression, the absence of a specific stimulus, or set of stimuli, that would trigger flowering, or a natural tendency towards vegetative reproduction.
Actions that counteract the low fecundity levels will depend on the outcome of such research. However, results so far indicate that until the research has been conducted, fecundity is likely to be enhanced by increased cross-breeding between individuals of the same or different populations. To facilitate such cross-breeding, care must be taken to retain genetic links between populations by providing contiguous habitat between them. Also, careful in-situ management of existing populations should focus on increasing the number of individual plants, and this should include the application of fire to stimulate seed release into favourable conditions for germination and establishment.
6.1.2 Habitat loss and fragmentation
The available habitat for M. deanei has been severely reduced and fragmented by urban development, quarrying, and associated disturbances. This is primarily a consequence of the species’ distributional range being centred upon the Sydney region, and its apparent preference for ridge-top locations and sites with lateritic soils. The urbanisation of the Sydney region has divided the species’ historical distribution into two distinct areas (ie northern and southern populations). Ongoing urban consolidation and expansion continues to threaten a number of populations. For example, undetected, though probably small, populations may be present in the rural-residential areas of Baulkham Hills and Hornsby LGAs where the threat of clearing is substantial (S. Douglas, pers. comm.).
Holsworthy Military Area contains a number of highly significant populations and large areas of contiguous and relatively undisturbed habitat, which are largely zoned as land for Environmental Protection. The Department of Defence is currently considering the development of a conservation agreement for Holsworthy with the Commonwealth Minister for Environment Protection, Heritage and the Arts, which would safeguard this area from negative impacts arising from future development (D. Carter, pers. comm.).
Sites that are considered to be at high risk of habitat loss and fragmentation include the 17 sites that have been recorded from freehold land. Only five of these sites are zoned as land for Environmental Protection (Sites BM1, 2, 3a; SU10; WA11), all others are zoned as either Rural, Residential or Special Users, and thus are potentially subject to development or disturbance.
Of the eight known sites on crown or public land, four are in council reserves which are zoned as land for Environmental Protection (Sites RY2, SU2b, SU3, SU7a-f). Here, appropriate management can safeguard them against further habitat loss. A fifth site along a fire trail is also zoned for Bushland Conservation (Site BM3b), whereas the remaining three sites are zoned as Rural or Open Space and should thus be considered to be potentially at risk of loss (Sites HO4, KU3&4).
6.1.3 Inappropriate fire regimes
Frequent fires over a long period have the capacity to eliminate resprouting species such as M. deanei because juveniles have a slow growth rate and therefore take a longer period of time to become fire resistant (Felton 1993). High frequency fire has been recorded as a threat to M. deanei populations within Holsworthy Military Area (Felton 1993), and possibly elsewhere.
Populations within Holsworthy Military Area were reportedly burnt every 1 to 5 years (Travers Morgan 1990). However military practices have subsequently changed, and no fires as a result of military exercises have occurred in the area since 1996 (M. Peterson, pers. comm.). Lightning strike and arson are now the major cause of fire with suppression of those fires hindered by unexploded ordnance (M. Peterson, pers. comm.).
It is also likely that fire exclusion is impacting on the species, particularly those populations that inhabit small urban bushland remnants. As discussed in Section 5, fire is likely to play an essential role in the maintenance of M. deanei populations by:
providing soil and light conditions that are conducive to germination and seedling growth; and
increasing stem density through vegetative growth.
Further research into aspects of the fire ecology of M. deanei are required to determine the appropriate fire regime for the species (see Table 7). In the absence of this information, it is important that land managers apply an appropriately conservative fire regime for the species that comprises:
a minimum fire frequency of 8 years;
moderate intensity fires in preference to high intensity fires, until the intensity of fire that the lignotuber can withstand has been determined; and
late summer or autumn burns, as seedlings emerging at these times should encounter favourable moisture conditions and therefore have a greater chance of establishment (Auld & Bradstock 1996).
Low intensity fires in habitat for the species should be avoided where possible (with the exception of those conducted and monitored under experimental conditions) until it can be demonstrated that such fires will trigger the release of seed and provide the appropriate conditions for seedling establishment.
The maximum fire-free interval for the species is not known. However, given the susceptibility of the species to shading and the potential for aging to reduce seed viability, it is recommended that fire exclusion for periods of greater than 20 years be avoided.
At sites where fire cannot be applied (e.g. due to remnant size or proximity to urban areas), other methods to trigger seedling recruitment could be trialled in an experimental manner. Such methods could include placing seeds in burn piles and burning the piles immediately.
6.1.4 Mechanical methods of bushfire fuel hazard reduction
Populations of M. deanei that are located in close proximity to residential developments or other assets are potentially threatened by mechanical methods of bush fire hazard reduction. Any Bush Fire Hazard Reduction Certificates issued under the Rural Fires Act 1997 must incorporate the mitigative actions for M. deanei identified in the Threatened Species Hazard Reduction List (TSHRL). Currently the TSHRL requires that no slashing, trittering or tree removal occurs at M. deanei sites. It is thus essential that the NPWS Wildlife Atlas contains records of all locations of the species that are accurate to within 100 metres.
In circumstances where the application of mechanical methods of fuel reduction cannot be avoided, selective hand removal of tree and shrub species (other than M. deanei) within 5 metres of M. deanei stands should be considered.
6.1.5 Construction and maintenance of tracks and easements
Track construction should be considered a significant threat due to the species’ preference for ridgetop habitat, where it is often easiest to build roads and powerlines. Also, several M. deanei populations occur on the edge of fire trails and along powerline easements, where they are at risk from mechanical damage during the maintenance and/or widening of these areas (Sites BM3b; HO9a-b, 10a-e, 18e; SU9c&d; WO1, see Appendix 3). One population (Site BH2) has most likely been destroyed by the re-establishment of a fire trail along which it grew (S. Douglas, pers. comm.).
Repeated disturbance in the form of mowing, slashing, or trittering is likely to destroy M. deanei plants, or to at least prevent flowering and seed set. To avoid further losses of populations along fire trails and easements, several measures should be taken: first, the NPWS Wildlife Atlas contains all known records, and the appropriate authority should ensure that the Atlas is consulted for location records and updated where new populations are found. Further surveys should be conducted in areas where the species is suspected to occur, and field staff should be trained in the identification of the species. Populations should then be marked, e.g. by coloured survey pegs. Wherever possible, physical disturbance at such sites should be avoided or not occur in intervals of less than 8 years. Note that a s132C licence (NPW Act) may be required for works that will impact on this species.
Unrestricted access, the creation of new tracks and the dumping of rubbish threaten several M. deanei populations, through mechanical damage, soil compaction and introduction of weed propagules. It also leads to associated changes in runoff and weed encroachment.
Examples of such disturbances are informal tracks for trail bikes (Site HO1, S. Douglas, pers. comm.), or four-wheel drives (Site SU5a-5d, Travers Morgan 1990). Dumping of rubbish, including green waste, building debris and car bodies, has also caused disturbance at several sites (Site SU5a-5d, Travers Morgan 1990; SU9a-b, M. Bremner pers. comm.; HO26, S. Douglas, pers. comm.). These combined threats are best addressed through the installation of barriers to prevent physical damage to M. deanei sites.
6.1.7 Weed invasion
Weed invasion has been recorded as a threat to M. deanei at a small number of sites. Weeds present at these sites include Lantana camara (Lantana), Asparagus densiflorus (Asparagus Fern), Eragrostis curvula (African Love Grass) and Ehrharta erecta (Panic Veldt Grass).The impact of weeds on M. deanei include direct competition to mature plants through shading, as well as the disruption of life cycle processes including recruitment.
The management of weeds at M. deanei sites requires targeted bush regeneration efforts that aim to restore and maintain areas of suitable habitat. However, it is important that land managers are aware that weed control measures have the potential to impact negatively upon the species and caution should be used when applying herbicides within or near habitat for the species.
The small tree species Pittosporum undulatum (Native Daphne) is also a threat to M. deanei at sites where fire has been excluded for a long period. This species contributes to a mesic shift in vegetation and will potentially shade out M. deanei. At sites where fire cannot be applied, this species should be treated as a weed and selectively culled to maintain light levels. A second native species found to compete with M. deanei is Devil’s Twine (Cassytha glabella), a leafless parasitic vine common in heath and woodland (Felton 1993). This species attaches to its host plant by means of suckers and extracts water and nutrients from the host. At least half of the populations visited by Felton were covered with this vine. Where possible, this species should be removed from M. deanei plants to avoid shading and competition for resources.
The hybridisation of M. deanei with other species of Melaleuca and Callistemon is a potential threat, particularly to those populations that occur in close proximity to urban areas. For example, the germination of seed collected from one site (SU3) revealed that only approximately 20% of progeny were ‘pure’ M. deanei, with the remaining progeny being hybrids with other Melaleuca and Callistemon species (probably M. armillaris and C. viminalis; R. Johnstone RBG pers. comm.). Further research is required to determine the extent of such hybridisation. Until this is done, the planting of other species of Melaleuca and Callistemon in close proximity to M. deanei sites should be avoided.
Table 7. Limits to current knowledge of Melaleuca deanei. The justification of the research and the methodology that may be used to address each question is broadly defined, as are the potential benefits of the increased knowledge.
Benefits of increased knowledge
The species’ capacity to regenerate, including the cause of low fecundity levels.
Implications for long term viability of the species.
Investigate the breeding system and the species’ ability to self-pollinate.
Investigate the level of gene flow within and among populations.
Investigate the need for a specific stimulus to trigger flowering.
Results will enable consent and determining authorities to effectively determine the impact of proposed developments on the species.
Better allocation of resources for the recovery program.
Appropriate fire regime
Inappropriate fire regimes are a threat to the species.
Investigations of specific aspects of the fire ecology of the species including seedbank longevity; the time required for seedlings to become fire resistant; the age of reproductive maturity; the effect of capsule age on seed viability; the minimum fire intensity that will trigger the release of seed; and the maximum fire intensity that the lignotuber can withstand.
Potential to increase population size through seedling recruitment.
Extent of hybridisation with other Melaleuca and Callistemon species
Hybridisation has been observed in at least one population.
Germination of seed collected from urban and non urban populations.
Investigations of source of genetic ‘contamination’ at sites where hybrids occur.
Land managers will be aware of the actual degree of this threat and will be able to implement appropriate threat abatement measures, eg removal of inappropriate plantings.
The community can be informed of the safe distance at which other Melaleuca and Callistemon species can be planted.