Threatened Species Unit, North East Branch
New South Wales Department of Environment and Conservation, 2004
4. Threats and Management Issues
- Clearing of native vegetation and habitat loss
- Habitat fragmentation
- Low population number
- Lack of knowledge of biological and ecological requirements
- Weed infestation and competition
- Road verge maintenance
Clearing of native vegetation is a major cause of loss of biological diversity and this has been recognised by listing this process as a Key Threatening Process under the TSC Act. Clearing of large areas of native vegetation for agricultural activities and urban development in the NSW North Coast Bioregion is probably the major cause of the decline of the Ripple-leaf Muttonwood population to a critical level. Much of its lowland floodplain rainforest habitat was cleared for agriculture by the early 1900s. More recently, increased sugar cane cultivation has resulted in with clearing more land for production, including areas previously kept as shelter belts.
Boatharbour Nature Reserve is one of eleven significant remnants of lowland rainforest on the floodplain (NPWS 1997). Its proclamation as a Bird and Animal Sanctuary in March 1927 helped to prevent it being cleared.
Habitat fragmentation is a threat to the viability of the remaining populations of Ripple-leaf Muttonwood. The pattern of large scale clearing of native vegetation has left the habitat remnants isolated from one another. As a result of isolation, the function of pollinators and seed dispersers is likely to have been interrupted and gene flow between the populations of Ripple-leaf Muttonwood may have ceased. Fragmentation is likely to result in increased inbreeding with associated risks of genetic reduction as well as increased susceptibility of each population to encroachment by weeds and other edge effects.
The currently known population of Ripple-leaf Muttonwood consists of a low number of individuals, including an estimated maximum of 16 mature individuals, in the wild. With a low population number, the genetic variation within the species may reduce over time and subsequently the capacity of the species to survive extreme environmental events, e.g. severe drought, and adapt to environmental change may be gradually reduced.
In the absence of relevant information concerning a species biological and ecological requirements, management must be based on assumptions and the precautionary principle. This lack of scientific knowledge, in combination with low population numbers and only a few populations, creates a risk that a management decision or lack of action may have a significant negative impact on the survival of the species. As such, investigation into potential threats is critical to ensure the recovery of the species.
All known Ripple-leaf Muttonwood populations are threatened by weed invasion and competition. Exotic species compete with and interrupt the recruitment of seedlings thus preventing them from reaching reproductive maturity. In particular, the Lantana has been found to compete for light and smother mature and juvenile Ripple-leaf Muttonwood plants.
The prominent weed species threatening the Ripple-leaf Muttonwood habitat in Boatharbour Nature Reserve are:
- Asparagus Fern (Protoasparagus africanus)
- Climbing Nightshade (Solanum seaforthianum)
- Corky Passionfruit (Passiflora suberosa)
- Glycine sp.
- Small-leaved Privet (Ligustrum sinense)
- Lantana (Lantana camara)
- Madeira Vine (Andredera cordifolia)
- Mistweed (Ageratina riparia) and
- Tradescantia (Tradescantia fluminensis).
Prominent weed species threatening the Ripple-leaf Muttonwood habitat near Tatham are:
- Small-leaved Privet (Ligustrum sinense),
- Lantana (Lantana camara) and
- Climbing Nightshade (Solanum seaforthianum).
In the habitat near Tatham, weed competition will become an increasing issue now that the area is fenced to exclude cattle grazing. The Honey Loquat (Gleditsia species) is also present near the Tatham habitat, and poses a future threat to the Ripple-leaf Muttonwood.
Camphor Laurel (Cinnamonum camphora) has been recorded near both sites. This species poses a future threat to Ripple-leaf Muttonwood.
Prominent weed species threatening the Ripple-leaf Muttonwood habitat in Mallanganee National Park are:
- Bush Lemon (Citrus sp.)
- Cape Gooseberry (Physalis peruviana)
- Climbing Nightshade (Solanum seaforthianum)
- Crofton Weed (Ageratina adenophora)
- Lantana (Lantana camara)
- Moth Vine (Araujia sericiflora) and
- Smooth Senna (Senna x floribunda).
Road verge maintenance, i.e. slashing, herbicide spraying or drainage works, adjacent to or in Mallanganee National Park and Boatharbour Nature Reserve may directly damage individual Ripple-leaf Muttonwood plants. State Forests NSW (SFNSW) maintains selected sections of road through Mallanganee National Park to access adjoining State Forest. The DEC maintains the other roads and trails in Mallanganee National Park and Boatharbour Nature Reserve. Lismore City Council, under contract from the Roads and Traffic Authority, maintains the verges of the Bangalow Road near Boatharbour Nature Reserve.
It is not known whether the Ripple-leaf Muttonwood has adaptations to enable it to survive fire events. The fire regime, i.e. frequency, intensity and season of burn, within which a population could persist are also unknown.
Whilst the vegetation communities of the known Ripple-leaf Muttonwood habitat are less fire prone, they adjoin areas that could carry an intense fire under extreme fire weather conditions. In Mallanganee National Park, the wet sclerophyll forest habitat of the Ripple-leaf Muttonwood is generally adjacent to the more fire prone dry sclerophyll forest dominated by Spotted Gum (Corymbia variegata). On the floodplain, the habitat of the Ripple-leaf Muttonwood in places adjoins pasture and grassland which become a fire hazard during the seasonal dry period. It is necessary to consider the risk and management of fire in Ripple-leaf Muttonwood habitat in context with the adjacent vegetation communities.
The response of the Ripple-leaf Muttonwood to disturbance associated with logging is not known. Historically, logging has occurred in areas of potential Ripple-leaf Muttonwood habitat on the Richmond Range.
The population of Ripple-leaf Muttonwood which occurs in the former Mallanganee Flora Reserve and the surrounding state forests were extensively logged in the 1920s, mainly for Hoop Pine (Joseph 2000a). Logging of the flora reserve ceased with its establishment but the state forest outside the flora reserve, which now makes up part of Mallanganee National Park, continued to be subject to selective logging since the 1920s. With the formation of the national park this area has not been logged during the last decade.
The disturbances associated with past logging practices may have impacted on the overall distribution of the Ripple-leaf Muttonwood.
Under the IFOA for the Upper North East Region, there are management prescriptions to protect known individuals and populations of Ripple-leaf Muttonwood (see Section 5.3). Private native forestry licensing also provides protection for the Ripple-leaf Muttonwood, however, there is potential for impact upon unknown individuals not identified in pre-logging surveys.
The response of the Ripple-leaf Muttonwood to grazing by cattle is poorly understood, however, cattle grazing is likely to contribute to the introduction of weeds and may prevent seedling establishment. The Ripple-leaf Muttonwood habitat near Tatham was previously used as a cattle shelter belt. Cattle are now excluded from the Tatham population by fencing. Other remnants of native floodplain vegetation on private property are likely to be similarly used for intermittent cattle grazing and this may threaten the survival of unknown populations of the Ripple-leaf Muttonwood.
Bush regeneration activities involve the clearing and removal of weeds, minimisation of soil disturbance, the selective use of herbicides and the encouragement of natural regeneration. Unskilled bush regeneration may result in direct and indirect damage to the Ripple-leaf Muttonwood and its habitat.
Illegal collection or souveniring of rare plants has occurred with other species. Illegal collection of a species such as the Ripple-leaf Muttonwood with a low population number is a possible threat to the survival of the populations and ultimately the species.