Pterostylis gibbosa (R.Br.) Illawarra Greenhood Orchid Recovery Plan
NSW National Parks and Wildlife Service, September 2002
ISBN 0 731 36905 X
8 Management issues
- 8.1 Level of current understanding
- 8.2 Threatening processes
- 8.3 Social and economic issues
- 8.4 Translocation/Ex-situ Conservation
- 8.5 Species Ability to recover
The management of the conservation of threatened species requires the development of a "recovery program" which considers (i) the biological and ecological aspects of the species; (ii) the social, political and organisational parameters that may affect the success or otherwise of the program; and (iii) the economic factors which may influence the operation of the program's implementation.
As such, this section identifies the management issues affecting Pterostylis gibbosa including:
- limits of our current understanding of the biology of the species and its' ecology in the three principal areas of occurrence;
- threats and reasons for decline; and
- social and economic factors which may influence the success or otherwise of the recovery plan.
There are significant gaps in our understanding of the biology of P. gibbosa. The most significant are a lack of knowledge of recruitment processes, the role of fire, what is the pollinator species, and the ecology of pollination. Active site management (particularly of isolated remnants) would be greatly assisted with improved understanding of the conditions required for recruitment. G. Bradburn (Illawarra ANOS) has collected some information in regards to seedlings at Yallah and Albion Park. This is very localised and show rapid increases in numbers of plants in some quadrats monitored over time.
The monitoring of known sites and the targeted surveys undertaken has significantly increased our understanding of the distribution and abundance of P. gibbosa. The limited number of known populations before the surveys provided only a narrow view of the preferred habitat of P. gibbosa. Additional surveys, particularly in the Hunter and Nowra areas, will help to further define the ecological requirements of P. gibbosa which will assist in managing known populations and their habitats, and further refine the prediction of potential habitat to target for future surveys.
The main potential threats to P. gibbosa plants, both for the plant and its pollinator(s), are habitat loss and degradation from development, land use incompatible with the requirements of the species, inappropriate fire regimes, and weed encroachment.
Habitat loss from urban development and agriculture has reduced the area of available habitat on the Cumberland Plain and Illawarra to isolated remnants. The capacity of the species to extend beyond its known range in the Illawarra, Hunter and Shoalhaven regions is limited by the availability of suitable habitat. In areas, such as the Hunter Valley and Nowra, there may be suitable habitat and these areas may be subject to future development pressures.
Any reduction of available habitat near existing populations will threaten P. gibbosa in the long term by rendering the populations more vulnerable to stochastic events. Small remnants are inherently more vulnerable since there is a greater likelihood that the entire habitat will be affected by chance events, such as repeated fires.
At least two populations of P. gibbosa occur on private land where the primary land use is grazing of domestic stock.
In the Hunter, the southern part of the low plateau on which P. gibbosa is found is already completely cleared and grazed. The orchid population is found adjacent to the fenceline, but not beyond it.
Routine agricultural activities are excluded from the provisions of the TSC Act, so there is no legal obligation to conserve populations if an agricultural activity is in conflict with the species' requirements. However, current landowners are sympathetic to the management of P. gibbosa.
Inappropriate fire regimes
Fire, by occurring at an inappropriate time of year or at inappropriate frequencies, is potentially a significant threat to P. gibbosa (see section 2.5 and 6.5.1). Fire between March and November will destroy the above ground parts of the plant. A single fire at this time of year is unlikely to kill individuals but repeated fires are likely to eliminate plants as there is no opportunity for plants to replenish food reserves stored in the underground tuberoids or to flower and set seed.
Too frequent fires may also encourage fire tolerant species which could outcompete P. gibbosa. Blady Grass Imperata cylindrica, a native grass already present at Yallah and Albion Park is favoured by frequent disturbance. Species such as Lantana Lantana camara, also at Yallah and Albion Park is a prolific invader of open spaces.
The prevention of fire, or having infrequent fires may also be a threat. Other understorey plants that are not deciduous have a competitive advantage in these circumstances. The level of leaf litter will build up and increase the risk of high intensity fires, which are likely to have a greater impact on P. gibbosa due to higher temperatures above and below the ground. P. gibbosa rosettes lie flat on the ground, so dense groundcover is likely to be detrimental by limiting light levels and space. In the absence of fire, some pioneer rainforest species such as Pittosporum undulatum have the opportunity to grow. At Yallah, young plants of P. undulatum are common. In the long term, the light levels under a dense canopy of such plants may be too low for P. gibbosa.
The environment that the plants were adapted to, prior to European arrival, is difficult to determine. The loss of native herbivores, introduction of exotic animals and plants, and changes to the fire regime have altered the habitat significantly in the past 200 years. Developing appropriate fire regimes in the absence of the native animals that helped crop the native groundcovers is difficult. It is believed that a combination of summer fires and light grazing by native animals create the open areas that P. gibbosa appears to favour.
Further research is needed to determine the appropriate intervals for ecological burns which also must consider the requirements of the mycorrhizal partner, Ceratobasidium cornigerum, and pollinators. Only by managing the community as a whole will the orchid persist in the long term.
Weeds, particularly Lantana camara, pose a potential threat to P. gibbosa. In the woodlands where P. gibbosa grows, L. camara is highly invasive. Large sections of the habitat at Yallah were infested before it was weeded by members of the Wollongong Australian Native Orchid Society (now Illawarra ANOS). L. camara, Blackberry Rubus fruticosus, Privet Ligustrum spp., Senna spp., Prickly Pear Opuntia spp. are some of the weed species found at Albion Park. Monitoring of weeds and ongoing control is essential at all populations in the Illawarra. In the Hunter Valley and the Shoalhaven sites, exotic species do not appear to be as abundant. No significant weeds were found in the understorey at either site.
Collecting from the wild
Pterostylis gibbosa is of value to orchid enthusiasts interested in terrestrial species. The species, however, is unlikely to ever become highly attractive to the general public since the flowers are small, cultivation is not simple and the species is deciduous. Nevertheless, collecting from the wild still occurs (Recovery Team pers. comm.).
The NPWS recognises that actions within this plan may have impacts on the public authorities and private individuals who own or manage land on which the species occurs. Personal and regular contact with landholders is a key strategy in encouraging awareness and involvement in the recovery effort.
Orchids appeal to many people particularly orchid enthusiasts. The ANOS has been actively involved in the recovery and management of this species.
It is considered that the plan will result in some positive impacts on sections of the community. For example, implementation of the plan will result in increased protection of natural woodland habitats, which have largely been lost in areas where P. gibbosa occurs.
However, preservation of habitats may also require that public access is restricted such as areas of the Croom Rd site. As this would not occur without public consultation such as through the exhibition of the PoM for the VCA being prepared. Any negative social consequences of restricted access should, therefore, be minimised.
It may also require restrictions on certain activities such as grazing. This is not considered to be a significant cost to the landholder as it would only apply to those sections of the land where P. gibbosa occurs. It is envisaged that any such restrictions will only occur following negotiations with the relevant land manager.
The NPWS recognises that the implementation of the actions for this Recovery Plan will result in some degree of economic impact. The proposed recovery strategy seeks to minimise these impacts through the prioritisation and targeting of recovery efforts.
Two of the five populations occur on private property. The cost to the landowners of maintaining populations of P. gibbosa is low, provided the land is not required for any other purpose.
Translocation is defined as the "deliberate transfer of plants or regenerate plant material from one place to another, including existing or new sites or those where the taxon is now extinct" (Australian Network for Plant Conservation 1997). Translocation may also involve the removal of plant material to undertake an ex-situ conservation program.
At this stage, translocation is not considered necessary for the survival of the species or appropriate given the current lack of knowledge of the species.
The conservation of threatened species is most successful when species are managed and protected in their natural habitat (in-situ). In relation to P. gibbosa, given the amount of commitment required and the probability of failure with any trial, the use of translocation is not encouraged.
Pterostylis gibbosa can persist in the long term at all known sites provided management is appropriate and threatening processes are managed and monitored. Appropriate management regimes are attainable through negotiations, liaison, assistance and community support at all sites.
The area of suitable habitat at Albion Park and Yallah is limited. Any reductions in the current habitat is likely to result in further declines in the populations. Management of potential habitat adjacent to where the orchids currently exist is important to provide opportunity for natural expansion of the populations under appropriate conditions.
If current sympathetic management continues by private landholders, the security of the long-term viability of these sites is more certain.
The areas where P. gibbosa is known to occur in the Shoalhaven area are now protected in Worrigee Nature Reserve. Development pressures in the Shoalhaven area are high however, and it is important that suitable habitat is identified so that targeted surveys can be undertaken and significant areas considered in strategic planning programs for the expansion of Nowra.