Publications archive - Publications
Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.
Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.
National Parks and Wildlife SA
In partnership with Threatened Plant Action Group, February 2003
Note: This publication has been superseded by the Recovery Plan for Twelve Threatened Orchids in the Lofty Block Region of South Australia 2010
Arachnorchis macroclavia is found in mallee woodland and grassy mallee woodland with sandy loam soils over limestone. Mallee species such as Eucalyptus gracilis, E. socialis and E.incrassata dominate the canopy at all five confirmed sites. A well-developed shrub layer is present at Agery, Muloowurtie and Pt Vincent. Species such as Alyxia buxifolia and Melaleuca uncinata and chenopods dominate the understorey at Agery and Muloowurtie. The Pt Vincent site comprises many thickets of Melaleuca uncinata and large open areas of sedges. The understorey at the Pt Julia site has a predominance of sedges, while at Mona both grasses and sedges dominate. See Appendix 1 for a more detailed list of associated plant species. Although mallee woodland and grassland were once widespread across Yorke Peninsula, it survives mostly in small remnant blocks and along roadsides.
The specific fungal endophyte that the orchid requires for nutrient has not been isolated and identified, and neither has the primary pollinator species, although it is likely to be a Thynnid wasp.
The main direct threats to Arachnorchis macroclavia and its critical habitat include grazing by vertebrate animals, competition from weeds, habitat damage by vehicles, dumping of soil or rubbish, herbicide drift, clearance of habitat for agriculture and road works. These activities have caused a decline in the area and quality of the orchid's critical habitat, and as a result, sub-populations are now very small (Table 1) and severely fragmented (Figure 2). It is highly unlikely that the orchid's pollinators would travel between sites, and consequently the genetic variation within each sub-population is likely to be severely diminished.
Weeds are a threat at Agery, Mona and Muloowurtie. The major weed is Bridal Creeper, and others of concern are Soursobs, Wild Oats and African Boxthorn. Table 2 outlines the weeds present at these sites.
As Table 3 indicates, there is evidence that kangaroos, rabbits or sheep are either present or able to gain access to all five sites monitored in 2001. Table 4 shows that the proportion of flowering Arachnorchis eaten at each site was generally high. (N.B. At Agery, Mona and the Pt Vincent property, flowers of closely related Arachnorchis dilatata complex species were also monitored.) In addition to eating spider-orchid flowers, sheep and rabbits also cause soil erosion and spread weeds.
At Mona and Muloowurtie, trail bikes and 4WD vehicles were creating access tracks, damaging vegetation and causing weed invasion. The situation was exacerbated by illegal firewood cutting and dumping of soil and rubbish. These activities remain a threat to A. macroclavia habitat, although the threat is somewhat diminished since the erection of fencing at both sites.
Clearance has in the past been a threat as well, because it is likely that the species was more common prior to the clearance of bushland for farming, and all known extant sub-populations are now small and isolated. Currently, three of the remaining sub-populations are in small blocks of remnant vegetation on farms, and not protected by any form of conservation management agreement.
|Pt. Julia property||Yes|
|Pt. Vincent property||Yes||Yes||Yes|
|Site||No. Monitored||E||D||U||(E + D + U)%|
|Pt. Julia property||1||
|Pt. Vincent property||47||6||13||6||53%|