National recovery plan for Twelve Threatened Spider-Orchid Caladenia R. Br. Taxa of Victoria and South Australia 2000 - 2004
James A. Todd
Department of Natural Resources and Environment, Victoria
Flora and Fauna Statewide Programs, March 2000
4. Decline and Threats
4.1 Decline
Most of the threatened Caladenia taxa covered in this plan have been described in the last ten years, the exceptions being C. audasii, C. hastata and C. rosella. For the recently described taxa, most have been split from larger complexes and hence little information is known of their former range, whether their range has declined and if so, the rate of decline. For some taxa, information on their current distributions is also lacking.
Inferences have been drawn in Table 2 about the past distributions of all taxa based on historic records, current distributions, extant population sizes and current habitat preferences. This information has been combined with pre-1750 Ecological Vegetation Class mapping where available (VicRFASC 1999, ECC in prep.) to estimate the former range of each taxon and hence the magnitude and rate of decline since European settlement. It is important to note that such inferences may be subject to large margins of error. This is particularly so for taxa that currently have small numbers of populations occupying a very narrow range. Such species are presumed to be occupying preferred habitat but in reality, they may be occupying habitat at the edge of their original range. Their survival at certain sites may be more attributable to disturbance history rather than any preference for a particular ecological niche.
For some taxa (eg. Caladenia thysanochila), it is likely that they once occupied a very restricted habitat and range while for other taxa (eg. Caladenia formosa), the species may have once been present over thousands of square kilometres. This information is important for assessing threats to known populations, when developing actions to counter-balance these threats and when looking at broader remedial actions such as plant re-introductions and trans-locations.
Table 2 lists the past and present distribution of twelve threatened Caladenia taxa of Victoria and South Australia and by inference a measure of the extent of decline since European settlement. Figures 1-12 show past and present records of the twelve threatened taxa within Victoria.
4.2 Threats
The Caladenia taxa are listed as threatened for varied reasons. Most of the taxa have small distributions, restricted habitats and a large proportion of their total population occurs at one or a few locations. Most taxa (C. amoena, C. audasii, C. fragrantissima ssp. orientalis, C. hastata, C. lowanensis, C. robinsonii, C. rosella, C. thysanochila, and C. versicolor, C. xanthochila) also have small total populations.
The single biggest issue for the decline of most of the taxa is habitat destruction. Five of the taxa (C. formosa, C. lowanensis, C. tensa, C. versicolor and C. xanthochila) occupy broad riverine plains habitats (of northern Victoria and western Victoria/south east South Australia) on reasonably fertile soils that have been cleared over large parts of their range for agricultural production. Extant populations tend to occupy fragmented forests and woodlands within agricultural landscapes and it is this fragmentation and the associated site degradation arising from it, that may now represent the greatest threat to the long-term conservation of these species. Habitat of C. amoena, C. audasii and C. rosella has been severely reduced and altered by historic mining activities and more recent urban development. For the remaining taxa (C. fragrantissima ssp. orientalis, C. hastata, C. robinsonii and C. thysanochila), habitat destruction has been caused by the urban and industrial development of their near-coastal habitat. These taxa now occupy areas close to and within urban development and the subsequent impacts associated with this and the management constraints placed on these sites are the largest threats to extant populations of these taxa.
Populations of the twelve threatened Caladenia taxa are currently under threat from a variety of sources of varying magnitude and concern (Table 5). The risk posed to extant populations by these threats may vary depending on geographical, environmental, biological and sociological factors. Threats may be acting singularly or in series to present a risk to populations. In addition to current threats, there are also potential threats that may place populations at risk at some time in the future if and when they occur.
Table 5 lists current and potential threats to the threatened Caladenia taxa of Victoria and South Australia.
Table 5: Current and potential threats and their risk to twelve threatened Caladenia taxa of Victoria and South Australia.
|
Species name |
Current threats/perceived risk |
Potential threats/perceived risk |
|||||||
|
Weed invasion |
Grazing |
Inappropriate fire regimes |
Site disturbance |
Reservation status |
Illegal collection |
Timber harvesting |
Other disturbance |
Stochastic event/accidental damage |
|
| Caladenia amoena |
Medium - current management is proving successful against annual weeds |
Medium - rabbit and kangaroo grazing and predation by slugs and snails - presently being managed by fencing/caging |
Low - low fuel levels and infrequent fires |
High - soil disturbance from kangaroos and rabbits; also disturbance by walkers and mountain bike riders |
Unreserved - Occurs on unreserved public land managed by PV as part of Plenty Gorge Parklands |
Medium - no evidence but plants are close to urban development |
Low - private land site may be subject to cutting for fire wood |
Medium - increasing soil disturbance with increasing kangaroo numbers |
High - one population is unprotected on private land and at risk of unsympathetic future landholders; total plant numbers are low |
| Caladenia audasii |
Medium/High - depending on site. Kingower site is heavily invaded by exotic herbs (eg. Freesia, annual grasses). Garden escapees from rubbish dumping is a growing problem at Deep Lead |
High - rabbits and kangaroos although all plants are protected |
Low - generally low fuel loads and infrequent fires. Habitat adapted to low fire frequency |
High - all sites occur in areas heavily utilised by visitors. One population (Kingower) is in a cemetery subject to maintenance works, gold fossicking and raking |
Reserved - One Tree Hill Regional Park at Bendigo |
High - past evidence at Deep Lead |
Low - one population (Deep Lead) occurs within State Forest (proposed Special Protection Zone) |
Medium - High - depending on future visitation; gold prospecting |
High - critically low population numbers leave this species very susceptible to extinction from stochastic events |
| Caladenia formosa |
Low - mostly annual species at low levels |
Low - generally low numbers of kangaroos and rabbits |
High - Fuel reduction burning in autumn |
Medium - low level timber harvesting (Nov-April); some rabbit burrow ripping; recreation (eg. horse riding, trail bikes) mostly restricted to tracks |
Reserved in South Australia - Mt Monster CP, Mt Scott CP (<10 plants?); believed unreserved in Victoria - may be reserved in small Bushland Reserve and Grampians NP |
Low - infrequently visited area |
Medium - occurs in state forest used for timber production (generally occupies habitat with 'non-preferred' timber species - proposed Special Protection Zone) |
Medium - may be increasing soil disturbance with increasing kangaroo/rabbit numbers or recreational users |
Low - total population > 1000 plants with disjunct populations over a wide range |
|
Species name |
Current threats/perceived risk |
Potential threats/perceived risk |
|||||||
|
Weed invasion |
Grazing |
Inappropriate fire regimes |
Site disturbance |
Reservation status |
Illegal collection |
Timber harvesting |
Other disturbance |
Stochastic event/accidental damage |
|
|
Caladenia fragrantissima ssp. orientalis |
Medium - largest threat from Coast Tea-tree, Coast Wattle and Maritime Pine |
Presumed Low - grazing pressures largely unknown |
High - Burning in autumn and winter |
Low - largely inaccessible coastal heathland areas; track slashing |
Unreserved - Wonthaggi Heathland 'Reserve' is proposed as a nature conservation reserve |
Medium - no evidence but plant no's are low and close to urban areas |
Nil |
Medium - slashing of fire breaks may cause soil disturbance; the presence of Cinnamon Fungus should be monitored |
High - total population < 100 plants known from only a few sites - plant numbers have declined dramatically in recent years |
| Caladenia hastata |
High - large threat from introduced shrubs (eg. Boneseed) and invasive native shrubs (eg. Coast Tea-tree, Coast Wattle) (Carr et al. 1992) |
Medium - some evidence of past grazing by rabbits - most plants are presently caged |
High - Recent burning in autumn and winter may be adversely affecting populations |
High - small site that is frequently visited; altered site hydrology; fluoride emissions from smelter |
Reserved - Point Danger Coastal Reserve; Discovery Bay Coastal Park |
High - no evidence but well known site with easy access |
Nil |
Low-Medium - close to dirt road - increasing traffic could deposit large amounts of dust on habitat; the presence of Cinnamon Fungus should be monitored |
High - small population in a restricted area |
| Caladenia lowanensis |
High - large threat from Perennial Veldt Grass and a range of other, mostly annual species |
High - rabbit and wallaby grazing on public land and sheep grazing on private land |
Low/medium - known sites have not been burnt for many years - habitat is most likely adapted to low fire frequency although further research is needed to determine appropriate fire regime. |
High - soil disturbance from rabbits; disturbance along and adjoining vehicle tracks and close to cemetery and rubbish tip |
Reserved - Kiata Flora Reserve; Glenlee Flora Reserve; ?West Wail Flora Reserve |
Medium - no evidence but well known site and easy access |
Low - some illegal firewood collection |
Low-High - depending on control of rabbits |
High - total population < 200 plants known from only three sites |
|
Species name |
Current threats/perceived risk |
Potential threats/perceived risk |
|||||||
|
Weed invasion |
Grazing |
Inappropriate fire regimes |
Site disturbance |
Reservation status |
Illegal collection |
Timber harvesting |
Other disturbance |
Stochastic event/accidental damage |
|
| Caladenia robinsonii |
High - large threat from introduced shrubs (eg. Boneseed) and invasive native shrubs (eg. Coast Tea-tree, Coast Wattle) (Carr et al. 1992) - control program in place |
Low-Medium - some rabbit grazing |
High - burning in autumn and winter |
High - area is close to urban development and used as a children's 'adventure' area; weed control measures have resulted in changes to site conditions |
Unreserved - Betty Clift Reserve is owned by the Mornington Peninsula Shire Council and zoned Public Conservation and Resource; No conservation agreement in place |
Medium - no evidence but highly visible populations close to walking tracks |
Low |
Medium-High - large-scale weed control activities have the potential to alter habitat and impact on populations; Cinnamon Fungus has been recorded in nearby areas |
High - small population occupying a very restricted area |
| Caladenia rosella |
Medium - threat from mostly annual grasses and herbs - presently being managed at most sites |
Medium - rabbit grazing and tubers often dug up by White-winged Choughs - many plants are caged; One population is fenced. |
Low - semi-urban areas with very infrequent fires |
Low-Medium - most sites are not well known but are sometimes heavily visited in spring |
Reserved - One Tree Hill Bushland Reserve; 3 private properties protected by TFN Conservation Covenants |
Medium - no evidence but some sites are well known |
Nil |
Low |
Medium - small populations (with a number of colonies) occupying restricted habitat |
| Caladenia tensa |
Low - High - dependent on site - introduced perennial grasses (eg. Perennial Veldt Grass) pose the largest threat to known populations. |
Medium - High - rabbit and/or kangaroo grazing at most sites |
May vary depending on area |
Low - High - dependent on site - populations at West Wail are under threat from use of recreational vehicles in reserve |
Reserved in Victoria - Kiata FR, Lt Desert NP (numerous plants); Reserved in South Australia - Cape Gantheaume CP, Billiat CP, Mt Boothby CP |
Low - no evidence |
Low |
Low-High - depending on site - rabbits are a major issue at Kiata; illegal firewood collection at West Wail |
Low - many plants distributed over a broad range |
|
Species name |
Current threats/perceived risk |
Potential threats/perceived risk |
|||||||
|
Weed invasion |
Grazing |
Inappropriate fire regimes |
Site disturbance |
Reservation status |
Illegal collection |
Timber harvesting |
Other disturbance |
Stochastic event/accidental damage |
|
| Caladenia thysanochila |
High - major threat from perennial grasses (eg. Sweet Vernal Grass, Yorkshire Fog Grass, Brown-top Bent) |
Medium - rabbits present in area but fencing is controlling this at present |
High - area has suffered from long-term absence of fire, low fire intensity and inappropriate timing |
Medium - Site is fenced but is highly visible and close to urban development |
Unreserved - Mt Eliza Regional Park is owned by the Mornington Peninsula Shire Council and zoned Public Conservation and Resource; No conservation agreement in place |
High - extremely low numbers of plants make them vulnerable to collection - rarity of taxon makes it a desirable 'collector's item' |
Nil |
Medium - Control of introduced grasses may lead to soil erosion and/or further weed invasion of other species |
High - Only two plants have ever been observed at a single site and these have not flowered for several years |
| Caladenia versicolor |
Low - very few weed species occur in the known habitat |
Medium - some grazing by wallabies/kangaroos and maybe rabbits |
Low - habitat is adapted to low fire frequencies and area has not been burnt for some time |
Low/Medium - uncontrolled access; vehicle and walking tracks |
Unreserved - Lake Fyans is uncommitted crown land that is currently subject to a Native Title Claim |
Low |
Medium - area has been used for timber harvesting in the past (proposed Special Protection Zone) |
Low - High - depending on future land use and reservation |
Medium - total population < 1000 plants and confined to a narrow range at a single site |
| Caladenia xanthochila |
High - major threat from annual grasses and herbs |
High - grazing by rabbits and maybe kangaroos |
Low - High - depending on site (Inglewood has been unburnt for some time and the vegetation has closed over) |
High - some past dumping of green waste and soil disturbance from rabbits and site works |
Unreserved - one site (Murtoa) is private land, the other (Inglewood) is state forest |
Medium - Murtoa is a well known site with easy access |
Medium - Inglewood site is within state forest used for timber harvesting |
High - Murtoa site may be subject to disturbance from recreational users |
High - total population < 120 plants in two disjunct populations |