Blunt wattle (Acacia aprica) Interim Recovery Plan 2003-2008
Interim Recovery Plan No. 152
Ben Bayliss
Department of Conservation and Land Management, WA, 2003
1. Background
History
The first collection of Acacia aprica was made in 1957 from an area south of Carnamah by J.W. Green. Surveys undertaken for this species in July 1996 and 1998 resulted in the location of six populations. In October 1999 a survey of remnant vegetation on private land by Departmental officers located a new population of around 100 plants. This population currently represents one of the largest and least disturbed of all populations identified to date. Associated with this population were 53 native plant species as well as a low abundance and number of weed species compared with road reserve populations.
A new population and subpopulation were located on August 2002 and January 2003 respectively. The appropriate land managers were notified by the Department and DRF markers installed.
Of the eight known natural populations of Acacia aprica, two contain 100 or more individuals. Seven contain fewer than ten plants and in one population the only known plant could not be relocated when resurveyed in January 2003. The destruction of several plants in Population 1 by vehicular activity within the road reserve was documented in December 1998.
An Interim Recovery Plan (IRP) was developed for the species in 1999 (Stack and English 1999). Information collected since that plan was completed has been incorporated into this plan and this document now replaces Stack and English (1999).
Description
Acacia aprica (Maslin and Chapman 1999) is an open multi-stemmed shrub to 2 m tall. The inflorescences are golden, globular to oblong and hang two per axil. The phyllodes are a dull medium-green, 6-14 cm long and 1-1.4 mm wide. They have eight close parallel nerves, which are of more or less of equal width. The seed pods are linear, up to 60 mm long and ca 2 mm wide. A. aprica is closely related to A. filifolia, which has narrower, slightly incurved rounded-quadrangular phyllodes, ovate to lanceolate bracteoles and mottled seeds (Maslin and Chapman 1999). It has also been confused with A. merinthophora, which it resembles in habit.
Distribution and habitat
A. aprica is endemic to the Carnamah-Coorow area of Western Australia with a range of approximately 10 km. It is currently known from 263 plants from 8 natural populations. Six of the extant populations are restricted to heavily disturbed linear road reserves, and one of about 100 plants is located in a small remnant on private land. Of the six road reserve populations, five consist of 10 plants or less. The species is found on gravely brown clayey sand, often with surface quartz. Associated species include Allocasuarina campestris, Acacia acuminata, Grevillea paniculata and Hakea scoparia.
Critical habitat
Critical habitat is habitat identified as being critical to the survival of a listed threatened species or listed threatened ecological community. Habitat is defined as the biophysical medium or media occupied (continuously, periodically or occasionally) by an organism or group of organisms or once occupied (continuously, periodically or occasionally) by an organism, or group of organisms, and into which organisms of that kind have the potential to be reintroduced (Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)).
The critical habitat for A. aprica ms comprises:
- The area of occupancy of known populations;
- Areas of similar habitat within 200 metres of known populations, i.e. (these provide potential habitat for natural range extension);
- Corridors of remnant vegetation that link populations (these are necessary to allow pollinators to move between populations and are usually road and rail verges);
- Areas of similar habitat that now contain translocated populations;
- Additional occurrences of similar habitat that do not currently contain the species but may have done so in the past (these represent possible translocation sites).
Habitat critical to the survival of the species, and important populations
Given that this species is listed as Critically Endangered it is considered that all known habitat for wild and translocated populations is habitat critical.
Benefits to other species/ecological communities
There are no other known listed threatened species or ecological communities in the habitat of Acacia aprica. However, recovery actions, such as weed control, implemented to improve the security of Acacia aprica are likely to improve the quality of the habitat in which the populations are located.
International Obligations
This plan is fully consistent with the aims and recommendations of the Convention on Biological Diversity, ratified by Australia in June 1993, and will assist in implementing Australia's responsibilities under that Convention. However, as Acacia aprica is not listed under any international agreement, the implementation of other international environmental responsibilities is not affected by this plan.
Role and interests of indigenous people
There are no known indigenous communities interested or involved in the management of areas affected by this plan. Therefore no role has been identified for indigenous communities in the recovery of this species.
Social and economic impacts
Some populations of Acacia aprica occur on private land and negotiations will continue with regard to the future management of these populations. The implementation of this recovery plan has the potential to have some limited social and economic impact, where populations are located on private property. Recovery actions refer to continued liaison between stakeholders with regard to these areas.
Evaluation of the Plan's Performance
The Department, in conjunction with the Recovery Team will evaluate the performance of this IRP. In addition to annual reporting on progress with listed actions and comparison against the criteria for success and failure, the plan is to be reviewed within five years of its implementation.
Biology and ecology
Acacia aprica appears to be a moderate disturbance opportunist. In 1998 three young plants, (two in Population 1 and a third in Population 5), were observed growing on old grader scrapes. Many Australian species of Acacia are highly adapted to surviving fires, which are a regular occurrence in most Australian habitats. Germination of Acacia seed is often stimulated by fire but germination also depends on factors such as fire intensity and seed depth in the soil. Some Acacia species are 'soft-seeded' and are damaged by fire (Cavanagh 1987). No specific information is available about the response of Acacia aprica to fire. However, from the response of other predominantly single stemmed, non lignotuberous acacias occupying a similar ecological niche, it is likely that Acacia aprica would be killed by fire. In such non-sprouting species that rely on post-fire germination to persist, fire intervals which exceed the longevity of both the plants and their associated seed banks may contribute to local population decline and possible extinction (Yates and Broadhurst 2002).
Officers of the Department's Threatened Flora Seed Centre observed low fruit production and predation of fruits during 1996, but in 1997 fruit production was greater and predation lower than the previous year. These variations are not uncommon in wild populations of native plants although the reasons for this are not clear.
A three year study assessing limitations on population growth of Acacia aprica was initiated in 1999 and the results published (Yates and Broadhurst 2002). This study examined:
- Size class structure and health of individual plants.
- Reproductive characteristics and potential over three consecutive flowering seasons from 1999 to 2001.
- Impact of invasive weeds and grazing on seedling establishment from seed sown in 2000 on trial plots adjacent to two existing populations.
Seedling emergence and subsequent performance were monitored in 2000 to 2001. Key findings from this study were that the availability of viable seeds is not a limiting factor for Acacia aprica, rather:
- Factors associated with seed germination and seedling establishment (the regeneration niche) appear to be a more likely explanation for population decline. This was highlighted by the fact that of all the treatments regimes imposed on the transplanted seedlings in the study, removal of annual weeds resulted in the greatest increase in survival and growth.
- Maintenance of stable populations of Acacia aprica will require in-situ management of the 'regeneration niche' through judicious use of fire to stimulate germination in conjunction with effective weed control.
Threats
This species is ranked as Critically Endangered under (IUCN 2000) Red List criteria B1ab(iii,v)+2ab(iii,v) due to the low number of extant plants (263), the extreme fragmentation of the populations, and decline in the quality of the habitat. The main threats are weed invasion, road and firebreak maintenance activities, chemical drift, grazing, and inappropriate fire regimes.
- Weed invasion, predominately by annual grasses, is a serious threat to all populations. The immediate habitat of Population 9 (low scrub over heath) is comparatively less impacted, however to the west of the population the remnant York Gum woodland is heavily weed infested. Weed incursion is increased by runoff from surrounding cleared areas and roads, influx of weed seeds from surrounding paddocks, and habitat disturbance due to road maintenance activities. Weeds compete with adult plants, suppress recruitment and exacerbate the threat of increased fire frequency by increasing the fuel load. Weed invasion has been identified as one of the greatest impediments to the likelihood of success of recruitment and establishment of new plants after disturbance such as fire (Yates and Broadhurst 2002).
- Inappropriate fire regimes would adversely affect the viability of populations, as seeds of Acacia aprica probably germinate following fire. The soil seed bank would therefore be rapidly depleted if fires recurred before regenerating or juvenile plants reached reproductive maturity to replenish the soil seed bank. However, it is likely that occasional fires are required for reproduction of this species. Weed invasion following fire events is also a significant threat to regeneration potential.
- Road, rail and firebreak maintenance activities threaten plants and habitat for all road verge and rail reserve populations of Acacia aprica. These include actions such as road verge grading, constructing drainage channels and mowing the roadside vegetation to improve visibility. These disturbance events also often encourage weed invasion. Young plants can be seen on old grader scrapes and these may be vulnerable to destruction from future maintenance activities. These disturbance events also usually encourage weed invasion into the habitat.
- Although the single plant originally identified at Population 6 on private land has not been relocated, repeated disturbance may affect any recruitment of new individuals from the potential seedbank. This also applies to Population 9 which is located within a privately owned remnant.
- Chemical drift from herbicide and fertiliser applications from nearby farmland may affect the species' growth and survival.
- Grazing by rabbits, kangaroos or stock has the potential to impact on Acacia aprica populations. In addition to grazing, rabbits may also have an impact by encouraging invasion of weeds through soil digging, addition of nutrients to soil, and introduction of weed seeds. Palatable weeds near populations can attract herbivorous animals, which are often unselective in their grazing.
| Pop. No. & Location | Land Status | Date / No. of Plants | Condition | Threats | ||
|---|---|---|---|---|---|---|
| 1. SE of Carnamah | *MRWA Road Reserve | 7.96 102 4.98 107 7.98 139 |
Moderate | Road maintenance activities, fire, weeds | ||
| 2. SE of Carnamah | MRWA Road Reserve | 7.96 2 4.98 2 5.99 2 7.00 2 |
Poor | Road maintenance activities, fire, weeds | ||
| 3. SE of Carnamah | Shire Road Reserve | 7.96 5 4.98 7 7.98 8 4.99 13 7.00 13 1.03 10 |
Very poor | Road maintenance activities, fire, weeds | ||
| 4. SE of Carnamah | Shire Road Reserve | 7.96 1 4.98 1 7.98 1 5.99 2 7.02 1 |
Poor | Road maintenance activities, fire, weeds | ||
| 4. b SE of Carnamah | Shire Road Reserve | 1.03 2 | Poor | Road maintenance activities, fire, weeds | ||
| 5. SE of Carnamah | Shire Road Reserve | 7.96 2 4.98 3 7.98 3 5.99 3 7.00 3 1.03 3 |
Very poor | Firebreak and fence maintenance, fire, weeds | ||
| 6. SE of Carnamah | Private property | 7.98 1 1.03 0 |
No living specimens | Road maintenance activities, fire, weeds | ||
| 7. SE of Carnamah | Private property | 11.99 100 | Healthy | Firebreak and fence maintenance, fire, weeds | ||
| 8. (8T) SE of Carnamah | Shire Reserve |
Year Translocated**
|
Translocation | Firebreak and fence maintenance, fire, weeds | ||
| 1998 | 1999 | 2000 | ||||
| Date No. 99 76 00 01 52 02 |
Date No. 99 181 00 164 01 159 02 159 |
Date No. - - 00 361 01 180 02 177 |
||||
| 9. SE of Carnamah | Shire Road Reserve | 7.02 7 1.03 6 |
Moderate? | Road maintenance activities, fire, weeds | ||
*MRWA = Main Roads Western Australia
**For Population 8T, numbers refer to plants surviving in each succeeding year from each particular translocation year.
Guide for decision-makers
Section 1 provides details of current and possible future threats. Any on-ground works (clearing, firebreaks, roadworks etc) in the immediate vicinity of Acacia aprica will require assessment. On-ground works should not be approved unless the proponent can demonstrate that they will not have an impact on the species, or on its habitat or potential habitat.
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