Spreading Grevillia (Grevillea humifusa) Interim Recovery Plan 2003-2008

Gillian Stack and Val English
Department of Conservation and Land Management, WA, 2003

1. Background

History

Grevillea humifusa was originally collected from the Eneabba area in May 1968 by H. Demarz, a collector for Kings Park and Botanic Garden (KPBG). It was then identified as a specimen of G. thelemanniana (prostrate form). It has been in cultivation since the 1960s as G. thelemanniana (grey-leaf prostrate form). A number of botanists have conducted surveys in the general area without locating new populations of G. humifusa. The private property area was burnt in 1995, prior to notification of the location of the population in 1996. However, many native species including G. humifusa are regenerating well, particularly since all plants on private property were fenced from stock in 1997. Less than 40% of the population is located on the private land, with the remainder on a road verge that is very vulnerable to road maintenance activities.

An Interim Recovery Plan 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

Grevillea humifusa is a lignotuberous prostrate shrub with trailing stems to 3 m long and angular branchlets with long soft hairs. The grey-green leaves are 1.5-2 cm long and are ascending to spreading. The inflorescences are 2 cm long and occur at the end of the branches. The flowers are pink to red, and the style is pink to red with a yellow tip. The grooved, oblong fruit is 12-15 mm long and 3-4 mm wide. G. delta and G. preissii are closely related to G. humifusa, but neither of these species has a trailing habit. G. delta also differs in its less crowded flowers and its hairier flower tube and flower stalk.

Distribution and habitat

Grevillea humifusa is endemic to the Eneabba area, where it is known from a single population of almost 1,500 plants. A major portion of this population is located on private property, in a pasture paddock. This area was fenced to exclude stock in 1997. It was burnt in 1995, but the plants have regenerated well. The remainder of the population occurs on adjacent Shire road reserves. The species occurs on an undulating plain of gravelly loam that supports very disturbed open low Eucalyptus loxophleba and E. wandoo woodland over species including Kennedia prostrata, Jacksonia sp. and Dianella revoluta.

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 Grevillea humifusa comprises:

  • the area of occupancy of the known population;
  • areas of similar habitat within 200 metres of the known population, i.e. open low Eucalyptus loxophleba and E. wandoo woodland on gravelly loam soils (these provide potential habitat for natural range extension);
  • corridors of remnant vegetation that link subpopulations (these are necessary to allow pollinators to move between subpopulations and are usually road and rail reserves); and
  • 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 Critically Endangered it is considered that all known habitat is habitat critical. There is only one known population, and this is therefore crucial to the survival of the species.

Benefits to other species/ecological communities

There are no other known threatened species or ecological communities in the immediate vicinity of Grevillea humifusa. However, recovery actions implemented to improve the quality or security of the habitat of the species, such as weed control and rehabilitation, will benefit the entire plant assemblage.

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 Grevillea humifusa 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 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

There are not likely to be any major social or economic impacts associated with the implementation of this plan. There are subpopulations located on private land and Shire managed road reserves. Recovery actions refer to continued negotiations between stakeholders with regard these areas.

Evaluation of the Plan's Performance

The Department of Conservation and Land Management, 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

Grevillea humifusa has a lignotuber and regenerates after fire. The occurrence of juvenile plants within Population 1b in July 1998 after the fire in 1995 suggests that seed germination may also be stimulated by fire.

While the pollinators of G. humifusa are unknown, a number of insects have been noted on the flowers, including meat ants, black bull ants, and honeybees. Olde and Marriott (1995) suggest that this species is probably pollinated by birds, but no birds were seen during field research into biology and ecology of this species (personal communication A. Harris ¹). They also noted that it set seed prolifically in its only known location. This has not been supported by the current research, and the difference may be due to variations in climate as 2002 was a very dry year. Alternatively, the difference in observations may be due to the length of time since fire occurred as fire can increase vigor, and stimulate flowering and fruit-set of existing plants that resprout from a lignotuber, as well as stimulate germination of soil-stored seed. Olde and Marriott's attempts to propagate this species led to the observations that germination could be improved by nicking the seed coat before sowing, and that it grows readily from firm, young-growth cuttings taken during most seasons (Olde and Marriott 1995).

Grevilleas generally have a low seed set relative to the number of flowers in each inflorescence. However, with the large number of flowers on each individual plant, seed set is still substantial for most species. The seed is protected in a hard follicle that splits to release the seed when mature. Grevillea spp. seed can be difficult to germinate. Techniques that have been found to enhance germination in some species include scarifying the seed, soaking the seed in water and removing the testa, and treating the seed with potassium nitrate (Fox et al. 1987). The long-term viability of seed varies between species, but can range from under a year to several years under natural conditions (Fox et al. 1987).

Threats

Grevillea humifusa was declared as Rare Flora under the Western Australian Wildlife Conservation Act 1950 in October 1996 and ranked as Critically Endangered (CR) in November 1998. It currently meets World Conservation Union (IUCN, 2000) Red List category 'CR' under criteria B1ab(iii)+2ab(iii) (IUCN 2000) as it is only known from a single population, with continuing decline in the condition of its habitat. The species is also listed as Endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).There are approximately 1500 plants known from one population. This population occurs in a highly disturbed area and the species is affected by loss and fragmentation of habitat. The main threats are weed competition, road and firebreak maintenance activities, rabbit grazing, and inappropriate fire regimes.

  • Weed competition from introduced grasses and clovers is a threat to Population 1a and 1b. Many weeds in the habitat of Population 1b remain from the time the area was paddock. Although adult plants appear to be able to compete successfully, weeds may smother G. humifusa seedlings. They also exacerbate the threat of fire by increasing the fuel load.
  • Road maintenance activities such as grading, chemical spraying and construction of drainage channels pose a significant threat to Population 1a, as many plants occur near the roads edge. Mowing of road reserve vegetation could also affect the habitat of this species. These disturbance events can stimulate seed germination, but also often encourage weed invasion. Any bitumen upgrade of the road would have a massive impact, and may only be avoided by realignment through private property to the south.
  • Firebreak maintenance is an issue that affects Population 1b on private land, as G. humifusa plants occur along the firebreaks.
  • Grazing by rabbits is evident in the population. Although the adult plants appear able to cope with grazing, the effect on recruitment of seedlings is likely to be significant. In addition to grazing, rabbits also impact on populations by encouraging invasion of weeds by digging, addition of nutrients to soil and introduction of weed seeds in their droppings. There is widespread subsoil collapse evident in Population 1b, which is possibly related to rabbit burrows. However, this disturbance may actually aid germination and may, in itself, be a minor issue.
  • Inappropriate fire regimes are a threat to G. humifusa. Adult plants regrow from a lignotuber after fire, and seed germination is presumed to be stimulated by fire. However, Grevillea seed generally has a short lifespan, and if fire recurred before adult plants could replenish the seedbank and re-establish lignotuber reserves, the only known population could be seriously threatened. Grassy weeds can create a large fuel load, increasing the heat of fires. In addition, fires allow the weed species present to increase in density.
  • Lack of associated habitat represents a threat to the population. The lack of associated native vegetation makes it more likely that pollinators will be infrequent or absent. In addition, the lack of available habitat for recruitment is of concern, as the population occurs on a road reserve and private land with cleared land adjacent.
Summary of population information and threats
Pop. No. & LocationLand StatusYear/No. plantsConditionThreats
1a. South of EneabbaShire road reserve 1996 150 *
1998 295
2002 920 (ca 40)
Disturbed but healthyWeed competition, road maintenance, inappropriate fire regimes, grazing
1b. South of EneabbaPrivate property1996 *
1998 314
2002 572 (ca 20)
Disturbed but healthy Weed competition, firebreak maintenance, inappropriate fire regimes, grazing
Numbers in brackets = number of juveniles. * = total for both subpopulations combined.

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 Grevillea humifusa will require assessment. On-ground works should not be approved unless the proponents can demonstrate that they will not have an impact on the species, its habitat or potential habitat.