Australasian Plant Conservation
Originally published in Australasian Plant Conservation 20(3) December 2011 - February 2012, p 10-12
Monitoring the endangered Tumut Grevillea (Grevillea wilkinsonii R.O. Makinson)
Greening Australia Capital Region, Aranda, ACT. Email: firstname.lastname@example.org
The Endangered Tumut Grevillea, Grevillea wilkinsonii.
Photo: Bindi Vanzella
The Tumut Grevillea, Grevillea wilkinsonii, is found only along a 20 km length of the Goobarragandra River near Tumut, NSW, and in one small population of seven individuals near Gundagai (NPWS 2001). This species is currently listed as Endangered on both the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 and the NSW Threatened Species Conservation Act 1995.
The species was discovered in 1982 by local naturalist, Mr Tom Wilkinson, and only formally named and described in 1993. Only two sites were known initially, one on public land (Travelling Stock Reserve (TSR) and the other on private property c. 3.5 km downstream. Between these sites, all river frontages (apart from 150 m of National Park) were privately owned. It was clear that to undertake any survey work, develop recovery actions or conduct ongoing monitoring of the Tumut Grevillea, gaining the interest and cooperation of private landholders was essential.
Early recovery activities for this species included fencing part of the TSR containing G. wilkinsonii, taking cuttings from plants at both known sites, and re-introducing propagated plants near the first site and at a picnic area a short distance upstream (NSW NPWS 2001).
The initial survey
An initial survey to measure the size and age structure of the natural population was undertaken in 1993. Landholders were contacted initially by telephone, then visited in person to seek permission to look for the Grevillea. The survey covered 27 km of the Goobarragandra River (plus other tributaries) however, the Tumut Grevillea was only found along a 4.5 km stretch of the river. All but one of the landholders cooperated in allowing access to survey the river banks. At a public meeting of 30 landholders in 1993, thirteen indicated interest in having plantings of Tumut Grevillea reintroduced onto their land.
From this first survey the population of Tumut Grevillea was estimated at 620, of which only about 25% were classed as adult, that is, greater than 1 m tall and with evidence of reproductivity. Threats to the species included flooding, stock browsing, fire, and competition from weeds and dense native shrub growth.
The original population was re-surveyed in 1998, this time with access to all private properties. All plants were recorded, mapped and photo points established at 13 separate colonies. Each plant was classed into one of three size categories; seedling (0.1-0.2 m), mid-sized (0.2-1.0 m) or adult (>1 m). Size was considered to be more important than age when classifying plants because those under 1 m tend to have few flowers, regardless of age. A total of 644 plants were counted, 46% of which were in the adult class. The planted specimens were also surveyed. These showed high survival rates but no seedlings were found to have recruited from these plants. The main impacts noted on the population in the five years since the initial survey were browsing damage by stock, and competition from vigorous native shrub growth and introduced weeds.
A third survey of the population was carried out in 2008 taking in an additional small colony which had been located in the intervening 10 years, 5 km downstream of the main distribution. The full 11 km length of the river between the upstream and downstream colonies was surveyed to investigate known colonies and to check for new ones. Four small new colonies were located within the original range. In order to determine the contribution of reintroduced plantings, colonies established between 1993 and 2006 at three sites within the natural distribution of the species were also monitored.
In 2008 the total number of Tumut Grevillea in the natural colonies was 514 with a size structure ratio of 19:25:56 percent (seedling : mid-sized : adults). This represented a decline of 130 plants from 1998. Most of the reduction occurred in the mid-sized class. However, at the reintroduced planting sites, a total of 251 plants were counted and mapped. The size structure ratio of 13:49:38 percent revealed that recruitment from these propagated plants had occurred. With the addition of 40 plants found at the four new sites, the total Tumut Grevillea population (encompassing 20 colonies) stood at 805.
Between September and December 2010 a series of major floods were experienced along the Goobarragandra River, causing stream bank erosion and damage to riparian vegetation within the distribution of the Tumut Grevillea. In early 2011 a survey was undertaken to assess the extent of flood damage to the Grevillea population.
Results from the survey found a total of 900 Tumut Grevillea in 19 colonies (one colony consisting of a single large plant could not be found). This was an increase of 12% on the 2008 total. Numbers within the original natural colonies had declined from 644 plants in 1998 to 514 in 2008 and then to 399 in 2011. This 22% reduction in population size between the 2008 and 2011 survey is likely to be attributable to the 2010 floods. The greatest impact of flooding was noted in the sub-adult group, with 35% fewer mid-size plants and 48% fewer seedlings.
Despite the magnitude of the floods, monitoring revealed that adult plants seemed resilient to flood disturbance, with only an 8% reduction in numbers. Most of this loss occurred at a single site, while declines at other sites seemed attributable to other factors such as inadvertent herbicide spraying. Many adult plants were noted to have been damaged by the battering of floodwaters or from being smothered with flood debris, however, most showed signs of recovery through re-sprouting from branches or from the base of canopies. Based on observations from the post-flood survey, disturbances such as those experienced in 2010 pose a sporadic threat to the Tumut Grevillea, and are more likely to impact on sub-adult plants in the population. Despite this, floods may also create new opportunities for recruitment by removing competing vegetation, creating bare earth and depositing sand and soil. Continued monitoring of these sites will be important to determine when recruitment occurs in the natural colonies or at new locations within the riparian range of the species.
On-going monitoring of the Tumut Grevillea along the Goobarragandra River has been essential in assessing its range and the development. It has also revealed that the overall increase in population size between 2008 and 2011 (from 805 to 900 plants) was the result of recruitment occurring predominately within the three reintroduced planting sites. This suggests that the establishment of new colonies of Tumut Grevillea by tubestock plantings is one means of promoting the conservation of this species.
Funding for the various surveys over the years has been provided by the Federal Envionment Department Endangered Species Program (1993, 1998), the NSW Department of Environment, Climate Change and Water (2008) and NSW Office of Environment and Heritage (2011). Bob Makinson (RBGSyd) and John Briggs (OEH) have been instrumental in organising surveys, and staff of NSW OEH, particularly David Hunter and Genevieve Wright have assisted with the surveys. Property owners who granted access to undertake these surveys are gratefully acknowledged.
NSW National Parks and Wildlife Service (2001) Approved Recovery Plan for the Tumut Grevillea (Grevillea wilkinsonii). NSW National Parks and Wildlife Service, Hurstville NSW