Tom Dexter, Jackie Miles, Deb Lenson
Key Words: Fire management, threatened ecosystem, Kangaroo Grass, weed management, Themeda
Introduction: In 2012, Eurobodalla Shire Council commenced a project to preserve local stands of declining Themeda Headland Grassland on Council managed land on three small headlands north of Narooma, NSW. Themeda Grassland on Seacliffs and Coastal Headlands is an Endangered Ecological Community (EEC) that grows on higher fertility soils and is listed under the NSW Threatened Species Conservation Act 1995.
Burning was trialed at two of the three sites to test whether fire could improve the environmental integrity of these sites. This trial has potential implications for the much larger stands of this EEC in various conservation reserves scattered along the NSW coastline as there are many which are not currently actively managed.
The three sites were slashed annually until 2010. While the dominant grass, Kangaroo Grass (Themeda triandra) was still present on all sites, the sites exhibited some decline in Kangaroo Grass cover and vigour, with weed present on all three sites (Fig 1). Slashing had kept the headlands free from shrubs however windrows of slashed grass suppressed Kangaroo Grass and appeared to encourage weed invasion. One of the sites, which was left unburnt for logistic reasons, was initially in worse condition than the other two due to the presence of an old vehicle track and more extensive weed cover particularly from Kikuyu (Pennisetum clandestinum).
The intensity of a burn is likely to vary on a seasonal basis and is dependent on the build-up of dead thatch and the prevailing conditions on the day. There is basis to believe that the traditional aboriginal burning would have taken place in Autumn and would have been a relatively cool burn. The optimum time to burn when considering the constraints of weed invasion is early spring.
Fig 1. Lines of bare ground indicate the location of windrows of dead grass from a history of mowing at Duesburys Beach headland
Works undertaken: Two successive burns were conducted in early spring on 2 of the 3 headlands, in August 2013 and August 2014 (Fig 2). The burn in 2013 was hotter than the burn in 2014 due to a higher build up of Kangaroo Grass thatch prior to the burn.
Follow-up weed control was implemented after the burns as the fire created gaps between the grasses and allowed targeted chemical control minimizing off target damage to Kangaroo Grass and other native species.
Data were collected on three occasions using ten 1 x 1 m quadrats, established along a 50 m transect spaced at 5 m intervals (one of these for each headland). The initial baseline data were recorded in Nov 2012, prior to the spring burns, and in each successive summer (2013/14 and 2014/15) following the burns.
Fig 2. Typical burn on the headlands
Results to date: The burnt areas (Figs 3 and 4) showed a significant decrease of annual exotic grasses; especially of Quaking Grass (Briza maxima) and Rats Tail Fescue (Vulpia spp.). The burnt areas also showed vigorous Kangaroo Grass growth and moderate seed production of that species. Two native species -Dwarf Milkwort (Polygala japonica) and Matgrass (Hemarthria uncinata Fig 5) not recorded prior to treatment were found after treatment in the quadrats. The most abundant native forbs, Swamp Weed (Selliera radicans) and Indian Pennywort (Centella asiatica) have persisted on the quadrats but not increased (Fig 6). Some exotic forbs – e.g. Yellow Catsear (Hypochaeris radicata) and Scarlet Pimpernel (Anagallis arvensis) have taken advantage of the removal of grass biomass and have also increased, further future analysis will determine whether this increase will impact on the native forbs. Perhaps the most important finding is the Coast Banksia (Banksia integrifolia) seedlings were killed by the fire allowing the sites to remain grassland.
The unburnt headland continues to deteriorate, with ongoing evidence of continued senescense of Kangaroo Grass, no Kangaroo Grass seed production, and exotic plants continuing to replace Kangaroo Grass in parts of the site. Kikuyu is the main exotic species on this site and is responsible for continued suppression of the native components of the grassland. There is also evidence of shrub invasion beginning to occur. It is anticipated that this site will be burnt in spring 2015.
Fig 3. Duesburys Point just after burning, Sept 2013
Fig 4. Same site 11 months later, Aug 2014
What we learned: Kangaroo Grass remains vigorous throughout the burnt sites. The results to date show annual burning to be generally beneficial to the herbaceous components and associated grasses of this EEC. There was a higher success of exotic annual grass control in the first year which is most likely attributed to a hotter fire and perhaps timing. The first year also had accumulated multiple years of thatch which may have assisted fire intensity. Supplementary chemical control was effective, particularly when the fire created gaps between the grasses, allowing for better targeted chemical control.
Future directions: So far the results have shown that an August fire followed by the targeted chemical control of exotic grasses has considerable positive influence on the overall environmental integrity of this ecosystem. The annual burning allows the EEC to remain a grassland by killing off Coast Banksia and Coastal Acacia seedlings. It invigorates Kangaroo Grass growth and reduces the biomass of exotic perennial grasses at least in the short term. This again creates an opportunity in the aforementioned targeted chemical control. The herbaceous composition of the headland also remains intact and future analysis will determine whether burning has either a neutral or positive effect on growth. Kikuyu, Paspalum (Paspalum dilitatum) and annual exotic weeds continue to be the main problem. Increased post-burn selective herbicide application or hand weeding and planting of Kangaroo Grass tubestock may help to restore the grassland more rapidly than use of fire with limited weed control alone. Ongoing funding is being sought to continue the works over coming years and achieve further positive future outcomes.
Acknowledgements: The works were undertaken by Eurobodalla Shire Council with funding from the NSW Environmental Trust. Fire assistance from the NSW Rural Fire Service and cultural advice provided by Elders of the Walbunja people.
Contact: Tom Dexter; Environment and Sustainability Project Officer; Eurobodalla Shire Council (PO Box 99 Vulcan St Moruya 2537, Australia. Email: tom.dexter@eurocoast.nsw.gov.au).
Fig 5. Hemarthria uncinata was only evident after fire. (Duesburys Beach headland.)
Fig 6. The forb Sellaria radicans persisted among the grass after fire.
EMR Project Summaries 