The 2009 Black Saturday bushfires affected up to 95% of Kinglake National Park (KNP), situated in the western section of the Victorian highlands. The fire burnt across much of the park in several hours and in places reached intensities never before recorded in Victoria’s history. In the aftermath of the fire event, the sheer scale and intensity of the bushfire raised some important and concerning questions for the local land managers, Parks Victoria:
- How had the fire affected populations of threatened plant taxa and vegetation communities?
- Were these populations and communities at immediate risk from other processes in the post-fire period?
- If they were at risk, what could be done to prevent further decline?
In an effort to respond to these questions, Parks Victoria initiated a vegetation monitoring and recovery program which began several months after the fire event and has continued until the present. This article discusses some of the challenges and responses encountered during the program and uses individual plant taxa and communities as case studies.
Swamp Bush-pea (Pultenaea glabra) – Nationally Vulnerable
Swamp Bush-pea is endemic to Victoria where it is known from several widely scattered locations. The species has been eliminated from many of its former occurrences by logging and land development. In KNP, Swamp Bush-pea is only known from one population in an area of damp heathy woodland which was burnt at high intensity during the bushfire.
The entire adult population was killed by the fire, however abundant seedling recruitment soon followed. The first seedling recruitment occurred in April 2009 in low lying swales, but a rain episode in June caused sheet erosion of the upper slopes, leading to deposition of silt onto seedlings resulting in their death. In August there was a second recruitment event and several thousand seedlings germinated.
Despite the high density of seedling recruitment, Parks Victoria was concerned that browsing pressure from native and feral herbivores such as Goats (Capra aegagrus hircus), Sambar Deer (Rusa unicolor) and Black Wallaby (Wallabia bicolor) would eliminate plants. If the adult population were killed, this could be detrimental if the fire had exhausted the soil seed-bank. To prevent grazing pressure, four 1.5 metre high exclusion fences were constructed around the majority of the population. These have been highly successful and in spring 2010 the population reached maturity and flowered profusely, later dropping large quantities of seed. The population is now considered to be relatively secure.
Fairy Lanterns (Thismia rodwayi) – Vulnerable in Victoria
Fairy Lanterns is arguably one of Australia’s most cryptic plant species. The body of the plant spends most of its life cycle below the ground, producing bright red flowering structures that appear below leaf litter. The species is believed to be dependent on mycrrohizal fungi that mostly grow under thick beds of leaves of the Musk Daisy Bush plant (Olearia argophylla). At KNP, Fairy Lanterns is only known from one population in wet forest on the upper slopes of Mount Disappointment.
Survey of the site several months after the fire revealed that all above ground parts of Musk Daisy Bush plants and surrounding leaf litter had been completely burnt. In the years that have followed, the habitat of this area has been drastically transformed by extremely dense regeneration of Mountain Ash (Eucalyptus regnans) saplings. Not surprisingly the Thismia rodwayi has yet to be relocated. Future monitoring of this site may help to answer currently unknown aspects of its ecology: is it eliminated completely by hot fires, or is it a mid-late succession specialist, only growing when large (and possible old-growth) groves of Musk Daisy Bush re-establish?
Cool Temperate Rainforest of the Plenty River
The western section of KNP includes the Mount Disappointment reference area, an area of tall wet forest that has been reserved as protected water catchment since 1881. The reference area contains the twin headwaters of the Plenty River which supports the most westerly occurrence of cool temperate rainforest along the Great Divide. Prior to the 2009 bushfire, this rainforest stand was believed to have remained unburnt for almost 300 years.
The extreme conditions on Black Saturday created severe fire storms that affected nearly every gully in the park, including the Plenty River headwaters. The rainforest stand was burnt at high intensity, killing many of the dominant Myrtle Beech (Nothofagus cunninghamii) trees and severely affecting the understorey. Monitoring since the fire has revealed that a large suite of rainforest-dependent plants have been temporarily eliminated, particularly fern species. The understorey has become dominated by thick regeneration of wet sclerophyll forest species, drastically transforming the original structure and composition of the rainforest and increasing the risk of further fires. It is predicted that many of the rainforest taxa will not recolonise the gully unless it is protected from further fire for at least another century. Ongoing monitoring will be essential to document the recovery of this important rainforest site.
A small number of Myrtle Beech (Nothofagus cunninghamii) plants were propagated and replanted at the site to assist in the long-term recovery of the rainforest. Re-shooting Sassafras (Atherosperma moschatum) trees had to be fenced to protect from severe browsing by Sambar Deer (Rusa unicolor), Black Wallaby (Wallabia bicolor) and Bobuck (Trichosurus cunninghami).
Mountain Ash forests of Mount Disappointment
Mount Disappointment supports a large stand of Mountain Ash (Eucalyptus regnans) which is relatively disjunct from the heartland of these forests to the east. Prior to the fire it was believed to be the largest stand of unlogged, old-growth ash forest in Australia. This stand supports some of the tallest hardwood trees in the world, including individuals reaching over 93 meters. Mountain Ash is a fire-sensitive species that normally dies if the canopy is affected, followed by mass recruitment from seed held in the canopy.
The 2009 bushfire burnt through the entire stand of these trees, leading to the loss of some very old individuals that were believed to have originated from previous fire events in the early 1700s and 1851. Despite the sad loss of these trees, there were some interesting findings from the post-fire study of these forests. Surprisingly, a few small stands of Mountain Ash survived the fire, likely due to their tall height and a chance event in fire behavior (such as a sudden wind change) so that their canopies remained un-scorched. Another theory has been proposed by researchers that the Mountain Ash of Mount Disappointment are more resilient to fire than other stands of these trees to the east due to their close proximity to surrounding dry sclerophyll forests (i.e. an evolutionary adaptation) (Tony Fitzgerald pers. comm.).
The regeneration of the wet forest understorey was fascinating to record. Within six months the tree ferns had re-shot and the ground was a carpet of green. Several herb and grass species that had never or rarely been recorded in the area germinated in massive numbers in the first 18 months. These species flowered and seeded prolifically before virtually disappearing again. Their seed will no doubt remain in the soil until the next fire event.
The post-fire vegetation surveys at KNP documented valuable information on the ecology of threatened flora and vegetation communities and identified potential risks in the post-fire period. This enabled Parks Victoria to undertake recovery management that included fencing to exclude herbivores, weed control works to reduce competition and replanting. The project highlighted the importance of ecological surveys in the post-fire period, to increase our knowledge of plant ecology and arrest threatening processes. Further monitoring in the long-term is required to assess the full impact of the fire on some threatened plant species and communities.
We would like to thank Tony Fitzgerald, Natalie Brida and Ion Maher (Parks Victoria) for coordinating the project and providing important contributions.