Roger Lembit, Convenor, Park Management Committee of NPA
On 16th October 2013 I was working in a gully near the end of the Dumbano Fire Trail in the Wollangambe wilderness north of Bell. On completing the site, I returned up the hill to the Trail to see a cloud of orange-grey smoke to the west. On checking in, I found that there was a bush fire in the Marrangaroo Demolition Training Area and I was required to evacuate and abandon work for the week.
That night the winds strengthened to a gale and within 24 hours the fire had raged eastwards past Mount Wilson, consuming most of the vegetation in its path.
I was back a week later documenting the fire’s impact on the native vegetation, as I had done after a previous fire in December 1997.
With increasing carbon dioxide in the atmosphere the Earth is warming. This has been predicted to have significant impacts on fire regimes in the Blue Mountains where I work. Fires have been predicted to become more frequent, to become more intense and to occur across a broader time period, i.e. the fire season will start earlier and extend longer. A fire of this intensity, so early in the season is almost unprecedented. Typically significant bush fires in the Mountains occur in summer, not mid-spring.
The Post-fire Scene
Many of the areas I had been walking through and working in over the previous 33 years had suffered a fire of very high intensity. Whilst vegetation on the ridges is often burnt at high intensity, this fire had a severe impact in gullies, scorching ferns at the back of caves; only the rainforests in the canyons escaped.
Shrub swamps, an endangered ecological community, were affected, but somehow significant areas of swamp vegetation were less affected than from the 1997 bush fire. In other areas of swamp the peat deposits were entirely consumed, with just bare, sandy earth remaining.
Then and Now
Just 8 days after the fire, shoots of grass trees had started to emerge. Sedges growing in the shrub swamps showed signs of greening within 14 days post fire. By the time 40 days after the fire was reached there were prolific new shoots from the base and stems of woodland eucalypts. Two months after the fire seedlings of Grevilleas and Hakeas had started to emerge.
Spring 2016 marked three years of recovery since the fire. By this time most of the ground layer and shrub species had recovered. Several species had flowering and set seed; some within the first year after the fire, some for the first time in 2016. Others are yet to flower.
Some species are capable of remaining in the soil for long periods of time and emerge with a germination trigger, such as fire.
One such plant is the Pink Flannel Flower, Actinotus forsythii. Pink Flannel Flower is a wiry herb known from heath and forest on sandstone. Fields of Pink Flannel Flower were observed on the ridges near Goochs Crater in February 2015. They were not evident before the fire and haven’t been seen since, apart from a few dead plants later in 2015.
Another is an uncommon woodland grass, Plintanthesis urvillei. This grass, with a red stem base, was observed in heath vegetation, but until spring 2016 could not be identified due to a lack of flowering specimens. It has not been recorded before on the Newnes Plateau, but in spring 2016 was common at one or two heath monitoring sites.
Some plant species are slow to come back after fire. A number of shrub species are yet to recover to pre fire abundance levels. Plant families which seem to have a relatively high number of plants slow to recover include the heath family, Ericaceae, and the Sandalwood family, Santalaceae.
The shrub, Native Currant, Leptomeria acida, only reappeared in spring 2016, although it may have been overlooked in the previous 6 to 12 months. Native Currant is a hemi-parasite; its roots parasitise roots of nearby plants such as Lomandras and grasses. It had been previously observed that Leptomeria plants demonstrate a delayed germination response to fire, emerging in the second year post fire.
Another plant which showed a delayed response is the sedge, Chordifex fastigiatus. Chordifex was highly abundant at some sites in some seasons prior to the fire, but was not evident for many months, despite apparently recovering by re-sprouting from underground rhizomes. It is yet to recover to pre fire levels of abundance.
Eucalypts were hit hard by the fire. Whilst they showed early signs of recovery, with basal and epicormic shoots, they have not recovered to the canopy density present prior to the fire. Only one species has recovered to a reproductive phase, with Blue Mountain Mallee (Eucalyptus stricta) having buds by spring 2016.
Fortunately most of the swamps are in good shape, steady rainfall in the month immediately after the fire avoided significant channelisation within the swamps. This is in contrast to the aftermath of the December 1997 bush fire when an intense rainfall event opened up channels, further damaging and drying peat sediments.