Recently a fairly dramatic change to the understorey has been occurring in some areas affected by the 2009 Bushfires. In some localities where the fires triggered mass germination of either Black Wattle (Acacia mearnsii) or Silver Wattle (Acacia dealbata) widespread defoliation and dieback of these species has become very apparent.
The cause of this dieback is an insect known as the Fireblight Beetle (Peltoschema orphana ). The Beetles lay eggs on the underside of the leaves and the small grub like larvae also feed on the foliage. The species (although native to Australia) has been identified as a significant pest when people have tried to establish Wattle plantations and the thick regrowth after fires of the wattles has mimicked these conditions.
The dieback has resulted in a rapid opening up of the understorey and more light and less competition will enable other species to grow. Look out for weeds taking advantage of this new open space, but hopefully the event can provide an opportunity for other native understorey species to flourish, while retaining enough Black and Silver Wattle trees to continue to provide important habitat for animals such as sugar gliders and various bird species.
The Beetle is thought to avoid summer heat by hibernating in spring. It emerges in Autumn to start eating new foliage and lay its eggs. The hatched larvae then form into new beetles and the cycle continues.
If you are wanting to restore native vegetation, you can save a lot of expense and wasted effort by working with nature as much as possible. Different sites will require different actions to get the desired results. The following examples show some of the different possibilities for action.
The overstorey trees in this gully, (mainly Blue Gums) are regenerating strongly, There are also plenty of understorey plants including various species of native daisy bushes coming back.The main threat to the site is destruction of the recovering vegetation by stock and weed invasion by transforming weeds. Some annual weeds such as Thistles are very common here now but as the trees and understorey grow back they will be shaded out. The real threat is weeds that will potentially outcompete the native plants and reduce the quality of the habitat for animals, in this case Blackberries are the main issue and a high priority should be to establish a plan for their control. There should be no need for any replanting of vegetation, because it should all be able to recover naturally, in order for this to happen the main priority should be to ensure that a good quality fence is built to keep stock away from this sensitive area.
The site above is a completely different story. This area is on an exposed west-facing ridge, it is steep, erosion prone and unproductive so the landholder has wisely decided to re-vegetate it.There are virtually no native species found on this site and given its position in the landscape and the history of grazing, in the near future there is not likely to be any appear on their own . This site needs a long process of rehabilitation it first needs to be fenced out from stock then planted with as many species as possible from its original vegetation type, so that it can eventually become a diverse and valuable habitat for native species. Ongoing control of high threat weeds will need to continue, especially in the first few years after planting to ensure that they do not get a stranglehold on the site and restrict the growth and development of the new plantings.
The above site along a small creek is in a degraded condition with a cover of exotic grasses and weeds and some dead trees present. On a positive note the site does have some surviving overstorey trees as well as some thickets of native understorey present. Again the first priority for this site will be to fence it out from stock. This will give any regenerating trees a much better chance of survival and allow the understorey to spread. Also again weed control of high threat weeds is a high priority. Once fenced is site can be monitored for the appearance of regenerating native plants that may come from seed stored in the soil, blown in by the wind, washed down the gully or dropped on the ground via birds. If regeneration is not occurring you may have to consider other control measures. Rabbits or other browsing animals could be killing new seedlings, you could build a rabbit proof area on the site to see if that makes a difference. Or perhaps thick grass is stopping germination, you could spray an area with herbicide or scalp off some topsoil to see if that helped trigger new plants to sprout. If all else fails you may go back and resort to planting out the open areas of the site with tube-stock.
The site above is quite a difficult one, It is steep, highly exposed and has poor soil. It formerly had pines growing on it before the fires. It has been sprayed for Blackberry but there are still plenty of Blackberry canes re-sprouting and other weeds such as Variegated Thistle covering the site. the other side of the ridge does have some native scrub growing on it which could provide a source of seed, but it also harbours plenty of Swamp Wallabies which will be keen to eat any newly planted seedlings. Turning this site back to native vegetation will probably be a slow process. One strategy may be to fence the site out from stock and replant the site with overstorey eucalypt and wattle species. The site is likely to be too exposed and weedy for understorey plants to survive. If a canopy can eventually be achieved (maybe up to 10 years later), Shade and protection will provide a better opportunity for understorey and a greater diversity of plants to be established.
This site above is typical of many in the Strzelecki Ranges. It is a very steep slope that was cleared for farming, although hindsight tells us that this was a bad mistake. Since given up for agriculture this gully has seen species such as Blackwood and Silver Wattle come back via soil stored seeds and root suckers, and daisy bushes blow in via their wind-blown seeds. The Eucalyptus overstorey however has disappeared, with no hope of natural replacement. The answer is to once again fence out the site from any stock that may be keen enough to wander down into the gully. Attempts to establish carefully selected Eucalyptus species can then be attempted, this will not be simple as Swamp Wallabies are again sure to be common at this site. One common (but expensive and labour intensive) option is to install mesh wire guards at least 1.2m tall around any plantings to allow them to grow above the height at which Wallabies can graze them). Another issue on this site is the large established Pine trees, Pinus radiata, the simplest way of dealing with the Pines may be to poison them.If they are allowed to persist they will reduce the habitat value of the site and regularly drop seed and produce new wildlings.
This last site on this post has seen a mass regeneration of some species after the fires. No stock on the site has seen thousands of seedlings emerge. The landholder is fencing, what is a very long gully, some areas of the gully have recovering remnants, other bits were formerly pasture with a thick carpet of new Wattles and other species coming up and other bits are bare. The uneven regeneration at this site means that planting may be necessary in some parts and not others. Carefully selection of species to plant is also necessary. There is no point wasting time and effort planting when thousands of plants of that species are already coming up on their own. Spots where overstorery trees are missing are probably the highest priority because unlike species that can be spread by wind-borne winged or fluffy seed or berries carried by birds Eucalyptus seed is only spread by release from its capsules.