Post-wildfire recovery at a wet sclerophyll/rainforest ecotone close to housing at Wanganui NSW

Joanne Green

Introduction. The Mt Nardi fire, on Wed 13^th Nov 2019, provided an opportunity to observe the effects of a relatively low intensity burn at a wet sclerophyll/rainforest ecotone on an 18 acre rural residential property at Wanganui, NSW.

Prior to the fire the vegetation had not been burned for 50 years and was dominated by Brush Box (Lophostemon confertus), Red Bloodwood (Corymbia gummifera) and Forest Oak (Allocasuarina torulosa) –  with a mesic understory of rainforest species including Red Bopple Nut (Hicksbeachia pinnatifolia ), Jackwood (Cryptocarya glaucescens), Bangalow Palm (Archontophoenix cunninghamiana)  and  Tree Heath (Trochocarpa laurina).  The forest was on a trajectory from wet sclerophyll towards a palm-dominated forest.

Since the fire,  the recovery has reset the ecosystem to a wet sclerophyll community with a diversity of heathy species in the understorey, although there is also massive germination and resprouting of rainforest species that indicates that the rainforest understorey will return over time. Table 1 at the end of this summary shows the recovery of both sclerophyll and rainforest species, and their presence or absence above ground prior to the fire.

Figure 1. Dead Bangalow Palm amid a sea of Brown Kurraong seedlings post fire. (Photo: J. Green)

Figure 2. Resprouting saplings of (a) Bolwarra and (b) Creek Fig (Photo J. Green)

Mortality and recovery.

Resprouting:  The fire varied in intensity as it burned downslope. The highest intensity was at the edge of the National Park at the highest elevation above a rocky face. Turpentine (Syncarpa glomulifera), Lomandra (Lomandra longifolia), heath species and younger trees appeared to be killed by fire. While Turpentine has not yet resprouted, Lomandra has resprouted and heath species such as Acacia and Zieria have regrown from seedlings.  Bangalow Palms (Archontophoenix cunninghamiana) are completely dead wherever the fire burned to their tops (growing points) and perhaps many more are dying, indicated by the presence of a fungus on their trunks. One tall Brushbox (Lophostemon confertus) is completely dead.

A community with old growth Forest Oak (Allocasuarina torulosa) is further downslope closer to the rainforest lined creek. The roots system of these trees, burned under the ground and the fire could only be doused by digging out the peat-like root system. Some of the Forest Oaks died but most have recovered.  Taller canopy trees of rainforest and sclerophyll species died back but are resprouting. Midstorey trees, less than 8m, are largely dead, dying or resprouting from the base (coppicing).  The trunks are completely dead but there are many root suckers of species such as Jackwood (Cryptocaryia glaucescens), Bolwarra (Eupomatia laurina), Grey Possumwood (Quintinia verdonii) and the rare Red Bopple Nut (Hickbeachia pinnalifolia).

Treeferns such as Cyathea australis, C. cooperi and C. leichhardtiana were the first resprounters and ground ferns such as Soft Bracken (Hypolepis muelleri) are proliferating following the  rain since the fire event.

Figure 3. Proliferation of rainforest pioneers germinating after fire including Poison Peach (Trema aspera), Pencil Cedar (Polyscias murrayi) and Bleeding Heart (Homolanthus populifolius). (Photo J. Green)

Figure 4. Heath species such as Zieria (Zieria smithii) pictured at the right. germinated alongside rainforest species despite not being in the previous above-ground flora. (Photo: J. Green)

Seed germination: Rainforest species germinating included: Red Cedar (Toona ciliata) , Pencil Cedar (Polyscias murrayi), Brown Kurrajong (Commersonia bartramia), Red Ash (Alphitonia excelsa) and Corkwood (Duboisia myoporoides).  Heath species recruiting included: a large amount of Tree Pea (Daviesia arborea), Zieria (Zieria smithii), Prickly Acacia (Acacia ulicifolia), and Hibbertia spp. Herbaceous species included: Forest Lobelia (Lobelia trigonocaulis),  Kreysigia (Tripladenia cunninghamii), Hairy Tree Foil Desmodium rhytidophllum and other vines of the pea family are covering large areas of the ground.

Weed regeneration

Alongside the natives,  diverse weeds are proliferating after fire, representing all growth forms. Some weed species may be playing a facilitation role for rainforest recovery, while others should be  targeted to reduce their inhibiting effect on native regeneration. Given the level of regeneration across functional groups, this community is likely to benefit from assisted natural regeneration focusing on removal of weed that is competing with native regeneration.  Where possible it is desirable to use the opportunity of the wildfire to deplete populations of weed at the site to increase the community’s resilience to future fire. No reintroductions or seed input is needed at the site.

Future directions.  Consideration needs to be made as to which ecosystem will be the target for future management.  Retaining a sclerophyll overstorey is desirable for habitat values and hence allowing replacement of those individuals that died will be important for future forest dominants.  The use of fire as a control method to control the massive germination of rainforest seedlings and Bangalow Palm dominants is under consideration. For the healthy understorey elements to remain in the soil seed bank for future regeneration would at least require their retention until they have flowered, fruited and recharged the soil seed bank.  But consideration will be given to retaining more fire-resistant rainforest vegetation on the side of the forest closer to the house to act as a fire buffer to supplement the existing 50m fuel free zone.

Contact: Joanne Green, Email jogreen909@gmail.com

Table 1.