) Research Report Intense fires promote uncommon post-fire ephemerals in CurrawangAcacia doratoxylon dry scrubs of Little River Gorge, East Gippsland Suzanne M Prober', Kevin RThiele’ and M Bramwell" 'CSIROSustainableEcosystems,PrivateBag5,Wembley,WesternAustralia6913 'DepartmentofEnvironmentandConservation,LMB 104,BentleyDeliveryCentre,WesternAustralia6983 'DepartmentofSustainabilityandEnvironment,574MainStreet,Bairnsdale,Victoria3875 Abstract Acacia scrubs are an unusual vegetation community in the Upper Snowy River region ofVictoria and New South Wales, occurring as sharply-delineated patches amongst eucalypt forest on steep, rocky, north towestfacing slopes. Theycan be dominatedbyarange ofAcacia species, butunder- storeys ofAcacia scrubs are generally reported as sparse and species poor, and little is known of their ecology. Extensive wildfires in 2003 provided an opportunity to compare the effects ofmild and intense fireson plantspecies composition and vigourinAcaciascrubcommunities ofthe Little River Gorge in eastern Victoria. Acacia scrubs atthis site were dominated byAcaciadoratoxylon, notpreviouslydescribedasadominantinAcaciascrubsinVictoria.Consistentwithearlierobserva- tions, understoreys in unburnt scrubs were usually sparse. Light burns led to minimal change in understoreyabundance,andsporadicestablishmentofarangeofspeciesthatwere uncommon inthe understorey ofunburnt sites. By contrast, burns that were intense enough to kill the Acacia overstorey stimulated dense establishmentand profuse growth ofspeciesthatwere rare or absent in the understoreyofunburntplots, leadingtoadramatic increase in nativeshrubrichnessandunderstorey abundance. Processes leading to these understorey changes are likely to involve both effects offire on seed dormancy, and release from intense competition for resources after overstorey death. Infrequent, intensefireshavepreviouslybeenrecognisedas importantforstimulatingrecruitmentof overstorey species and thus the perpetuation ofAcacia scrubs in far south-eastern Australia. This study indicated that a diverse range ofunderstorey species are also dependent on intense fires in these communities, where they appear to behave as post-fire ephemerals. Further, many ofthese species are listed as rare or vulnerable in Victoria, and thus the appropriate fire management of Acaciascrubsisofsignificantconservation interest. (The VictorianNaturalist124(6),2007,320-331 Introduction Dry sclerophyll forests or ‘scrubs’ dominat- kettlewelliae and A. silvestris') have been ed by Acacia species form an anomalous recorded as dominants in different scrub vegetation community in the Snowy River patches (Costin 1954, Clayton-Greene and region of eastern Victoria. They oceur as Wimbush 1988, Keith and Bedward 1999). sharply-delineated patches on steep, rocky In the Snowy River region, Clayton-Greene northandwestfacingslopeswithinamatrix andWimbush (1988)foundAcaciasilvestris ofeucalypt-dominated vegetation. Together was dominant in most stands. The under- with related scrubs ofsouth-eastern NSW, storey ofAcacia scrubs is usually reported these scrubs form the only class ofvegeta- as sparse,with scattered shrubs andminimal tion east ofthe Great Dividing Range in ground cover, but a dense shrub layer, par- which Acacia is the dominant tree (Keith ticularly ofPhilotheca trachyphylla (some- 2004). They are not closely related to any times without the Acacia overstorey) can other classes ofvegetation in the region, also occur (Forbes et al. 1982, Clayton- although they share some floristic similari- Greene and Wimbush 1988, Keith 2004). ties with rocky outcrops in the adjacent Keith (2004) describes the community as sclerophyll forests (Keith 2004). In eastern typically species-poor, with only about a Victoria, they are known as rocky outcrop dozen speciesper0.1 hectare. scrubs(EVC27, Woodgateetal. 1994; pre- Little is known about the ecology ofdry viously rocky-outcrop open scrubland com- Acacia scrubs (Clayton-Greene and munityofForbesetal. 1982). Wimbush 1988). The even-aged nature of Various Acacia species (A. binervia, A. matureAcacia stands indicates that intense blayana, A. doratoxylon, A.falciformis, A. fires are important for their regeneration. 320 The Victorian Naturalist Research Report In these conditions, mature trees are killed fuel loads and weather conditions, leading and gennination andgrowth ofseedlings is to a mosaic of unburnt, lightly burnt and stimulated (Clayton-Greene and Wimbush intensely burntareas acrossthegorge. 1988). However, there is little documenta- Methods tion of effects of fire on other species in Sampling these communities, and patterns in species composition relating to other environmen- Floristic sampling focused on two areas of tal factors arepoorly understood. known Petrogalepenicillata habitat on the Extensive wildfires in 2003 provided an northern slopes of Little River (37° 06’ S, opportunity to study the effects of fire on 148° 20’ E) and Fann Creek (a tributary of dry Acacia scrub communities on Lower Little River, 37° 07’ S, 148° 20’ E). Devonian volcanics of the Little River Vegetation was dominated by tall Acacia Gorge in East Gippsland, Victoria. We scrubon dryslopesand spurs, withE. alhens undertook stratified floristic surveys to woodlands on locallycooler(eastern) aspects, assess short-term impacts of mild and and shrubland dominated by P. trachyphylla intense fire on understorey composition on exposed rocky outcrops. Some intergrad- and vigour, and to establish benchmarks ingoccurred amongthese communities, espe- for monitoring vegetation response to fires ciallyatFarmCreek. over a longer time frame. Surveys were Sampling was undertaken in November also relevant to management of habitat of 2004 to January 2005, and was confined to the Brush-tailed Rock Wallaby Petrogale vegetation with a prominent Acacia over- penicillata (.IE Gray 1825), as the Little storey. Quadrats were 10 x 10 m, and per- River Gorge area provides the last remain- manentlymarkedto allow long-term moni- ingrefuge forthis species in Victoria. toring. Although the study was undertaken almost two years after the Bogong The StudyArea Complex fires, a range of fire intensities The Little River, upstream of its junction was easily distinguishable: with the Snowy River in East Gippsland, • Sites with deep, non-charred, ground- forms Victoria’s deepest gorge. The area is layer litter and occasional live shrubs highly dissected, with steep slopes and deep with sparse to abundant twig-lichens valleys ranging in elevation from 200 to [Usnea sp.), wereclassed as unburnt. 1000 m A.S.L., and occupies a rain shadow • Sites with visible charcoal and partially mm with an average ofaround 600 rainfall burnt twigs, llre-scars on trees and larger per annum. Soils are derived from Lower shrubs, no twig-lichens, and <20% kill of Devonian volcanics (rhyodacites), and con- theAcacia canopy were classed as lightly trast with the coarse grained granodiorites burnt. and UpperOrdovician sediments(siltstones. • Sites with >80% kill of the overstorey schists, slates, shales and claystones) occur- Acacia trees were classed as intenselv ring immediately to the north and east burnt. (Clayton-Green andWimbush 1988). At each site we aimed to sample four Typical vegetation ofthe local region is replicates each of unburnt, lightly burnt grassy woodland dominated by White Box and intensely burnt Acacia scrub. Eucalyptus alhens, grading to other euca- However, no unburnt sites were found at lypt forests and woodlands at higher alti- Little River, so the final sampling design tudes and on poorer soils. Dry Acacia comprised four unbumt plots (Farm Creek scrubs occuras scatteredpatches associated only), eight lightly burnt plots and eight with steep rocky valleys and slopes intenselyburntplots (both sites). amongst these vegetation types, both on Plots were placed so as to sample the rhyodacites and sediments, but rarely on rangeoftopographicclassespresentateach granodiorites (Clayton-Greene and site (NE to NW slopes, drainage lines and Wimbush 1988). rocky spurs). Within each topographic Large areas of the Little River valley class, we sought to place plots ofeach fire were burnt in the extensive Bogong intensityclasswithin close proximity, lead- Complex wildfires during .lanuary 2003. ing to paired (lightly-burnt and intensely- Fire intensity varied depending on aspect. burnt) plotsat Little River, and sets ofthree Vol. 124 (6) 2007 321 Research Report (unburnt, lightly-burnt and intensely-burnt sional solutions, compared with minimal plots) at Farm Creek. Plots were randomly improvement in higher dimensions, led to placedwithintheseconstraints. selection ofthe three-dimensional solution for further exploration. Stress values of Floristicmonitoring Percentage foliage projective cover was the selected solutions were 0.1 1 for the presence-absence and 0.10 for the quanti- visually estimated for all higher plant and tative analysis.

Intense Fires Promote Uncommon Post-fire Ephemerals In Currawang 'Acacia Doratoxylon' Dry Scrubs of Little River Gorge, East Gippsland

Similar Intense Fires Promote Uncommon Post-fire Ephemerals In Currawang 'Acacia Doratoxylon' Dry Scrubs of Little River Gorge, East Gippsland