Flora and fauna of Barmah State Forest and their management.  E. A. Chesterfield, R. H. Loyn and M. A. Macfarlane.  January 1984.  73 pp. + App. (unpubl.)

SUMMARY

This report considers the flora and fauna of Barmah State Forest, northern Victoria in relation to harvesting of timber, grazing by domestic and feral animals and altered flood regimes. Observations were made between 1977 and 1980, with major studies of the forest in 1978 and 1979.

The vegetation was mapped according to the dominant overstorey and understorey species. The major structural types included rushland, grassland, forest and woodland. Eight understorey types were recognised in river red gum forest (Eucalyptus camaldulensis Dehnh.); these were correlated with differences in overstorey height ranging from 20 m to 33 m. Height differences are believed to reflect long-term differences in flood patterns within the forest. Four different understoreys were mapped in forest with mean dominant heights of 28 m; differences in tree density are believed to be factors contributing to these patterns. Possible mechanisms include competition for soil moisture and the effect of toxic chemicals leached from red gum crowns and leaf litter.

Historical evidence suggests some major changes have occurred in the vegetation, particularly as a result of river regulation and grazing. Grasslands were once more extensive than at present, and over the last fifty years the area of grassland has been reduced by more than half as a consequence of the regrowth of trees and rushes. Rushlands now dominated by giant rush (Juncus ingens N. A. Wakefield) may have previously supported common reed (Phragmites australis (Cav.) Trinn. ex Steud.) or cumbungi (Typha angustifolia L.) These palatable species probably occupied more extensive areas prior to grazing by stock and feral animals.

More than 400 plant species were recorded in the forest, of which approximately 30% were introduced. At least one third of the flora was associated with box ridges, which comprise only 3.5% of the forest area. Five species once recorded on the box ridges are now believed to be absent from the forest (i.e. banksia sp., broom ballart (Exocarpus sparteus R. Br.), river bottlebrush, (Callistemon paludosus F. Muell.), early black wattle (Acacia decurrens (J. Wendl.) Willd.) and yarran (Acacia omalophylla A. Cunn. ex Benth.) and it is possible that species of cypress pine and she-oak have also disappeared. Many species are confined to small communities or are represented by only a few individuals, a possible consequence of the past grazing history. The forest is important for the conservation of a number of species that are otherwise rare or uncommon in Victoria, i.e. graceful swamp wallaby-grass (Amphibromus gracilis P. F. Morris), daisy (Brachycome muelleroides G. L. Davis), flat sedge (Cyperus flaccidus R. Br.), silky umbrella grass (Digitaria ammophila (Benth.) D. K. Hughes), variable spike-rush (Eleocharis minuta Baeck.), slender sunray (Helipterum strictum (Lindl.) Benth.), hypsela (Hypsela tridens F. E. Wimmer), fairy spectacles (Menkea crassa E. Shaw), small scurf-pea (Psoralea parva F. Muell.), Rorippa sp. nov. 's', short rat-tail grass (Sporobolus mitchellii (Trin.) C. E. Hubbard ex S. T. Blake), Stellaria sp. nov., wild violet (Swainsona microcalyx ssp. adenophylla (Black) A. Lee) and rye beetle-grass (Tripogon loliiformis (F. Muell.) C. E. Hubbard). Of these, slender sunray, fairy spectacles and wild violet and the undescribed taxa, Stellaria sp. and Rorippa sp. (Sydney Herbarium) are new additions to the Victorian flora.

Twenty-six species of mammals were recorded in the forest, including seven introduced placental mammals. Results show that whereas native aquatic, aerial and arboreal mammals were well-represented and some were common and widespread, medium-sized native terrestrial species did not occur in the forest. At present all wholly terrestrial mammals are introductions, with the exception of the eastern grey kangaroo (Macropus giganteus Shaw).

Limited historical information suggests that at least four species are now absent from the region. Reasons for their disappearance are unclear, but probably include grazing by cattle and sheep as well as predation by and competition with exotic species. Most mammals living in the forest appear to be well-adapted to current management practices and flooding regimes.

The forest was found to have considerable local significance as a breeding site for water-birds, and has wider significance for some species (e.g. ibis, and in past years egrets), at least in years of extensive flooding of the forest. Most water-birds only breed in the forest during a spring flood and the numbers of species and individuals that commence nesting are determined by water-levels in October. Deep floods are needed to stimulate breeding by some species (e.g. egrets); such floods were usual prior to 1934. In1977, there was no flood and no colonial water-birds nested. In 1978 and 1979 many ibis started to nest, but water receded too rapidly (specially in 1979) and breeding success was poor. The ideal situation appears to consist of a deep flood in early spring followed by gradual recession, with some water remaining in low-lying parts of the forest well into January.

The nomadic behaviour of water-birds is emphasised, and the need for management to consider an area much larger than Barmah alone. The forest bird fauna appears to be well-adapted to seasonal flooding, and many species benefit from a flood without being dependent on it in the short term. Populations on the forest study areas were remarkably similar in the two seasons.

Comparisons between study areas suggest that harvesting procedures that provide for the retention of significant numbers of old trees, some of which are alive, have some benefit for birds. Grazing appears to have had little effect on the species of forest bird present, though it has probably affected their relative abundances. Effects of grazing on swamp vegetation may have contributed to the decline or demise of certain water-birds (e.g. brolga (Grus rubicundus (Perry)), magpie goose (Anseranas semipalmata (Latham)) , little bittern (Ixobrychus minutus (Linnaeus)) and possibly others). Uncommon species worthy of special consideration by management are white-bellied sea-eagles (Haliaeetus leucogaster (Gmelin)), peregrine falcons (Falco peregrinus Tunstall), superb parrots (Polytelis swainsonii (Desmarest)) and all breeding water-birds.