Bulletin No. 28
Forest utilisation and the flora and fauna in Boola Boola State forest in south-eastern Victoria. R.H. Loyn, M.A. Macfarlane, E.A. Chesterfield and J.A. Harris. 1980. Forests Commission, Victoria. 80 pp.
This Bulletin describes a series of studies made from 1973 to 1977 on the flora and fauna of Boola Boola State Forest in central Gippsland in south-eastern Victoria. The aim was to study the effects of utilisation of the forest on the vegetation, insects, birds and mammals that inhabit it.
Boola BooJa Forest has been utilised systematically for sawlogs and pulpwood since the late 1940s and is now a mosaic of different age-classes. Some old trees have been Ieft in most logging coupes and many gullies and steep slopes have been left unutilised or lightly utilised. Utilised areas have regenerated naturally, sometimes after a light fire.
The vegetation of the forest is similar to that of many foothill forests in Gippsland, with silvertop (Eucalyptus sieberi) and various stringybarks on the ridges, and mountain grey gum (E. cypellocarpa), narrow- Ieaf peppermint (E. radiata) and arborescent wattles (Acacia dealbata and A. melanoxylon) in gullies. Yertchuk (E. consideniana) grows with heath vegetation on poorly drained soils, and red box (E. polyanthemos) and red ironbark (E. sideroxylon) occur on dry slopes. The forest was found to contain 433 species of higher plants (369 native, 64 introduced), 105 species of birds (102 native, 3 introduced), and 25 species of mammals (19 native, 6 introduced; bats and aquatic species excluded). Comparisons were made between the flora and fauna of even-aged regrowth resulting from utilisation and that of remaining stands of mature uneven-aged forest, within the silvertop/stringybark community. Gullies and yertchuk heath communities were also studied. Habitats of birds and mammals were identified by observations throughout the forest.
The results indicate that regrowth eucaJypt stands have a higher proportion of silvertop than mature forest. Floristically, regrowth was less diverse but the older regrowth stands contained many characteristics of mature forest. With increasing regrowth age, forest wire grass (Tetrarrhena juncea) increased at the expense of tussock grass (Poa spp.) but declined again when stands reached an age of about 15 to 20 years. Understorey and shrub layers were more dense in regrowth than in mature forest.
Changes in the fauna followed vegetation changes. Insect activity appeared to increase immediately after utilisation but after 10 to 15 years was similar to that in mature forest. More insects were found on ridges than in gullies, except in the early stages after utilisation. Different insect orders responded in different ways; for example on ridges, flies were most numerous in young regrowth, whereas beetles were most common in mature forest.
Bird populations were low in young regrowth but increased with regrowth age. This increase was related to vegetation structure and appeared to reach a maximum 15 to 30 years after utilisation and then to decline slightly as stands attained a simple two-layer structure from 30 to 100 years. The high populations of birds found in uneven-aged mature forest were not attained in any regrowth study areas, although some species were more common in regrowth than in mature forest. Young regeneration (aged 0 to 10 years) supported some species that were rare or absent elsewhere in the forest, whereas older stands were populated predominantly by common forest birds. Species that were slow to colonise regrowth (and depended largely on mature forest older than 100 years) included some hole-nesting birds and birds that feed on insects in the bark, on mistletoe nectar or berries, or on eucalypt nectar. Gullies supported high and diverse bird populations. Total populations in gullies were still high after selective logging, although some species had increased and others decreased. Bird communities in gullies differed from those on ridges, with some species occurring mainly in gullies and others on ridges. Yertchuk heath supported a few birds not found elsewhere; these species were found mainly in open areas with stunted trees, although bird populations were higher in the taller stands.
Small mammal populations increased to a peak 15 to 20 years after utilisation and were low both in recently utilised areas and in mature forest. Abundance of small mammals was positively related to the density of understorey vegetation. Wombats and swamp wallabies were common throughout the forest, both in regrowth and mature stands. Yertchuk heath was found to support high and diverse populations of terrestrial mammals including two species of bandicoot. Arboreal mammals were the group most adversely affected by utilisation, and few were observed in regrowth. Densities were low on ridges even in mature forest, and gullies supported the highest density and diversity of these species. Numbers of arboreal mammals were at least as high in selectively logged gullies as in mature gullies, but fewer species were present.
The practice of leaving some dead and living cull trees in utilised areas has contributed to the structural diversity of regrowth and provided habitat for many birds and mammals at all stages of succession, although the density of scattered cull trees in Boola Boola Forest (0 to 15 per hectare) was insufficient for regrowth to support all the bird and mammal species found in mature forest. Results suggest that regrowth differs from mature forest in structure, in abundance of hollow trees and in presence of certain birds and mammals for a long time, probably in the order of 100 years.
In Boola Boola Forest about 25 to 30% of the area has been left unutilised or only lightly utilised, and this has helped to ensure the survival of most bird and mammal species. Utilisation has concentrated in silvertop/stringybark forest, where stands with a particularly high proportion of silvertop appear to be among the habitats least attractive to many species of birds and arboreal mammals. More diverse stands of merchantable forest are important for animals such as the yellow-bellied glider. Most species with exacting habitat requirements have naturally localised populations that can be avoided by logging operations if their locations are known.
In Boola Boola, retained gullies have been particularly valuable because of the high bird and mammal populations they support and the variety of habitats that occur there, not only along streams but on associated steep slopes. Streamside strips that are wide enough to include a range of transitional vegetation contain preferred habitats for many birds and mammals, and in future operations, tongues of reserved vegetation leading to other selected patches on ridges would benefit species, such as the yellow-bellied glider, which move between gullies and ridges. Patches of mature forest on ridges would also be useful for species that avoid gullies and so would be at a disadvantage if gullies remained as the only mature stands in a forest. They could include habitats representative of the original forest (replicated for scientific purposes), habitats of high intrinsic value (e.g. with a high diversity of eucalypts), habitats of uncommon animals, and distinctive habitats such as yertchuk heath.