Coastal Valley Grassy Woodlands are a class of grassy woodland (i.e. savannas) occurring principally in the coastal valleys and plains of eastern Australia. They are characterised by an open canopy of eucalypts and related trees above a species-rich ground layer dominated by perennial tussock grasses, herbs and other herbaceous plants. Shrubs may be scattered or locally form denser patches. The composition and structure of the woodlands vary in response to rainfall, soil fertility, topography, fire and disturbance. Fire is an important ecological influence on the vegetation.
Coastal Valley Grassy Woodlands occur primarily on relatively fertile soils in comparatively dry valleys and plains on the coastal side of the Great Dividing Range, where local rain shadow effects restrict the development of wetter forest types. Despite sharing a characteristic grassy woodland structure, these Grassy Woodlands are floristically heterogeneous across their geographical range. The Grassy Woodlands have been extensively cleared and modified throughout their range. Human disturbance has substantially altered the ecology of many surviving remnants. In New South Wales, occurrences are distributed discontinuously from the northern river valleys to the South Coast, including the Cumberland Plain of Western Sydney. Cumberland Plain Woodland, a critically endangered ecological community, forms one of the best-known regional expressions of the broader Coastal Valley Grassy Woodlands.
Description
Coastal Valley Grassy Woodlands generally take the form of open forest or woodland approximately tall. The canopy is typically discontinuous, allowing substantial light to reach the understorey and supporting a dense and species-rich herbaceous layer. Beneath the canopy, shrubs occur as scattered individuals or clumps and are predominantly sclerophyllous, although their density varies considerably according to site quality and disturbance history. The ground layer is characteristically dense and species-rich, comprising perennial tussock grasses, herbs and scrambling or climbing plants. Geophytic orchids and lilies may become particularly conspicuous during favourable seasons or following fire.
The structure of the vegetation varies across its range. Some communities form relatively tall open forests, whereas others have a more open, park-like woodland structure with widely spaced trees and a predominantly grassy ground layer. Tree density may also have been substantially reduced in areas historically subjected to clearing or grazing. At the southern end of the range, some communities assigned to Coastal Valley Grassy Woodlands may naturally contain relatively few trees or locally occur without a tree canopy.
The vegetation class encompasses numerous regionally distinct plant communities that have been described under a variety of names. In the Cumberland Plain, these include Cumberland Shale Plains Woodland and Cumberland Shale-Sandstone Ironbark Forest, while the Hunter Valley includes Central Hunter Ironbark-Spotted Gum Forest. Northern New South Wales examples include Northern Hinterland Valleys Red Gum Grassy Forest and Far North Ranges Red Gum Grassy Forest. In southern New South Wales, communities within the class have historically been described under names including Bega Dry Grass Forest, Candelo Dry Grass Forest, Bega Valley Shrub/Grass Forest, South Coast Grassy Woodland and Far South Coast Grassy Woodland. These names represent different classifications of vegetation now included, wholly or partly, within Lowland Grassy Woodland in the South East Corner Bioregion, which belongs to the Coastal Valley Grassy Woodlands class.
Canopy Rough-barked apple (Angophora floribunda) and forest red gum (Eucalyptus tereticornis) are among the most characteristic trees of the vegetation class and occur throughout much of its geographical range. Other widespread canopy species include spotted gum (Corymbia maculata), narrow-leaved ironbark (Eucalyptus crebra), thin-leaved stringybark (Eucalyptus eugenioides) and grey box (Eucalyptus moluccana).
Canopy composition changes substantially with latitude and locality. In the far north, large-leaved spotted gum (Corymbia henryi), pink bloodwood (Corymbia intermedia) and grey ironbark (Eucalyptus siderophloia) become characteristic components. In the Hunter Valley, communities may instead be dominated by combinations of narrow-leaved ironbark, spotted gum, grey box and forest red gum. On the Cumberland Plain, forest red gum and grey box are particularly characteristic, with ironbarks locally prominent. Farther south, grassy woodlands of the Bega Valley and surrounding lowlands commonly contain forest red gum, while rough-barked apple, yellow box (Eucalyptus melliodora) and snow gum (Eucalyptus pauciflora) may occur in some stands.
Understorey
The shrub layer is generally less prominent than the grassy ground layer and varies considerably between communities. Blackthorn (Bursaria spinosa) is among the most widespread shrubs, while other sclerophyllous shrubs occur according to region, substrate and disturbance history. Some communities, particularly grassy open forests of the Hunter Valley, may have only a sparse shrub layer or lack one almost entirely. Grasses and other herbaceous plants provide much of the vegetation cover beneath the trees. Dominant tussock grasses occurring widely within the class include purple wiregrass (Aristida ramosa), threeawn speargrass (Aristida vagans), barbed-wire grass (Cymbopogon refractus), paddock lovegrass (Eragrostis leptostachya) and kangaroo grass (Themeda triandra). Smaller grasses and sedges include knob sedge (Carex inversa), Dichelachne micrantha and weeping grass (Microlaena stipoides).
The relative abundance of these species varies geographically. Kangaroo grass and weeping grass, for example, are important components of Lowland Grassy Woodland in the South East Corner, where they occur beneath forest red gum and other scattered eucalypts. The prominence of grasses and herbs throughout the class distinguishes these communities from neighbouring forests in which shrubs or a denser tree canopy form a greater proportion of the vegetation.
Floristic variation Despite their common structural characteristics, Coastal Valley Grassy Woodlands are not floristically uniform. Their discontinuous distribution in separate coastal valleys has produced a series of regionally distinctive assemblages. Quantitative comparisons have found that Coastal Valley Grassy Woodlands in different regions of New South Wales are floristically distinct and support substantial numbers of locally restricted or endemic species. Regional assemblages are often distinct and may contain substantial numbers of locally restricted species. Their similarities are largely attributable to a comparatively small group of widespread and abundant plants that contribute strongly to the characteristic appearance of the vegetation, while representing only a small proportion of its total floristic diversity.
Floristic diversity also displays a strong latitudinal pattern, with overall diversity declining towards the south, particularly among woody species. Similarities between geographically separated variants are largely attributable to a comparatively small group of widespread and abundant species. These plants contribute strongly to the characteristic appearance of Coastal Valley Grassy Woodlands but represent only a small proportion of their total floristic diversity. Consequently, woodlands separated by several hundred kilometres may share a recognisable open eucalypt canopy and grassy understorey while differing substantially in their complete assemblages of trees, shrubs, grasses and herbs.
Distribution and environment
In New South Wales they generally occur below , in areas receiving approximately of annual rainfall. They are particularly associated with coastal rain shadows, where lower rainfall and relatively fertile soils favour grassy woodland rather than the denser forests characteristic of many wetter parts of the eastern seaboard. Typical substrates include relatively deep and moderately fertile clay and loam soils derived principally from shale and granite.
In New South Wales, the class occurs in the valleys of the Clarence, Macleay, Manning and Hunter rivers; the Kangaroo, Moruya, Araluen and Bega Valleys; and on the Cumberland Plain and south-western Illawarra plain. A localised occurrence is also recognised around the Gippsland Lakes in Victoria. Tozer's broader treatment places Coastal Valley Grassy Woodlands throughout coastal New South Wales and into South East Queensland. The environments occupied by the class vary considerably over this geographical range. Northern examples occur in warm subtropical valleys and hinterlands, whereas the southernmost occurrences experience cooler temperate conditions. Differences in rainfall, temperature, geology and soil fertility contribute to substantial regional variation in floristic composition, despite the persistence of a broadly similar open-canopy and grassy structure.
The vegetation class encompasses numerous plant communities that differ according to climate, geology and geography. Examples recognised in contemporary New South Wales vegetation classification include Cumberland Shale Plains Woodland and Cumberland Shale-Sandstone Ironbark Forest on the Cumberland Plain, Central Hunter Ironbark-Spotted Gum Forest in the Hunter region, Northern Hinterland Valleys Red Gum Grassy Forest on the North Coast, and Southeast Lowland Grassy Woodland in south-eastern New South Wales. Although grouped within the same vegetation class, these regional forms are not simply geographical repetitions of a single plant community. Comparative analysis has found considerable floristic differentiation among Coastal Valley Grassy Woodlands, with many species restricted to particular portions of the geographical range. Their common classification reflects a combination of structural, environmental and floristic characteristics, including the prevalence of an open eucalypt canopy and a substantial grassy and herbaceous ground layer.
Northern New South Wales and South East Queensland At the northern end of the range, Coastal Valley Grassy Woodlands occur in the coastal and hinterland valleys of northern New South Wales, including parts of the Clarence Valley. Communities assigned to the class include Northern Hinterland Valleys Red Gum Grassy Forest and Far North Ranges Red Gum Grassy Forest. Forest red gum (Eucalyptus tereticornis) remains an important canopy species in northern examples, while subtropical trees such as large-leaved spotted gum (Corymbia henryi), pink bloodwood (Corymbia intermedia) and grey ironbark (Eucalyptus siderophloia) become increasingly characteristic towards the northern end of the distribution. The broader Coastal Valley Grassy Woodland assemblage extends beyond the New South Wales border into South East Queensland. This northern extension occupies the warmer end of the climatic gradient represented by the vegetation class and contributes to the greater woody-plant diversity recorded in its northern communities.
Hunter Valley