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Semi-arid Dwarf Grasslands Diagnostic features for identification in the field
For more information on identification of plants associated with dwarf grasslands click on appropriate photo:
Description of community and habitat
Dwarf grasslands occur in Central Otago where the annual rainfall is below 500mm, and the brown grey earth soils are shallow or of low fertility. They often occur where severe depletion has taken place, as a result of over-grazing by rabbits and stock. However, there is little information about dwarf grasslands.
On Flat Top Hill, Walker (1994) found that dwarf grasslands are widespread, occupying flat, west-facing sites such as denuded ridge crests and saline toeslopes of fans. Here, native species richness is relatively high (c. 62%). Raoulia australis (scabweed) is the most abundant native plant, with dwarf grasses and small herbs also present.
Species present
On Flat Top Hill, the native component of dwarf grasslands are dominated by scabweed (Raoulia australis), while Colobanthus brevisepalus, the wee grasses Poa maniototo and Poa lindsayii, and Raoulia beauverdii and Stellaria gracilenta are common. Of note are the native ephemeral annual herbs, which can be found in Springtime:- Ceratocephalus pungens, Myosurus minimus ssp. novae-zelandiae and Myosotis pygmaea var. minutiflora. Exotic plants tend to dominate the community, and include scarlet pimpernel (Anagallis arvensis), the succulent stonecrop (Sedum acre), sheeps sorrel (Rumex acetosella) and haresfoot trefoil (Trifolium arvense).
Pisa Flats (Pisa RAP 45) at the head of Lake Dunstan in the Upper Clutha valley, is documented as having stony soils, dominated by scabweed, with the fine grass Rytidosperma maculatum and Leucopogon colensoi, while exotic grasses, haresfoot trefoil and sorrel are confined to moister hollows and depressions. Several rare cushion plants including Myosotis uniflora, rare herbs such as Leptinella n.sp. and Galium n.sp and a daisy perhaps endemic to the site (Craspedia n.sp.) are found in the cushionfield especially on the shoulder of the terraces.
Information from:
Otago Conservation Management Strategy, Volume II Forty Special Places. 1995. Dept of Conservation.
Grove, P. Ed. 1995. Lindis, Pisa and Dunstan Ecological District. A survey report for the Protected Natural Areas Programme.
Walker, S; Mark, A.F., and Bastow Wilson, J. 1995: The vegetation of Flat Top Hill: an area of semi-arid grassland/shrubland in Central Otago, New Zealand. NZ Journal of Ecology, 19(2): 175-194.
Vegetation History
The Central Otago region has a complex history of disturbance. Post-glacial forest may never have extended to the drier basin of Central Otago, and the establishment of grassland, possibly through natural fires, preceded human settlement by several centuries (Wardle, 1985; McGlone, 1989; McGlone et al., 1995). Human impact since Polynesian times has led to changes in soils and vegetation. those changes brought about by pastoral use of the land since European settlement may be traced from early (e.g. Buchanan, 1868; Zotov, 1938) and recent descriptive accounts (e.g. Mark, 1965). the induced vegetation has widely been described as "desert", "steppe" or semi-desert". There are few endemic species, and the region has been particularly vulnerable to invasion by exotic species (Wardle, 1963, 1985).
Degradation has often been blamed on the rabbit pest, which can reach plague proportions, although burning and overgrazing by sheep and feral goats have also contributed. Dwarf grasslands occupy those semi-arid sites which are either very dry (sunny faces; shallow free-draining soils) and/or continue to receive high stocking pressures (rabbits and/or sheep).
Information taken from: Walker, S; Mark, A.F., and Bastow Wilson, J. 1995: The vegetation of Flat Top Hill: an area of semi-arid grassland/shrubland in Central Otago, New Zealand. NZ Journal of Ecology, 19(2): 175-194.
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