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Pisa Flats
Landforms and soils
A small area mainly on a terrace surface of outwash gravels of the Albert Town glacial advance, together with the terrace face towards the Clutha River. A remnant area of soil strongly affected by soluble salts (Manorburn sandy solonetzic loam) is featured with associated brown-grey (Molyneux) earths. The area is centred around a cluster of saline ‘slick spots’ - patches of almost bare deflated ground with drainage restricted by a shallow clay pan.
 for sketch map of landscape units
for sketch map of soils
Information taken from: Allen, R.B. and McIntosh, P.D., 1994. Soil and Plant communities and their management, Pisa Flats, Central Otago. Landcare Research Contract Report LC 9394/131.
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Vegetation
Six main plant communitites occur at Pisa Flats. A gorup of grasses and herbs found throughout semi-arid Central Otago is common ot all these communities: Trifolium arvense, Poa maniototo, Rumex acetosella, Rytidosperma maculatum, Veronica verna, Vulpia bromoides.
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for sketch map of plant communities
Information taken from: Allen, R.B. and McIntosh, P.D., 1994. Soil and Plant communities and their management, Pisa Flats, Central Otago. Landcare Research Contract Report LC 9394/131.
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Communities associated with salt-free soils of low pH:
1. Raoulia australis/Hypochoeris radicata herbfield 2.Convulvulus vericundus/Vittadinia australis herbfieldFound mainly on shady terrace slopes, swales and channels of ephemeral streams. Most Rosa rubiginosa bushes at the site were located in this plant community. lacks scabweed, and has a low frequency of Hypochoeris radicata. 3. Raoulia australis/Scleranthus uniflorus/Myosotis uniflora herbfield
Common species include: Agrostis muscosa, Stellaria gracilenta, Raoulia australis, Colobanthus brevisepalus, Craspedia spp, and Lepidium sisymbrioides subsp. sisymbrioides. Relatively high frequencies of Myosotis uniflora and Hypochoeris radicata. Scleranthis uniflorus and Hypericum perforatum virtually confined to this community. 4. Raoulia australis/R.monroi herbfield.
High frequencies of Raoulia monroi, and unnamed Galium and Leptinella species (uncommon in the other communities). Leucopogon fraseri and Bromus hordaceus are relatively common here.
Plant communitites associated with soils of higher pH and conductivity:
5. Poa grasslandThis community occupies soils with salt-free to salty surface horiszons with mean conductivity of 152uS that are moderately acid to moderately alkaline (mean pH 6.2). Common species include: Aceana agnipila, Echium vulgare, Bromus mollis, Trifolium dubium, Trifolium fragiferum, Poa pratensis, Erodium cicutarium, Leontodon taraxacoides, Myosotis discolor, Trifolium striatum, Spergularia rubra and Lolium perenne. It includes the only records of Atriplex buchananii and Cerastium semidecandrum, and has relatively high frequency of Hordeum histix. Poa maniototo and Rumex acetosella, which are very common in all other communities, have a relatively low frequency here. 6. Carmichaelia petriei/Raoulia australis shrub herbfield
Carmichaelia petriei shrubs of a wide range of sizes are associated with Raoulia australis and R. apici-nigra and common exotic grasses such as Trifolium arvense, Rumex acetosella, Leontodon taraxacoides, Veronica verna and Vulpia bromoides. Soils here are slightly acid, salt-free, on gravelly hummocks between areas of higher pH soils on the lower terrace. Surface horizons have a mean pH of 6.7 and conductivity of 145uS. There are three main variants which are distirubtes in three main habitats, and the dominant species vary accordingly:
5a. Atriplex buchananii salt pan
Characterised by crusted silty soils of the highest pH and conductivity. Few plants, including the salt tolerant hordeum histrix and clover Trifolium fragiferum.5b. Poa cita/Poa pratensis grassland
Found on dunes with silty calcareous soils.5c. Poa pratensis/Lolium perenne grassland
Characteristic of the periodically moist swales and watercourses draining the main (lower) terrace. FloraSixty vascular plants were recorded here. Species distribution is related to soil characteristics. Plants of low pH soils are mainly native, e.g. Leucopogon fraseri, Scleranthus uniflorus and Raoulia monroi, while near neutral soils are dominated by exotic pasture species, weeds, and species that tolerate raised salinity, e.g. Atriplex buchananii and Trifolium fragiferum. Between these extremes are species which tolerate a wide range of environments including Vulpia bromioides, Veronica verna, Rytidosperma maculatum, Trifolium arvense, Rumex acetosella and Bromus tectorum. Atriplex buchananii on saline soils, and Myosotis uniflora and Lepidium sisymbrioides in cushionfield were recorded only at this location. Other uncommon species recorded in the cushionfield are Epilobium microphyllum, Colobanthus brevisepalis, Raoulia monroi and Scleranthus uniflorus. These species, together with stands of Poa cita grassland and Carmichaelia petriei shrubland, which are possibly all that remains of a previously more widely distributed vegetation, confers high conservation value at the site. Almost all similar land in the upper Clutha has been cultivated, fertilised or irrigated. Discussion
Although small and significantly modified, this area represents the best remaining native saline vegetation on the Upper Clutha terraces. Small areas of saline soils were formerly a characteristic feature of the basins of the Central Otago Ecological Region. There are now few such areas still retaining their native flora, which generally included species like Atriplex buchananii normally found in coastal saltmarsh or spray zones. In the Upper Clutha land system most have been destroyed by border-dyke irrigation. This area has survived be being among the most saline and least attractive for irrigation. The landholder reports the former presence of scabweed cushions on soil pedestals, indicating that about 60cm of deflation of loessic soil has occurred. Sources of information:
Grove, Philip. (Ed) 1995: Lindis, Pisa and Dunstan Ecological District. A survey report for the Protected Natural Areas Programme, New Zealand Protected Natural Areas Programme Series No 36, Dept of Conservation. Allen, R.B. and McIntosh, P.D., 1994. Soil and Plant communities and their management, Pisa Flats, Central Otago. Landcare Research Contract Report LC 9394/131.