The ecology of the Ellesmere Lake flats : a study of edaphic succession

Abstract

Lake Ellesmere is a large, shallow, non-tidal lagoon in Canterbury, New Zealand, lying to the west of Bank’s Peninsula, and separated on its southern side from the Pacific Ocean by a narrow shingle spit, through which the lake is periodically discharged whenever its level is sufficiently above that of the sea. The brackish water of the lake thus varies considerably in its salinity, which is however sufficient to give a definite halophytic stamp to the vegetation of the marginal lake flats. The soils of these have a high potential fertility but are largely unproductive because of periodic flooding and high salinity.

Attempts to ameliorate these adverse conditions by the building of stopbanks (to prevent flooding) and by the sinking of artesian bores (to wash out the salt) have been partially successful. Large schemes for providing a permanent outlet to the lake have also been devised, but have not yet been successfully applied.

Before beginning any such extensive project however, it is desirable to know the pattern of soil quality in the land to be reclaimed, not only to indicate whether or not the project is economically desirable, but also to indicate methods by which the reclamation can best be achieved. A generalised soil survey of the area has now been completed by officers of the Soil Bureau, but this was not made with reference to the vegetation. If it could be shown that the various plant communities are reliable indicators of the varying combinations of soil properties, much of the work for a detailed soil survey could be eliminated.

Thus it is the purpose of this study to characterise the various plant communities present, to indicate their extent, to examine the conditions under which they exist, and to elucidate by how much their presence is determined by the soil conditions.