Palaeoecological investigations of sediment cores from two lake basins in the Tutira and Putere districts of Hawke's Bay demonstrate the impact of volcanic activity, fires, and storms on the vegetation and soil stability before human settlement and deforestation. A "disturbance curve" derived from the classification and ordination of pollen records, and correlated with charcoal and sediment records, illustrates relative forest disturbance over. time. Before anthropogenic forest clearance in Hawke's Bay, forest composition fluctuated frequently as a result of disturbance from fires, droughts, and a major volcanic eruption. Each natural disturbance, indicated by short-term increases of seral taxa, was followed by complete forest redevelopment. Cyclonic storms were not a major cause of disturbance to lowland podocarp/hardwood forests in the region, nor to the bracken-scrubland vegetation that replaced the forest after clearance. However, storms scoured and rapidly transported riverbank sediments into the lake basins. Compared with the preceding natural disturbances, deforestation by early Maori settlers represents a type and B95051 Received 1 November 1995; accepted 21 August 1996magnitude of disturbance previously unrecorded in the cores.

The salt tolerance of 31 species-29 halophytes constituting a large proportion of the more important species in salt marshes of Otago, and 2 glycophytes-was examined in water culture. The effects of salinity on growth and survival were the main parameters measured. There were considerable differences between species; most could not grow in sea water (3.5 % NaC1), although a small number could grow in hypersaline conditions of up to 7.5% NaCI. Some species had a salt requirement for maximum growth, the greatest being 1.5 % NaC1, but most grew best in freshwater. No species required saline solutions to survive. In general, the salt tolerance of species decreased from the lower to the upper marsh, which generally parallels field salinities.There were, however, important differences between the shapes of the salt tolerance growth curves, these being related to habitat and, in particular, to the variability of salinity.

Descriptions of, and keys to the three species of Spartina in New Zealand: S. alterniflora, S. anglica, S. x townsendii, are presented with distribution maps for each. The introduction, history, planting, and spread of each species is discussed as is its ecology, especially in relation to past and future potential for spread. In some places the problems caused by its spread are virtually insurmountable. With renewed appreciation of estuarine wetlands in their natural states, planting of any species of Spartina around the coast of New Zealand should not be allowed to take place. S uitable control and eradication measures need to be developed where Spartina is already present.

Soil seed banks at 21 sites covered with poor quality pasture, bracken femland, scrubland of broom or gorse, and various forest types, were examined by germinating seed in soil samples. At most sites the composition of upper and lower soil layers was similar. Persistent, deeply buried seed banks of Cytisus scoparius, Ulex europaeus, and more rarely Sophora microphylla, were discovered at seven sites, four of which lacked that particular species in the above-ground vegetation, and are thus considered to be of a former vegetation type. Forest sites tended to have more seeds and more species represented in the soil seed bank. Although an average of only 35% of the species in the seed bank were represented above ground at the sampling point, this rose to 60% within 5 m, and 72% within 10 m of that point. Those species further away were mostly widespread pasture weeds, even within forest sites, and are interpreted as being recently dispersed and transient. Large quantities of Juncus spp. in some sites are believed to be transported by water movement through the soil. Some species, including certain site dominants, were poorly or never represented in the soil seed bank. It is considered that the seed bank has an important role in establishing the initial floristic composition following disturbance. However, differential seedling survival, resprouting, and competition probably help in maintaining the predisturbance vegetation at non-forest sites. Where forest is disturbed, especially by burning, there is the potential for a completely different vegetation to develop from the seed bank.

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