Factors influencing vegetation distribution on a slope in South Westland, New Zealand

Abstract

The vegetation of a slope consisting of two surfaces- a late Otira Glaciation moraine overlying an early Otira outwash surface is reported. The study area was located between the Omoeroa and Waikukupa Rivers in Westland National Park. Three transects, from the bottom of the slope (on the outwash surface), up the slope to the top of the moraine were established. A total of 43 plots were assessed primarily for vascular species abundance and tree species basal area. Classification of species abundance along these transects using the TWINSPAN procedure resulted in seven vegetation types. These showed an orderly grouping from pakihi and 'heath forest' (pink pine/manuka) vegetation on the older surface, to rimu/kamahi/rata forest on the younger moraine. These vegetation type boundaries were reinforced by establishing the distribution of the basal areas of the major tree species found along one of the transects.

The soils of the vegetation types found along one of the transects were characterized. No distinct differences in the measured chemical properties were found between the soils; however, slope position influenced the moisture regime and hence the soil profile morphologies.

The main factors influencing the distribution of the vegetation appeared to be the difference in the age of the two surfaces, differences in the soil moisture regimes and the presence of fire on the oldest surfaces.