New Zealand Journal of Botany abstracts
Pre-settlement woody vegetation of Central Otago, New Zealand
Susan Walker
William G. Lee
Landcare Research
Private Bag 1930
Dunedin, New Zealand
Email: walkers@landcareresearch.co.nz
Geoffrey M. Rogers
Department of Conservation
P.O. Box 5244
Dunedin, New Zealand
Abstract The potential woody vegetation of Central Otago, South Island, New Zealand, immediately prior to human settlement, is described using complementary lines of evidence. Generalised additive models based on a database of present species locations and environmental surfaces are used to predict the potential distribution of woody species in relation to the environment across a study area of 15 500 km2. Twelve biogeographic zones are classified on the basis of the predicted distributions of the 15 most common potential canopy tree species. The likely structure and composition of each zone is assessed using (1) model-predicted occurrences of more common canopy, subcanopy, and shade-intolerant species, and present-day locations of rarer woody species, (2) compiled information from the subfossil wood, charcoal, and pollen records, and (3) the presence of plant species and life forms in zones of environmental stress. We conclude that water deficit and winter temperature minima are not sufficiently severe to have excluded tall woody vegetation from the intermontane basin and valley floors of Central Otago, and that low forest and shrublands would have dominated here prior to human settlement. At low elevations, grassland was probably confined to floodplains and local areas of shallow or permanently moist soils, while saline soils supported distinctive herbaceous communities. Tall conifer-hardwood and Nothofagus forests are predicted to have once covered the montane and subalpine range slopes. Analysis of environmental tolerances suggests that shrublands may also have dominated above the regional treeline (770-1380 m a.s.l. in Central Otago) although tall tussocks probably increased in dominance towards the range summits. We discuss the strengths and limitations of the different approaches to vegetation reconstruction. Remaining uncertainties may be resolved with a combination of palaeoecological and physiological research and the application of spatial process modelling. Implications of the work for conservation management are discussed.
Keywords pre-settlement forest and shrubland; deforestation; prediction; regression; species-environment relationships; potential vegetation pattern; restoration
B03035; Received 11 September 2003; accepted 18 March 2004; Online publication date 21 September 2004
New Zealand Journal of Botany, 2004, Vol. 42: 613-646
0028-825X/04/4204-0613 © The Royal Society of New Zealand 2004
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