Vegetation/environment relationships in lowland and montane vegetation of the Kawarau Gorge, Central Otago, New Zealand

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Abstract
Vegetation patterns In the valley of the Kawarau Gorge, Central Otago, were examined using ordination and classification. Two-way Indicator Species Analysis revealed fifteen communities, many of which were dominated by the shrubs Rosa rubiginosa and Discaria toumatou, but which mostly differed in understorey species. Other distinct communities included scabweed, thyme/ brier, pasture, bracken, dense shrubland, and subalpine snow tussock grassland. Classification divisions were correlated to the 21 environmental factors measured at each site by using rank correlation coefficients. Various factors distinguished some of the fifteen communities, while higher level classification divisions were correlated with a number of factors Including position within the valley, altitude, aspect, grazing by rabbits, gravel, soil acidity, soil carbon, and the nutrients potassium and magnesium. Detrended Correspondence Analysis revealed a very clear xeric/mesic vegetation gradient In the first axis, and a poorly defined herbaceous/woody vegetation gradient in the second. Third and fourth axes could not be interpreted from vegetation alone. Vegetation/environment relations were examined using multiple regression, comparing the ordination gradients with the environmental factors. The first axis was related primarily to aspect and altitude, while the second was mainly related to altitude, soil acidity, and position within the valley. Third and fourth axes were also interpretable, the third being mainly related to grazing by sheep and the fourth to grazing by rabbits. Although the communities were rather poorly defined by composition, the environment/vegetation analyses demonstrate strong and interpretable relationships, in contrast to the findings of Hubbard & Wilson (1988) and Wilson et ai (1989) who concluded from similar poor community definition, that the vegetation was out of equilibrium with the environment. The strong relationships found in this study support their other hypotheses, particularly those involving complicated environmental control or stochastic variation in species composition.