Observations on water potential and drought resistance of trees and shrubs after a period of summer drought around Dunedin, New Zealand

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Abstract
An exceptional summer drought allowed observations of plant responses in April 1985. Some species avoided drought and maintained a high water potential even though adjacent species were wilted (e.g., native trees such as Sophora microphylla, Hoheria angusfifolia, and the introduced shrub, Ribes sanguineurn); others tolerated low water potentials without showing obvious signs of stress (e.g., the native Leptosperinurn ericoides and the introduced broom, Cytisus scoparius). A further group showed both wilted and non-wilted individuals with wilted plants always showing lower water potentials than adjacent nonwilted plants of the same species. Species that showed wilting were ranked in order of drought resistance by observations at sites where some species were wilted and others were not. The maximum water potentials observed in wilted shoots were highly correlated with their drought resistance with the most sensitive species (e.g., Coprosma australis and C. robusta) showing wilting at the highest water potentials and the most resistant (e.g., Teline monspessuiana) at the lowest. The range of water potentials in the field was large (from > −1 MPa to < −6 MPa) and although some species (e.g., Nothofagus jusca. Plagianthus betulinus) showed similar minima to those recorded in 1983 ( a drought-free summer), others (e.g.. Podocarpus hallii, Leptospermum spp. and Brachyglottis repanda) showed much lower minimum water potentials.