Patterns of Stomatal Conductance in Six Evergreen Tree Species from a New Zealand Cloud Forest

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Abstract
Stomatal conductances were measured through a single austral summer on six evergreen tree species [Ixerba brexioides A. Cunn, Quintinia acutifolia Kirk, Weinmannia racemosa Lin. f.) (Jane and Green 1983), Myrsine salicina Hew. ex Hook.f., Coprosma australis [A. Rich.] Robinson and Pseudopanax colensoi [Hook. f. ] Philipson) in cloud forests of the Kaimai Ranges, North Island, New Zealand. Stomatal closure occurred earlier in the day as the summer progressed and, on some occasions, was complete by early afternoon. Stomatal closure appeared to be related to atmospheric saturation deficit (SD), since predawn plant water deficits were low and maximum deficits were well above turgor loss point; temperatures were also moderate, ca. 20.degree. C. Poor root system development, resulting from high soil water contents maintained by the prevalent fog, was the probable cause of the stomatal sensitivity to relatively low SD. We suggest that the combination of poor root systems, reduced photosynthesis, and lower temperatures, all linked to the frequent fog, may lead to increased susceptibility of the vegetation to damage by drought.