Frequency of cloud cover on New Zealand mountains in relation to subalpine vegetation

Abstract

Daily satellite images of New Zealand have been used to test the hypothesis that in areas of dense, persistent cloud and fog, subalpine Noth-ofagus forest is replaced by scrub and conifer/broadleaved forest. Examination of 30 localities over a total of 347 days shows that total cloud frequency ranges from 56 to 92%, and frequency of dense cloud from 24 to 72%; cloud cover is broadly correlated with precipitation. The western flanks of the Southern Alps are the cloudiest area, whereas the least cloudy mountains are Te Moehau on the Coromandel Peninsula and the inner ranges in the east of the South Island. Although the distribution of individual species can be related to climatic factors, there is no convincing correlation between cloud frequency and the distribution of contrasting forest types; to account for the latter, it seems necessary to invoke historical factors such as glaciation and volcanic eruptions