Dry spells in New Zealand as a factor in plant ecology

[First paragraph...]
Although most of New Zealand receives a rainfall which is sufficient in total amount to meet the needs of plants, in most places spells of deficient rainfall of varying lengths have significant effects on vegetation. For example, after a few weeks without rain in summer or autumn the growth of pasture is frequently reduced to such an extent that dairy production declines. In the Kaingaroa area, pine trees were adversely affected after four very dry months in the summer of 1945-46 (Rawlings 1961 ) although they were apparently not harmed in the 1963-64 summer when two periods of approximately five weeks with negligible rain caused severe farm losses. The distribution of indigenous species and of natural plant communities depends in part on the incidence of dry spells-either directly, on account of differences in drought tolerance; or indirectly, through such effects as increased risk of forest fire when summer droughts are frequent. For full understanding, such topics must be examined in terms of water relationships of individual plants or of plant associations in their particular climatic environment. Nevertheless, a broad-scale comparative study of the occurrence of dry spells should provide a useful background for any detailed ecological study