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Abstract
Investigations of the upland vegetation of the Kaimai Ranges have revealed widespread mortality affecting a wide range of species and forest types. The mortality is not caused by browsing by Introduced mammals, although they can be shown to have slowed recent forest recovery. Dendrochronological data define 2 mortality episodes closely linked with severe droughts which occurred in 1914 and 1946. Continued ill-thrift in the surviving vegetation and slow growth in the seral forests is the result of complex causes which include Changes in soil water table, increased exposure of residual trees, low nutrient status of the soils, and attacks by pathogens. On steeper slopes the mortality appears to have contributed to a period of Increased erosion, and for this reason further study of the return frequency of the periods of mortality may enable the frequency of the erosion episodes to be determined. The association of drought with the primary causes of the mortality suggests that it may be an under-rated ecological factor in these temperate evergreen forests.