Vegetation change (1968-2013) on a small rock stack adjoining Slipper Island (Whakahau), Coromandel, New Zealand

Abstract

Changes in vegetation structure and composition between 1968 and 2013 were assessed on a small rock stack adjoining Slipper Island/Whakahau, located off the east coast of the Coromandel Peninsula. The rock stack, an example of what is an historically rare New Zealand ecosystem, consists of a steep-sided column of fissured andesite with a gently sloped crowning summit (c. 80 m2) that reaches c. 20 m asl. Significant vegetation change occurred in the 45 years between visits, including the arrival of new species (14), predominantly exotic herbs and grasses (7), but most significantly the pioneering native trees Metrosideros excelsa and Pittosporum crassifolium. Total vegetation cover frequency on the summit had increased (from 63% to 77%), with a shift from dominance of herbs and grasses to shrubs with incipient forest development. The rock lily Arthropodium bifurcatum (recognised as a distinct form of Arthropodium cirratum in the 1968 survey) had been lost and the light-demanding creeping shrub Pimelea urvilleana confined to seaward facing ledges. Dominance by M. excelsa is expected to increase leading to canopy closure and further compositional changes.