North island serai tussock grasslands: 2. autogenic succession: Change of tussock grassland to shrubland

Abstract

The physiognomic stability of seral tussock grassland and tussock-shrubland was assessed by relating species cover and shrub density to environmental and temporal factors using ordination and regression analyses. Four small-leaved, sclero-phyllous shrub species—Dracophyllum subulatum, D. longifolium, Leptospermum scoparium, and Kunzea ericoides—are rapidly invading Chiono-chloa rubra ssp. rubra tussock communities, changing tussock grassland to shrubland within 45-55 years. Elapsed time since the last fire disturbance, slope, and topographical position are reliable factors for predicting rates of vegetation change. Rates of shrub invasion are fastest on steep slopes and on topographically exposed sites, and slowest on flat mesic sites dominated by close-canopied Chiono-chloa rubra ssp. rubra tussock grassland. The cover of wind-dispersed shrubs did not decrease with distance from seed source, but the cover of bird-dispersed shrubs did. The study highlighted the transient nature of some North Island tussock grasslands and the implications for management policy in terms of maintaining floristic, community, and landscape diversity, and problems with deliberate burning to maintain early successional vegetation. © 1994 Taylor & Francis Group, LLC.