vegetation analysis

Human impacts in Aotearoa New Zealand have considerably damaged native ecosystems, and conservation efforts must therefore preserve remaining ecosystems and restore degraded areas. However, restoration efforts must address several challenges including species authenticity, plant survival and seedling regeneration in the presence of exotic competition, browsing mammals, and vagaries of climate. Styx Mill Conservation Reserve (SMCR), Christchurch, contains a remnant freshwater wetland in a floodplain complex where restoration activities were initiated in 2000 under a 40-year plan.

Vegetation changes were investigated on 27 transects in agriculturally unimproved short tussock grasslands dominated by Festuca novae-zelandine in the Harper-Avoca catchment, Canterbury. These were remeasured at 5 or 10 year intervals between 1965 and 1990. Change was widespread. It was characterised by invasions by exotic species, declines in native species (including F. novae-zelandine), and a trend towards vegetation dominated by the flatweeds Hieracium lepidulum and H. pilosella, and the grass Agrostis capillaris.

A technique for inferring long term time trends in vegetation from permanent quadrat data using the different patterns in the scattergram of the mean and rates of change of attributes, e.g., cover, from individual quadrats over short periods is described. The technique is illustrated using point intercept cover data for Hieracium species from permanent transects in the Waimakariri measured at intervals over 35 years. There was an exponential increase of 8.6% of Hieracium spp. percentage cover once they appeared in a quadrat up to about 15% cover.