VEGETATION AND PEAT CHARACTERISTICS IN THE DEVELOPMENT OF LOWLAND RESTIAD PEAT BOGS, NORTH ISLAND, NEW ZEALAND

摘要

A chronosequence of restiad peat bogs (dominated by Restionaceae) in the lowland warm temperate zone of the Waikato region, North Island, New Zealand, was sampled to identify the major environmental determinants of vegetation pattern and dynamics. Agglomerative hierarchical classification of vegetation data from 69 plots in nine different-aged bogs, initiated from c. 600 to c. 15,000 cal yr BP, identified eight groups. Six of these groups formed a sequence from sedges through Empodisma minus, the main peat-forming restiad species, to phases dominated by a second restiad species, Sporadanthus ferrugineus. The sequence reflected bog age and paralleled patterns of temporal succession over the last 15,000 years (from early successional sedges through mid-successional Empodisma to late successional Sporadanthus) derived from previous studies of plant macrofossils and microfossils in peat cores. This indicated that different-aged bogs in the Waikato region could be used to interpret temporal succession. The remaining two classificatory groups comprised plots from sites modified by drainage, fire, or weed invasion and currently dominated by non-restiad species. The relationships between environmental variables and the six groups representing restiad bog succession indicated that, as succession proceeds, von Post decomposition index and nutrients in the top 7.5 cm peat zone decrease. The most useful indicators of successional stage were von Post, total P, total N, and % ash. Environmental response curves of the dominant plant species separated the species along nutrient and peat decompositional gradients, with early successional species having wider potential environmental ranges than late successional species. Empodisma minus, a mid-successional species, also had a relatively wide environmental range, which probably contributes to its key role in restiad bog development.