New Zealand's forest and shrubland communities: a quantitative classification based on a nationally representative plot network

Question: What are the composition, structure and extent of contemporary, common woody vegetation communities in New Zealand? How do the woody plant communities we describe, based on representative sampling, compare to those of previous New Zealand classifications? Methods: We used cluster analysis to classify data from 1177 systematically located vegetation plots, calculated spatial extent and ecological statistics for each alliance defined, and combined forest alliances into groups to assess correspondence with earlier mapped classifications. We used plot-based data on vegetation structure to infer potential community changes. Results: Twenty-four alliances were recognized, each of 19 to 105 plots, with estimated extents of 144 000-794 000 ha. Stand structure data suggest that 15 alliances are largely stable whereas nine may undergo compositional change. Among alliances, the proportion of exotic species ranged from 0 to 50%. Our forest and shrubland classification is another stage in progressively revising such classifications (i.e. forest class maps, vegetative cover map, ECOSAT woody classification and land cover database) produced over the last five decades. Conclusions: Compared to the previous classifications, our new classification incorporates alliances in disturbed landscapes, as well as those that are compositionally dynamic and which are also invaded by exotic species. It also provides greater partitioning within Nothofagus forests, but fails to distinguish some rare forest types, such as those dominated by Agathis australis. Our classification can contribute to a framework for national reporting of ecological indicators and management of woody vegetation.