Modelling relationships between environment and canopy composition in secondary vegetation in central North Island, New Zealand

Relationships between composition of secondary vegetation and environment were studied in central North Island, New Zealand. A classification procedure was used to identify broad compositional groups which included forest, broadleaved scrub, shrub-fernland, sclerophyllous scrub and shrubland, and tussock-shrubland. Generalised additive models (GAMs) were used to examine relationships between species' distributions and mean annual temperature and rainfall, stand age, distance from intact forest, slope, topography, and drainage. There were marked differences in the environmental relationships of individual species. We conclude that temperature and rainfall have a dominant role in determining succession after disturbance at a regional scale, but distance from intact forest, topography, slope and solar radiation, become important at local scales. Variation unaccounted for by these environmental factors is most likely linked to historical factors such as variation in disturbance and/or grazing and browsing regimes. Intervention by managers will probably be required in the future if the current diversity of secondary vegetation in central North Island is to be maintained.