Tree species richness and turnover throughout New Zealand forests

Patterns of mortality, recruitment, and forest turnover were investigated using permanent plot data from temperate forests in 14 localities throughout New Zealand. Tree mortality and recruitment rates were calculated from tagged trees greater than or equal to 10 cm diameter at 1.4 m on individual 400 m(2) plots, and turnover rates were calculated as the mean of mortality and recruitment rates. Turnover rates (1.4% per year) were very similar to those recorded for tropical forests (i.e. 1.5% per year). As was shown in tropical forests, we also found significant relationships between forest turnover and species richness. In New Zealand forests there was also a decrease in species richness and turnover rates with increasing latitude. Although species richness is well known to decline with latitude, our study provides support for a possible link between seasonality and disturbance with tree turnover and species diversity. While tree mortality and recruitment rates were approximately in balance at some localities, in others there were imbalances between mortality and recruitment rates.