Regeneration in gaps and under closed high canopy, representing the gap and mature phases of the forest growth cycle, was investigated in two small areas within forest dominated by Beilschmiedia tawa
(A. Cunn.) Kirk (tawa) at Rotoehu in the North Island of New Zealand. Significant differences in regeneration occurred between phases, and within phases diameter distributions varied among species. These results suggest differing replacement strategies among species, largely reflecting differences in shade-tolerance. Of the four major regenerating species, shade-tolerant tawa and Dysoxylum spectabile
(Forst, f.) Hook. f. (kohekohe) commonly develop to advanced stages beneath closed canopies; relatively intolerant Litsea calicaris
(A. Cunn.) Kirk (mangeao) and Knightia excelsa
R. Br. (rewarewa) seldom do, apparently requiring gap formation for development to maturity. In the area where tawa and kohekohe were co-dominant in the canopy, they tended to replace each other, thus maintaining their co-dominance.
In forests where the gap phase is important, replacement trends may best be gauged from gap regeneration alone. Of the indices of species' relative importance tested, four juveniles of largest diameter appeared the most appropriate predictor of future canopy occupation in gaps.