We review the biology and ecology of Metrosideros excelsa (Myrtaceae), an endemic angiosperm evergreen tree. Metrosideros excelsa belongs to a conspicuous and widely distributed Pacific Basin genus, with centres of diversity in both New Zealand and New Caledonia. Metrosideros excelsa is an iconic tree species that forms a significant component of northern New Zealand's exposed coastal headland and cliff vegetation. Where conditions are more favourable, M. excelsa forms tall coastal forest, ranging from simple young high-density stands to diverse mature forest. Inland, M. excelsa stands are confined to the margins of lakes and rivers on the Central Volcanic Plateau, where some may originate from early Māori plantings. Metrosideros excelsa is reliant on stochastic disturbance events (e.g. landslides, volcanic eruptions) to create open sites necessary for regeneration. Mass flowering (December-January), followed by abundant production of wind-dispersed seed maximises chance colonisation of such sites. Since human settlement in New Zealand, the distribution of M. excelsa forest has declined by c. 90% and the southern limit of the species has retreated north. Natural regeneration on the mainland is limited by the infrequency of large-scale disturbances and increased anthropogenic and herbivore pressures. Consequently, M. excelsa forest has become rare and localised on the mainland; monitoring and active management are fundamental to the species' long-term conservation.

Tephra eruptions have significant long-lasting impacts on vegetation, and potentially explain extant vegetation patterns in volcanic landscapes. We quantified the effects of the AD 1655 Burrell Lapilli deposit, Mt Taranaki, on treeline vegetation. Where lapilli depth was 25-40 cm, a succession close to primary was initiated. Where lapilli depth was 5-25 cm, the canopy was opened, but some vegetation survived. Total tree basal area remains lower in affected vegetation (158 cf. 206 m 2 ha −1 ), whereas total tree density is higher where a moderate disturbance stimulated regeneration (8433 cf. 6656 stems ha ). Compositional patterns result from interspecific differences in morphology and resilience, as well as light, substrate and temperature tolerance. Light-demanding, cold-tolerant taxa were able to take advantage of the newly created open sites, whereas shade-tolerant, less hardy species lost their competitive advantage at the treeline elevation. The successional trajectory of the treeline vegetation has been set back and altered, and there is no evidence of convergence.

Changes in vegetation structure and composition between 1968 and 2013 were assessed on a small rock stack adjoining Slipper Island/Whakahau, located off the east coast of the Coromandel Peninsula. The rock stack, an example of what is an historically rare New Zealand ecosystem, consists of a steepsided column of fissured andesite with a gently sloped crowning summit (c. 80 m 2 ) that reaches c. 20 m asl. Significant vegetation change occurred in the 45 years between visits, including the arrival of new species (14), predominantly exotic herbs and grasses (7), but most significantly the pioneering native trees Metrosideros excelsa and Pittosporum crassifolium. Total vegetation cover frequency on the summit had increased (from 63% to 77%), with a shift from dominance of herbs and grasses to shrubs with incipient forest development. The rock lily Arthropodium bifurcatum (recognised as a distinct form of Arthropodium cirratum in the 1968 survey) had been lost and the light-demanding creeping shrub Pimelea urvilleana confined to seaward facing ledges. Dominance by M. excelsa is expected to increase leading to canopy closure and further compositional changes.