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.

A new species ofMelicytus, M. drucei, is described and illustrated. It has some features in common with diploid M. flexuosus and an undescribed taxon which forms part of the tetraploid M. alpinus complex, and is believed to be a stable triploid hybrid between these two.

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.

Ecological compensation is widely used, and often criticised, for promulgating poor outcomes for biodiversity. There is a lack of systematic research on ecological compensation and, to date, limited research globally into the perspectives of the various stakeholders involved. We undertook 116 semistructured interviews with practitioners working with ecological compensation in New Zealand. Participants consider that benefits to biodiversity are the chief attraction of ecological compensation (49.2% of all responses), with the disadvantages mainly relating to the difficulties of practical implementation of the concept. Our results also show that 96.5% of participants support the concept fully or to a limited extent and most (83%) participants consider that it contributes to sustainable management, with significant support (87.9%) for a statutory approach. Formal statutory guidance at a national level in New Zealand, and an increased focus upon follow-up and monitoring, is considered likely to generate more robust exchanges.

Descriptions of both reinstated species are provided.