Biological flora of New Zealand 14:Metrosideros excelsa, pōhutukawa, New Zealand Christmas tree

Abstract

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.

Seed banks and post‐fire recovery of invasive alien Metrosideros excelsa in South Africa: Implications for control

“…The post-fire population in our study was almost half as numerous as the pre-fire population, with post-fire regeneration largely accounted for by basal resprouting while recruitment from seed was insubstantial. Metrosideros excelsa showing some, albeit limited, capacity to regenerate vegetatively and sexually after fire, is consistent with ambiguous evidence regarding the species' adaptations (or lack thereof) to fire in its native range (Bergin & Hosking, 2006;Bylsma et al, 2014). However, our findings cast doubt over whether the capsules of M. excelsa protect seeds from heat and dehydration during fires and thus whether they represent a fire-adaptive trait (cf.…”

“…There was no significant difference in the viability of seeds from green and dry capsules indicating that seeds mature early in the fruiting season and may be viable despite appearing green or immature. Our quantification of the viable seed crop of trees is crudely comparable or exceeds, estimations of the reproductive output of the species in its native range (up to 40,000 flowers per tree with 10% of ovules developing into viable seeds; Bergin & Hosking, 2006;Bylsma et al, 2014), although the measures used to express reproductive output are not directly comparable in the different studies. Nevertheless, the reproductive output of M. excelsa in its South African introduced range seems at least as high as that in its native range, which is to be expected given that species generally have fewer natural enemies in their introduced ranges than in their native ranges (Keane & Crawley, 2002).…”

Comparison of combination of dimensionality reduction and classification techniques for identifying tree species using integrated QuickBird imagery and Lidar data

“…Pohutukawa (Metrosideros excelsa) is an example; this is a native tree species in New Zealand which has been subject to fires and land clearance, and more recently possum (Didelphimorphia) browsing. 5 Pohutukawa is a multistemmed tree up to 25 m high with large, rounded crowns. Identifying and mapping this tree species have been mostly based on field data such as in Simpson, 6 which is costly and time-consuming to perform.…”

Pattern and process of vegetation change (succession) on two northern New Zealand island volcanoes

“…Light is a key resource controlling plant species colonization of new sites and replacement in forest understories. The shade tolerance of key species in M. excelsa forest and scrub has been quantified using hemispherical photography (Bylsma et al 2014). Light environment occupancy of key canopy species differs significantly (P<0.001) according to the distribution of understory light environments available.…”