Tree fern trunks provide establishment surfaces and habitat for a range of plant taxa including many understorey shrubs and canopy trees. The importance of these habitats for augmenting forest biodiversity and woody plant regeneration processes has been the subject of conjecture but has not been robustly assessed.
Meteorological data from stations around and within the Kaimai Ranges and data from temporary sites are used to characterise the climate of the ranges. Lowland climate is warm temperate with ample rainfall but the upland region is cooler, wetter and frequently enveloped in fog. Frequent fog plays an important part in the climate of upland regions. By modifying light, moisture and temperature regimes fog may be a significant determinant of plant associations and may severely restrict growth.
Approximately 50,000 ha of native wet Metrosideros forest on the island of Hawai'i experienced a drastic reduction (dieback) of the tree canopy between 1954 and 1977. Two general hypotheses have previously been suggested to explain this phenomenon: 1) Metrosideros dieback has resulted from recently introduced pathogens, and 2) the dieback has naturally occurred previously in Hawai'i, and is related to plant succession under periodic conditions of climatic instability which effect the soil moisture regime.