Stand-level dieback andMetrosideros regeneration in the montane rain forest of Hawaii

Abstract

Approximately 50,000 ha of native '6hi'a (Metrosideros polyrnorpha) rain forest on the windward side of the island of Hawaii experienced a pronounced dieback of the tree canopy during the 1960s and early 1970's. The forests affected were located between 600 and 1,500 m elevation where the median annual rainfall was greater than 2500 mm. Dieback stands were found on a variety of different substrates ranging from 500-10,000 years in age. Most of the stands that experiencel dieback had canopy cover greater than 60% prior to 1960.In 1976 and 1977 we established 43 relevrs in dieback and non-dieback forest stands to assess canopy tree vigor, composition and structure of the vegetation, and to describe substrate characteristics. Metrosideros population structure and tree vigor were resampled for 25 of these relevrs in 1982 and 1985-1986. The results of air photo analysis and ground sampling showed that dieback has not expanded very much within the study area since 1977. However, 5 of the relevrs sampled in 1977 continued to decline in tree canopy vigor between 1977 and 1982 while 2 others showed a slight recovery in vigor over this same period.Seedling and sapling regeneration has been extremely vigorous in most of the sites that experienced a breakdown of the canopy while, in stands with an intact, dense tree canopy no such regeneration occurred. It appears that most of the stands which experienced canopy dieback have the potential to become closed forest communities again, dominated by Metrosideros. The natural recovery process may be disrupted in some areas due to additional competition for light and nutrients from invading populations of both native and alien plant species that have become established following canopy dieback.

Population structure, stand‐level dieback and recovery of Scalesia pedunculata forest in the Galápagos Islands

“…The same phenomenon has been observed and studied in other Pacific island forests, for example in New Zealand's Nothofagus forests (Wardle and Allen, 1983;Ogden, 1988), Hawaii's Metrosideros forests (Mueller-Dombois, 1983, 1987aJacobi et al, 1988), in the montane Nothofagus pullei forests of Papua New Guinea (Ash, 1982;Arentz, 1983Arentz, , 1988 and in subalpine Abies forests of Japan (Kohyama and Fujita, 1981 ;Kohyama, 1988). However, natural dieback is not restricted to Pacific islands.…”

“…Metrosiderospolymorpha is a slow-growing tree species with a life span of at least 10 times that of Scalesia pedunculata. Anthropogenically influenced successional displacement also occurs and seems to be increasing where aggressive alien species invade (Jacobi et al, 1988). Such displacement appears to occur now also in some parts of the Scalesia forest area in the Galapagos Islands.…”

Eucalypt decline in Australia, and a general concept of tree decline and dieback

“…Natural climatic variations do not alter the competitive balance between trees and other plants, so dieback caused by climatic extremes is followed by recovery or regeneration of the same species (e.g. Jacobi et al, 1988). On the other hand, eucalypt stands suffering chronic decline are eventually replaced by low scrub because the competitive balance is upset by environmental changes.…”

A global perspective on forest decline

“…This type of dieback also has been reported for certain forms of Nothofagus dieback in New Zealand [7]. In Hawaii, a new form of displacement dieback by alien species invasion has become a concern in natural area management [30,31]. Such displacement of native tree regeneration is indicative of the fragility of indigenous island forests [32].…”