Nothofagus(Fagaceae) forest on Mt Giluwe, New Guinea

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Abstract
Populations of Nothofagus spp. (Fagaceae) were studied on Mt Giluwe, New Guinea (6°S, 144°E, 2300–2800 m alt.). Nothofagus spp. formed monospecific stands transitional with a taxonomically diverse forest, replaced abruptly by gymnosperm forest above 2800 m altitude. Extensive stands of N. pullei had a single dominant size class and, at 30–79 cm d.b.h., many cohorts were subject to dieback associated with pathogenic Phytophthora spp. and pinhole borers. Regeneration in dieback patches was dominated by N. pullei suckers, forming a new cohort. In the absence of dieback, all Nothofagus species reached a maximum d.b.h of 100–150 cm and regenerated, especially in canopy gaps, forming a mixed size structure. A variety of canopy tree taxa were established in stands containing large N. grandis trees, forming a transition or succession to the taxonomically diverse forest. Regular growth rings of parenchyma and, less clearly, vessels were apparently annual. Dieback typically occurred in trees with 100–180 rings. Basal area increment ring-1 reached a maximum at 40–60 cm d.b.h. and declined to a minimum at about 150 cm d.b.h. The maintenance of forest dominance and diversity is discussed in relation to the dieback-regeneration cycle.