Zum Baumgruppensterben in pazifischen Inselwäldern
[Dieback in some Pacific island forests]
This paper, presented in November 1983 at the Heinz-Ellenberg-Colloquium in Göttingen, reports on the structurally and functionally significant phenomenon of forest-stand dieback in some Pacific island forests. Three recent research developments are highlighted. The first relates to the research history and five important facts revealed in connection with the Hawaiian Metrosideros forest dieback. The five facts elucidate the dieback as a natural and recurring phenomenon in primary succession. In most cases stand-level dieback is associated with reproduction of the same dying canopy species. The second development relates to the occurrence of similar stand-level diebacks in Nothofagus forests of Papua New Guinea and New Zealand and also in other Metrosideros forests of New Zealand. Research in these forests has revealed likewise that their diebacks are not caused by diseases. Even in the opossum infested Metrosideros forests of New Zealand, the leaf-eating activity of this exotic animal cannot anymore be considered the sole cause for stand-level dieback. The third development refers to an international forest dieback symposium held in February 1983 in Dunedin, New Zealand. A major outcome was the necessary recognition of three factor complexes in the etiology of forest dieback. Two of these complexes refer to stand-external forces, such as biotic diseases and abiotic stresses. The third factor complex is seen as residing within the tree stand or population itself. It relates particularly to the life stage, stand density and reproduction mode of the affected stand. This third factor complex assumes the highest rank in the dieback examples cited. The forests described are not "climax forests" in Whittaker's sense of continuously reproducing tree populations. Instead they are "mosaic forests" comprised of segments of similarly structured or even-aged tree populations, i.e. cohort stands.