Pacific Science Volume 37, Number 4, 1983

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Pacific Science is a quarterly publication devoted to the biological and physical sciences of the Pacific Region.


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    37: Index - Pacific Science
    (University of Hawai'i Press, 1983)
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    Concluding Synthesis
    (University of Hawai'i Press, 1983-10) Mueller-Dombois, Dieter
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    Soil Weathering Stage, Vegetation Succession, and Canopy Dieback
    (University of Hawai'i Press, 1983-10) Walker, J. ; Thompson, C.H. ; Jehne, W.
    A conceptual model that provides a means of viewing changes in vegetation as responses to weathering of soil mantles over thousands of years has been developed from investigations of vegetation communities on a soil chronosequence on sand dunes extending back in time to at least the last interglacial. Progressive and retrogressive phases in natural plant succession are indicated by this sequence. A similar model is used to postulate that the various canopy dieback symptoms and agents observed in the New England tablelands of New South Wales, Australia, represent the mechanisms by which changes are occurring in retrogressive ecosystems that have been disturbed by human land use. We suggest that investigations of the etiology of diebacks need to be made in the context of temporal changes in soil fertility associated with the degree of soil weathering.
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    Crown Symptoms of Regrowth Dieback
    (University of Hawai'i Press, 1983-10) Plazer, C.
    Symptoms in the crowns of Eucalyptus obliqua and E. regnans trees affected by "regrowth dieback" are reevaluated and amplified using tree climbing, tree felling, and optical study methods. A distinction is made between the dying upper branches and the lower crown of dieback-affected trees. Declining branches showed an increase in mortality or absence of growing shoots, naked buds, and accessory buds with increase in dieback severity. Mean distance between leaf scars indicated that growth rate of shoots was slowed before death. With increase in dieback severity of a branch, leaf size and leaf area index were reduced. Leaves on dieback-affected branches showed increased chlorosis and reddish colors. There are common features linking dieback-affected shoots with shoots showing mild "witches brooming."Twiginhabiting insects are considered of only secondary importance. There was no evidence of any culturable microorganism from the vascular system. The symptoms could be the result of water deficits and high leaf temperatures. Alternatively, the symptoms are suggestive that microbes such as a virus or more especially a mycoplasma are involved.
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    Armillaria Root Rot in Eucalypt Forests: Aggravated Endemic Disease
    (University of Hawai'i Press, 1983-10) Kile, G.A.
    Species of the woody root rot fungus Armillaria are indigenous in cool temperate rain forest, mixed forest, and wet and dry sclerophyll eucalypt forests in Australia. Four species have been described or identified from southeastern Australia: A. luteobubalina Watling and Kile, A. fumosa Kile and Watling, A. hinnulea Kile and Watling, and A. novae-zelandiae (Stevenson) Boesewinkel. The latter species was first described from New Zealand, and A. hinnulea also occurs in that country. Armillaria novae-zelandiae and A. hinnulea occur in wet forests (rain forest, mixed forest, and wet sclerophyll communities), while A. luteobubalina and A. fumosa are found mainly in dry sclerophyll forests. Armillaria luteobubalina is so far the only species known to behave as a primary pathogen in native forests. While the fungus has an extensive geographical distribution in southeastern Australia, damage is most severe in selectively logged forests in the central highlands of Victoria, where it is estimated that approximately 3-5% of the forest area is moderately to severely affect~. The fungus kills all species of eucalypts and a wide range of the under- story trees and shrubs present in the forests. Most infections occur in small (0.1-1.0 ha), well-defined patches, but larger (up to 20-30 ha), more diffuse infections also occur. Evidence of primary pathogenicity includes (a) constant association of the fungus with disease; (b) the pattern of disease development within stands (the fungus spreads by root contact from infected food bases); (c) correlation between root infection and symptom development in large trees; (d) evidence of host resistance to infection; and (e) pathogenicity in pot and field trials. There is no evidence that climatic stress or other pests or pathogens initiate disease. Within the forest, the fungus has a discontinuous distribution. Studies of genotypes of the fungus (identified by analyses of mating alleles, since Armillaria sp. are bifactorial heterothallic, or intraspecific antagonism), suggest that A. luteobubalina consists of a community of genetically distinct mycelia. Individual genotypes may contract, expand, or coalesce, depending on circumstance. The development and status of the community depends on the two processes of new basidiospore infection and local spread by vegetative growth through root systems. Similar patterns of genotype distribution and clonal development were evident in logged and unlogged forest. It is concluded that root rot caused by the fungus is endemic in these forests but that logging has aggravated the disease.
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    Nothofagus dieback on Mt. Giluwe, Papua New Guinea
    (University of Hawai'i Press, 1983-10) Arentz, Frans
    The phenomenon of patch dieback in stands of Nothofagus on Mt. Giluwe, in the southern highlands of Papua New Guinea, is described. Ecological studies that have been carried out are reviewed. Based upon the results of surveys on Mt. Giluwe, the role of Phytophthora cinnamomi in contributing to the dieback is examined. A comparison is made of Nothofagus dieback on Mt. Giluwe with Metrosideros dieback in Hawaii.
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    Defoliation as a Means of Assessing Browsing Tolerance in Southern Rata (Metrosideros umbellata Cav.)
    (University of Hawai'i Press, 1983-10) Payton, I.J.
    Old and young trees of southern rata (Metrosideros umbel/ata) were artificially defoliated to examine their response to foliage loss. Partial (50%) or total defoliation before budbreak depressed shoot growth more markedly in old than in young trees. Fifty percent leaf loss shortly after budbreak or at the end of the growing season did not significantly impair shoot growth in either age class. By contrast, total postbudbreak defoliation resulted in the death of most shoots in both old and young trees. While the terminal buds of both old and young trees totally defoliated in late autumn showed good overwinter survival, only in the young trees were there sufficient energy reserves to enable some of these shoots to flush the following season. Young trees proved to be more resilient to foliage loss, suggesting a more positive carbon balance (energy surplus) in young trees than in older trees.
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    Regeneration of Southern Rata (Metrosideros umbellata) and Kamahi (Weinmannia racemosa) in Areas of Dieback
    (University of Hawai'i Press, 1983-10) Allen, R.B. ; Rose, A.B.
    During the 1950s, dieback of southern rata (Metrosideros umbel/ata) and kamahi (Weinmannia racemosa) was documented in the conifer/ hardwood forests of the Kokatahi and Fox catchments in Westland, New Zealand. Thirty years later, southern rata was usually absent as a live tree in dieback stands. Kamahi, although absent from the canopy in the Kokatahi, had partially recovered at Fox, where it was still a dominant canopy species. Regeneration studies on a range of sites indicate that in the short term, kamahi and Quintinia acutifolia will become the structurally dominant canopy species in many of the dieback stands, and southern rata will at best be a minor component.
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    Forest Instability and Canopy Tree Mortality in Westland, New Zealand
    (University of Hawai'i Press, 1983-10) Stewart, Glenn H. ; Veblen, Thomas T.
    Many researchers in New Zealand have accepted equilibrium models of vegetation change that assume within-stand self-replacement of the dominant tree species as the norm. Consequently, many discontinuous stand structures have been used as evidence of forest instability. For example, the patterns of regeneration and mortality in the rata-kamahi forests of Westland have led many to believe that the present canopy tree mortality is excessive. As a result, there has been considerable research on browsing by the introduced brush-tailed possum as the primary cause of the mortality. We suggest that any interpretation of this forest pattern must include a consideration of the influences on the vegetation of natural disturbances. Abundant evidence suggests that at least some of the mortality is due to senescence of cohorts of trees that originated at approximately the same time after events such as windthrow and mass movements. It may be that browsing by possums hastens the death of trees already susceptible as a result of natural stand development processes.
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    The Possum and Rata-Kamahi Dieback in New Zealand: A Review
    (University of Hawai'i Press, 1983-10) Batcheler, C.L.
    Browsing by the introduced Australian brush-tailed possum (Trichosurus vulpecula) has been generally accepted in New Zealand during the past 30 yr as the principal cause of damage to hardwood forests dominated by rata (Metrosideros spp.) and kamahi (Weinmannia racemosa). Recently, this view has been challenged, and assertions have been made that the forests in a North Island tract were in poor order before possums invaded, that their natural collapse was only a matter of time, and that there is ample evidence relating the more dramatic changes in South Island forests to geological and meteorological events. In this paper, the evidence for repeated coincidence of increase of possum numbers and spectacular modification of the forests is reexamined. Such coincidences, the continued good health of montane hardwood forests where possums have not attained high numbers, and some experimental data, lead to the conclusion that the possum is responsible for dieback in rata-kamahi forests. Control of possums is therefore vital if the forests are to be maintained.
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