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Cylindrocarpon dieback of Eucalyptus obliqua regrowth forests in Tasmania


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Jehne, Walter 1982 , 'Cylindrocarpon dieback of Eucalyptus obliqua regrowth forests in Tasmania', Research Master thesis, University of Tasmania.

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Many of the natural Eucalyptus obliqua and E. regnans regrowth
forests throughout Tasmania have recently been affected by crown
dieback which frequently results in the death of scattered former
dominant and co-dominant trees. The unexplained dieback occurs in
some of the best natural eucalypt forests and was of major concern
to the future, productivity and stability of these forests. The
investigations described in this thesis, were aimed at studying the
aetiology of the dieback complex and evaluating the consequences of
regrowth dieback in the natural development of these forests. The relationship between dieback and the natural transition of
regrowth forests to cool temperate rainforest was examined. These
initial studies indicated that the dieback may be a natural factor
in the development of these forests that has occurred previously and
is unlikely to result in tree deaths beyond those associated with
normal forest development. Furthermore the dieback of former
dominant trees may also be natural during the transition of regrowth
forests to mature forests and be related to relatively higher stress
in dominant trees than in the former subdominant trees which survive
to form natural oldgrowth forests. While these studies should
substantially reduce concern about the unexplained dieback of
regrowth forests they also provide a new perspective of forest
growth within which factors likely to contribute to regrowth dieback
could be investigated and interpreted.
A wide range of factors which may have contributed to the drought
stress and dieback in the regrowth forests were investigated.
Shallow soils with low capacities for holding moisture, periodic lwterloggj ng and drought stress, and the restriction of the fine
root systems of regrowth trees relative to those of understorey
plants were all associated with dieback. However, these factors
could not explain the high level of fine root decay and the
progressive dieback of trees even during periods and on sites
favourable for plant growth. Therefore the involvement of potential
root pathogens was examined. Nematodes and Pythiilln spp. were
inconsistently isolated from rhizosphere soil and eucalypt roots and
may contribute to a root rot complex. Phytophthora cinnamomi which
was isolated infrequently from forest soils could not be isolated
from the fine roots of regrowth trees and is unlikely to be a major
factor in the dieback. However, a previously undescribed
Cylindrocarpon sp. was consistently isolated from diseased fine
roots of regrowth trees and was confirmed to be pathogenic on E.
obliqua seedlings. Consequently detailed studies were conducted on
the role of the Cylindrocar:e_on sp. in the infection and decay of E.
obliqua roots and in the causation of the dieback complex. The population and activity of Cylindrocarpon sp. increased in soils
from E. obliqua forest from low levels following burning to a
maximum in 70-90 year old forests. This closely parallels the
intensification of dieback in these forests. The Cylinjrocarpon sp.
appeared to be natural in these ~. obliqua forests and was well
adapted for growth and survival in the conditions existing in the
regrowth forests.

Item Type: Thesis - Research Master
Authors/Creators:Jehne, Walter
Keywords: Eucalyptus obliqua, Fungal diseases of plants, Cylindrocarpon
Copyright Holders: The Author
Copyright Information:

Copyright 1982 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M. Ag. Sci.) - University of Tasmania, 1984. Biblography: l. 174-197

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