332
M.J. Brown and J. Read
through toxic waste production, including SOz emissions from smelters
and downstream deposits of toxic sediments on riparian vegetation (e.g. ,
Kirkpatrick, 1977). Much of the rainforests of western Tasmania are
situated on highly prospective rocks, which can contain for example
copper, gold, silver, lead , zinc, and iron, and the pressure for exploration
and mining is continuing, albeit with modern techniques which are much
more environmentally benign.
Fire
Anthropogenic fire is a major threat to Tasmanian rainforest; as it is also
in South America (Veblen and Alaback, Chapter 9). Kirkpatrick and
Dickinson (1984) report that 8% of the total area of lowland rainforest in
the state has been burned since 1950. If attrition at this rate was uniformly
spread, then an area of rainforest could burn on average every 500 years .
There are some areas of Nothofagus forest in northwestern Tasmania
where this frequency may be realistic, but there have been devastating
fires in the conifer communities at rates which clearly do not conform to a
"natural" cycle. For example Brown (1988) found that about 30% of
King Billy pine (Athrotaxis selaginoides) stands had been fire killed in the
last 100 years. Given that most of these stands contained individuals 800
to 1000 years old , such an attrition rate is clearly not part of a natural fire
cycle. Similarly Cullen and Kirkpatrick (1990b) report that one third of
the area which supported pencil pines (Athrotaxis cupressoides) has been
burnt since 1960. The pencil pines reach ages of 900 to 1300 years
(Ogden, 1978), so that such rates again are clearly unsustainable. The
rainforest conifers Athrotaxis spp . and Lagarostrobos and Nothofagus
gunnii are all extremely fire sensitive and lack mechanisms for recovery
from even mild fires. This sensitivity appears to contrast with the South
American conifer , Fitzroya cupressoides, which does regenerate following
light (but not intense) fires (Veblen & Ashton , 1982). Athrotaxis spp. and
Lagarostrobos are mast-year seeders and rely almost totally on seed
regeneration from marginal unburnt stems for recovery after fire even
though they exhibit vegetative spread in undisturbed forests (Gibson &
Brown, 1991; Shapcott, 1991; Cullen & Kirkpatrick,1990a,b). Other
dominant and subdominant rainforest elements can recover after fire,
both from seed and from vegetative sprouts (Barker, 1991). If there are
no further fires; the rainforest canopy is eventually restored, but there is a
relatively high probability of reburn in areas of easy access, especially in
the first 20 years after fire (Jackson , 1968; Kirkpatrick, 1977; Hill &
Read, 1984; Barker, 1991). Repeated fires eventually removed even the
resistant rainforest species (Ellis , 1985; Podger et aI., 1988).
Diseases , Weeds, and Pests
There are several fungal pathogens which cause disease in Tasmanian wet
forests. Eucalyptus obliqua and E. regnans dominate mixed forests in a
number of humid and fog-prone valleys in northwestern Tasmania. These
M.J. Brown and J. Read
through toxic waste production, including SOz emissions from smelters
and downstream deposits of toxic sediments on riparian vegetation (e.g. ,
Kirkpatrick, 1977). Much of the rainforests of western Tasmania are
situated on highly prospective rocks, which can contain for example
copper, gold, silver, lead , zinc, and iron, and the pressure for exploration
and mining is continuing, albeit with modern techniques which are much
more environmentally benign.
Fire
Anthropogenic fire is a major threat to Tasmanian rainforest; as it is also
in South America (Veblen and Alaback, Chapter 9). Kirkpatrick and
Dickinson (1984) report that 8% of the total area of lowland rainforest in
the state has been burned since 1950. If attrition at this rate was uniformly
spread, then an area of rainforest could burn on average every 500 years .
There are some areas of Nothofagus forest in northwestern Tasmania
where this frequency may be realistic, but there have been devastating
fires in the conifer communities at rates which clearly do not conform to a
"natural" cycle. For example Brown (1988) found that about 30% of
King Billy pine (Athrotaxis selaginoides) stands had been fire killed in the
last 100 years. Given that most of these stands contained individuals 800
to 1000 years old , such an attrition rate is clearly not part of a natural fire
cycle. Similarly Cullen and Kirkpatrick (1990b) report that one third of
the area which supported pencil pines (Athrotaxis cupressoides) has been
burnt since 1960. The pencil pines reach ages of 900 to 1300 years
(Ogden, 1978), so that such rates again are clearly unsustainable. The
rainforest conifers Athrotaxis spp . and Lagarostrobos and Nothofagus
gunnii are all extremely fire sensitive and lack mechanisms for recovery
from even mild fires. This sensitivity appears to contrast with the South
American conifer , Fitzroya cupressoides, which does regenerate following
light (but not intense) fires (Veblen & Ashton , 1982). Athrotaxis spp. and
Lagarostrobos are mast-year seeders and rely almost totally on seed
regeneration from marginal unburnt stems for recovery after fire even
though they exhibit vegetative spread in undisturbed forests (Gibson &
Brown, 1991; Shapcott, 1991; Cullen & Kirkpatrick,1990a,b). Other
dominant and subdominant rainforest elements can recover after fire,
both from seed and from vegetative sprouts (Barker, 1991). If there are
no further fires; the rainforest canopy is eventually restored, but there is a
relatively high probability of reburn in areas of easy access, especially in
the first 20 years after fire (Jackson , 1968; Kirkpatrick, 1977; Hill &
Read, 1984; Barker, 1991). Repeated fires eventually removed even the
resistant rainforest species (Ellis , 1985; Podger et aI., 1988).
Diseases , Weeds, and Pests
There are several fungal pathogens which cause disease in Tasmanian wet
forests. Eucalyptus obliqua and E. regnans dominate mixed forests in a
number of humid and fog-prone valleys in northwestern Tasmania. These