322
M.J . Brown and J. Read
Definition and Extent
Tasmania lies at 39.5 to 43S S and rainforest is found within areas where
mean annual rainfall ranges from 1300 mm to 3500 mm and mean annual
temperatures from 5 to l2°C (Gibson , Brown, & Davies , 1991). Thus the
forests fall within the perhumid category as outlined by Veblen and
Alaback (see Chapter 9). The climate is distinctly seasonal with cold
winters and uniform to winter-dominated rainfall (Read, in press). In
drier areas, the rainforests are found primarily in riverine gullies, southeast slopes, and at higher altitudes in cloud-forests where the annual
rainfall is augmented by stripping of moisture from cloud and fog. The
effective summer monthly rainfall in such areas is at least 40mm (Jackson,
1983), and the forests must have some topographic protection from fire.
In common with the rainforests of South America, those in Tasmania
are dominated by a mixture of broadleaved trees and conifers. Cool
temperate rainforests in Tasmania are characterized as forests with trees
greater than 8 m in height dominated by species of Nothofagus, Atherosperma , Eucryphia, and/or the conifers Athrotaxis (the only extant
southern hemisphere representatives of the Taxodiaceae) , Lagarostrobos,
Phyllocladus (both Podocarpaceae) , and Diselma (Cupressaceae) , and
with the ability to regenerate in the absence of broad-scale disturbance
such as wildfire (Jarman & Brown , 1983). In common with Chile, the
genus Nothofagus, particularly the evergreen N . cunninghamii , is almost
ubiquitous in the forests. The vegetation intergrades at high altitudes with
subalpine and alpine vegetation. At low altitudes on very poorly drained
sites the rainforests intergrade with swamp forests which are often
dominated by blackwood (Acacia melanoxylon). Over most of their range
in the lowlands, the rainforests are the end point of a fire-determined
succession from wet eucalypt forests or mixed forest (Gilbert, 1959;
Ashton, 1981a,b) . The wet eucalypt forests contain giant Eucalyptus
stems, which can be more than 100m tall (Ashton , 1981b) over an
understory of either broad-leaf sclerophyll trees or a closed canopy of
rainforest trees. Such forests are unique to Australia (Ashton, 1981b) and
can be viewed either as mature eucalypt forest or as developing rainforests
(Jarman & Brown, 1983). Following fire in the mixed forest there is
abundant regeneration of eucalypts and a broad-leaf wet sclerophyll
understorey which is replaced subsequently (after about 80 to 100 years
without fire), by rainforest species. The eucalypts are self-thinning and in
old mixed forest stands are few and scattered. The continuum in eucalypt
stocking from dense to sparse makes practical demarcation between rainforest and mixed forest very difficult. The Forestry Commission in
Tasmania currently adopts a 5% eucalypt crown cover as the practical
limit to eucalypt forest.
The total area of rainforest in Tasmania has been estimated at
765,000ha (Brown & Hickey, 1990), but recent estimates indicate that
the Nothofagus-dominated component may be about 600,000 ha. The
largest continuous patch is in the north west and has an area of 65,000 ha
M.J . Brown and J. Read
Definition and Extent
Tasmania lies at 39.5 to 43S S and rainforest is found within areas where
mean annual rainfall ranges from 1300 mm to 3500 mm and mean annual
temperatures from 5 to l2°C (Gibson , Brown, & Davies , 1991). Thus the
forests fall within the perhumid category as outlined by Veblen and
Alaback (see Chapter 9). The climate is distinctly seasonal with cold
winters and uniform to winter-dominated rainfall (Read, in press). In
drier areas, the rainforests are found primarily in riverine gullies, southeast slopes, and at higher altitudes in cloud-forests where the annual
rainfall is augmented by stripping of moisture from cloud and fog. The
effective summer monthly rainfall in such areas is at least 40mm (Jackson,
1983), and the forests must have some topographic protection from fire.
In common with the rainforests of South America, those in Tasmania
are dominated by a mixture of broadleaved trees and conifers. Cool
temperate rainforests in Tasmania are characterized as forests with trees
greater than 8 m in height dominated by species of Nothofagus, Atherosperma , Eucryphia, and/or the conifers Athrotaxis (the only extant
southern hemisphere representatives of the Taxodiaceae) , Lagarostrobos,
Phyllocladus (both Podocarpaceae) , and Diselma (Cupressaceae) , and
with the ability to regenerate in the absence of broad-scale disturbance
such as wildfire (Jarman & Brown , 1983). In common with Chile, the
genus Nothofagus, particularly the evergreen N . cunninghamii , is almost
ubiquitous in the forests. The vegetation intergrades at high altitudes with
subalpine and alpine vegetation. At low altitudes on very poorly drained
sites the rainforests intergrade with swamp forests which are often
dominated by blackwood (Acacia melanoxylon). Over most of their range
in the lowlands, the rainforests are the end point of a fire-determined
succession from wet eucalypt forests or mixed forest (Gilbert, 1959;
Ashton, 1981a,b) . The wet eucalypt forests contain giant Eucalyptus
stems, which can be more than 100m tall (Ashton , 1981b) over an
understory of either broad-leaf sclerophyll trees or a closed canopy of
rainforest trees. Such forests are unique to Australia (Ashton, 1981b) and
can be viewed either as mature eucalypt forest or as developing rainforests
(Jarman & Brown, 1983). Following fire in the mixed forest there is
abundant regeneration of eucalypts and a broad-leaf wet sclerophyll
understorey which is replaced subsequently (after about 80 to 100 years
without fire), by rainforest species. The eucalypts are self-thinning and in
old mixed forest stands are few and scattered. The continuum in eucalypt
stocking from dense to sparse makes practical demarcation between rainforest and mixed forest very difficult. The Forestry Commission in
Tasmania currently adopts a 5% eucalypt crown cover as the practical
limit to eucalypt forest.
The total area of rainforest in Tasmania has been estimated at
765,000ha (Brown & Hickey, 1990), but recent estimates indicate that
the Nothofagus-dominated component may be about 600,000 ha. The
largest continuous patch is in the north west and has an area of 65,000 ha