16. A Comparison of the Ecology and Conservation Management
329
Dynamics of the Rainforest Dominants
All three of the dominant angiosperms in lowland rainforest are capable
of continuous regeneration with self-replacement (Read & Hill, 1988).
The order of dominance of these species is not simply a function of their
relative shade tolerance as found in the temperate Nothofagus forests of
South America (Veblen et al., 1981, 1983) and New Zealand (Wardle ,
1984). Nothofagus cunninghamii and Eucryphia lucida are less shade
tolerant than Atherosperma (Read 1985;Read & Hill, 1985, 1988), yet
Atherosperma is subdominant in the forests in which it cooccurs with
Nothofagus. Both Nothofagus and Eucryphia regenerate continuously in
communities containing Atherosperma both by root and basal stem suckers
and from seed in canopy gaps. Atherosperma regenerates mainly from
basal stem suckers and has a very limited germinative capacity (Hickey,
Blakesley & Turnesr, 1983), because there is a high proportion of
malformed seed. The rate of seedling establishment is low due to high
browsing pressure from native herbivores. Individual stems of Atherosperma do not exhibit the height-growth potential of Nothofagus nor are
they as long-lived. Thus the species is usually codominant or subdominant
to Nothofagus. In rainforest gullies surrounded by eucalypt forest in the
drier outlying patches in eastern Tasmania, Atherosperma is the sole
dominant. In these situations dominance is achieved because Atherosperma can disperse more readily than Nothofagus and can occupy sites
where fires are more frequent. Nothofagus cunninghamii is able to
regenerate in the absence of large-scale disturbance on optimal sites
because there are no other more shade-tolerant species able to compete
effectively in canopy gaps (Read & Hill, 1985, 1988). Such gap replacement is a feature also of Nothofagus in high-altitude forests in New
Zealand and Chile, and at high latitudes in Child (e.g., June & Ogden,
1978; Veblen, Donoso, Schlegel, & Escobar, 1981). However , continuous
regeneration of Nothofagus is less frequent in the forests with higher
species richness that occur on optimal sites in Chile and New Zealand
(e.g., Veblen et al., 1981; Wardle, 1983, 1984). In such situations, Nothofagus may be maintained by infrequent catastrophic disturbances, such as
vulcanism, landslides, and wind throw.
The Tasmanian endemic Nothofagus gunnii is the only winter-(cold)
deciduous species native to Australia. It is found mostly above 800m, but
extends down to 550m above sea level (Robertson & Duncan, 1991). It
occurs as codominant with Athrotaxis selaginoides , Nothofagus cunninghamii, and Phyllocladus aspleniifolius in closed implicate rainforests
(Jarman et al., 1984; Read & Hill, 1988). The populations in closed
forests suggest episodic regeneration, consistent with the high-light compensation point and high dark rate of respiration of the species (Read &
Hill, 1985, 1988). In upland exposed situations, the species has a competitive advantage conferred by its high cold tolerance and its deciduous habit,
but even in relatively open implicate forests, the species sometimes shows
skewed-normal rather than the usual reverse-J size class distributions.
329
Dynamics of the Rainforest Dominants
All three of the dominant angiosperms in lowland rainforest are capable
of continuous regeneration with self-replacement (Read & Hill, 1988).
The order of dominance of these species is not simply a function of their
relative shade tolerance as found in the temperate Nothofagus forests of
South America (Veblen et al., 1981, 1983) and New Zealand (Wardle ,
1984). Nothofagus cunninghamii and Eucryphia lucida are less shade
tolerant than Atherosperma (Read 1985;Read & Hill, 1985, 1988), yet
Atherosperma is subdominant in the forests in which it cooccurs with
Nothofagus. Both Nothofagus and Eucryphia regenerate continuously in
communities containing Atherosperma both by root and basal stem suckers
and from seed in canopy gaps. Atherosperma regenerates mainly from
basal stem suckers and has a very limited germinative capacity (Hickey,
Blakesley & Turnesr, 1983), because there is a high proportion of
malformed seed. The rate of seedling establishment is low due to high
browsing pressure from native herbivores. Individual stems of Atherosperma do not exhibit the height-growth potential of Nothofagus nor are
they as long-lived. Thus the species is usually codominant or subdominant
to Nothofagus. In rainforest gullies surrounded by eucalypt forest in the
drier outlying patches in eastern Tasmania, Atherosperma is the sole
dominant. In these situations dominance is achieved because Atherosperma can disperse more readily than Nothofagus and can occupy sites
where fires are more frequent. Nothofagus cunninghamii is able to
regenerate in the absence of large-scale disturbance on optimal sites
because there are no other more shade-tolerant species able to compete
effectively in canopy gaps (Read & Hill, 1985, 1988). Such gap replacement is a feature also of Nothofagus in high-altitude forests in New
Zealand and Chile, and at high latitudes in Child (e.g., June & Ogden,
1978; Veblen, Donoso, Schlegel, & Escobar, 1981). However , continuous
regeneration of Nothofagus is less frequent in the forests with higher
species richness that occur on optimal sites in Chile and New Zealand
(e.g., Veblen et al., 1981; Wardle, 1983, 1984). In such situations, Nothofagus may be maintained by infrequent catastrophic disturbances, such as
vulcanism, landslides, and wind throw.
The Tasmanian endemic Nothofagus gunnii is the only winter-(cold)
deciduous species native to Australia. It is found mostly above 800m, but
extends down to 550m above sea level (Robertson & Duncan, 1991). It
occurs as codominant with Athrotaxis selaginoides , Nothofagus cunninghamii, and Phyllocladus aspleniifolius in closed implicate rainforests
(Jarman et al., 1984; Read & Hill, 1988). The populations in closed
forests suggest episodic regeneration, consistent with the high-light compensation point and high dark rate of respiration of the species (Read &
Hill, 1985, 1988). In upland exposed situations, the species has a competitive advantage conferred by its high cold tolerance and its deciduous habit,
but even in relatively open implicate forests, the species sometimes shows
skewed-normal rather than the usual reverse-J size class distributions.