16. A Comparison of the Ecology and Conservation Management
323
(J . Hickey, personal communication). The mixed forests are estimated at
113,000 ha and a further 47,000 ha of " pur e" rainforest contains eucalypts
at less than 5% cover (Hickey & Savva, 1992).
History
The fossil history of cool temperate rainforests in Tasmania is summarized
here from Hill (1990a). There appears to have been a progressive floristic
simplification since the Tertiary. Following the break up of Gondwana,
the climatic changes of the Tertiary included a decline lit, but increased
variability of, temperatures, and decreased rainfall and humidity, with
increased seasonability. The rainforest fossil record indicates that species
have undergone only limited evolutionary change since then. They appear
to have suffered from a lack of migratory routes from which to replenish
the vegetation. The Early Eocene flora has a high species richness , but
Eucryphia is the only recognizable modern high-latitude taxon present.
Later Eocene sites indicate complex forest containing some taxa which
have modern high-latitude cool temperate affinities. Oligocene deposits
again exhibit high species diversities; and include mixtures of species with
affinities to modern species from temperate high latitudes and equatorial
high altitudes (Hill, 1990b). They include the Tasmanian genera Lagarostrobos, Microstrobos , Phyllocladus, A throtaxis, Nothofagus subgenus
Menziesospora , and genera such as Nothofagus subgenus Fuscaspora and
subgenus Nothofagus, Dacrycarpus, and Araucaria sect. Columbea, which
are now absent from Tasmania, but are found in South America or New
Zealand (Hill, 1990a,b; Wells & Hill, 1989). In a review of the evidence
for extensive past distributions of Gondwanan floral elements in the
Tertiary, Hill and Carpenter (1991) identify at least six Australian fossils
with extant relatives only in South America and a further six South
American fossils with modern analogs in Australia. There is a gap in the
rainforest fossil record until the later Pliocene to early Pleistocene. Fossil
rainforest deposits from this period provide evidence of an essentially
modern rainforest vegetation (Hill & Macphail, 1985), and it appears that
the current floristic composition and richness were reached prior to the
Quaternary glaciations (Hill, 1990a). During the Quaternary, these forests
appear to have retreated and expanded in response to glacial and interglacial cooling and warming. The exact number and timing of glaciations
is uncertain, but at least three and possibly six have been postulated
(Kiernan and Hannan, 1991; Colhoun & Fitzsimmons, 1990; Keirnan,
1989). Macphail (1979) has documented the palynological evidence for
advances and contractions of forest during the Holocene, however interpretation of climatic influences on the vegetation is confounded by possible
anthropogenic fire-caused changes. The Tasmanian Aborigines have been
present for at least 20,000 to 30,000 years (Kiernan, Jones, & Ranson,
1984; Cosgrove, 1989) and evidence of their burning of the vegetation is
documented in the vegetation itself (e.g., Bowman & Brown, 1986), as
323
(J . Hickey, personal communication). The mixed forests are estimated at
113,000 ha and a further 47,000 ha of " pur e" rainforest contains eucalypts
at less than 5% cover (Hickey & Savva, 1992).
History
The fossil history of cool temperate rainforests in Tasmania is summarized
here from Hill (1990a). There appears to have been a progressive floristic
simplification since the Tertiary. Following the break up of Gondwana,
the climatic changes of the Tertiary included a decline lit, but increased
variability of, temperatures, and decreased rainfall and humidity, with
increased seasonability. The rainforest fossil record indicates that species
have undergone only limited evolutionary change since then. They appear
to have suffered from a lack of migratory routes from which to replenish
the vegetation. The Early Eocene flora has a high species richness , but
Eucryphia is the only recognizable modern high-latitude taxon present.
Later Eocene sites indicate complex forest containing some taxa which
have modern high-latitude cool temperate affinities. Oligocene deposits
again exhibit high species diversities; and include mixtures of species with
affinities to modern species from temperate high latitudes and equatorial
high altitudes (Hill, 1990b). They include the Tasmanian genera Lagarostrobos, Microstrobos , Phyllocladus, A throtaxis, Nothofagus subgenus
Menziesospora , and genera such as Nothofagus subgenus Fuscaspora and
subgenus Nothofagus, Dacrycarpus, and Araucaria sect. Columbea, which
are now absent from Tasmania, but are found in South America or New
Zealand (Hill, 1990a,b; Wells & Hill, 1989). In a review of the evidence
for extensive past distributions of Gondwanan floral elements in the
Tertiary, Hill and Carpenter (1991) identify at least six Australian fossils
with extant relatives only in South America and a further six South
American fossils with modern analogs in Australia. There is a gap in the
rainforest fossil record until the later Pliocene to early Pleistocene. Fossil
rainforest deposits from this period provide evidence of an essentially
modern rainforest vegetation (Hill & Macphail, 1985), and it appears that
the current floristic composition and richness were reached prior to the
Quaternary glaciations (Hill, 1990a). During the Quaternary, these forests
appear to have retreated and expanded in response to glacial and interglacial cooling and warming. The exact number and timing of glaciations
is uncertain, but at least three and possibly six have been postulated
(Kiernan and Hannan, 1991; Colhoun & Fitzsimmons, 1990; Keirnan,
1989). Macphail (1979) has documented the palynological evidence for
advances and contractions of forest during the Holocene, however interpretation of climatic influences on the vegetation is confounded by possible
anthropogenic fire-caused changes. The Tasmanian Aborigines have been
present for at least 20,000 to 30,000 years (Kiernan, Jones, & Ranson,
1984; Cosgrove, 1989) and evidence of their burning of the vegetation is
documented in the vegetation itself (e.g., Bowman & Brown, 1986), as