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Paleobotany of Australia and New Zealand conifers
Source:
Bibliographic web page at http://pole.botany.uq.edu.au/abstracts.html, Copyright © 1995 by Mike Pole.
All text below this point is quoted verbatim.
Pole, M. (1993). Keeping in touch: vegetation prehistory on both sides of the Tasman. Australian Systematic Botany 6:387-397.
At the end of the Cretaceous New Zealand broke away from the Australian-Antarctic continental mass and was physically isolated by the Tasman Sea. Early in the Tertiary New Zealand moved a long way north relative to Australia, but with the rapid northward movement of Australia, starting in the Eocene, Australia overtook New Zealand, so that much of the South Island of New Zealand now lies south of Tasmania. The northward and relative movements of the two blocks provide an interesting framework for comparing the development of their vegetation.
In the Late Cretaceous New Zealand and Australia were physically attached and shared a flora dominated by podocarp and araucarian conifers and deciduous angiosperms, consistent with growth in a polar latitude with periods of winter darkness.
When New Zealand broke away and moved north, a typically evergreen angiosperm-dominated flora developed. This showed similarities to the extant and fossil flora of the Australian mainland. To the south, Tasmania developed a quite distinct flora often dominated by conifers.
In the early-mid Miocene, when New Zealand lay at the same latitude as south eastern Australia, a change from Nothofagus dominated rainforest to, at times, drier vegetation including wet sclerophyll with Eucalyptus, occurred in both regions. This may record the roughly synchronous effects of more northerly tracking Sub Tropical High Pressure systems.
In the Late Miocene/Pliocene there was a return to Nothofagus-podocarp dominance in both Australia and New Zealand.
Today, the conifer dominated communities of Tasmania have largely retreated to montane regions where they form dwarf shrublands, and have disappeared from the Australian mainland. In New Zealand the situation has quite reversed from that of much of the Tertiary, and conifers now form a prominent part of many rainforest communities.
The evidence suggests Australia and New Zealand can be thought of as a single biogeographic entity, with the vegetation in both landmasses responding principally to climate change, with relatively free exchange, at least in one direction, of plants, rather than evolving in isolation since Late Cretaceous oceanic rifting.
Pole, M. S. (1992). Early Miocene flora of the Manuherikia Group, New Zealand. 2. Conifers. Journal of the Royal Society of New Zealand 22, 287-302.
Remains of six conifer taxa are described from early Miocene sediments of the Manuherikia Group, New Zealand. Two of these are new, Retrophyllum vulcanense sp. nov. and Podocarpus alwyniae sp. nov.. The others are Araucaria sp. sect. Eutacta, present as impressions of vegetative shoots and isolated ovuliferous cone scales, shoots of Dacrycarpus dacrydioides (A. Rich.) de Laubenf., a single impression of a Phyllocladus sp. phylloclade, and an impression of an unidentified shoot. This is the first record of the genus Retrophyllum from New Zealand.
Pole, M. S. (1992). Early Miocene flora of the Manuherikia Group, New Zealand. 3. Possible cycad. Journal of the Royal Society of New Zealand 22, 303-306.
Hill, R. S., and Pole, M. S. (1992). Leaf and Shoot Morphology of Extant Afrocarpus, Nageia and Retrophyllum (Podocarpaceae) Species, and Species with similar Leaf Arrangement from Tertiary sediments in Australasia. Australian Systematic Botany
Pole, M. S. (1993). Miocene broad-leaved Podocarpus from Foulden Hills, New Zealand. Alcheringa 17, 173-177.
Pole, M. S., Hill, R. S., Green, N., and Macphail, M. K. (1993). The Oligocene Berwick Quarry flora - rainforest in a drying environment. Australian Systematic Botany 6, 399-427.
The Late Oligocene to possibly earliest Early Miocene Berwick Quarry macrofossil flora was first described very early in this century by Henry Deane, but has since been largely ignored. Recent work at the quarry has led to major new collections and a reinvestigation of the flora.
Seventeen taxa of macrofossils have been recovered, including Agathis, Dacrycarpus, four species of Lauraceae, Gymnostoma, Nothofagus, Eucalyptus, an indeterminate Myrtaceae and Proteaceae, three possible Cunoniaceae, and six unidentified taxa.
The Berwick Quarry flora contains species which are consistent with rainforest in the region, however, the flora is also notable for the presence of leaves of Eucalyptus, leaving little doubt that the flora at Berwick Quarry represents a mixture of rainforest and open forest taxa. The vegetation was probably a mosaic of open and closed forest, representing some of the earliest evidence for seasonality in Australia during the development of the modern flora.
Pole, M. S. (1993). Early Miocene flora of the Manuherikia Group, New Zealand. 10. Paleoecology and stratigraphy. Journal of the Royal Society of New Zealand 23, 393-426.
A stratigraphic sequence of vegetation is recognised from macrofossil assemblages in Lower-Mid Miocene fluvial-lacustrine sediments of the Manuherikia Group, New Zealand. Temperature, water-level, drainage, fire and rainfall were probably the factors that divided the distribution of plant taxa in to several distinct communities. These communities are compared with structural vegetation types presently recognised in eastern Australia, including notophyll vine forest (sometimes with podocarp conifers), microphyll forest, araucarian notophyll vine forest, tall open-forest (at times probably closed forest with sclerophyll emergents), notophyll feather palm vine forest, and fern fields.
The earliest assemblage in the Cromwell region represents Nothofagus forest (microphyll fern forest or microphyll vine forest), or at least a forest in which Nothofagus was probably an important element. Rainfall was high, but the associated presence of Allocasuarina indicates forest edge conditions, or perhaps disturbance by fire, which removed the canopy long enough for this genus to have a temporary advantage. Temperature may have been cooler than that required for subtropical rainforest, or alternatively, soil nutrients may have been low.
The succeeding Araucarian zone may indicate lower rainfall (and perhaps warmer conditions than when Nothofagus dominated the vegetation), allowing the araucarians to compete with the rainforest trees and the Allocasuarina to persist, but not low enough to result in a high frequency of fires. Vegetation was araucarian notophyll vine forest.
The Eucalyptus zone suggests that rainfall continued to fall to the point at which the frequency of fires rose to at least once every 350 years, and a tall-open forest developed. The part of this zone in which Allocasuarina was absent may represent the peak frequency of fires, which were detrimental to Allocasuarina.
A dramatic increase in rainfall and possibly soil-nutrients seems to have eliminated fire and caused the local replacement of Eucalyptus and Allocasuarina by a podocarp notophyll evergreen vine forest, including Elaeocarpaceae, Lauraceae, Myrtaceae, Podocarpaceae and, in areas of impeded drainage, palms.
A return to drier conditions, or a large fire, heralded the regrowth of Eucalyptus - Allocasuarina woodland or open forest.
Rainforest conditions are probably represented in the highest part of the sequence. At various times there were wide expanses of raised peat bog with a generally treeless cover. Climate was mesothermic.
Pole, M. S. (1995). Late Cretaceous macrofloras of Eastern Otago, New Zealand: Gymnosperms. Australian Systematic Botany 8, 1067-1106.
Six new coniferous fossils are described from the Late Cretaceous of eastern Otago, New Zealand. These include two new species of Araucaria, A. desmondii, for which a new section, Perpendicula is erected, and A. taieriensis. Syntypes of Dammara oweni Ett. and D. uninervis Ett. are illustrated and concluded to be a single species of Araucaria, A. oweni. The diagnosis of Araucarioides Bigwood and Hill is emended and a new species, A. falcata (the first record of this genus from New Zealand) is described. Podozamites taenioides Cantrill is also placed into Araucarioides. Two new genera and species of Podocarpaceae are described, Kaia minuta and Katikia inordinata. A new genus and species, Otakauia lanceolata, is described and placed in the Taxodiaceae. The type specimen of Sequoia novae-zeelandiae Ett. (Taxodiaceae) is re-examined and its cuticle described for the first time. Its identity is confirmed, but it is placed in Sequoiadendron which follows a more recent nomenclatural change involving extant species. A range of more poorly preserved conifer material is illustrated.
The original vegetation grew in near-polar latitudes and would have experienced long periods of winter-darkness.
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