Geoff Hope

Neogene paleoenvironmental and paleoclimatic change in southern temperate ecosystems — a southern perspective

Recently, a greatly increased number of macrofossil and pollen analytical records from Australasia and southern South America has permitted, for the first time, a comprehensive overview of past vegetation and climate change in southern temperate ecosystems. While the course of Neogene climatic change has been comparable to that of the temperate northern hemisphere, a distinctive southern hemisphere vegetation has evolved, not primarily because of its common Gondwana origin, but as a consequence of the minor amplitude of Quaternary change, absence of large ice sheets, and failure of full-glacial environments to persist through interglacials.

Environmental change in the Baliem Valley,* montane Irian Jaya, Republic of Indonesia

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Tropical vegetational change in the late Pleistocene of New Caledonia

The south eastern plateau of New Caledonia (22°S) preserves remnants of a deep regolith of ultramafic soils which is extensively gullied or eroded to form large alluvial fans. Dated sediments from four closed basins on the Plaine des Lacs (ca. 220 m altitude) show that organic muds were accumulating prior to 30,000 yr B.P. Over the next 5000–14,000 years limonitic clays infilled two basins as a result of slope instability in their catchment. Resistant laterite and bog iron surfaces became exposed during the period 30,000–15,000 yr B.P. by erosional events that seem to have been of greater magnitude than any in the earlier Pleistocene. Two sites, Lake Emeric and Lake Suprin, were chosen for pollen analysis. During the phases of organic deposition of these lakes, Nothofagus forests collapsed several times and were replaced by Gymnostoma maquis, apparently as a result of fires. These Pleistocene fires were associated with some inorganic deposition, presumably due to the substantial loss of primary forest cover. Regeneration of forest usually followed after an estimated gap of several centuries. Thus, fire was able to cause forest retreats of the same order of magnitude as that caused by massive fires today. The low nutritional status of the soils or lateritic crusts means that, as now, forest had difficulty reclaiming sites. Human activity is unknown prior to 3000 years ago, so the major erosion is presumed to have had natural causes. Thus, many of the wide-ranging changes are the result of natural instability in the sub-tropics, and some may be much older than hitherto thought. Climate change towards periods of dry, fire-prone, conditions may have been an underlying cause. In the Holocene, some climatic factor, possibly cyclonic storms, seems to prevent organic sedimentation. Switching from cyclone-free to cyclone-prone at the end of the Pleistocene may reflect temperature change in sea surfaces in the region.

Pollen morphology of the Myrtaceae. Part 1: tribes Eucalypteae, Lophostemoneae, Syncarpieae, Xanthostemoneae and subfamily Psiloxyloideae

A family-wide palynological study of Myrtaceae was conducted using scanning electron microscopy (SEM) and light microscopy (LM). In this part of the study, the pollen morphology of 18 genera and 150 species from the Myrtaceae tribes of subfamily Myrtoideae, Eucalypteae, Lophostemoneae, Syncarpieae, Xanthostemoneae and subfamily Psiloxyloideae are presented. It was found that the most commonly observed pollen in these groups was parasyncolpate with a rugulate exine, whereas some species possessed an apocolpial island. The large, and sometimes syndemicolpate, pollen of Eucalypteae genera Angophora and Corymbia differed from all other genera. Most Eucalyptus pollen had endopores with a thickened exine.

Pollen morphology of the Myrtaceae. Part 4: tribes Kanieae, Myrteae and Tristanieae

Pollen morphology of 44 genera and 101 species from the Myrtaceae tribes Kanieae, Myrteae and Tristanieae was surveyed using scanning electron microscopy (SEM) and light microscopy (LM). Most Myrteae pollen were brevicolpate and granulate, which is unique within Myrtaceae, and these are most likely ancestral characters for this tribe. Two main pollen types were observed in tribe Kanieae, one form being with syncolpate colpi and a distinctive granulate exine, and the other with parasyncolpate colpi and a less ornamented exine. Genera Tristania and Thaleropia of tribe Tristanieae produce the smallest pollen in Myrtaceae, whereas Octamyrtus of tribe Myrteae produces the largest pollen observed in Myrtaceae.

Pollen morphology of the Myrtaceae. Part 3: Tribes Chamelaucieae, Leptospermeae and Lindsayomyrteae

The pollen morphology of 36 genera and 147 species from the Myrtaceae tribes Chamelaucieae, Leptospermeae and Lindsayomyrteae was surveyed using scanning electron microscopy (SEM) and light microscopy (LM). Syncolpate pollen were observed in all genera of Leptospermeae and some genera of Chamelaucieae. Genera of tribe Chamelaucieae displayed five distinct colpal morphologies, which makes it the tribe with the most diverse pollen in Myrtaceae. Six genera of Chamelaucieae, including Actinodium, Chamelaucium, Darwinia, Homoranthus, Pileanthus and Verticordia, produce large acolpate pollen not observed in any other Myrtaceae. Two of these genera produce distinct pollen; Actinodium is the only genus to have prolate-spheroidal shaped pollen, and Pileanthus pollen is large and dicolporate. A number of anomalous aperture types occurred in species of Chamelaucieae, including monocolporate (Homoranthus thomasii), pentacolporate (Calytrix oldfieldii) and hexacolporate (Sannantha tozerensis). Pollen of Lindsayomyrteae appeared similar to those of Leptospermeae and Chamelaucieae, and on the basis of pollen features, could be related to these two tribes.

Pollen morphology of the Myrtaceae. Part 2: tribes Backhousieae, Melaleuceae, Metrosidereae, Osbornieae and Syzygieae

Pollen morphology of 16 genera and 101 species from the Myrtaceae tribes Backhousieae, Melaleuceae, Metrosidereae, Osbornieae and Syzygieae was surveyed using scanning electron microscopy (SEM) and light microscopy (LM). The most common pollen type observed in these tribes was parasyncolpate with arcuate or angular colpi, and a rugulate exine pattern. There was little size variation in observed pollen, except for larger pollen in tribe Melaleuceae. All Metrosideros pollen grains had apocolpial islands, as well as all Callistemon species viewed by LM. Choricarpia of tribe Backhousieae had pollen with a distinctive exine pattern. Dicolporate pollen were observed in two tribes, Metrosidereae (Tepualia) and Syzygieae (Acmena), and may be of systematic value. The dicolporate grains of these two genera were also easily distinguishable from each other by using size and pollen side shape as diagnostic characters. Two pollen types were observed within the genus Melaleuca, and a number of pollen types were observed within the species-rich genus Syzygium.

Land-sea correlations in the Australian region: 460 ka of changes recorded in a deep-sea core offshore Tasmania. Part 1: the pollen record

Abstract Long, well-dated records of climate change in Australia are rare because most of the continent is prone to deflation and sediments are difficult to date beyond 40 ka. Deep-sea cores, containing terrigenous material, provide an ideal alternative to terrestrial records, because of continuous sedimentation and a robust chronology derived from oxygen isotopes. In this paper, the first of a series of two, we present pollen and spores data from core Fr1/94-GC3 from the East Tasman Plateau. This core is positioned at the southern extreme of the East Australia Current and simultaneously records changes in both oceanography and environments both offshore and in southeastern Australia. In an area of slow sedimentation, this core provides a continuous record of vegetation change in southeastern Australia and the southern Tasman Sea over approximately the last half a million years. Through time, glacial periods have progressively become warmer and shorter. Alpine plant taxa become more restricted with time and rainforest taxa expand to a far more restricted degree during the present interglacial period than the previous one, representing a fundamental shift in the vegetation of Tasmania. We apply transfer functions to reconstruct past rainfall and land temperatures based on the palynoflora that are then compared against the marine proxy record.