Janelle Stevenson

Predictability of biomass burning in response to climate changes

Climate is an important control on biomass burning, but the sensitivity of fire to changes in temperature and moisture balance has not been quantified. We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo- fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote-sensing observations of month-by-month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.

Predicting sheetwash and rill erosion over the Australian continent

Soil erosion is a major environmental issue in Australia. It reduces land productivity and has off-site effects of decreased water quality. Broad-scale spatially distributed soil erosion estimation is essential for prioritising erosion control programs and as a component of broader assessments of natural resource condition. This paper describes spatial modelling methods and results that predict sheetwash and rill erosion over the Australian continent using the revised universal soil loss equation (RUSLE) and spatial data layers for each of the contributing environmental factors. The RUSLE has been used before in this way but here we advance the quality of estimation. We use time series of remote sensing imagery and daily rainfall to incorporate the effects of seasonally varying cover and rainfall intensity, and use new digital maps of soil and terrain properties. The results are compared with a compilation of Australian erosion plot data, revealing an acceptable consistency between predictions and observations. The modelling results show that: (1) the northern part of Australia has greater erosion potential than the south; (2) erosion potential differs significantly between summer and winter; (3) the average erosion rate is 4.1 t/ha. year over the continent and about 2.9 x 10(9) tonnes of soil is moved annually which represents 3.9% of global soil erosion from 5% of world land area; and (4) the erosion rate has increased from 4 to 33 times on average for agricultural lands compared with most natural vegetated lands.

Terminal Pleistocene to mid-Holocene occupation and an early cremation burial at Ille Cave, Palawan, Philippines

Excavations at a cave site on the island of Palawan in the Philippines show occupation from c. 11000 BP. A fine assemblage of tools and faunal remains shows the reliance of hunter-foragers switching from deer to pig. In 9500-9000 BP, a human cremation burial in a container was emplaced, the earliest yet known in the region

A late Quaternary record of environmental change and human impact from New Caledonia

A late Quaternary vegetation record is presented from a lowland site on the leeward southwest coast of New Caledonia. Plum Swamp is a backswamp on the Plum River at around 10 m a.s.l., just within the ultramafic terrain that dominates the southern third of New Caledonia. Pollen analysis, charcoal analysis, radiocarbon dating and stratigraphic analysis are employed to reconstruct the vegetation and sedimentary history of the valley. The vegetation record commences at around 20,000 yr BP and shows that from this time up until the late Holocene the valley was forested. The greater representation of taxa more prevalent at higher altitudes during the late glacial suggests a response to cooling and an enrichment of the lowland forest with more montane elements. The late glacial transition between 14,000 and 9000 yr BP is a period of instability within the valley when vegetation is disturbed by fire. Forest recovers after this and there is increasing stability until the arrival of people in the late Holocene at around 3000 yr BP. The initial colonisers of New Caledonia had a profound effect upon the vegetation of the valley, converting the lowland forest to a stunted and species poor maquis on the ultramafic sediments and Melaleuca woodland on the non-ultramafic substrates. However, sedimentary processes are relatively unchanged during this time. Dramatic geomorphic change does occur in the catchment though, during the latter part of the 20th Century as a consequence of mining. q 2001 Elsevier Science B.V. All rights reserved.

Mid- to late Holocene landscape change and anthropogenic transformations on Mo'orea, Society Islands: A multi-proxy approach

Archaeology’s ability to generate long-term datasets of natural and human landscape change positions the discipline as an inter-disciplinary bridge between the social and natural sciences. Using a multi-proxy approach combining archaeological data with palaeoenvironmental indicators embedded in coastal sediments, we outline millennial timescales of lowland landscape evolution in the Society Islands. Geomorphic and cultural histories for four coastal zones on Mo‘orea are reconstructed based on stratigraphic records, sedimentology, pollen analysis, and radiocarbon determinations from mid- to late Holocene contexts. Prehuman records of the island’s flora and fauna are described utilizing landsnail, insect, and botanical data, providing a palaeo-backdrop for later anthropogenic change. Several environmental processes, including sea level change, island subsidence, and anthropogenic alterations, leading to changes in sedimentary budget have operated on Mo‘orea coastlines from c. 4600 to 200 BP. We document significant transformation of littoral and lowland zones which obscured earlier human activities and created significant changes in vegetation and other biota. Beginning as early as 440 BP (1416–1490 cal. ad), a major phase of sedimentary deposition commenced which can only be attributed to anthropogenic effects. At several sites, between 1.8 and 3.0 m of terrigenous sediments accumulated within a span of two to three centuries due to active slope erosion and deposition on the coastal flats. This phase correlates with the period of major inland expansion of Polynesian occupation and intensive agriculture on the island, indicated by the presence of charcoal throughout the sediments, including wood charcoal from several economically important tree species.

Seasonal distribution of pollen in the atmosphere of Darwin, tropical Australia: Preliminary results

Pollen loads in the atmosphere of Darwin, a city located in the wet‐dry tropics of Australia, have been monitored for the period March 2004 to November 2005 as part of a large research program looking at atmospheric particles and human health. Seven pollen types dominate the pollen spectrum, the herbaceous families of Poaceae (grasses) and Cyperaceae (sedges), as well as several native tree and shrub taxa, Acacia, Callitris, Casuarina, Arecaceae and Myrtaceae. The pollen loads were found to have a strong seasonal component associated with the alternating wet (November to March) and dry (April to October) seasons of the region. Seventy percent of the yearly pollen load is captured during the dry season, with the peak pollen period occurring at the onset of the dry season (April–May) when most grasses are in flower. The daily pollen concentration decreases as the dry season progresses, accompanied by a change in composition; fewer herbaceous but increasing woody taxa. Preliminary health outcomes reveal a positive association between hay fever, Poaceae and Acacia pollen, as well as a significant association between total fungal spore concentrations and asthma. The Darwin record contrasts significantly with surveys conducted in the subtropical and temperate cities of Australia where temperature as opposed to rainfall and the prevalence of northern hemisphere exotic tree species have a greater influence over the seasonality and composition of the pollen loads.

The palaeo-environmental history of Big Willum Swamp, Weipa: An environmental context for the archaeological record

Abstract The environmental history of Big Willum (Waandriipayn) Swamp and the surrounding landscape is reconstructed for the last 8000 years through the analysis of pollen, charcoal and mineral magnetics. The data provide a Holocene record of vegetation and fire in an area where few records exist. Swamp initiation at Big Willum began prior to 8000 cal. BP, with swamp–like conditions maintained until 2200 cal. BP, after which it became a permanent deep water body, reaching its present day extent between 600–400 cal. BP. From 7000–1200 cal. BP the surrounding woodland was essentially stable. Fire is present throughout the record, with only one period of pronounced burning outside of the historic period, at around 1000 cal. BP, leading to a slightly more open understorey/woodland. The hydrological change at 2200 cal. BP that led to Big Willum becoming a more permanent water body overlaps with the end of the most intensive period of shell mound formation and the commencement of earth mound building at nearby Wathayn. This is suggestive that change in, or diversification of, mound types may in part be linked to environmental transformations in the late Holocene. One possibility is that greater water security allowed for increasing and more permanent exploitation of inland locations.

Past and future global transformation of terrestrial ecosystems under climate change

Future predictions from paleoecology Terrestrial ecosystems will be transformed by current anthropogenic change, but the extent of this change remains a challenge to predict. Nolan et al. looked at documented vegetational and climatic changes at almost 600 sites worldwide since the last glacial maximum 21,000 years ago. From this, they determined vegetation responses to temperature changes of 4° to 7°C. They went on to estimate the extent of ecosystem changes under current similar (albeit more rapid) scenarios of warming. Without substantial mitigation efforts, terrestrial ecosystems are at risk of major transformation in composition and structure. Science, this issue p. 920 Global vegetation change since the Last Glacial Maximum is used as an indicator of transformation under warming scenarios. Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

Polynesian colonization and landscape changes on Mo’orea, French Polynesia: The Lake Temae pollen record:

An analysis of sediment cores from Lake Temae utilizing pollen, accelerator mass spectrometry (AMS) dating, magnetic susceptibility measurements, and charcoal particle counts was undertaken to assess landscape transformation following Polynesian colonization of Mo’orea in the Society Islands. A significant influx of terrigenous sediment accompanied by increases in charcoal and the presence of the Polynesian cultigen Colocasia (taro) are indicative of human presence on the island by at least 1060–980 cal. yr BP. Polynesian arrival resulted in the rapid alteration of lowland vegetation illustrated in the pollen record by the removal of the coastal tree Pandanus and the promotion of more economically important trees such as Cocos. The most significant period of burning in the charcoal data overlaps with archaeological evidence for expansion into the island interior and the establishment and growth of more intense agricultural practices from 700 to 500 cal. yr BP. The pollen record also documents the apparent abandonment of the coastal plain near Lake Temae during this phase of inland expansion with the terrestrial landscape returning to an environment similar to that found before colonization. A final phase of environmental transformation commenced with European contact at the end of the 18th century and is marked most clearly in the Lake Temae sequence with the conversion of the system to a freshwater body accompanied by the expansion of the freshwater reed Typha and a level of burning not seen at any time over the previous 1000 years. Importantly, the new data from Lake Temae support the colonization model for central Eastern Polynesia of ca. 1000 cal. yr BP and refute the late settlement scenario for the Society Islands.