[1] 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. , et al. (2012), Predictability of biomass burning in response to climate changes, Global Biogeochem. Cycles, 26, GB4007,
2007. A high-resolution record of vegetation and climate through the last glacial cycle from Caledonia Fen, southeastern highlands of Australia.ABSTRACT: A blocked tributary has provided a rare site of long-term sediment accumulation in montane southeastern Australia. This site has yielded a continuous, detailed pollen record through the last ca. 140 000 years and revealed marked vegetation and environmental changes at orbital to sub-millennial scales. Radiocarbon and optically stimulated luminescence (OSL, or optical) ages provide some chronological control for the last ca. 70 000 years. Most of the sediment is inorganic but with well preserved pollen that accumulated under unproductive and probably largely ice-covered lake conditions. The lake was surrounded by low-growing plants with an alpine character. Exceptions include three discrete periods of high organic sedimentation in the basin and forest development in the surrounding catchment. The two major periods of forest expansion are related to the last interglacial and the Holocene, with the third, shorter period considered to represent an interstadial in the early part of Marine Isotope Stage (MIS) 3. The latter part of the last glacial period is characterised by abrupt sub-millennial, amelioration events that may relate to documented global oscillations emanating from the North Atlantic. There are systematic changes through the record that can be partly attributed to basin infilling but the progressive reduction and regional extinction of some plant taxa is attributed to a long-term trend towards climatic drying.
Pollen and charcoal analyses of Ocean Drilling Program (ODP) Site 820 on the continental slope, about 60 to 80 km off the northeastern Queensland coast, provide a continuous record of vegetation through the last 1.5 m.y. that complements and extends Quaternary records from the adjacent mainland. Through most of the record, the gross composition of the vegetation, indicated by pollen of drier and wetter rainforests, open sclerophyll vegetation, freshwater swamps and mangroves, changed little although fluctuations did occur that may relate to cyclical changes in climate and sea level. In addition, a reduction in temperatures within the middle Pleistocene might have caused a change in mangrove composition and an increase in higher-altitude taxa, particularly ferns. Evidence exists for the disappearance or reduction in range of a number of gymnosperms throughout the record. Earlier disappearances were probably caused by increased climatic variability and correspond with those elsewhere in Australia. The replacement of araucarian drier forest by open sclerophyll vegetation and the extinction of a species of Dacrydium may relate to an increase in burning caused by the activities of Aboriginal people. The initiation of this change is dated between -150 and 100 k.y. ago, well before the date for a similar change in terrestrial records from the region. However, the date is in line with that from Lake George in southeastern Australia and adds substantially to the evidence of a very early time of arrival of Aborigines and for their impact on the Australian landscape.
The late Quaternary vegetation communities of the south-central highlands of Victoria are reconstructed from analyses of pollen and charcoal, and associated environmental conditions derived from the record of Nothofagus cunninghamii and alpine and sclerophyll taxa preserved in four subalpine Sphagnum bogs. The highest site occurs amid Eucalyptus paucifiora woodland, the two intermediate sites are surrounded by Eucalyptus delegatensis forest and the lowest by a mixed forest ofE. delegatensis/Eucalyptus regnans. Small pockets of N. cunninghamii occur within the eucalypt forests, and in close proximity to all four sites. Around 32 000 BP the vegetation consisted of a mosaic of alpine feldmark and herbfield, with small scattered groves of Nothofagus and Eucalyptus well below 1100 m. Summer temperatures were probably 5°C lower than present with lowest values, probably 7° to 8°C below present, possibly between 17 000 and 13 500 BP, at which time alpine communities reached their greatest extent and much of the Central Highlands was treeless. After ca 13 500 BP herbaceous alpine taxa disappeared and there was an associated movement upslope of Nothofagus and tall open forest taxa to their maximum post-glacial extent, as temperatures and effective precipitation increased, ca 6000 BP. The retraction of cool temperate rainforest and wet sclerophyll or tall open forest towards present day values indicates lower effective precipitation, generally rising temperatures and increased fire hazard. More recently, European activities have increased the stress on the remaining forests. The study of four sites has demonstrated the importance of analysing a number of sites within a given area in order to overcome the limitations imposed by sites which were sub-optimal due to one or more factors including poor preservation, problems of dating, variable sedimentation rates, and the influence of streams which flow close to all sites. While the local environment varies between sites, and some vegetation changes are successional, this study shows that the local records complement one another, to some extent reinforcing the regional picture of vegetation and environmental change.
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