Search

Background: Air quality modelling of smoke from wildfires requires knowledge of emission factors and how these vary. Aims: Experimental fires were used to test the variation of emission factors with fuel load to improve a smoke forecasting model. Methods: Gas and particle-phase chemical composition of smoke plumes from laboratory-scale fires was measured with different fuel loads and at different stages of fire progression. Key results: Different fine woody debris loads had no significant effect on the emission factors. In contrast, different stages of the fire produced significant differences in emission factors. The lowest emission factors for most species (except carbon dioxide) were observed during the flaming fire front, which accounted for half the total emissions. Importantly, we found that emission ratios relative to carbon monoxide were consistent across different fuel loads and throughout the fire's progression. Conclusions: By modelling the modified combustion efficiency, it is possible to simultaneously model the emissions of carbon monoxide and the emissions of nearly all other pollutants throughout the progression of a fire. Implications: The emissions of carbon monoxide, fine particulate matter and other key pollutants all scale with the intensity of the fire, simplifying the task of modelling these emitted pollutants downwind of prescribed fires. Emissions of most pollutants from laboratory-based experimental wildland fires are shown to be independent of the fraction of fine woody debris in the fuel load and to closely track the emissions of carbon monoxide in time, thereby simplifying modelling. Approximately half the emissions occur during the flaming stage of combustion. [ABSTRACT FROM AUTHOR]

Eucalyptus pellita and Acacia mangium are widely planted in the tropics and managed over five-to-fifteen-year rotations for wood and wood products. This study compares the growth of routine plantings of A. mangium with trial plantings of E. pellita and nearby native forests across six broadly distributed locations on Melville Island, northern Australia. In addition to tree growth measurements, litter mass and chemical properties, and topsoil (0–10 cm) physical and chemical parameters were assessed. Melville Island has a pronounced seasonal rainfall and soils that range from loamy sand to sandy loam textures; across the sites sampled soils comprised 65–85% sand and 8–16% clay. Across our sites, the maximum mean annual increment of E. pellita was 31.12 m3/ha/year compared to 14.64 m3/ha/year for A. mangium , with stand volume strongly positively correlated with clay content. On a site basis tree volume growth correlated strongly with soil clay content, with lower survival on sites with less clay in the predominantly sandy soils. The higher E. pellita growth compared with A. mangium reduced available phosphorous and calcium in topsoil, indicating that addition of P and Ca in subsequent rotations will be important to maintain and increase E. pellita productivity. The N 2 -fixing species, A. mangium , significantly increased nitrogen in litter (1.88 ± 0.04%) and in top soil (0.15 ± 0.01%) compared to E. pellita (litter 0.93 ± 0.05%; topsoil 0.11 ± 0.01%) so that carbon to nitrogen (C/N) ratios in Acacia litter (23.90 ± 0.81) and soil (23.06 ± 0.91) were significantly lower than in Eucalyptus (litter 46.30 ± 2.66; top soil 27.66 ± 1.65). Topsoil C/N also decreased with increasing soil clay content in all land uses (A. mangium, E. pellita, native forests) indicating better conditions for decomposer activity and turnover in sites with higher clay content soils. The Eucalyptus plantation drawdown of N and PO 4 3- in topsoil suggests that future plantings of E. pellita may benefit from additional N fixed into biomass and soil organic matter by the preceding A. mangium plantations. Tree growth correlations with rainfall and soil characteristics showed growth is best explained by annual rainfall, soil texture (as a percentage of clay or of sand), soil electrical conductivity, and soil bulk density. Overall, in tropical long dry season regions, for plantation development on sandy soils, E. pellita is a better choice than A. mangium. • Eucalyptus pellita had higher productivity than Acacia mangium. • While A. mangium increased soil N, E. pellita tended to decline soil N status. • E. pellita was more efficient at taking up soil available P and Ca. • E. pellita growth is influenced by rainfall, bulk density, and sand content. • Stocking rate should be higher in clayey sites with higher water availability. [ABSTRACT FROM AUTHOR]

Aims Exposure of Eucalyptus tree stems to the radiant heat of forest fires can kill cambial cells and their embedded regenerative meristems, thus preventing epicormic resprouting and recovery of the tree. Currently, there is no tissue-level method to quantify the viability of cambial cells in Eucalyptus following heat exposure. The first aim of this study was to adapt and validate the tetrazolium reduction method of testing for cell viability in Eucalyptus. The second aim was to apply the method to establish a threshold level of cambium cell viability in Eucalyptus obliqua to enable the identification of a critical temperature. Methods The study used the tetrazolium reduction method to quantitatively determine phloem–cambium cell viability in Eucalyptus. Circular sections of bark with underlying phloem and cambium were cut from mature E. obliqua and samples ranging in mass from 1 to 30 mg were exposed for 1 min to temperature treatments ranging from 20 to 85 °C and kept for 20–22 h at room temperature in 0.8% 2,3,5-triphenyl tetrazolium chloride (TTC) to test for cell viability. The 1,3,5-triphenyl tetrazolium formazan (TPF) formed was cold extracted with ethanol and quantified as absorbance at 485 nm. Important Findings The TTC reduction method reliably quantified a decline in cell viability with rising temperature in tissue sections that included vascular cambium, and identified 60 °C as the critical temperature for cambium–phloem cells of Eucalyptus species. Cell viability, calculated as [TPF Treatment °C]/[TPF 20 °C], declined by 90% between 20 and 85 °C. The cell viability results confirmed that significant tissue necrosis occurred in Eucalyptus at temperatures between 50 and 70 °C, after 1 min of in vitro tissue heating. The decline in cell viability with increasing temperature shown by the TTC method was consistent with an independently derived count of live cells following temperature treatment and neutral red staining. [ABSTRACT FROM AUTHOR]