Fensham Roderick John, Low Choy Sama J, Fairfax Russell James, Cavallaro Paul C
Queensland Herbarium, Environmental Protection Agency, Mt Coot-tha Road, 4066 Toowong, Qld, Australia.
J Environ Manage. 2003 Aug;68(4):421-36. doi: 10.1016/s0301-4797(03)00111-7.
Accounting of carbon stocks in woody vegetation for greenhouse purposes requires definition of medium term trends with accurate error assessment. Tree and shrub cover was sampled through time at randomly located sites over a large area of central Queensland, Australia using aerial photography from 1945 to 1999. Calibration models developed from field data for the same land types as those represented within the study area allowed for the extrapolation of overstorey and understorey cover, basal area and biomass values and these were modelled as trends over the latter half of the 20th century. These structural attributes have declined over the region because of land clearing with values for biomass changing from a mean of 58.0(+/-1.2)t/ha in 1953 to 41.1(+/-1.0)t/ha in 1991. The biomass of Acacia on clay and Eucalypt on texture contrast soils land types has declined most dramatically. Within uncleared vegetation there was an overall trend of increase from 56.1(+/-1.2)t/ha in 1951 to 67.6(+/-1.3)t/ha in 1995. The increase in structural attributes within uncleared vegetation was most pronounced for the Eucalypt on texture contrast soils and Eucalypt on clay land types. It was demonstrated that the sites sampled were representative of their land types and that spatial bias of the photography, undetected tree-killing, sampling error, inherent variability of structural attributes and measurement error should not have impacted greatly on bias or precision of trend estimates for well-sampled land types. Certainly the errors are not likely to be substantial for trends averaged over all land types and they provide an accurate assessment of the magnitude and direction of change. The technique presented here would appear to be a robust means of accounting for the above-ground woody component of woodlands and open forests and will also contribute to a broader understanding of savanna dynamics.
为实现温室气体减排目标，对木本植被碳储量进行核算需要定义中期趋势并进行准确的误差评估。1945年至1999年期间，利用航空摄影技术，在澳大利亚昆士兰州中部的大片区域内，对随机选定地点的树木和灌木覆盖情况进行了长期采样。根据与研究区域内相同土地类型的实地数据建立的校准模型，可用于推断上层和下层植被覆盖、基部面积和生物量值，并将这些值模拟为20世纪后半叶的趋势。由于土地开垦，该地区的这些结构属性有所下降，生物量值从1953年的平均58.0（±1.2）吨/公顷降至1991年的41.1（±1.0）吨/公顷。粘土上的金合欢和质地对比土壤上的桉树的生物量下降最为显著。在未开垦的植被中，总体趋势是从1951年的56.1（±1.2）吨/公顷增加到1995年的67.6（±1.3）吨/公顷。未开垦植被中结构属性的增加在质地对比土壤上的桉树和粘土上的桉树上最为明显。结果表明，所采样的地点代表了其土地类型，摄影的空间偏差、未检测到的树木死亡、采样误差、结构属性的固有变异性和测量误差对采样良好的土地类型的趋势估计偏差或精度影响不大。当然，对于所有土地类型的平均趋势，误差不太可能很大，并且它们提供了对变化幅度和方向的准确评估。这里介绍的技术似乎是一种可靠的方法，可用于核算林地和开阔森林的地上木本成分，也将有助于更广泛地了解稀树草原动态。
