Vieira Simone, Trumbore Susan, Camargo Plinio B, Selhorst Diogo, Chambers Jeffrey Q, Higuchi Niro, Martinelli Luiz Antonio
Laboratório de Ecologia Isotópica, Centro de Energia Nuclear na Agricultura, P.O. Box 96, CEP 13400-970, Piracicaba, São Paulo, Brazil.
Proc Natl Acad Sci U S A. 2005 Dec 20;102(51):18502-7. doi: 10.1073/pnas.0505966102. Epub 2005 Dec 9.
Quantifying age structure and tree growth rate of Amazonian forests is essential for understanding their role in the carbon cycle. Here, we use radiocarbon dating and direct measurement of diameter increment to document unexpectedly slow growth rates for trees from three locations spanning the Brazilian Amazon basin. Central Amazon trees, averaging only approximately 1 mm/year diameter increment, grow half as fast as those from areas with more seasonal rainfall to the east and west. Slow growth rates mean that trees can attain great ages; across our sites we estimate 17-50% of trees with diameter >10 cm have ages exceeding 300 years. Whereas a few emergent trees that make up a large portion of the biomass grow faster, small trees that are more abundant grow slowly and attain ages of hundreds of years. The mean age of carbon in living trees (60-110 years) is within the range of or slightly longer than the mean residence time calculated from C inventory divided by annual C allocation to wood growth (40-100 years). Faster C turnover is observed in stands with overall higher rates of diameter increment and a larger fraction of the biomass in large, fast-growing trees. As a consequence, forests can recover biomass relatively quickly after disturbance, whereas recovering species composition may take many centuries. Carbon cycle models that apply a single turnover time for carbon in forest biomass do not account for variations in life strategy and therefore may overestimate the carbon sequestration potential of Amazon forests.
量化亚马逊森林的年龄结构和树木生长速率对于理解它们在碳循环中的作用至关重要。在这里，我们使用放射性碳测年法和直接测量直径增量，来记录巴西亚马逊河流域三个地点的树木出人意料的缓慢生长速率。亚马逊中部的树木平均直径增量仅约为每年1毫米，其生长速度仅为东西部季节性降雨较多地区树木的一半。生长速率缓慢意味着树木可以达到很高的年龄；在我们所有的研究地点，我们估计直径大于10厘米的树木中有17% - 50%的树龄超过300年。虽然构成大部分生物量的少数突出树木生长较快，但数量更多的小树生长缓慢，树龄可达数百年。活树中碳的平均年龄（60 - 110年）在根据碳储量除以每年分配给木材生长的碳量计算出的平均停留时间范围内（40 - 100年），或略长于此范围。在直径增量总体较高且生物量中较大比例为大型、快速生长树木的林分中，观察到碳周转更快。因此森林在受到干扰后可以相对较快地恢复生物量，而恢复物种组成可能需要几个世纪。在森林生物量中对碳应用单一周转时间的碳循环模型没有考虑到生命策略的变化，因此可能高估了亚马逊森林的碳固存潜力。
