Phillips Oliver L, Lewis Simon L, Baker Timothy R, Chao Kuo-Jung, Higuchi Niro
Earth and Biosphere Institute, School of Geography, University of Leeds, Leeds LS2 9JT, UK.
Philos Trans R Soc Lond B Biol Sci. 2008 May 27;363(1498):1819-27. doi: 10.1098/rstb.2007.0033.
Long-term monitoring of distributed, multiple plots is the key to quantify macroecological patterns and changes. Here we examine the evidence for concerted changes in the structure, dynamics and composition of old-growth Amazonian forests in the late twentieth century. In the 1980s and 1990s, mature forests gained biomass and underwent accelerated growth and dynamics, all consistent with a widespread, long-acting stimulation of growth. Because growth on average exceeded mortality, intact Amazonian forests have been a carbon sink. In the late twentieth century, biomass of trees of more than 10cm diameter increased by 0.62+/-0.23tCha-1yr-1 averaged across the basin. This implies a carbon sink in Neotropical old-growth forest of at least 0.49+/-0.18PgCyr-1. If other biomass and necromass components are also increased proportionally, then the old-growth forest sink here has been 0.79+/-0.29PgCyr-1, even before allowing for any gains in soil carbon stocks. This is approximately equal to the carbon emissions to the atmosphere by Amazon deforestation. There is also evidence for recent changes in Amazon biodiversity. In the future, the growth response of remaining old-growth mature Amazon forests will saturate, and these ecosystems may switch from sink to source driven by higher respiration (temperature), higher mortality (as outputs equilibrate to the growth inputs and periodic drought) or compositional change (disturbances). Any switch from carbon sink to source would have profound implications for global climate, biodiversity and human welfare, while the documented acceleration of tree growth and mortality may already be affecting the interactions among millions of species.
对分布广泛的多个样地进行长期监测是量化宏观生态格局和变化的关键。在此,我们研究了20世纪后期亚马逊老龄森林在结构、动态和组成方面协同变化的证据。在20世纪80年代和90年代,成熟森林生物量增加,生长和动态加速,所有这些都与广泛且长期的生长刺激相一致。由于平均生长超过死亡,完整的亚马逊森林一直是碳汇。在20世纪后期,整个流域直径超过10厘米的树木生物量平均每年增加0.62±0.23吨碳/公顷。这意味着新热带老龄森林的碳汇至少为0.49±0.18亿吨碳/年。如果其他生物量和死有机物质成分也按比例增加,那么即使不考虑土壤碳储量的任何增加,这里的老龄森林碳汇也已达到0.79±0.29亿吨碳/年。这大约相当于亚马逊森林砍伐向大气排放的碳量。也有证据表明亚马逊生物多样性近期发生了变化。未来,剩余的亚马逊老龄成熟森林的生长响应将趋于饱和,并且这些生态系统可能会由于更高的呼吸作用(温度)、更高的死亡率(因为产出与生长输入和周期性干旱达到平衡)或组成变化(干扰)而从碳汇转变为碳源。从碳汇到碳源的任何转变都将对全球气候、生物多样性和人类福祉产生深远影响,而记录在案的树木生长和死亡率加速可能已经在影响数百万物种之间的相互作用。