Phillips O L, Baker T R, Arroyo L, Higuchi N, Killeen T J, Laurance W F, Lewis S L, Lloyd J, Malhi Y, Monteagudo A, Neill D A, Vargas P Núñez, Silva J N M, Terborgh J, Martínez R Vásquez, Alexiades M, Almeida S, Brown S, Chave J, Comiskey J A, Czimczik C I, Di Fiore A, Erwin T, Kuebler C, Laurance S G, Nascimento H E M, Olivier J, Palacios W, Patiño S, Pitman N C A, Quesada C A, Saldias M, Lezama A Torres, Vinceti B
Earth and Biosphere Institute, School of Geography, University of Leeds, Leeds LS2 9JT, UK.
Philos Trans R Soc Lond B Biol Sci. 2004 Mar 29;359(1443):381-407. doi: 10.1098/rstb.2003.1438.
Previous work has shown that tree turnover, tree biomass and large liana densities have increased in mature tropical forest plots in the late twentieth century. These results point to a concerted shift in forest ecological processes that may already be having significant impacts on terrestrial carbon stocks, fluxes and biodiversity. However, the findings have proved controversial, partly because a rather limited number of permanent plots have been monitored for rather short periods. The aim of this paper is to characterize regional-scale patterns of 'tree turnover' (the rate with which trees die and recruit into a population) by using improved datasets now available for Amazonia that span the past 25 years. Specifically, we assess whether concerted changes in turnover are occurring, and if so whether they are general throughout the Amazon or restricted to one region or environmental zone. In addition, we ask whether they are driven by changes in recruitment, mortality or both. We find that: (i) trees 10 cm or more in diameter recruit and die twice as fast on the richer soils of southern and western Amazonia than on the poorer soils of eastern and central Amazonia; (ii) turnover rates have increased throughout Amazonia over the past two decades; (iii) mortality and recruitment rates have both increased significantly in every region and environmental zone, with the exception of mortality in eastern Amazonia; (iv) recruitment rates have consistently exceeded mortality rates; (v) absolute increases in recruitment and mortality rates are greatest in western Amazonian sites; and (vi) mortality appears to be lagging recruitment at regional scales. These spatial patterns and temporal trends are not caused by obvious artefacts in the data or the analyses. The trends cannot be directly driven by a mortality driver (such as increased drought or fragmentation-related death) because the biomass in these forests has simultaneously increased. Our findings therefore indicate that long-acting and widespread environmental changes are stimulating the growth and productivity of Amazon forests.
先前的研究表明，在20世纪后期，成熟热带森林样地中的树木更替、树木生物量和大型藤本植物密度都有所增加。这些结果表明森林生态过程发生了协同变化，这可能已经对陆地碳储量、通量和生物多样性产生了重大影响。然而，这些发现存在争议，部分原因是监测的永久样地数量相当有限，且监测时间较短。本文的目的是利用现有的、涵盖过去25年的亚马逊地区改进数据集，来描述“树木更替”（树木死亡并补充进入种群的速率）的区域尺度模式。具体而言，我们评估更替是否正在发生协同变化，如果是，这些变化是在整个亚马逊地区普遍存在，还是仅限于一个区域或环境带。此外，我们还探究这些变化是由补充率、死亡率的变化还是两者共同驱动的。我们发现：（i）直径10厘米及以上的树木在亚马逊南部和西部较肥沃土壤上的补充和死亡速度，是亚马逊东部和中部较贫瘠土壤上的两倍；（ii）在过去二十年中，整个亚马逊地区的更替率都有所上升；（iii）除亚马逊东部的死亡率外，每个区域和环境带的死亡率和补充率都显著增加；（iv）补充率一直超过死亡率；（v）补充率和死亡率的绝对增加在亚马逊西部的样地中最大；（vi）在区域尺度上，死亡率似乎滞后于补充率。这些空间模式和时间趋势并非由数据或分析中明显的人为因素导致。这些趋势不可能直接由死亡率驱动因素（如干旱增加或与破碎化相关的死亡）引起，因为这些森林中的生物量同时也在增加。因此，我们的研究结果表明，长期且广泛的环境变化正在促进亚马逊森林的生长和生产力。
