Long-term fire and vegetation change in northwestern Amazonia

Amazonian forest plots are used to quantify biodiversity and carbon sequestration, and provide the foundation for much of what is known about tropical ecology. Many plots are assumed to be undisturbed, but recent work suggests that past fire, forest openings, and cultivation created vegetation changes that have persisted for decades to centuries (ecological legacies). The Yasuní Forest Dynamics plot is one of the most biodiverse places on earth, yet its human history remains unknown. Here, we use charcoal and phytolith analysis to investigate the fire and vegetation history of the Yasuní forest plot, and compare results with nearby forest plots in Colombia (Amacayacu) and Peru (Medio Putumayo-Algodón (MPA)) to explore the spatial variability of past disturbances and ecological legacies in northwestern Amazonia. Three 14C dated charcoal fragments provided evidence for a modern (1956 CE) and a past fire event ca. 750 years ago at Yasuní, compared with fire ages of 1000-1600 years ago documented at Amacayacu and MPA. Small-scale disturbances and localized canopy-openings also occurred in the Yasuní plot. Phytolith assemblages from Yasuní and Amacayacu showed more variability in past vegetation change than MPA. Low-intensity, non-continuous disturbances occurred at all three plots in the past, and our results highlight the variability of past human activities both in space and time in northwestern Amazonia. Our data also suggest that post-Columbian human disturbances from the Rubber Boom (AD 1850-1920) and subsequent oil exploration have likely left stronger ecological legacies than those left by pre-Columbian peoples in our studied regions.

亚马逊森林样地（Amazonian forest plots）被用于量化生物多样性与碳封存（carbon sequestration）量，同时也是当前绝大多数热带生态学认知的核心基础。尽管多数样地被认为未受干扰，但近期研究表明，过往的火灾、林隙形成与人类垦殖活动所引发的植被变化，可存续数十年至数百年之久，即生态遗留效应（ecological legacies）。亚苏尼森林动态样地（Yasuní Forest Dynamics plot）是全球生物多样性最丰富的区域之一，但其人类活动历史至今仍不明确。本研究通过炭屑与植硅体（phytolith）分析，探究亚苏尼森林动态样地的火灾与植被历史，并将结果与哥伦比亚境内的阿马卡亚库（Amacayacu）样地、秘鲁境内的Medio Putumayo-Algodón（MPA）样地进行对比，以解析亚马孙西北部地区过往干扰与生态遗留效应的空间异质性。经碳14（14C）测年的3块炭屑碎片证据显示，亚苏尼样地曾在距今约750年前发生过一次火灾，另有一次现代火灾发生于公元1956年；而阿马卡亚库与MPA样地记录到的火灾年代则为距今1000至1600年前。亚苏尼样地同样存在小规模干扰与局域林隙形成事件。亚苏尼与阿马卡亚库样地的植硅体组合显示，其过往植被变化的幅度较MPA样地更为显著。过往所有三个样地均发生过低强度、非连续性的干扰事件，本研究结果凸显了亚马孙西北部地区人类活动在时空维度上的异质性。本研究数据同时表明，在本研究涉及的区域内，后哥伦布时期的橡胶繁荣（公元1850-1920年）与后续石油勘探活动所引发的人类干扰，其留下的生态遗留效应，较哥伦布时代前的人类活动更为显著。