Long-term forest dynamics in Peruvian Amazonia

热带森林正在迅速变化。在监测热带森林地块的基础上进行的研究表明，在过去30年里，森林积累了额外的生物量，这可能是二氧化碳施肥的结果。其他的变化还包括某些种类的数量增加，如藤本植物（参考文献[25]在支持案例中）和生长更快的树冠树[26]。这些变化对全球都很重要，因为（a）热带森林在全球碳循环中发挥着重要作用[27];（B）增长率的提高可能意味着它们正在充当短期碳汇（例如[8]）;（c）一些研究（例如[27]）表明热带森林本身可能易受气候变化的影响，如果死亡率上升，可能会停止吸收新的二氧化碳，或者实际上开始释放二氧化碳，这将对气候系统以及区域和全球范围的经济产生影响。对所观察到的变化的一个可能解释是，森林并没有处于平衡状态，但仍然对过去某个时候发生的干扰作出反应。这可能包括自然干扰，如干旱[33]或风暴[34]，或人为干扰，例如，清除森林种植作物和积极土壤[35]。后一种观点近年来在南美洲的考古发现[36]的基础上得到了支持，这些发现表明，在欧洲殖民化的前夕，土著人口比以前认为的要多得多，因此可能对森林产生了重大影响。测试森林在遥远的过去是否受到干扰的一种方法是使用古生态记录。泥炭序列捕获植物的花粉粒并将其保存在地层中;分析这些花粉使我们能够重建过去的植被群落以及它们随时间变化的方式。如果过去30-40年记录的趋势只是过去扰动引发的持续时间更长的趋势的最近部分，那么花粉记录应该显示随时间的显著变化（特别是在过去100-1000年）。如果森林在监测开始之前实际上处于平衡状态，那么花粉组合在这段时间内应该没有显着变化。虽然以前在亚马逊河流域的一些地点进行过花粉分析，但现有的记录存在两个问题。首先，在过去一千年中，很少有时间分辨率足够的记录来检测森林覆盖的波动（在大多数情况下，在过去一千年中只有一两个样本）。其次，具有古生态潜力的地点位于已建立的监测点附近的情况极为罕见。Lähteenoja等人[20]最近发现，秘鲁北方森林监测区域的泥炭迅速积累，这为解决这些问题提供了一个独特的机会。该项目旨在确定（1）这些地点目前植被的组成和生态;（2）这些泥炭序列提供良好花粉记录的潜力;（3）森林群落的历史;（4）现代花粉雨与周围植被之间的关系，以帮助解释花粉。这项研究将为今后在这一地区开展工作奠定基础，在这一地区，综合新生态学和古生态学可能具有相当大的潜力，可以解决长期生态学问题。

Tropical forests are changing rapidly. Studies based on monitoring forest plots across the tropics show that, over the past 30 years, forests have accumulated additional biomass, possibly as a result of fertilization by carbon dioxide. Other changes have included an increasing abundance of certain taxa such as lianas (ref. [25] in the Case for Support) and faster-growing canopy trees [26]. These changes are important globally because (a) tropical forests play a major role in the global carbon cycle [27]; (b) increased growth rates may mean that they are acting as a short-term carbon sink (e.g. [8]); (c) some studies (e.g. [27]) suggest that tropical forests may themselves be vulnerable to climate change, and could either stop sequestering new carbon dioxide or actually start releasing it if mortality rates increase, which would have consequences for the climate system and economies on regional and global scales. One possible explanation for the observed change is that forests are not in equilibrium but are still responding to disturbances which took place at some time in the past. This could include natural disturbances, such as droughts [33] or storms [34], or human disturbances caused by, for example, clearing forest to grow crops and actively fertilizing the soils [35]. This latter idea has gained ground in recent years [37] on the basis of recent archaeological discoveries in South America [36] which suggest that, on the eve of the European colonization, indigenous populations were much larger than previously thought, and thus may have had a significant impact on the forests. One way to test whether or not forests have been disturbed in the distant past is to use the palaeoecological record. Peat sequences trap pollen grains from vegetation and preserve them in stratigraphic layers; analysing this pollen allows us to reconstruct past vegetation communities and the way they have changed over time. If the trends recorded over the last 30-40 years are only the most recent part of a trend which has been continuing for much longer, triggered by a past disturbance, then pollen records should show pronounced changes over time (particularly in the last 100-1000 years). If the forests were in fact in equilibrium before monitoring began, then the pollen assemblages should show no significant change during this interval. Although pollen analysis has previously been undertaken at a number of sites in Amazonia, there are two problems with the existing records. Firstly, there are few records with sufficient temporal resolution in the last thousand years to detect fluctuations in forest cover (in most cases, there are only one or two samples in the last thousand years). Secondly, sites with palaeoecological potential situated close to established monitoring plots are extremely rare. The recent discovery by Lähteenoja et al. [20] of rapidly accumulating peats in an area of forest monitoring in northern Peru offers a unique opportunity to resolve these problems. This project seeks to establish (1) the current composition and ecology of the vegetation at these sites today; (2) the potential of these peat sequences to provide good pollen records; (3) the history of the forest communities; (4) the relationship between the modern pollen rain and the surrounding vegetation to assist in interpreting the pollen. This study will form the foundation for future work in this region where there may be considerable potential for integrated neo- and palaeoecology to address questions of long-term ecology.