Long-term forest dynamics in Peruvian Amazonia

热带雨林正在迅速变化。基于对热带地区森林地块监测的研究表明，在过去30年里，森林积累了更多的生物量，这可能是二氧化碳施肥的结果。其他变化包括某些分类群的数量增加，如藤本植物(参考文献)。[25]在需要支持的情况下)和生长较快的树冠树[26]。这些变化在全球具有重要意义，因为：(A)热带森林在全球碳循环中发挥主要作用[27]；(B)增长速度加快可能意味着它们将成为短期的碳汇(例如[8])；(C)一些研究(例如[27])表明，热带森林本身可能容易受到气候变化的影响，如果死亡率上升，它们可以停止固存新的二氧化碳，或者实际上开始释放新的二氧化碳，这将对区域和全球范围的气候系统和经济产生影响。对观察到的变化的一种可能的解释是，森林并不处于平衡状态，但仍在对过去某个时候发生的干扰做出反应。这可能包括自然干扰，如干旱[33]或风暴[34]，或人为干扰，例如，开垦森林种植农作物和积极施肥土壤[35]。根据南美洲最近的考古发现[36]，后一种观点在最近几年得到了支持[37]，这些发现表明，在欧洲殖民前夕，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。泥炭序列从植被中捕获花粉颗粒，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年记录的趋势只是由过去的扰动引发的持续时间更长的趋势的最新部分，那么花粉记录应该显示出随着时间的推移而发生的显著变化(特别是在最近100-1000年)。如果在监测开始之前，森林实际上是平衡的，那么花粉组合在这段时间内应该不会有明显的变化。尽管之前在亚马逊的一些地点进行了花粉分析，但现有记录存在两个问题。首先，在过去一千年中，很少有记录具有足够的时间分辨率来检测森林覆盖的波动(在大多数情况下，最后一千年中只有一到两个样本)。其次，具有古生态潜力的地点靠近已建立的监测地块是极其罕见的。L等人最近的发现。[20]在秘鲁北部森林监测区迅速积累泥炭为解决这些问题提供了独特的机会。该项目旨在建立(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。这项研究将为该区域今后的工作奠定基础，该区域可能有相当大的潜力综合新生态和古生态来解决长期生态问题。

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.