Combining long-term field data and remote sensing to test how tree diversity influences aboveground biomass recovery in logged tropical forests

这个项目的首要目标是测试热带森林生态系统的功能是否存在的问题，比如它们产生了多少生物量，这取决于它们的多样性，因此，重新种植具有不同物种混合物的退化森林是否可以加速其恢复，并通过碳信用额帮助资助重新种植费用。退化的次生林比未受干扰的老的增长。这种退化主要是由于有选择的采伐造成的，这对森林的功能（例如森林的生产力和储存的碳量）及其生物多样性产生了负面影响。这一点很重要，因为在热带以外的温带草原等生态系统中开展的工作表明，生物多样性与包括初级生产力在内的一系列生态系统功能之间存在积极关系。然而，热带地区科学研究的挑战意味着我们对热带森林生态系统中树木多样性水平与地上生物量生产之间是否存在正相关关系的证据要少得多。事实上，一些生态理论表明，这些生态系统中的物种在生态上是如此相似，以至于许多物种可能会消失，而对这些生态系统的功能几乎没有影响。20年前，我们开始与沙巴（马来西亚婆罗洲）当地的林业工作者、环保人士和科学家合作，建立一个长期实验，以测试这些热带森林生态系统中的生物多样性和生态系统功能之间是否存在关系。该项目称为“沙巴生物多样性实验”，是世界上最大的生态实验之一，因此对恢复和可持续管理热带森林的实际工作特别重要。该试验采用了现有的“富集种植”森林恢复活动，在500公顷的采伐森林中种植了100，000多棵本地树种的幼苗，使自然再生对照地块的恢复率与种植不同树种（1、4或16个树种）和混合树种的恢复率进行了有力的比较。我们将评估相对于附近古老森林的恢复进度，特别是邻近未受干扰的地区，我们已经反复绘制和测量了50公顷区域内的每棵树（Danum Valley ForestGeo Plot），作为全球森林健康监测网络的一部分。我们研究地块的面积很大，这意味着很难使用传统的实地方法重复监测它们的细节。因此，我们将把联合收割机定向实地采样与尖端遥感技术相结合，探索树木富集种植如何影响数百公顷退化森林的树冠结构、地上碳储量和植物多样性的恢复。我们的项目将利用两种互补技术：激光雷达和卫星遥感为我们的研究地点获得的现有数据。机载激光雷达使用安装在飞机或直升机上的激光器精确测量植被的高度，并以精美的细节重建森林树冠和底层地形的3D结构，从而可以在整个景观中准确绘制森林碳储量。为了获得更详细和更长期的图像，该项目还将使用免费提供的卫星时间序列数据（哨兵1-2，Landsat 8和PlanetScope图像）绘制森林地上碳储量的年度变化图（使用Google Earth Engine）。在最后阶段，我们将与当地的合作伙伴，包括沙巴林业局合作，他们还将对森林恢复的效益进行分析，并交流这些结果，以便为当地和区域的森林养护和恢复及其储存的碳的管理政策提供信息。

The over-arching goal of this project is to test the unanswered question of whether the functioning of tropical forest ecosystems-such as how much biomass they produce-depends on how diverse they are and therefore whether replanting degraded forests with diverse mixtures of species can accelerate their recovery and help fund replanting costs through carbon credits.Tropical forests are being lost all over the world and of the remaining area more is degraded secondary forest than undisturbed old growth. This degradation occurs largely through selective logging which has negative effects of the functioning of the forest (e.g. how productive it is and how much carbon it stores) as well as on its biodiversity. This is important because work outside of the tropics in ecosystems like temperate grasslands has demonstrated a positive relationship between biodiversity and a range of ecosystem functions, including primary productivity. However, the challenges of scientific research in the tropics mean we have much less evidence of whether there is a positive relationship between levels of tree diversity and aboveground biomass production in tropical forest ecosystems. Indeed, some ecological theory suggests that species in these ecosystems are so similar ecologically that many species could be lost with little or no impact on how these ecosystems function. Twenty years ago, we started a collaboration with local foresters, conservationists and scientists in Sabah (Malaysian Borneo) to set up a long-term experiment to test whether there is a relationship between biodiversity and ecosystem functioning in these tropical forest ecosystems. The project, the Sabah Biodiversity Experiment, is one of the world's largest ecological experiments, making it of particular relevance to real-world efforts to restore and sustainably manage tropical forests. The experiment has adopted the existing forest restoration activity of 'enrichment planting' to plant more than 100,000 seedlings of native tree species across an area of 500 hectares of logged forest, allowing the recovery rates of naturally regenerating control plots to be robustly compared with those planted with different diversities (1, 4 or 16 species) and mixtures of tree species. We will assess restoration progress relative to nearby old growth forest, especially the neighbouring undisturbed area where we have repeatedly mapped and measured every tree within a 50-hectare area (the Danum Valley ForestGeo Plot) as part of a global network to monitor forest health.The large size of our research plots means they are difficult to repeatedly monitor in fine detail using traditional field methods. We will therefore combine targeted field sampling with cutting-edge remote sensing technologies to explore how tree enrichment planting has shaped the recovery of canopy structure, aboveground carbon stocks and plant diversity across hundreds of hectares of degraded forest. Our project will take advantage of existing data acquired for our study sites using two complementary technologies: LiDAR and satellite remote sensing. Airborne LiDAR uses a laser mounted on an airplane or helicopter to precisely measure the height of the vegetation and reconstruct the 3D structure of the forest canopy and underlying terrain in exquisite detail, allowing forest carbon stocks to be accurately mapped across entire landscapes. To get a more detailed and longer-term picture, the project will also use freely available satellite timeseries data (Sentinel 1-2, Landsat 8 and PlanetScope imagery) to map annual changes in forest aboveground carbon stocks (using Google Earth Engine).In the final phase we will work with local partners including the Sabah Forestry Department on a cost-benefit analysis of forest restoration and communicate these results so that they can inform their local and regional management policies for the conservation and restoration of forests and the carbon that they store.