Determination of deforestation rates of the world's humid tropical forests

A recently completed research program (TREES) employing the global imaging capabilities of Earth-observing satellites provides updated information on the status of the world's humid tropical forest cover. Between 1990 and 1997, 5.8 +/- 1.4 million hectares of humid tropical forest were lost each year, with a further 2.3 +/- 0.7 million hectares of forest visibly degraded. These figures indicate that the global net rate of change in forest cover for the humid tropics is 23% lower than the generally accepted rate. This result affects the calculation of carbon fluxes in the global budget and means that the terrestrial sink is smaller than previously inferred.     

Beyond deforestation: restoring forests and ecosystem services on degraded lands

Despite continued forest conversion and degradation, forest cover is increasing in countries across the globe. New forests are regenerating on former agricultural land, and forest plantations are being established for commercial and restoration purposes. Plantations and restored forests can improve ecosystem services and enhance biodiversity conservation, but will not match the composition and structure of the original forest cover. Approaches to restoring forest ecosystems depend strongly on levels of forest and soil degradation, residual vegetation, and desired restoration outcomes. Opportunities abound to combine ambitious forest restoration and regeneration goals with sustainable rural livelihoods and community participation. New forests will require adaptive management as dynamic, resilient systems that can withstand stresses of climate change, habitat fragmentation, and other anthropogenic effects.     

基于近邻几何特征的TLS林分点云分类研究

目的在地面激光雷达点云分类任务中多存在特征维度较高的问题,然而当点云数量较多,分类任务中构造较高维度的特征往往需要较多的计算成本和运行内存。为了解决这一问题,本研究提出用近邻点构造5个几何特征训练成熟分类器,以期在将林分点云分为地面、树干与枝叶3个类别的同时达到降低特征维度的目的。方法在构造特征的过程中采用近邻值为140的快速KDtree搜索近邻点,获得近邻点后利用其计算协方差矩阵特征值、法向量、曲率、方差和最大高程差构造5个几何特征训练分类器。为了检验本研究构造的特征在林分点云分类中的稳定性,分类器分别采用随机森林和xgboost做比较研究。本研究的实验数据均来自地面激光雷达扫描获得的单站蒙古栎人工林点云数据。结果使用随机森林和xgboost分类器训练的模型在测试集中正确估计样本数量和样本总量的比值分别为0.932 1和0.936 3。这两个分类器在地面、树干和枝叶这3个类别中的查准率达到0.97、0.93、和0.91以上,且在这3个类别中的分类结果中xgboost较随机森林均有千分级的优势。结论结果表明本研究构造的特征能够完成林分点云分类任务,在保证点云分类准确率的基础上,既减少了特征维度,又有助于提高特征计算效率,具有较高的稳定性。本研究的分类结果可为林分参数反演和生物量估计等研究奠定基础。      

Baseline map of carbon emissions from deforestation in tropical regions

Policies to reduce emissions from deforestation would benefit from clearly derived, spatially explicit, statistically bounded estimates of carbon emissions. Existing efforts derive carbon impacts of land-use change using broad assumptions, unreliable data, or both. We improve on this approach using satellite observations of gross forest cover loss and a map of forest carbon stocks to estimate gross carbon emissions across tropical regions between 2000 and 2005 as 0.81 petagram of carbon per year, with a 90% prediction interval of 0.57 to 1.22 petagrams of carbon per year. This estimate is 25 to 50% of recently published estimates. By systematically matching areas of forest loss with their carbon stocks before clearing, these results serve as a more accurate benchmark for monitoring global progress on reducing emissions from deforestation.     

北京山地天然栎林垂直结构研究

森林垂直结构的定量分析在森林生态系统管理中具有重要意义。以北京山地天然栎林为例,根据树冠光竞争高度原理设计划分林分垂直层次的方法,对栎林的垂直结构分析方法和所采用的参数进行验证,并对划分出的不同层次间林木胸径、树高和树冠长度3个指标进行方差分析。结果表明:该方法能较为客观地对天然栎林进行垂直层次定量划分,并对其他群落类型也有参考价值。     

Explaining the abundance of ants in lowland tropical rainforest canopies

The extraordinary abundance of ants in tropical rainforest canopies has led to speculation that numerous arboreal ant taxa feed principally as "herbivores" of plant and insect exudates. Based on nitrogen (N) isotope ratios of plants, known herbivores, arthropod predators, and ants from Amazonia and Borneo, we find that many arboreal ant species obtain little N through predation and scavenging. Microsymbionts of ants and their hemipteran trophobionts might play key roles in the nutrition of taxa specializing on N-poor exudates. For plants, the combined costs of biotic defenses and herbivory by ants and tended Hemiptera are substantial, and forest losses to insect herbivores vastly exceed current estimates.     

海南霸王岭热带山地雨林树木苗期构筑型研究

为了解热带山地雨林主要树种苗期构筑型特征 ,笔者综合考虑树种在热带山地雨林群落中的重要性、林窗更新进程中的作用及苗圃出苗情况后 ,2 0 0 2年 7— 8月在海南霸王岭自然保护区东二保护站苗圃选择了热带山地雨林中 2 0种主要树木的幼苗 ,分不同苗龄进行了构筑型特征系统观测 .对苗龄≤ 3个月和 3个月 <苗龄≤ 12个月的幼苗 ,采用了不同的指标体系进行研究 .对比了幼苗的构筑型特征 ,并讨论了构筑型与生态对策、群落结构的关系 .结果表明 :大多数热带树木幼苗萌发方式为子叶出土、子叶叶状对生 ;初生叶多为互生 ,其次为对生、轮生 ;分枝角度中 30°和 6 0°居多 ,其次为 4 5°、75°;幼苗枝下高与树高之间符合指数函数关系 ,而树高与基径之间符合幂函数关系 ;Rauh型、Massart型树木通常采取K对策 ,Leeuwenberg型、Attims型树木通常采取r对策 ,Roux型采取r对策或K对策 ,Aubreville型的生态对策在二者之间 .     

Long-term change in the nitrogen cycle of tropical forests

Deposition of reactive nitrogen (N) from human activities has large effects on temperate forests where low natural N availability limits productivity but is not known to affect tropical forests where natural N availability is often much greater. Leaf N and the ratio of N isotopes (δ(15)N) increased substantially in a moist forest in Panama between ~1968 and 2007, as did tree-ring δ(15)N in a dry forest in Thailand over the past century. A decade of fertilization of a nearby Panamanian forest with N caused similar increases in leaf N and δ(15)N. Therefore, our results indicate regional increases in N availability due to anthropogenic N deposition. Atmospheric nitrogen dioxide measurements and increased emissions of anthropogenic reactive N over tropical land areas suggest that these changes are widespread in tropical forests.     

Biomass of tropical forests: a new estimate based on forest volumes

Recent assessments of areas of different tropical forest types and their corresponding stand volumes were used to calculate the biomass densities and total biomass of tropical forests. Total biomass was estimated at 205 x 10(9) tons, and weighted biomass densities for undisturbed closed and open broadleaf forests were 176 and 61 tons per hectare, respectively. These values are considerably lower than those previously reported and raise questions about the role of the terrestrial biota in the global carbon budget.     

南岭国家级自然保护区森林群落枯立木分布与地形因子的相关性

应用典范对应分析（canonical correspondence analysis,CCA）方法和Kruskal-Wallis（非参数ANOVA）分析方法研究了南岭国家级自然保护区山地森林群落枯立木分布与地形因子的关系.结果表明：（1）调查枯立木77株,分属17科25属32种;（2）海拔、坡度、坡向、坡位和坡形等5个地形因子的综合作用对枯立木的分布格局具有显著影响（P＜0.01）,地形因子与3个排序轴均有较强的相关性,地形因子在第1排和第2排序轴的位置明显反映其生态特点;（3）海拔对枯立木多度的影响显著,海拔是影响枯立木分布的首要控制因子.     

海南铜铁岭热带低地雨林植物区系研究

海南铜铁岭热带低地雨林的物种种类十分丰富,在2 600 m2的样地中有维管束植物88科、186属、258种.植物分布区类型组成,主产热带、亚热带的科占79.55%,热带分布属占旧世界分布属的95.08%;热带分布种占种总数的98.84%.热带分布的科、属中,以泛热带分布的科、属最多,分别占科、属总数的62.50%,28.49%.种的分布中以热带亚洲分布及其变型和中国特有成分占的比例最高,分别为55.43%和33.72%;分布至温带的科、属、种分别占科、属、种总数的19.32%,4.92%,1.16%.结果显示了铜铁岭低地雨林的热带北缘的性质.     

Mayan urbanism: impact on a tropical karst environment

From the first millennium B.C. through the 9th-century A.D. Classic Maya collapse, nonurban populations grew exponentially, doubling every 408 years, in the twin-lake (Yaxha-Sacnab) basin that contained the Classic urban center of Yaxha. Pollen data show that forests were essentially cleared by Early Classic time. Sharply accelerated slopewash and colluviation, amplified in the Yaxha subbasin by urban construction, transferred nutrients plus calcareous, silty clay to both lakes. Except for the urban silt, colluvium appearing as lake sediments has a mean total phosphorus concentration close to that of basin soils. From this fact, from abundance and distribution of soil phosphorus, and from continuing post-Maya influxes (80 to 86 milligrams of phosphorus per square meter each year), which have no other apparent source, we conclude that riparian soils are anthrosols and that the mechanism of long-term phosphorus loading in lakes is mass transport of soil. Per capita deliveries of phosphorus match physiological outputs, approximately 0.5 kilogram of phosphorus per capita per year. Smaller apparent deliveries reflect the nonphosphatic composition of urban silt; larger societal outputs, expressing excess phosphorus from deforestation and from food waste and mortuary disposal, are probable but cannot be evaluated from our data. Eutrophication is not demonstrable and was probably impeded, even in less-impacted lakes, by suspended Maya silt. Environmental strain, the product of accelerating agroengineering demand and sequestering of nutrients in colluvium, developed too slowly to act as a servomechanism, damping population growth, at least until Late Classic time.     

热带亚热带森林凋落物交互分解的养分动态

为了探究全球变暖对森林凋落物分解速率及养分释放的影响，笔者在跨气候带的大尺度下进行了森林凋落物的交互分解实验.在热带的尖峰岭和亚热带的鼎湖山各选样地1个，它们有相似的海拔高度、土壤类型、年均降雨量及干湿季节律，年均气温为主要差异，达3.7 ℃.各样地分别收集了10种当地的优势树种的凋落叶.其中2个样地各自的优势种青皮和锥栗，2个样地均有的共同种荷木做为单种样.10种凋落叶的等重量混合为混合样，共计6类凋落叶，交互置于2个样地分解.结果表明:6类凋落叶在尖峰岭的分解速率显著大于在鼎湖山的分解速率.凋落叶分解的表观Q10在3.7～7.5范围内.在这个增温范围内，凋落叶分解加快的程度可达1.36～3.06倍，鼎湖山凋落叶第1年归还的N、P和C将分别增加32.42、1.033和741.1 kg/hm[[sup]]2[[/sup]]只在鼎湖山的分解中，分解速率常数k值与凋落叶初始质量参数木质素/N、木质素、木质素/P、木质素纤维素商(HLQ)、C有显著的较高相关性，而在尖峰岭的分解中k值与凋落叶初始质量参数无显著相关性.      

南亚热带森林演替植物幼苗生态位适应度模拟

适应度和生态位适应度既有相似性也存在区别,该文在综述两者概念的基础上,利用生态位中心、实际生态位和生态位宽度构建生态位适应度,分析两者存在的关系.结果发现生态位适应度和适应度具有一定的相关性,幼苗的生理特性可以用于表征物种在演替过程中的适应度,但是生态位适应度的动态提前于适应度的动态;同时利用限制因子构建的生态位适应度模型可以了解演替过程中影响物种演替的限制因子.该文的研究提供了一种利用物种生理特性定量研究演替过程中物种适应度动态的方法.      

西双版纳热带林生长动态模型及可持续经营模拟

为研究中国热带森林的可持续经营方式,在中国西南西双版纳的山地雨林中设置了12块固定观测样地,并在定期观测数据基础上估计林分生长量、林木进界率与径阶保留率等.据此建立林分自然生长的径级分布模型,择伐作业对保留木影响的损伤模型,采伐后由于林窗效应对林木生长影响的经验模型,进界生长模型等热带森林生长动态数学模型并估计了林分初始状态、林分动态转移因子等参数.以森林经营实践的内在逻辑和关键过程为基础设计了森林生长和经营模拟系统的框架概念,应用面向对象的方法设计系统的各个独立程序模块,用VBA 语言与EXCEL结合开发了系统应用软件.应用本模拟系统对西双版纳热带林的择伐经营模式作了所有可能参数组合的模拟经营实验,提出了热带林区国营林场和村寨集体林最适宜的可持续经营指标和标准.     

Enhanced upper tropical tropospheric COS: impact on the stratospheric aerosol layer

Carbonyl sulfide (COS) is considered to be a major source of the stratospheric sulfate aerosol during periods of volcanic quiescence. We measured COS at the tropical tropopause and find mixing ratios to be 20 to 50% larger than are assumed in models. The enhanced COS levels are correlated with high concentrations of biomass-burning pollutants like carbon monoxide (CO) and hydrogen cyanide (HCN). The analysis of backward trajectories and global maps of fire statistics suggest that biomass-burning emissions transported upward by deep convection are the source of the enhanced COS in the upper tropical troposphere.     

辽东山区次生林主要树种种群结构和格局

用“径级大小替代年龄大小”和“空间差异替代时间变化”的方法,分别研究了辽东山区4种主要群落（柞木林、硬阔林、杨桦林和杂木林）主要树种种群的结构和分布格局,以及应用方差/均值比的t值检验法、聚块性和扩散型指数分析其格局状况,并用聚集强度指数负二项参数K值度量了它们的聚集程度.结果表明:①蒙古栎、水曲柳、核桃楸、枫桦和山杨龄级存在明显的低龄缺损,为间歇型种群,其中蒙古栎、水曲柳和核桃楸属于增长型种群,枫桦和山杨属衰退型种群,色木槭、紫椴和春榆种群年龄结构呈不规则的倒J型种群结构,龄级完整,属于稳定型增长种群;②这些主要树种种群中,除了杨桦林群落中枫桦和山杨格局呈随机分布外,其他种群的格局都趋于聚集分布;③各主要树种种群等级分布格局具有一定的规律性,即种群在幼苗和幼树阶段为聚集分布,而在中树和大树阶段为随机或均匀分布,且各主要树种种群从幼苗到大树格局聚集强度逐渐降低,种群呈扩散趋势;④辽东山区次生林主要树种种群结构和格局的形成主要是由于其生物学特性和所处环境作用的结果.