林冠结构和地形对亚热带常绿落叶阔叶林林下幼苗物种多样性和功能多样性的影响

森林结构和地形是森林生态系统最明显的特点,也是影响林下幼苗存活和物种多样性的关键因子。该研究采用半球面摄影方法提取八大公山生长监测样地（共1.2 hm²）林冠结构参数,通过调查地表层木本植物幼苗的组成和多度,获取常见植物幼苗叶片功能性状,结合详细的地形信息,利用空间同步自回归模型探究林冠结构变量及地形因子对幼苗物种多样性及功能多样性的影响。结果表明：（1）八大公山亚热带山地常绿落叶阔叶林林冠结构复杂度较高,最大林冠高的平均值达到19.94 m,叶面积指数、平均叶倾角和林冠覆盖度分别为2.94、30.88°和0.87;（2）林冠结构变量和地形因子能够解释32.6%~48.4%的林下幼苗物种多样性指数变异和28.5%~70.2%的功能多样性变异,但地形因子对幼苗物种多样性的影响很小;（3）预测在亚热带常绿落叶阔叶林高海拔的山坡上,有较低的叶面积指数和平均叶倾角群落有较高的幼苗物种多样性;而在低海拔山脊上,较低的叶面积指数和平均叶倾角群落林下幼苗层有较高的功能多样性。此结果对科研人员和林业工作者开展野外森林更新情况评估和样方调查将有所帮助。     

Age‐related Crown Thinning in Tropical Forest Trees

Gap dynamics theory proposes that treefall gaps provide high light levels needed for regeneration in the understory, and by increasing heterogeneity in the light environment allow light‐demanding tree species to persist in the community. Recent studies have demonstrated age‐related declines in leaf area index of individual temperate trees, highlighting a mechanism for gradual changes in the forest canopy that may also be an important, but less obvious, driver of forest dynamics. We assessed the prevalence of age‐related crown thinning among 12 tropical canopy tree species sampled in lowland forests in Panama and Puerto Rico (total N = 881). Canopy gap fraction of individual canopy tree crowns was positively related to stem diameter at 1.3 m (diameter at breast height) in a pooled analysis, with 10 of 12 species showing a positive trend. Considered individually, a positive correlation between stem diameter and canopy gap fraction was statistically significant in 4 of 12 species, all of which were large‐statured canopy to emergent species: Beilschmiedia pendula, Ceiba pentandra, Jacaranda copaia, and Prioria copaifera. Pooled analyses also showed a negative relationship between liana abundance and canopy gap fraction, suggesting that lianas could be partially obscuring age‐related crown thinning. We conclude that age‐related crown thinning occurs in tropical forests, and could thus influence patterns of tree regeneration and tropical forest community dynamics.     

Spatial scale and sampling resolution affect measures of gap disturbance in a lowland tropical forest: implications for understanding forest regeneration and carbon storage

Treefall gaps play an important role in tropical forest dynamics and in determining above-ground biomass (AGB). However, our understanding of gap disturbance regimes is largely based either on surveys of forest plots that are small relative to spatial variation in gap disturbance, or on satellite imagery, which cannot accurately detect small gaps. We used high-resolution light detection and ranging data from a 1500 ha forest in Panama to: (i) determine how gap disturbance parameters are influenced by study area size, and the criteria used to define gaps; and (ii) to evaluate how accurately previous ground-based canopy height sampling can determine the size and location of gaps. We found that plot-scale disturbance parameters frequently differed significantly from those measured at the landscape-level, and that canopy height thresholds used to define gaps strongly influenced the gap-size distribution, an important metric influencing AGB. Furthermore, simulated ground surveys of canopy height frequently misrepresented the true location of gaps, which may affect conclusions about how relatively small canopy gaps affect successional processes and contribute to the maintenance of diversity. Across site comparisons need to consider how gap definition, scale and spatial resolution affect characterizations of gap disturbance, and its inferred importance for carbon storage and community composition.     

华南海岸英罗港红树植物木榄种群结构的空间异质性(英文)

The spatial heterogeneity, including distribution pattern, tree perimeter and height differentiation, and canopy structure heterogeneity, of Bruguiera gymnorrhiza (L.) Lamk populations at Yingtuo Bay, South-China Coast was investigated using the positioning index (CE), differentiation index (TC and TH), Shannon-Wiener diversity index (D), and Ripley‘s K-functions. Most populations showed random distribution and low differentiation in perimeters and heights of individuals, while a few showed clumped distribution and clear differentiation. Canopy and gap patches were analyzed at multiple horizontal and vertical scales using geographic information system (GIS). The mosaic patterns of canopy and gap patches are different among populations, and could be quantitatively described with the Shannon-Wiener diversity index based on crown projection. The spatial heterogeneity of the canopy structure changed with spatial scales, but this kind of change would remain relatively stable over a range of scales. This scale range could be regarded as the referenced scale for a regeneration or ecological management unit for the forest.     

华南海岸英罗港红树植物木榄种群结构的空间异质性

采用位置指数(CE)、分异指数(TC和TH)、Shannon-Wiener多样性指数(D)以及Ripley的K-方程,探讨了华南海岸英罗港树植物木榄种群的分布格局、胸转和树高分异以及冠层结构方面的空间异质性.多数种群呈现随机分布,其个体胸转和树高的分异程度较低;页少数种群呈现集群分布,其个体胸围和树高的分异程度明显.采用地理信息(GIS)对冠层和空隙斑块进行了多种水平垂直尺度的分析,冠层与空隙斑块之间的镶嵌格局因种群而异,这种可基于树冠抽影用Shannon-wiener多样性指数时行定量描述.冠层结构的窨异质性阻碍空间尺度而变化,但这种变化在一定尺度范围内保持相对的稳定.迷一尺度范围可作为木榄红树森更新或生态管理单位的参考尺度.     

天童国家森林公园常绿阔叶林不同演替阶段群落光环境特征比较

常绿阔叶林是我国中亚热带东部典型植被类型,根据野外踏查和固定样地调查发现,天童国家森林公园内发育着常绿阔叶林一个完整的演替系列,包含着6个不同演替阶段。应用W inScanopy For C anopy A na lys is软件对研究区内不同演替阶段群落冠层进行分析,得到不同群落冠层和林下的光环境特征指标:PPFD(光合光量子通量密度)和相关的冠层结构形态学指标G ap fraction(空隙度)、LA I(叶面积指数)、M LA(平均叶倾角),通过对这些指标的分析比较,得到的基本规律大致是林冠层的光合有效光量子通量密度随演替逐渐降低,林冠下面的光合有效光量子通量密度随着群落演替的进展变化更为明显。马尾松林的林冠空隙度明显高于其他阶段的群落,总的趋势是随群落演替的进展而降低。叶面积指数随演替的进展而呈增加趋势。平均叶倾角随演替的进展先增大而后减小。这些结果反映了常绿阔叶林不同演替阶段群落由于不同树种树冠形态学结构的差异和微环境的不同,形成了特定群落内的特定光环境。     

西双版纳热带雨林林窗空间分布格局及其特征数与林窗下植物多样性的相关性

林窗作为森林群落中一种重要的干扰方式, 对林下物种构成有着重要的影响。开展林窗空间格局及其特征指数与林下植物多样性关系研究对于探讨林窗对林下生物多样性的影响有重要意义, 有助于进一步了解群落动态, 在物种多样性保护方面也具有指导作用。本研究在西双版纳热带雨林地区随机选取3块大小为1 ha的热带雨林为研究样地, 采用轻小型六旋翼无人机搭载Sony ILCE-A7r可见光传感器, 分别获取各个样地的高清数字影像, 结合数字表面高程模型以及各个样地的地形数据用以确定各样区的林窗分布格局, 并进一步提取出各林窗的景观格局指数。结合地面样方基础调查数据, 对各样地各林窗下植物多样性情况进行统计, 旨在分析热带雨林林窗空间分布格局以及林窗下植物多样性对各林窗空间格局特征的响应情况。研究表明, 西双版纳州热带雨林林窗呈大而分散的空间分布, 林窗空间格局特征指数如林窗形状复杂性指数、林窗面积都与林下植物多样性呈显著正相关关系。在面积小的林窗下, 较之林窗形状复杂性因子, 林窗面积大小对林下植物多样性影响更显著; 在面积达到一定程度后, 相对于面积因子, 林窗形状复杂性指数对林下植物多样性影响更显著, 各样地林窗皆趋于向各自所处样地顶极群落发展。     

An indirect method of estimating leaf area index in a tropical deciduous forest of India

Rapid, reliable and meaningful estimates of leaf area index (LAI) are essential to functional characterization of forest ecosystems including biomass and primary productivity studies. Accurate LAI estimates of tropical deciduous forest are required in studies of regional and global change modeling. Tropical deciduous forest due to higher species richness, multiple species association, varied phenophases, irregular stem densities and basal cover, multistoried canopy architecture and different micro-climatic conditions offers dynamism to the understanding of the LAI dynamics of different PFTs in an ecosystem. This investigation reports a new indirect method for measurement of leaf area index (LAI) in a topical moist deciduous forest in Himalayan foothills using LAI-2000 Plant Canopy Analyzer. We measured the LAI in two seasons (summer; leaf senescence stage and post-monsoon; full green stage) in three (dry miscellaneous, sal mixed and teak plantations) plant functional types (PFT) in Katerniaghat Wildlife Sanctuary, India. Ground LAI values ranged between 2.41 and 6.89, 1.17 and 7.71, and 1.92 and 5.19 during post-monsoon season and 1.36–4.49, 0.67–3.1 and 0.37–1.83 during summer season in dry miscellaneous, sal mixed and teak plantation, respectively. We observed strong correlation between LAI and community structural parameters (tree density, basal cover and species richness), with maximum with annual litter fall (R² > 0.8) and aboveground biomass (AGB) (R² > 0.75). We provided equations relating LAI with AGB, which can be utilized in future studies for this region and can be reasonably extrapolated to other regions with suitable statistical extrapolations. However, the relations between LAI and other parameters can be further improved with incorporation of data from optimized and seasonal sampling. Our indirect method of LAI estimation using litter fall as a proxy, offers repetitive potential for LAI estimate in other PFTs with relatively time and cost-effective way, thereby generating quicker and reliable data for model run for regional and global change studies.     

First direct landscape-scale measurement of tropical rain forest Leaf Area Index, a key driver of global primary productivity

Leaf Area Index (leaf area per unit ground area, LAI) is a key driver of forest productivity but has never previously been measured directly at the landscape scale in tropical rain forest (TRF). We used a modular tower and stratified random sampling to harvest all foliage from forest floor to canopy top in 55 vertical transects (4.6 m²) across 500 ha of old growth in Costa Rica. Landscape LAI was 6.00 ± 0.32 SEM. Trees, palms and lianas accounted for 89% of the total, and trees and lianas were 95% of the upper canopy. All vertical transects were organized into quantitatively defined strata, partially resolving the long-standing controversy over canopy stratification in TRF. Total LAI was strongly correlated with forest height up to 21 m, while the number of canopy strata increased with forest height across the full height range. These data are a benchmark for understanding the structure and functional composition of TRF canopies at landscape scales, and also provide insights for improving ecosystem models and remote sensing validation.     

Small Canopy Gaps Influence Plant Distributions in the Rain Forest Understory1

This study tested three hypotheses regarding how plants respond to the spatial heterogeneity in light availability in the rain forest understory: (1) understory plants occur preferentially in the lighter parts of the understory; (2) under–story palms are more shade tolerant than other understory plants; (3) rain forest plants differ in their ontogenetic response to understory light conditions. The study was carried out in old–growth rain forest in the Yasuní National Park, Amazonian Ecuador. The hypotheses were tested by comparing the distributions of 20 plant species (1454 individuals) over microsites with differing degrees of exposure to canopy gaps to the background distribution of these microsites in the forest. The gap exposure of a given microsite was described by an index based on the number and size of gaps in the canopy to which the site was exposed. Two plant height classes were studied: 0.80–2.49 and 2.50–5 m. The first and third hypotheses were accepted, while the second hypothesis was rejected. The results for the individual species corresponded well with what is known from earlier studies about the ecology of these species or close relatives, suggesting that the patterns observed can be generalized for Neotropical rain forests. Notably, the most abundant species in the study represent several different life history strategies. Thus, abundance in the rain forest understory can be achieved by several different strategies. This suggests that niche differentiation in terms of response to small changes in understory light conditions may be an important factor in the maintenance of the high local plant species richness of tropical rain forests.     

Saplings distribution in relation to topography and canopy openness in an evergreen broad-leaved forest

We examined the spatial distribution of saplings in relation to topography and stand structure in a subtropical evergreen broad-leaved forest in the northern part of Okinawa Island, Japan. The distributions of most species were influenced mainly by topography but also by canopy openness. Species were arranged along a topographical gradient from concave areas with low canopy openness to convex areas with high canopy openness. Canopy species were arranged along a gradient from unstable fertile areas to stable infertile areas. Species occurring mostly in convex areas had a narrower distribution range than those in concave sites. Thus, habitat heterogeneity provided by topography and stand structure appears to be important factors for maintaining high species diversity in the understory of this subtropical evergreen broad-leaved forest.     

沿海基干林带结构调控对林分冠层结构参数及林地土壤的影响

以上海浦东沿海水杉基干林带为研究对象,分析水杉林分间伐以及间伐后林下套种其他树种构建复层林2种结构调控措施下林分冠层及林地土壤的变化。结果表明:间伐和复层林构建可显著促进上层乔木树高和胸径的生长,也有助于林下乔灌木和草本植物的发育;未间伐水杉林带LAI最高,其次为复层林带,间伐林分最低。各林分林隙分数的分布特征与LAI相反;3种林分土壤全N、全P和速效K含量差异不显著,而间伐林和复层林土壤速效P、水解N和有机质含量比未间伐林有进一步改善,但间伐林分和复层林带之间土壤养分状况没有显著差异;林分结构调控增加了0～50cm土壤有机碳储量,其中以0～15cm土层有机碳密度最高。复层林带和间伐林土壤呼吸速率比未间伐林分别提高了42%和33%。     

Airborne LiDAR technique for estimating biomass components of maize: A case study in Zhangye City,Northwest China

Crop biomass is an important ecological indicator of growth, light use efficiency, and carbon stocks in agro-ecosystems. Light detection and ranging (LiDAR) or laser scanning has been widely used to estimate forest structural parameters and biomass. However, LiDAR is rarely used to estimate crop parameters because the short, dense canopies of crops limit the accuracy of the results. The objective of this study is to explore the potential of airborne LiDAR data in estimating biomass components of maize, namely aboveground biomass (AGB) and belowground biomass (BGB). Five biomass-related factors were measured during the entire growing season of maize. The field-measured canopy height and leaf area index (LAI) were identified as the factors that most directly affect biomass components through Pearson's correlation analysis and structural equation modeling (SEM). Field-based estimation models were proposed to estimate maize biomass components during the tasseling stage. Subsequently, the maize height and LAI over the entire study area were derived from LiDAR data and were used as input for the estimation models to map the spatial pattern of the biomass components. The results showed that the LiDAR-estimated biomass was comparable to the field-measured biomass, with root mean squared errors (RMSE) of 288.51 g/m² (AGB), and 75.81 g/m² (BGB). In conclusion, airborne LiDAR has great potential for estimating canopy height, LAI, and biomass components of maize during the peak growing season.     

海南岛热带天然针叶林主要树种的空间格局及关联性

天然针叶林在热带地区虽较为少见, 但其对维持热带地区的生物多样性和生境异质性具有特殊意义。在我国热带天然针叶林集中分布面积最大的海南霸王岭林区, 作者选择伴生阔叶树种优势度不同的两种典型南亚松(Pinus latteri)天然林(简称纯林和混交林), 采用点格局法分析了其林冠层、亚林层和林下层主要树种的空间分布格局及其关联性。结果表明: (1)纯林中林冠层的南亚松主要为聚集分布, 混交林中在较小尺度上为聚集分布, 在较大尺度上为随机分布。(2)纯林中亚林层树种在较小尺度上为聚集分布, 在较大尺度上为随机分布, 在混交林中主要为聚集分布。(3)纯林中林下层树种主要呈现为随机分布, 而在混交林中主要为聚集分布。(4)随着尺度的增加, 林冠层与其他两个层次的树种, 在纯林中表现出从空间无关联到正关联的变化趋势, 而在混交林中则表现出从空间无关联到负关联的变化趋势。(5)亚林层与林下层树种在各个尺度上都表现为空间正关联。由此可见, 热带天然针叶林中优势种南亚松对伴生阔叶树种的分布格局具有重要影响。     

基于多角度植被指数的马尾松林LAI反演方法

CHRIS/PROBA是目前具有最高空间分辨率（17 m×17 m）的星载多角度高光谱数据,该款数据在反演植被垂直结构参数,如树高、叶面积指数（leaf area index,LAI）等方面具有重要的应用前景。基于四尺度几何光学模型得到马尾松（Pinus massoniana Lamb.）冠层的归一化差分植被指数（normalized difference vegetation index,NDVI）各向异性分布规律,利用CHRIS红光特征波段和近红外特征波段构建一种新型多角度植被指数（normalized hotspot-dark-spot difference vegetation index,NHDVI）,并将其应用于CHRIS数据对马尾松林的LAI遥感估算上。结果显示：（1）相比归一化差分植被指数（NDVI）与土壤调节植被指数（soil adjusted vegetation index,SAVI）而言,NHDVI能很好地融合光谱信息与角度信息,与地面实测LAI的决定系数达到0.7278;（2）利用NHDVI-LAI统计回归模型方法来反演LAI值,将得到的LAI值与地面实测值进行相关性分析,结果拟合优度达到0.8272,均方根误差RMSE为0.1232。与传统植被指数相比,包含角度信息的多角度植被指数对LAI的反演在精度上有较大提升,同时比基于辐射传输模型的反演方法更简易、实用。     

三种人工林分的冠层结构参数与林下光照条件

以样方法为基础,用半球面影像技术测定了桉树林、湿地松林和混交林（木荷+青冈+银木荷）3种人工林分的冠层结构(叶面积指数LAI和林冠孔隙度CO)和林下光照条件(林下直射光TransDir和林下散射光TransDif),并分析了冠层结构与林下光照条件之间的关系.测定结果表明,桉树林、湿地松林和混交林的LAI平均值分别是1....     

山西灵空山天然松栎混交林群落特征与冠层结构

以2011年建设的山西灵空山4 hm²天然松栎混交林森林动态监测样地为研究平台,以400个10 m×10 m样方为测量单元,于2016年进行群落特征研究,采用半球面影像法(DHP)分析冠层结构和林下光照特征.结果表明: 样地内共有乔木5558株,共计25种,分属于10科15属.冠层开阔度(CO)集中在15.0%～25.0%,叶面积指数(LAI)集中在1.5～2.5,林下光环境参数集中在10.0%～30.0%.建群种在样地内的分布对冠层结构和林下光环境影响显著;冠层结构对林下光环境所有参数的影响方向一致,其中采用叶面积指数评价冠层结构动态的效果更佳;冠层开阔度和叶面积指数对林下光环境产生相反的影响,且均对散射光入射率影响程度最大.温性松栎混交林的林冠层整体较为均匀,林下光分布较为集中,林分树种组成与冠层结构对林下光照影响显著.     

Estimating leaf area index and light extinction coefficient using Random Forest regression algorithm in a tropical moist deciduous forest,India

Leaf area index (LAI) and light extinction coefficient (k) are the key structural parameters controlling many canopy functions like radiation and water interception, radiation extinction, water and gas exchange. The present study aims at developing predictive models for generating spatial distribution of LAI and k by integrating remote sensing imagery and field data. The study was carried out in a tropical moist deciduous forest of Uttarakhand, India. Various spectral variables were derived from Landsat 8 Operational Land Imager (OLI) data of 8 May 2017 to predict LAI and k. In-situ measurements of LAI, incident Photosynthetically Active Radiation (PAR) above canopy (I_o) and below canopy (I) were taken using CI-110 Plant Canopy Imager. Canopy gap fraction and k (using Beer-Lambert's equation) were calculated. Random Forest (RF) algorithm was used to predict the spatial distribution of LAI and k using the best predictor variables. The best predictor variables for LAI included band 6 (Short wave infra-red (SWIR) -1) and band 7 (SWIR-2), tasseled cap wetness, Moisture Stress Index (MSI), and Normalized Difference Moisture Index (NDMI). For prediction of k, the best predictor variables were band 6 (SWIR-1) and band 7 (SWIR-2), NDMI, tasseled cap wetness, MSI and Normalized Difference Vegetation Index (NDVI). These variables were selected to generate RF-based models to predict LAI and k. On validation, the models were able to predict LAI with R² = 0.79 and % RMSE = 14.25% and k with R² = 0.77 and % RMSE = 11.98%. The predicted LAI and k followed an inverse relation in accordance with the Beer Lambert's Law. The results showed that RF can be effectively applied to predict the spatial distribution of LAI and k.     

广东南澳岛不同森林群落的林窗环境对移植树苗生长的影响

在广东南澳岛四个森林群落内移植了大叶相思（Acacia auriculaeformis),尾叶桉（Eucalyptus urophylla)和荷木（Schima superba)三种树苗,通过测定群落内林窗和非林窗生境中的叶面积指数,透光率和幼苗的生长高度,观察林窗环境对移植树苗生长的影响。结果表明：林窗的叶面积指数比非林窗的小;林窗的透光率大于非林窗;各群落的叶面积指数和爱光率有季节性的变化,变化幅度各不同,三种幼苗在林窗内比非林窗的乔木层下生长快;大叶相思和尾叶桉幼苗在林窗内的高度增长量显著大于非林窗下的,荷木虽也存在差异,但不如前两者显著。这些结果反映了不同生态特性的树种对林窗的反应不同。     

粤北山地常绿阔叶林自然干扰后冠层结构与林下光照动态

以粤北车八岭2008年受冰灾破坏的山地常绿阔叶林为研究对象,设置2 hm2固定样地开展连续3a(2008—2010年)的群落调查,并采用半球面影像技术(Hemispherical photography)获取冠层结构和林下光照指标,分析灾后森林演替过程中冠层结构和林下光照的动态。研究发现:1)灾后森林恢复过程中,样地林下光照(直射光、散射光和总光照)均随林冠开度的减少、叶面积指数的增加而减少;2)从2008到2010年,各年度冠层结构和林下光照的差异均极显著(P<0.0001),但年间差异程度有逐年减少的趋势;3)灾后森林恢复前3a,林下直射光对林下总光照的贡献大于散射光,其时空波动性也大于散射光;4)林冠开度对冠层结构的反映程度比叶面积指数高,冠层结构对林下散射光的影响比对直射光大。灾后林木先是迅速生长然后生长速度缓慢下来并逐渐稳定,随森林逐渐郁闭林下光照也随之减少,其中林冠开度用于评价冠层结构动态的效果更佳,林下直射光比散射光的时空变化更复杂。