林窗几何特征的测定方法

林窗面积、形状及边界木高是决定林窗环境异质性的3个林窗几何特征,影响林窗内植物更新。林窗几何特征的快速测量方法是林窗研究的基础,测量方法可分为2类:基于地面实际测量的地面法和基于林窗林冠照片的相片法。地面法费时费力,受人为因素影响大,可测量林冠林窗和扩展林窗的面积,但不能测量林窗形状和边界木高。相片法具有简单、客观、可重复的优点,但仅适用于林冠林窗。相片法共有5种:"平面相片法"、"航片法"、"半球面影像法"、"双半球面影像法"和"改进的半球面影像法"。前3种测量方法只能测量林冠林窗面积;"改进的半球面影像法"可测量林冠林窗面积和形状,且精度高于前3种相片法,但所需参数最多;"双半球面影像法"可测量林窗面积、形状及边界木高这3个林窗几何特征,且精度较高,但拍摄要求较高。     

一种测量林窗面积的改良方法:等角椭圆扇形法

目前测量林窗面积较精确的方法为:测量从林窗中心沿8或16个罗盘方向到林窗林冠边缘的距离,再将林窗近似成等角8或16边形估测其面积(本文称这类方法为等角多边形法)。研究表明,等角8或16边形法均会低估林窗面积,本文提出一种改良方法:等角椭圆扇形法,野外测量与前者相同,计算时将相邻距离间的部分近似为椭圆扇形,以所有椭圆扇形面积之和估测林窗面积。用配对t检验对等角多边形法和等角椭圆扇形法的林窗面积进行比较,结果表明:(1)等角16边形法与等角8或4边形法存在极显著差异(P<0.001),比后两者,分别高10.96%和61.66%,这表明等角条边形法均会低估林窗面积;(2)等角椭圆扇形16分法比等角16边形法大10.16%,且二者之间存在极显著差异(P<0.001),因此,等角16边形法的测量值位于等角椭圆扇形16分法和等角8边形法之间;由(1)和(2)可推断等角椭圆扇形16分法比等角8边形法更准确;(3)等角椭圆扇形8分法与等角椭圆扇形16分法没有显著差异(P=0.715),但与等角8边形法存在显著差异(P<0.05),因此,等角椭圆扇形8分法比等角8边形法更准确。另外,本文的两个等角8边形法(基于两组不同罗盘方位的测量距离)求得的林窗面积之间存在极显著差异(P<0.01),而两个等角椭圆扇形8分法之间却没有差异(P=0.778),这表明等角椭圆扇形8分法的结果更稳定。     

基于机载激光雷达的中亚热带常绿阔叶林林窗特征

机载激光雷达(LiDAR)是一种新型主动式遥感技术,能直接获取多尺度高精度的冠层三维结构信息,将其推广到森林干扰生态学领域,可为林窗研究提供应用支撑.以湖南中亚热带常绿阔叶林为研究对象,利用小光斑LiDAR数据进行林窗识别和几何特征估测.选择合适的分辨率和内插方法生成冠层高程模型,采用计算机图形学方法估测林窗面积、边界木高度和形状指数,并进行野外观测验证.结果表明: 林窗识别率为94.8%,主要影响因素是林窗面积和林窗形成木类型;估测的林窗面积和边界木高与野外观测值呈较强线性相关,R²值分别为0.962和0.878,其中估测的林窗面积平均比野外观测值高19.9%,估测的林窗边界木高度平均比野外观测值低9.9%;区域内林窗密度为12.8个·hm^-2,占森林面积13.3%;林窗面积、边界木高和形状指数的平均值分别为85.06 m²、15.33 m和1.71,区域内多为较小面积、边缘效应不太显著的林窗.
     

热带次生林林窗干热季光照特征初步分析

利用西双版纳干热季 ( 3～ 4月 )次生林林窗光照观测资料 ,探讨了林窗光照的时空变化特征。结果表明 :由于天气现象 (雾 )、太阳高度和林窗树木的共同影响 ,使得林窗区域光照强度在时空上均存在明显的差异 ;上午光照强度的时间变化不明显 ,光强高值区在林窗西南侧边缘 ;中午受太阳辐射的影响 ,各测点光强均迅速上升 ,尤以林窗偏东侧林缘最为突出 ,实际林窗边缘的光强远远大于扩展林窗边缘 ;平均光强最大区域由林窗西南侧向东北侧林缘移动 ,而林窗偏西侧受树木遮蔽影响 ,光强虽有增加 ,但由于实际林窗边缘的高光强维持时间较短 ,平均光强较小 ,特别是偏西侧的扩展林窗边缘 ,遮蔽影响较大 ,各时刻的光强均不大 ,形成平均光强的低值区 ;使得中午林窗区域光照强度不对称性更加显著 ,光强水平梯度增大 ;下午由于太阳西进 ,林窗区域均受到树木遮蔽影响 ,光强降低 ,水平梯度变化趋于和缓。在西双版纳干热季作为林窗主要热力作用面之一的林窗地表面 ,在不同时段其最大光强的数值和出现区域以及高光强维持时期均存在较大差异 ;使得林窗区域的光强分布存在时间差异和空间不对称性 ,如此的光强分布势必造成林窗不同区域热力作用的不同 ,进而导致林窗区域热量传输和热量储存的不同 ,产生不同的热力效应。本研究结果?     

红松阔叶混交林林隙大小及光照对草本植物的影响

在小兴安岭红松阔叶混交林中选取的6个林隙内,以每个林隙中心为起点,沿东西和南北两个方向,每隔2 m平行布置1个1 m×l m的固定样方.2011年6月和9月利用估测法测定样方内不同高度等级草本植物的覆盖度和多度,记载样方内基质特征.6-9月每月选择阴天,利用冠层分析仪拍摄鱼眼照片,用Gap Light Analyzer 2.0软件计算相对光强.分析不同林隙间相对光强、草本植物覆盖度和丰富度的差异,以及各物种覆盖度与直射光、漫射光和基质的关系.结果表明:开阔区和林冠下的大林隙相对光强均大于小林隙,而且从林隙中心到林隙边缘的漫射光、直射光变化范围也大于小林隙;不同区域大、小林隙到达地面的直射光大小顺序为北部大于南部;在Z1～Z4区域内,大林隙的草本植物覆盖度和丰富度均大于小林隙,其中大、小林隙物种丰富度之间的差异达到了显著水平.另外,大多数草本植物覆盖度与漫射光和基质之间显著相关,只有少数草本植物覆盖度与直射光呈相关关系.     

林窗对格氏栲天然林更新层物种多样性和稳定性的影响

采用物种多样性指数和改进的M.Godron稳定性法研究林窗干扰对格氏栲(Castanopsis kawakamii)自然保护区天然林更新层物种多样性和稳定性的影响.结果表明:林窗干扰改善了微环境,表现在林窗和林下乔灌层树种重要值和多样性存在差异.林窗乔木层中丰富度指数R、优势度指数D、Shannon-Wiener指数H、均优多指数Z均高于林下,均匀度指数Js和群落优势度指数C低于林下;灌木层中R、D、H、Js、Z指数均高于林下,群落优势度指数C低于林下,林窗物种多样性更为丰富,生态优势种不明显,群落向复杂化和均匀化方向发展.林窗与林下乔木层Jaccard相似性系数Cj、Sorenson相似性系数CS、Bray-Curtis指数CN相对较低,Morista-Horn指数CmH较高,林窗对树种更新具有促进作用;灌木层相似性系数Cj、Cs、CN、CmH均较高,物种组成基本一致.根据M.Godron稳定性原理拟合出稳定性模型,林窗和林下乔木层分别为对数模型与二次函数模型,林窗和林下灌木层最佳拟合模型均为对数模型.林窗乔木层植物处于稳定状态,林下乔木层植物不稳定;林窗和林下灌木层植物均处于稳定状态.林窗和林下乔木层树种中以桂北木姜子(Litsea subcoriacea)重要值最高,说明其在森林更新中占有重要地位,可能对格氏栲种群更新产生较大影响.林下乔木层中格氏栲重要值较低,格氏栲更新存在困难,而林窗干扰促进了格氏栲的向上生长和重要值的提升,可有效实现格氏栲种群的更新和恢复.     

辽东山区天然次生林两个不同坡向林窗光温空间分布特征

为探讨辽东山区次生林林窗干扰特征,对不同坡向雪/风干扰后形成林窗内的光温空间分布特征进行了研究。结果表明:东北和东南坡向的林窗中,各时段光量子通量密度(PPFD)和气温的空间分布格局类似但大小并不相同;8:00—10:00 PPFD最高值均出现在林窗中央偏西(东北坡169μmol·m-2·s-1,东南坡350μmol·m-2·s-1),11:00—13:00PPFD最高值出现在林窗中央偏北侧(东北坡234μmol·m-2·s-1,东南坡400μmol·m-2·s-1),而14:00—16:00均以林窗东侧PPFD最大(东北坡74μmol·m-2·s-1,东南坡56μmol·m-2·s-1),且两个坡向的PPFD在各时段大小差异显著(P0.05)。两个坡向林窗内平均气温的空间分布均表现为8:00—10:00西高东低,11:00—13:00北高南低,14:00—16:00东高西低的趋势,而在各时段的差异为8:00—10:00、11:00—13:00东北坡气温显著低于东南坡(P0.01),14:00—16:00则显著高于东南坡(P0.01)。上述结果表明,林窗坡向及林窗内位置不同,使其光温环境发生异质性,进而影响到林窗区域种子萌发、幼苗生长发育及植物种群分布等,最终影响到森林的更新。     

格氏栲天然林林窗植物物种多样性与系统发育多样性

林窗环境异质性导致群落物种多样性与系统发育多样性(phylogenetic diversity, PD)存在差异, 研究不同大小的林窗中群落的物种多样性与系统发育多样性有助于揭示林下生物多样性的形成及维持机制。本文以格氏栲(Castanopsis kawakamii)天然林为研究对象, 通过Pearson相关性分析与广义线性模型探讨了林窗内物种多样性与系统发育多样性间的相互关系及其环境影响因素。结果表明: (1)大林窗(面积 > 200 m²)植物种类及多度均高于中林窗(50 m² ≤ 面积 < 100 m²)、小林窗(30 m² ≤ 面积 < 50 m²)和非林窗(面积 = 100 m²)。大林窗群落系统发育结构趋于发散, 中、小林窗和非林窗群落系统发育结构受到生境过滤和竞争排斥综合作用。(2)群落系统发育多样性指数与物种丰富度(species richness, SR)、Margalef丰富度指数和Shannon-Wiener指数均呈显著正相关, 这与林窗内稀有种种类组成多于优势种有关。(3)林窗面积对物种多样性存在显著正效应; 土壤全氮含量对系统发育多样性和系统发育结构存在显著正效应。林窗形成提高了格氏栲天然林群落物种多样性和系统发育多样性, 林窗面积与土壤全氮共同驱动了格氏栲天然林林窗物种多样性和系统发育多样性的变化。     

江淮分水岭落叶阔叶林林窗光环境特征及其对绞股蓝生长特性的影舷

根据对江淮分水岭地区落叶阔叶林(枫香,Liquidambar formosana)林窗与林下入射光的总光照强度、不同波段的光照强度和光谱成分的比较分析,以及相应生境下绞股蓝(Gynostemma pentaphyllum)生长特性和总皂甙含量的对比研究,结果表明,林窗入射光全波长的日总光照强度、蓝光(400～510 nm) 、黄绿光(510～610 nm)、红橙光(610～720 nm)和近红外光(720～1100 nm)的光强,以及除近红外光以外的其余色光光谱成分均高于林下,其中蓝光和红橙光的光照强度及其光谱成分比其它色光明显高于林下,且幅度有季节性差异.在4、7和10月份,林窗中的蓝光相对光照强度分别高于林下8.32%～28.83%、30.00%～579.17%和6.70%～88.74%,红橙光分别高出8.72%～28.83%、30.19%～502.69%和6.76%～91.57%,蓝光光谱成分分别比林下增加了5.76%、33.14%和17.29%,红橙光分别比林下增加了5.04%、53.34%和10.23%.林窗下的绞股蓝净光合速率、总干物质重和总皂甙含量皆高于林下;同时林窗的光环境使干物质向茎分配比例增大,且这些差异有明显的季节性.     

江淮分水岭落叶阔叶林林窗光环境特征及其对绞股蓝生长特性的影响

根据对江淮分水岭地区落叶阔叶林(枫香,Liquidambar formosana)林窗与林下人射光的总光照强度、不同波段的光照强度和光谱成分的比较分析,以及相应生境下绞股蓝(Gymostemma pentaphyllum)生长特性和总皂甙含量的对比研究,结果表明,林窗入射光全波长的日总光照强度、蓝光(400—510nm)、黄绿光(510—610nm)、红橙光(610—720nm)和近红外光(720—1100nm)的光强,以及除近红外光以外的其余色光光谱成分均高于林下,其中蓝光和红橙光的光照强度及其光谱成分比其它色光明显高于林下,且幅度有季节性差异．在4、7和10月份,林窗中的蓝光相对光照强度分别高于林下8．32％～28．83％、30．00％～579．17％和6．70％～88．74％,红橙光分别高出8．72％～28．83％、30．19％～502．69％和6．76％～91．57％,蓝光光谱成分分别比林下增加了5．76％、33．14％和17．29％,红橙光分别比林下增加了5．04％、53．34％和10．23％．林窗下的统股蓝净光合速率、总干物质重和总皂甙含量皆高于林下;同时林窗的光环境使干物质向茎分配比例增大,且这些差异有明显的季节性。     

Estimation of canopy gap size and gap shape using a hemispherical photograph

Gap size and gap shape are two important properties of forest gaps that can influence microsite conditions in a forest stand and determine the recruitment and establishment of trees. There is no universally adopted method for measuring the gap size, although several options are available. In addition, few methods have been proposed for measuring the gap shape. This paper proposes a photographic method of estimating canopy gap size and gap shape. The proposed method is based on a vertical hemispherical photograph of the gap and is thus named the hemispherical photograph method (HPM). We tested the accuracy of the HPM measure of gap size by two ground-based methods and compared the HPM with other methods. Our results indicate that the HPM measurement of the canopy gap size is accurate, but is significantly influenced by the location of the camera. Compared with the ground-based methods, the HPM is more objective and repeatable. Compared with other photographic methods, HPM is more accurate due to the more actual assumptions, but is more labor-intensive because more field measurements are necessary. We conclude that the HPM is a powerful tool for comparative and long-term studies of forest gaps.     

Modelling Direct Radiation and Canopy Gap Regimes in Tropical Forests

Spatial and temporal variation in the below‐canopy light environment of tropical forests is not well known and its measurement is technically challenging. Distributions of gap and understory areas in forests are likewise little known because of the resource requirements of forest structural censuses and a lack of consensus over how gaps should be defined. A basic model of forest structure, based on tree allometries from the 50 ha Forest Dynamics Plot on Barro Colorado Island (BCI), Panama, and a solar positioning algorithm were used to predict spatial and temporal variation in the distribution of direct light at the forest floor. Predicted duration of direct sunlight was then compared with the distribution of gap and understory areas, delimited according to four standard gap definitions, giving predictions for the correspondence between direct light regimes and forest structure. At least 36 percent of the areas of gaps of all sizes was predicted to receive < 1 h of direct sunlight per day, and the understory to receive direct sunlight for ≥ 1 h per day in up to 15 percent of its area, even when not in proximity to gaps. The predicted distribution of light changed over the course of the year with the greatest spread of light throughout the forest floor coinciding with the months when maximum daily solar elevation peaked. These predictions suggest a partial decoupling of light regimes from canopy structure, with implications for gap definitions, patch models of forest development and current understanding of tree seedling recruitment patterns.     

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.     

Methods for estimating understory light conditions using crown projection maps and topographic data

Four types of indices of canopy characteristics were compared to estimate understory light conditions using crown projection maps and topographic data. Crown area (CA) was formulated from the crowns in a focal sub-block (20 m×20 m). Canopy shade index (CSI) was formulated from the crowns in a focal sub-block and the surrounding sub-blocks with topographic effect. Site shade index (SSI) incorporated the shade of the slopes into CSI and represented the total physical closure of the site. Site light index (SLI) incorporated the azimuth of the site into SSI and evaluated the light condition of the understory. We tested the methods using the data on steep old-growth Cryptomeria japonica forests on Yakushima Island and the three-dimensional canopy structures of the forests were digitized on a geographic information system. The results were validated by the basic indices obtained by hemispherical photographs: canopy openness (CO) and gap light index (GLI). The three-dimensional structure of the surrounding canopies and topography had significant effects on the understory light conditions. CA had no significant correlation with CO, whereas CSI and SSI had significant negative correlations with CO. Although SLI had the highest negative correlation with GLI (R²=0.69), CSI had practical utility in the estimation of GLI (R²= 0.65). Our method is applicable to past crown projection maps that have been recorded at many forest research sites, thus making it possible to reconstruct past understory light conditions and to compare them with present conditions.     

应用全天空照片估计林分透光孔隙度(郁闭度)

林分结构通过影响林内环境与生物因子,决定森林生态系统服务功能发挥;同时,通过调整林分结构亦可达到森林合理经营的目标。林分透光孔隙度(郁闭度)是决定林分结构的重要因子之一,它可以用来表征光、水等环境因子通过林冠进入林内的再分布状况。因此,合理、精确地确定林分内的郁闭状况,无论在森林经营与管理,还是在森林生态精细研究中,都显得十分重要。本文在以往研究的基础上,详细介绍了应用全天空照片(Hemispherical photograph/whole sky photograph)确定林分内一定高度(通常为1 m)的林分郁闭度或林分透光孔隙度(两者互补)的方法与步骤,重点讨论了在应用全天空照片确定林分郁闭度/透光孔隙度时选择的有效范围和应注意的实际问题。     

Subcanopy gaps in temperate and tropical forests

Abstract We present a model of gaps in the vertical structure of forest vegetation. The traditional model of a forest gap assumes the existence of a ‘hole’ in the uppermost canopy layer, often extending down to near the ground. The present model extends the concept to gaps at any level, including those in lower layers below an intact canopy or subcanopy. It assumes that gaps at any level represent spaces with unused resources, especially favourable for plant growth and survival. Evidence from temperate and tropical forests indicates that gaps in the subcanopy and understorey layers below intact canopies are common, and that plants have higher growth rates in them than in non-gap sites. We also extend this model to below-ground gaps in the root zone.     

Leaf growth dynamics of two congener gymnosperm tree species reflect the heterogeneity of light intensities given in their natural ecological niche

Chamaecyparis obtusa var. formosana and Chamaecyparis formosensis are congener gymnosperm tree species native to Taiwan cloud forests; occupying different niches there. While the seedlings of C. formosensis occur predominantly under bright conditions in large forest gaps, seedlings of C. obtusa var. formosana are mainly found below the canopy of mature forests or in small gaps. It is well known that congener species occupying different niches typically differ in several ecophysiological and morphological traits, but the differences in growth dynamics of such species are still totally unclear, as the diurnal growth dynamics of gymnosperm leaves have not been investigated before. Modern methods of digital image sequence processing were used in this study to analyse the leaf growth dynamics of the two species. We found that both species show similar base–tip gradients and pronounced diurnal growth rhythms with maxima in the evening. Differences between the two species concerning their growth dynamics correlated closely with their ecological amplitudes and abundances. Chamaecyparis obtusa var. formosana grew faster than C. formosensis in low light intensity, typical for closed-canopy situations, and reacted quickly by increasing or decreasing growth rate when light intensity changed within a range typically found below small canopy gaps. In contrast to this, C. formosensis grew better in light intensities typical for open vegetation situations, but reacted slower towards changes of light intensity. Based on those results, the hypothesis can be developed that fluctuations of leaf growth dynamics reflect heterogeneities of the light environment within the niche occupied by a given species.     

林窗对长苞冷杉自然更新幼苗存活和生长的影响

 长苞冷杉(Abies georgei)林是我国西南亚高山针叶林的重要类型之一,分布于海拔3 200～4 200 m。目前对于该森林林窗对树苗更新的调节还很少了解。通过1997～2000年对20个林窗的连续观测调查,研究了滇西北白马雪山自然保护区西坡亚高山长苞冷杉林林窗大小和林窗位置对自然更新幼苗存活和生长的影响。长苞冷杉针叶林林窗大小分布为,面积大于100 m2的大林窗占20%左右,中等林窗面积为50～100 m2,占35%左右,小林窗面积小于50 m2,占45%左右。4个生长季节的连续观测结果表明：林窗与林下非林窗内的幼苗大小和幼苗存活数量差异明显。林窗由小到大,单位面积内的自然更新苗木数量逐渐增加,大林窗中更新苗为小林窗的1.5倍左右,而林下的更新苗很少,0.5 ind.·10 m-2。中等林窗和小林窗内的幼苗数量在从南到中心到北的位置上几乎没有明显的差异;大林窗中存在由南到北的位置差异,更新幼苗数量逐渐增加。从更新幼苗的生长来看,中等林窗内的幼苗,高度最大、生长最快,定居阶段的平均年高生长为(7.8±0.5) cm·a-1,小林窗次之,大林窗和林下幼苗个体最小,生长最慢。更新幼苗的基径随林窗大小的变化与高度变化相似。进一步从林窗位置来看,中、小林窗幼苗大小和年平均高生长量几乎无位置差异,大林窗则由南到北,幼苗由大变小,年高生长量逐渐减低。从幼苗存活数量、生长大小来看,中等林窗大小是长苞冷杉幼苗更新的适宜面积,这为该类型退化亚高山针叶林恢复提供了一定的参考。