祁连山区青海云杉林冠层叶面积指数的反演方法

doi:10.3773/j.issn.1005-264x.2009.05.004

摘要/Abstract

摘要：

叶面积指数(Leaf area index, LAI)是陆地生态系统的一个十分重要的结构参数。随着空间精细化模型的发展和基于过程的分布式模拟技术的应用, 对LAI的区域估算显得越来越重要, 但目前尚缺乏有效的估算手段。该项研究以青海云杉(Picea crassifolia)林为研究对象, 利用LAI-2000冠层分析仪、鱼眼镜头法和经验公式法对林冠层LAI进行了测定, 观测值分别为1.03~3.70、0.48~2.26和2.27~8.20, 显然, 仪器测定值偏低。针对针叶的集聚效应导致仪器测定值偏低的现象, 利用跟踪辐射与冠层结构测量仪(TRAC)测定的青海云杉林聚集系数计算调整系数, 对鱼眼镜头法获取的LAI值进行订正。根据高分辨率的遥感数据反演青海云杉林的植被指数与LAI的关系, 最后获得了较合理的该地区林冠层LAI的空间分布图。

关键词: 林冠层叶面积指数, 鱼眼镜头法, 青海云杉, 遥感数据(QuickBird), 祁连山区

Abstract:

Aims There is increasing need for regional estimates of leaf area index (LAI) because it is an essential input for many eco-hydrological processes models; however, there has been a lack of effective methods for its estimation. Picea crassifolia is the dominant species in the forest ecosystem of Qi- lian Mountains and is critical to the eco-hydrological processes of the ecosystem. Our objective is to compare methods for determining canopy LAI of this P. crassifolia forest.
Methods We investigated canopy LAI with an LAI-2000 canopy analyzer, hemispherical photography and allometric regression on tree height and diameter at breast height (DBH). The value was underestimated by the two instruments because of clumping in the conifer forest. In order to adjust the LAI measured and obtain the spatial distribution of LAI, we first measured the clumping index by Tracing Radiation and Architecture of Canopies (TRAC). Then we calculated the adjusting coefficient by the clumping index, which was used to adjust the LAI value measured by hemispherical photography. Then, we determined the relationship between adjusted LAI and vegetation indexes retrieved by high resolution remote sensing data (QuickBird) and estimated the spatial distribution of canopy LAI.
Important findings The values of canopy LAI were 1.03-3.70 by LAI-2000 canopy analyzer, 0.48-2.26 by hemispherical photography, and 2.27-8.20 by allometric regression. LAI value by allometric regression on tree height and DBH was used for assessing the measurement accuracy by the other two indirect measurement techniques. We found the two instruments (LAI-2000 canopy analyzer and hemispherical photography) under estimated the canopy LAI of the forest by about 3.14-3.86 times. We built statistical models between adjusted LAI and vegetation indexes and selected the optimal model, i.e., correlation between normalized difference vegetation index and LAI, through validating.

Key words: canopy leaf area index, hemispherical photography, Picea crassifolia, remote sensing data (QuickBird), Qilian Mountains

赵传燕, 沈卫华, 彭焕华. 祁连山区青海云杉林冠层叶面积指数的反演方法. 植物生态学报, 2009, 33(5): 860-869. DOI: 10.3773/j.issn.1005-264x.2009.05.004

ZHAO Chuan-Yan, SHEN Wei-Hua, PENG Huan-Hua. METHODS FOR DETERMINING CANOPY LEAF AREA INDEX OF PICEA CRASSIFOLIA FOREST IN QILIAN MOUNTAINS, CHINA. Chinese Journal of Plant Ecology, 2009, 33(5): 860-869. DOI: 10.3773/j.issn.1005-264x.2009.05.004

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链接本文: https://www.plant-ecology.com/CN/10.3773/j.issn.1005-264x.2009.05.004

https://www.plant-ecology.com/CN/Y2009/V33/I5/860

图/表 8

图1 研究区在西水自然保护区的相对位置和采样点的分布

Fig. 1 Location of study area in Xishui natural reserve and distribution of sampling sites

表1 祁连山排露沟流域6个固定样方青海云杉林的林分特征

Table 1 Stand characterisitcs of Picea crassifolia forest in six sampling plots of Pailugou catchment on Qilian Mountains

样方号 No. of sample	坡度 Slope (°)	经度Longitude (E)	纬度Latitude (N)	坡向 Aspect (°)	海拔 Altitude (m)	株数 No. of plants (株·hm^-2)	树高 Height of trees (m)	胸径DBH (cm)	胸高断面积Basal area at DBH (cm²)	冠层盖度Canopy gap fraction (%)
No. 1	30	100.28°	38.55°	25	2 655	1 350	9.84	7.41	172.56	68.98
No. 2	27	100.29°	38.54°	30	2 835	2 475	9.44	7.13	159.85	77.02
No. 3	25	100.30°	38.54°	12	2 889	2 225	7.78	7.20	162.93	80.34
No. 4	21	100.30°	38.54°	8	3 005	2 200	7.04	7.23	164.28	71.70
No. 5	22	100.30°	38.54°	18	3 106	825	6.88	2.49	19.47	57.01
No. 6	34	100.30°	38.54°	355	3 260	375	5.21	2.43	18.56	22.15

图2 35号样圆树木相对位置和半球图像获取位置图

Fig. 2 Relative positions of trees and sampling positions for hemispherical photography in the sampling plot 35

表2 鱼眼镜头、LAI-2000冠层分析仪和异速函数测定的林冠层叶面积指数的相关系数(r)

Table 2 Correlation coefficients (r) between leaf area index (LAI) of canopy obtained by fisheyes, LAI-2000 canopy analyzer and allometric equation

	鱼眼镜头4环LAI平均值 Average LAI by Fisheyes 4R	鱼眼镜头5环LAI平均值 Average LAI by Fisheyes 5R	冠层分析仪4环LAI平均值 Average LAI by LAI-2000 4R	冠层分析仪5环LAI平均值 Average LAI by LAI-2000 5R	异速函数获得的LAI The LAI by allometric equation
鱼眼镜头4环LAI平均值 Average LAI by Fisheyes 4R	1
鱼眼镜头5环LAI平均值 Average LAI by Fisheyes 5R	0.99	1
冠层分析仪4环LAI平均值 Average LAI by LAI-2000 4R	0.28	0.29	1
冠层分析仪5环LAI平均值 Average LAI by LAI-2000 5R	0.25	0.25	0.95	1
异速函数获得的LAI The LAI by allometric equation	0.69	0.68	0.29	0.27	1

图3 LAI-2000冠层分析仪与鱼眼镜头4环测定的青海云杉林林冠层叶面积指数(LAI)值散点图

Fig. 3 Scatter plot of the values of canopy leaf area index (LAI) of the Picea crassifolia forest obtained by LAI-2000 canopy analyzer and Fisheyes 4R

图4 青海云杉林林冠层鱼眼镜头获得的叶面积指数(LAI)与各植被指数的散点图 NDVI: 归一化植被指数 Normalized difference vegetation index RVI: 比值植被指数 Ratio vegetation index ARVI: 大气阻抗植被指数 Atmospherically resistant vegetation index MSAVI: 修正的土壤调节植被指数 Modified soil-adjusted vegetation index EVI: 改进型植被指数 Enhanced vegetation index SAVI: 土壤调节植被指数 Soil- adjusted vegetation index

Fig. 4 Scatter plots between canopy leaf area index (LAI) of the Picea crassifolia forest obtained by Fisheyes and six kinds of vegetation indexes

图5 研究区青海云杉林冠层叶面积指数(LAI)空间分布

Fig. 5 Spatial distribution of canopy leaf area index (LAI) of the Picea crassifolia forest in the study area

图6 研究区青海云杉林冠层叶面积指数(LAI)随海拔高度的变化粗线为叶面积指数的变化趋势线; 细线为叶面积指数的变化曲线 The thick line represents the trendline of LAI variation with the increase of altitude; The fine line represents the variation of LAI with the increase of altitude

Fig. 6 Variation of canopy leaf area index (LAI) of the Picea crassifolia forest in the study area with the increase of altitude

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