利用直接法和间接法测定针阔混交林叶面积指数的季节动态

doi:10.3724/SP.J.1258.2014.00079

摘要/Abstract

摘要：

利用光学仪器法能够快速、高效地测定森林生态系统的叶面积指数(leaf area index, LAI)。然而, 评估该方法测定针阔混交林LAI季节动态准确性的研究较少。该研究基于凋落物法测定了小兴安岭地区阔叶红松(Pinus koraiensis)林LAI的季节动态, 其结果可代表真实的LAI。参考真实的LAI, 对半球摄影法(digital hemispherical photography, DHP)和LAI-2000植物冠层分析仪测定的有效叶面积指数(effective LAI, L_e)进行了评估。首先对DHP测定LAI过程中采用的不合理曝光模式(自动曝光)进行了系统校正。同时, 测定了光学仪器法估测LAI的主要影响因素(包括木质比例(woody-to-total area ratio, α)、集聚指数(clumping index, Ω_E)和针簇比(needle-to-shoot area ratio, γ_E))的季节变化。结果表明: 3种不同方法测定的LAI均表现为单峰型的季节变化, 8月初达到峰值。从5月至11月, DHP测定的L_e比真实的LAI低估50%-59%, 平均低估55%; 而LAI-2000植物冠层分析仪测定的L_e比真实的LAI低估19%-35%, 平均低估27%。DHP测定的L_e经过自动曝光, α、Ω_E和γ_E校正后, 精度明显提高, 但仍比真实的LAI低估6%-15%, 平均低估9%; 相对而言, LAI-2000植物冠层分析仪测定的L_e经过α、Ω_E和γ_E校正后, 精度明显提高, 各时期与真实的LAI的差异均小于9%。研究结果表明, 考虑木质部和集聚效应对光学仪器法的影响后, DHP和LAI-2000植物冠层分析仪均能相对准确地测定针阔混交林LAI的季节动态, 其中, DHP的测定精度高于85%, 而LAI-2000植物冠层分析仪的测定精度高于91%。

关键词: 集聚效应, 半球摄影法, LAI-2000植物冠层分析仪, 叶面积指数, 凋落物法, 针叶寿命, 木质比例

Abstract:

Aims Leaf area index (LAI) is a commonly used parameter for quantifying canopy structure and can be quickly measured by indirect optical methods in a forest stand, but few studies have evaluated the accuracy of optical methods to estimate seasonal variations of LAI in a mixed conifer-broadleaved forest. The aims of this study are to (1) develop a practical field method for directly measuring seasonal variations in LAI for mixed conifer-broadleaved forest; (2) evaluate the accuracy of optical methods (digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer) for measuring the seasonality of LAI; and (3) determine how much the accuracy of estimating the seasonality of LAI can be improved by using optical methods after correcting for influencing factors (e.g., woody materials and clumping effects within a canopy).
Methods The seasonal variations of LAI in a mixed broadleaved-Korean pine (Pinus koraiensis) forest were estimated from litterfall and used to evaluate optical LAI (effective LAI, L_e) measurements using the DHP and the LAI-2000 plant canopy analyzer. We corrected a systematic error due to incorrect automatic photographic exposure for DHP measurements. In addition to optical L_e, we also measured the seasonality of other major factors influencing the determination of LAI, including woody-to-total area ratio (α), clumping index (Ω_E) and needle-to-shoot area ratio (γ_E).
Important findings The LAI from different methods all showed a unimodal form, and peaked in early August. Effective LAIs from the optical methods underestimated LAI throughout the growing seasons (from May to November). L_e from DHP underestimated LAI by an average of 55% (ranging from 50% to 59%) and from LAI-2000 plant canopy analyzer by an average of 27% (ranging from 19% to 35%). The accuracy of L_e from DHP after correcting for the automatic exposure, α, Ω_E and γ_E was greatly improved, but the LAI was underestimated by 6%-15% (with mean value of 9%) from May to November. In contrast, the accuracy of L_e from LAI-2000 plant canopy analyzer after correcting for the α, Ω_E and γ_Ewas also greatly improved, the difference between corrected L_e from LAI-2000 plant canopy analyzer and observed LAI was less than 9%. The results from our study demonstrate that seasonal variations in LAI in mixed conifer-broadleaved forests can be optically measured with high accuracy (85% for DHP and 91% for LAI-2000 plant canopy analyzer), as long as corrections are made for the influences of woody materials and foliage clumping on the measurement.

Key words: clumping effects, digital hemispherical photography (DHP), LAI-2000 plant canopy analyzer, leaf area index, litter collection method, needle life span, woody-to-total area ratio

刘志理, 金光泽, 周明. 利用直接法和间接法测定针阔混交林叶面积指数的季节动态. 植物生态学报, 2014, 38(8): 843-856. DOI: 10.3724/SP.J.1258.2014.00079

LIU Zhi-Li, JIN Guang-Ze, ZHOU Ming. Measuring seasonal dynamics of leaf area index in a mixed conifer-broadleaved forest with direct and indirect methods. Chinese Journal of Plant Ecology, 2014, 38(8): 843-856. DOI: 10.3724/SP.J.1258.2014.00079

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链接本文: https://www.plant-ecology.com/CN/10.3724/SP.J.1258.2014.00079

https://www.plant-ecology.com/CN/Y2014/V38/I8/843

图/表 10

表1 小兴安岭凉水典型阔叶红松林9 hm2监测样地物种组成及主要树种的比叶面积

Table 1 Composition and specific leaf area (SLA) of major tree species in a 9 hm2 typical mixed broadleaved-Korean pine forest plot at Liangshui in the Xiaoxing’an Mountains, China

主要树种 Major tree species	密度 Density (trees·hm^-2)	平均胸径 Mean DBH (cm)	胸高断面积 Basal area (m²·hm^-2)	相对优势度 Relative dominance (%)	比叶面积 SLA (cm²·g^-1)
红松 Pinus koraiensis	133	42.81	24.15	57.09	83.79 (3.74)
臭冷杉 Abies nephrolepis	101	16.17	3.01	7.11	80.80 (5.43)
云杉 Picea spp.	20	18.99	1.06	2.51	59.41 (9.70)
紫椴 Tilia amurensis	81	13.35	3.01	7.11	243.59 (14.26)
色木槭 Acer mono	238	7.73	2.43	5.74	305.04 (50.08)
风桦 Betula costata	67	13.02	2.04	4.82	199.79 (11.55)
裂叶榆 Ulmus laciniata	108	7.73	1.48	3.50	261.40 (5.65)
水曲柳 Fraxinus mandschurica	45	12.54	1.27	3.00	338.36 (13.63)
其他 Others	1 580	2.96	3.85	9.10	-
总计 Total	2 373	7.41	42.30	100.00	-

图1 小兴安岭凉水典型阔叶红松林9 hm2监测样地地形图及凋落物收集器设置。

Fig. 1 Distribution of litter traps and contour map of a 9 hm2 typical mixed broadleaved-Korean pine forest plot at Liangshui in the Xiaoxing’an Mountains, China.

表2 常绿针叶树种的叶寿命

Table 2 Needle life span for evergreen needle tree species

树种 Tree species	最大值 Maximum	最小值 Minimum	平均值±标准偏差 Mean ± SD
红松 Pinus koraiensis	3.48	2.69	3.08 ± 0.25
臭冷杉 Abies nephrolepis	4.63	3.11	3.68 ± 0.52
云杉 Picea spp.	4.35	3.51	3.91 ± 0.27

图2 阔叶红松林主要树种生长季节总叶面积增加比例的季节动态(平均值±标准偏差)。A, 落叶阔叶树种。B, 常绿针叶树种。

Fig. 2 Seasonal changes of increases in proportion of the total leaf area for major tree species in the growing season in the mixed broadleaved-Korean pine forest (mean ± SD). A, deciduous broadleaf tree species. B, evergreen needle tree species.

图3 阔叶红松林主要树种叶面积指数的季节动态(平均值±标准偏差)。A, 落叶阔叶树种。B, 常绿针叶树种。

Fig. 3 Seasonal changes of leaf area index (LAI) for major tree species in the mixed broadleaved-Korean pine forest (mean ± SD). A, deciduous broadleaf tree species. B, evergreen needle tree species.

图4 阔叶红松林木质比例和集聚指数的季节变化(平均值±标准偏差)。

Fig. 4 Seasonal changes of woody-to-total area ratio and clumping index in the mixed broadleaved-Korean pine forest (mean ± SD).

表3 阔叶红松林常绿针叶树种针簇比的季节动态(平均值±标准偏差)

Table 3 Seasonal dynamics of needle-to-shoot area ratio for evergreen needle tree species in the mixed broadleaved-Korean pine forest (mean ± SD)

月份 Month	红松 Pinus koraiensis	臭冷杉 Abies nephrolepis	云杉 Picea spp.
May	1.46 ± 0.22	1.19 ± 0.22	1.44 ± 0.34
June	1.49 ± 0.24	1.21 ± 0.30	1.47 ± 0.43
July	1.69 ± 0.38	1.11 ± 0.30	1.29 ± 0.33
Aug.	1.78 ± 0.45	1.16 ± 0.34	1.31 ± 0.33
Sept.	1.72 ± 0.28	1.10 ± 0.23	1.28 ± 0.35
Oct.	1.65 ± 0.36	1.07 ± 0.21	1.26 ± 0.29
Nov.	1.65 ± 0.26	1.10 ± 0.23	1.30 ± 0.36
平均值 Mean	1.63	1.13	1.34
变异系数 CV (%)	7.3	4.6	6.3

图5 不同方法测定阔叶红松林叶面积指数的季节动态(平均值±标准误差, n = 64)。真实的叶面积指数基于凋落物法测定, DHP测定的有效叶面积指数是利用DHP软件测定, LAI-2000测定的有效叶面积指数是利用C2000软件测定, 校正后的DHP叶面积指数指对DHP测定的有效叶面积指数进行自动曝光、木质比例、集聚指数和针簇比的校正, 校正后的LAI-2000叶面积指数指对LAI-2000测定的有效叶面积指数进行木质比例, 集聚指数和针簇比的校正。

Fig. 5 Seasonal dynamics of leaf area index (LAI) in a mixed broadleaved-Korean pine forest estimated by using different methods (mean ± SE, n = 64). The true LAI is derived from litter collection; effective LAI from DHP is calculated directly by DHP software; effective LAI from LAI-2000 is calculated directly by C2000 software; Corrected DHP LAI is derived by correcting effective LAI from DHP for the automatic exposure, woody-to-total area ratio, clumping index and needle-to-shoot area ratio; Corrected LAI-2000 LAI is derived by correcting effective LAI from LAI-2000 for the woody-to-total area ratio, clumping index and needle-to-shoot area ratio.

图6 光学仪器法(DHP和LAI-2000)与凋落物法测定叶面积指数差异性的季节动态(平均值±标准误差, n = 64)。A, DHP。B, LAI-2000。差异(%) = (凋落物法测定的叶面积指数-DHP或LAI-2000测定的叶面积指数)/凋落物法测定的叶面积指数×100%, DHP或LAI-2000测定的叶面积指数均分别包括有效叶面积指数和校正后的叶面积指数(校正方法同图5)。

Fig. 6 Seasonal dynamics of the difference between the litter collection leaf area index (LAI) and the optical LAI including both DHP and LAI-2000 (mean ± SE, n = 64). A is for the DHP method. B is for the LAI-2000 method. Difference (%) = (litter collection LAI - DHP or LAI-2000 LAI) / litter collection LAI × 100%, DHP or LAI-2000 LAI all includes effective LAI and corrected LAI (the correction scheme is the same as that in Fig. 5).

图7 DHP和LAI-2000测定叶面积指数差异性的季节动态(平均值±标准误差, n = 64)。差异(%) = (LAI-2000测定的有效叶面积指数-DHP测定的叶面积指数)/LAI-2000测定的有效叶面积指数×100%, DHP测定的叶面积指数包括DHP测定的有效叶面积指数(校正前)和对DHP测定的有效叶面积指数只进行自动曝光校正的叶面积指数(校正后)。

Fig. 7 Seasonal dynamics of the difference between the leaf area index (LAI) from DHP and the LAI from LAI-2000 (mean ± SE, n = 64). Difference (%) = (Le from LAI-2000 - LAI from DHP) / Le from LAI-2000 × 100%, LAI from DHP includes Le from DHP (uncorrected) and corrected LAI from DHP that calculated by Le from DHP after correcting for only the automatic exposure (corrected).

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