Improving the accuracy of indirect methods in estimating leaf area index using three correction schemes in a Larix gmelinii plantation

doi:10.17521/cjpe.2015.0467

Abstract

Abstract:

Aims Woody materials and clumping effects are key error sources in estimating leaf area index (LAI) by optical methods. However, how to correct the error caused by woody materials has not reached consensus. The aims of this study are (1) to evaluate the accuracy of optical methods for estimating effective LAI (L_e) in a deciduous needle leaf forest stand, and (2) to develop a practical correction scheme to improve the accuracy of optical methods in estimating LAI.Methods L_ewas estimated by two indirect methods (i.e., digital hemispherical photography (DHP) and LAI-2000 plant canopy analyzer method (LAI-2000 method) in an annual maximum leaf area period in a Larix gmelinii plantation. Then, we developed three correction schemes to improve the accuracy of indirect methods in estimating LAI. Meanwhile, two direct methods (i.e., litter collection and allometry methods) were used to estimate LAI. Taking LAI from litter collection as a reference, we evaluated the effectiveness of three correction schemes and tested the influence of zenith angle ranges on the correction results.Important findings With zenith angle ranges of 0-45° (rings 1-3), 0-60° (rings 1-4), 45°-60° (ring 4) and 0-75° (rings 1-5), L_eobtained from DHP underestimated LAI from both litter collection and allometry by 19%-32% and 18%-29%, respectively. L_efrom LAI-2000 method with four zenith angles also underestimated LAI from both litter collection and allometry by 9%-30% and 8%-28%, respectively. Although the contribution of woody materials to LAI was overestimated in correction scheme A, it was effective in correcting L_efrom DHP with zenith angles of 45º-60º (ring 4), and also effective for L_efrom LAI-2000 method with zenith angles of rings both 1-3 and 1-4. Correction scheme B was all effective in correcting L_efrom DHP with four zenith angle ranges. Generally, correction scheme C was more effective than other two schemes in correcting L_efrom both DHP and LAI-2000 method with four zenith angle ranges. These results indicate that the zenith angle range is a key factor for determining the accuracy of optical methods in estimating LAI besides woody materials and clumping effects.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201606006

Key words: leaf area index, litter collection, allometry, digital hemispherical photography, LAI-2000 plant canopy analyzer method, zenith angle

Ming ZHOU, Zhi-Li LIU, Guang-Ze JIN. Improving the accuracy of indirect methods in estimating leaf area index using three correction schemes in a Larix gmelinii plantation[J]. Chin J Plant Ecol, 2016, 40(6): 574-584.

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Figures/Tables 7

References 47

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主要树种 Dominant species	密度 Stem density (individuals·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¹⁾ SLA¹⁾ (cm²·g^-1)	叶生物量方程²⁾ Allometric equations for leaf biomass²⁾ B_leaf = aDBH^b
主要树种 Dominant species	密度 Stem density (individuals·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¹⁾ SLA¹⁾ (cm²·g^-1)	a	b
兴安落叶松 Larix gmelinii	350	28.93	24.29	84.49	134.23	0.014	3.934
水曲柳 Fraxinus mandshurica	156	9.50	2.15	7.47	338.36	8.570	2.180
色木槭 Acer mono	294	5.81	1.01	3.50	305.04	17.179	1.948
紫椴 Tilia amurensis	239	5.62	0.72	2.50	243.59	1.694	2.507
其他 Others	261	4.92	0.59	2.05	-	-	-
总计 Total	1 300	13.25	28.75	100.00	-	-	-

主要树种 Dominant species	密度 Stem density (individuals·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¹⁾ SLA¹⁾ (cm²·g^-1)	叶生物量方程²⁾ Allometric equations for leaf biomass²⁾ B_leaf = aDBH^b
主要树种 Dominant species	密度 Stem density (individuals·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¹⁾ SLA¹⁾ (cm²·g^-1)	a	b
兴安落叶松 Larix gmelinii	350	28.93	24.29	84.49	134.23	0.014	3.934
水曲柳 Fraxinus mandshurica	156	9.50	2.15	7.47	338.36	8.570	2.180
色木槭 Acer mono	294	5.81	1.01	3.50	305.04	17.179	1.948
紫椴 Tilia amurensis	239	5.62	0.72	2.50	243.59	1.694	2.507
其他 Others	261	4.92	0.59	2.05	-	-	-
总计 Total	1 300	13.25	28.75	100.00	-	-	-

校正方案 Correction scheme	校正公式 Correction equation	木质部 Woody materials	冠层水平上的集聚效应 Clumping effects beyond shoots	簇内水平上的集聚效应 Clumping effects within shoots	生态学特性 Ecological characteristics
校正方案A Correction scheme A	LAI = L_eγ_E /Ω_E- WAI	WAI, 通过光学仪器法在无叶期测定 WAI, which was measured by optical methods in leafless periods	Ω_E, 基于Chen和Cihlar (1995)提出的CC法, 通过DHP-TRAC软件获得, 计算时选择40°-45°天顶角 Ω_E, which was obtained through DHP-TRAC software based on CC method developed by Chen and Cihlar (1995), with zenith angles of 40°-45°	γ_E, 测定兴安落叶松的γ_E, 然后根据小样方内兴安落叶松和其他阔叶树种的胸高断面积进行加权, 得到各样点林分水平上的γ_E值 γ_E, γ_Efor Larix gmelinii was first measured, and the γ_E for the stand was obtained by weighting γ_E for Larix gmelinii and other broadleaf species based on the basal area	未考虑木质部对LAI贡献率的季节变异, 且过度校正了木质部的集聚效应 Ignoring seasonal variations of the contribution of woody materials to LAI, and overestimated the clumping effects of woody materials
校正方案B Correction scheme B	LAI = L_eγ_E /Ω_E- SAI	SAI, 利用WAI乘以SAI占WAI的比例获得, 比例值为0.2 (Liu et al., 2015b) SAI, which was calculated by multiplying WAI by the ratio of SAI to WAI. The ratio was 0.2 (Liu et al., 2015b)	同校正方案A Same as correction scheme A	同校正方案A Same as correction scheme A	一定程度上校正了木质部对LAI贡献率的季节变异, 过度校正了木质部的集聚效应 Slightly correcting seasonal variations of the contribution of woody materials to LAI, but also overestimated the clumping effects of woody materials
校正方案C Correction scheme C		α_stem, 用SAI除以L_e 获得 α_stem, which was calculated by SAI divided by L_e	同校正方案A Same as correction scheme A	同校正方案A Same as correction scheme A	合理校正了木质部对LAI的贡献率, 避免过度校正木质部的集聚效应 Reasonably correcting seasonal variations of the contribution of woody materials to LAI, and avoid over estimating the clump- ing effects of woody materials

校正方案 Correction scheme	校正公式 Correction equation	木质部 Woody materials	冠层水平上的集聚效应 Clumping effects beyond shoots	簇内水平上的集聚效应 Clumping effects within shoots	生态学特性 Ecological characteristics
校正方案A Correction scheme A	LAI = L_eγ_E /Ω_E- WAI	WAI, 通过光学仪器法在无叶期测定 WAI, which was measured by optical methods in leafless periods	Ω_E, 基于Chen和Cihlar (1995)提出的CC法, 通过DHP-TRAC软件获得, 计算时选择40°-45°天顶角 Ω_E, which was obtained through DHP-TRAC software based on CC method developed by Chen and Cihlar (1995), with zenith angles of 40°-45°	γ_E, 测定兴安落叶松的γ_E, 然后根据小样方内兴安落叶松和其他阔叶树种的胸高断面积进行加权, 得到各样点林分水平上的γ_E值 γ_E, γ_Efor Larix gmelinii was first measured, and the γ_E for the stand was obtained by weighting γ_E for Larix gmelinii and other broadleaf species based on the basal area	未考虑木质部对LAI贡献率的季节变异, 且过度校正了木质部的集聚效应 Ignoring seasonal variations of the contribution of woody materials to LAI, and overestimated the clumping effects of woody materials
校正方案B Correction scheme B	LAI = L_eγ_E /Ω_E- SAI	SAI, 利用WAI乘以SAI占WAI的比例获得, 比例值为0.2 (Liu et al., 2015b) SAI, which was calculated by multiplying WAI by the ratio of SAI to WAI. The ratio was 0.2 (Liu et al., 2015b)	同校正方案A Same as correction scheme A	同校正方案A Same as correction scheme A	一定程度上校正了木质部对LAI贡献率的季节变异, 过度校正了木质部的集聚效应 Slightly correcting seasonal variations of the contribution of woody materials to LAI, but also overestimated the clumping effects of woody materials
校正方案C Correction scheme C		α_stem, 用SAI除以L_e 获得 α_stem, which was calculated by SAI divided by L_e	同校正方案A Same as correction scheme A	同校正方案A Same as correction scheme A	合理校正了木质部对LAI的贡献率, 避免过度校正木质部的集聚效应 Reasonably correcting seasonal variations of the contribution of woody materials to LAI, and avoid over estimating the clump- ing effects of woody materials

数值 Value	0-45º (1-3环 Rings 1-3)		0-60º (1-4环 Ring 1-4)		45º-60º (4环 Ring 4)		0-75º (1-5环 Rings 1-5)
数值 Value	DHP	LAI-2000法 LAI-2000 method	DHP	LAI-2000法 LAI-2000 method	DHP	LAI-2000法 LAI-2000 method	DHP	LAI-2000法 LAI-2000 method
最大值 Maximum	4.25	7.03	4.27	5.87	5.25	5.83	4.39	5.83
最小值 Minimum	3.03	2.96	3.4	2.54	3.13	2.20	3.44	2.45
平均值 Mean	3.72^c	4.96^A	3.89^bc	4.42^AB	4.33^a	3.80^B	4.04^b	4.11B
标准偏差 Standard deviation	0.31	1.18	0.2	1.07	0.58	1.15	0.28	0.98
与凋落物法LAI的差异 Difference with LAI from litter collection (%)	32	9	28	18	19	30	25	24
与异速生长方程法LAI的差异 Difference with LAI from allometry (%)	29	8	26	17	18	28	23	24