IDENTIFICATION OF THE SPECTRAL CHARACTERISTICS OF SALTMARSH VEGETATION USING INDIRECT ORDINATION: A CASE STUDY FROM CHONGMING DONGTAN, SHANGHAI

doi:10.17521/cjpe.2006.0034

Abstract

Abstract:

Remote sensing is a major source of spatial information of the attributes of the earth's surface, and remote sensing technology has become a primary tool for vegetation classification at large scales. The relationship between vegetation and their spectral characteristics is key for interpreting remote sensing images. This study related characteristics of saltmarsh vegetation at the intertidal zone of Chongming Dongtan Nature Reserve, Shanghai, to patterns of their spectral reflectance. Paired measurements of saltmarsh community and spectral characteristics were carried out along three transects covering the major variations in vegetation and environment within the study area. The spectral characteristics were measured by a ground FieldSpec Pro JR spectroradiometer and the spectral data were converted to simulate the 10 bands of Compact Airborne Spectrographic Imager (CASI) bandset. The spectral data sets were then ordinated using Principal Component Analysis (PCA), an indirect ordination technique. The eigenvalue of the first PCA axis was 19.9, which represented 98.5% of the variation in the spectral data. A sequence of bare mudflat, Scirpus mariqueter community, Spartina alterniflora community and Phragmites australis community changed along the first ordination axis showed a strong correspondence with variation in the bands six to ten, i.e. the simulated CASI wavebands covering the 736 to 870 nm wavelengths. A significant relationship between the first axis PCA scores for the spectral data of quadrats and their percentage community cover and height also was identified. The second axis accounted for only 1.4% of the variation in the spectral data and it proved impossible to demonstrate any close link between any specific plant community type and a distinct set of spectral characteristics because of its low representation of the variation in the spectral data.

Our study has demonstrated that the variation in the spectral data of saltmarsh vegetation at Chongming Dongtan Nature Reserve can be identified using the indirect ordination technique of PCA and then applying correlation and regression analyses to explain the relationships between the variation in the spectral data with the vegetation and ecological data. Our results indicate that PCA is of value for identifying relationships between community types and the spectral data of CASI bandsets for saltmarsh vegetation. This could provide an effective and practical approach for classification of saltmarsh vegetation at large scales and for monitoring spatio_temporally dynamic patterns of saltmarshes at Chongming Dongtan Nature Reserve. Further work is required in order to test these conclusions. The method has been evaluated for a single season with a limited sample of saltmarsh plant communities, and the application of PCA and spectral data of CASI bandsets to other saltmarsh vegetation as well as multi_seasonal spectral data are necessary to determine whether similar patterns emerge and whether the approach has more general applicability in terms of characterizing remote sensing/spectral imagery and community types in saltmarsh vegetation.

Key words: Chongming Dongtan, Saltmarsh vegetation, Spectroradiometer, CASI, Canopy reflectance, Indirect ordination

GAO Zhan_Guo, ZHANG Li_Quan. IDENTIFICATION OF THE SPECTRAL CHARACTERISTICS OF SALTMARSH VEGETATION USING INDIRECT ORDINATION: A CASE STUDY FROM CHONGMING DONGTAN, SHANGHAI[J]. Chin J Plant Ecol, 2006, 30(2): 252-260.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2006.0034

https://www.plant-ecology.com/EN/Y2006/V30/I2/252

Figures/Tables 6

Fig.1 The location of Chongming Dongtan Nature Reserve,Shanghai,and the Landsat_TM satellite image of August, 2003

Table 1 The Compact Airborne Spectrographic Imager(CASI)default vegetation bandset and the wavelength ranges

CASI波段 CASI band	1		2	3		4	5	6		7	8		9	10
波长 Wavelengths (nm)	441~461		548~557	666~674		694~703	705~711	736~744		746~753	775~784		815~824	860~870

Fig.2 The PCA ordination plot for the spectral data sets of Compact Airborne Spectrographic Imager (CASI) bandset of the wetland vegetation at Chongming Dongtan, Shanghai

Fig.3 Patterns of variation in the 10 CASI wavebands in relation to the first two axes of the PCA ordination, proportional circles correspond to values for each waveband in each quadrat with higher values corresponding to larger circles

Table 2 The correlation between the spectral data sets of 10 CASI wavebands and the first two axes of PCA

CASI波段 CASI band	1	2	3	4	5	6	7	8	9	10
PCA第一排序轴 PCA axis 1	0.25	-0.24	0.38^*	0.01	-0.51^*	-0.99^*	-0.99^*	-0.99^*	-0.99^*	-0.99^*
PCA第二排序轴 PCA axis 2	0.79^*	0.43^*	0.88^*	0.65^*	0.15	-0.74^*	-0.79^*	-0.78^*	-0.78^*	-0.78^*

Table 3 The correlation between the first two axes of PCA and the ecological and enviro nmental factors

	群落高度 Community height	群落盖度 Community cover	高程 Elevation	土壤含水量 Soil water content
PCA第一排序轴 PCA axis 1	-0.830^**	-0.685^**	-0.292^*	-0.078
PCA第二排序轴 PCA axis 2	-0.790^**	-0.842^**	-0.298^*	-0.234

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