Canopy scale characteristics of grassland under different grazing intensities based on UAV lidar and multispectral data

doi:10.11686/cyxb2020573

Abstract

Abstract:

Grazing activities not only affect ecological processes of grasslands， but also change the spatial pattern of grassland communities. This research utilized airborne lidar carried by an HS-600 unmanned aerial vehicle （UAV） with a RIEGL laser system and flying at a height of 119 m， and multi-spectral remote sensing to obtain grassland canopy data with sub-meter resolution. The grassland canopy spatial pattern and its scale characteristics under different grazing intensities were studied using wavelet analysis （i.e. the deconvolution of observed lidar waveforms to extract wavelet data）， to quantify the spatial characteristics and scales of three canopy parameters： canopy height （CH）， fractional vegetation cover （FVC） and normalized difference vegetation index （NDVI）， in terms of their response to grazing intensity. It was found that the wavelet variances of grassland CH， FVC， and NDVI show a downward trend with increase in grazing intensity， indicating that the periodic fluctuation energy of its spatial pattern decreases， and the overall grassland canopy spatial structure tends to be more uniform at higher grazing intensity. The analysis of wavelet variance and the real part of coefficients showed that the spatial pattern of FVC and NDVI has two main characteristic scales of 116-140 m and 170-180 m， and a spatial variation period of about 110 m， and the spatial pattern scale characteristics were comparatively stable with change in grazing intensity. The spatial pattern of CH was more complicated. The larger-scale pattern described above was evident， but moderate and heavy grazing resulted in many smaller patches forming with comparatively larger variation in CH and vegetation cover on a smaller spatial scale.

Key words: spatial heterogeneity, spatial pattern, wavelet analysis, characteristic scale, grazing intensity, vegetation coverage

Jie SHEN, Lei DING, Xiao-ping XIN, Xiang ZHANG, Da-wei XU, Lu-lu HOU, Rui-rui YAN. Canopy scale characteristics of grassland under different grazing intensities based on UAV lidar and multispectral data[J]. Acta Prataculturae Sinica, 2022, 31(3): 1-15.

Figures/Tables 13

Fig.1 Location and overview of the experimental area

Fig.2 Research plot section sampling example and control profile data example

Table 1 Research data sources

植被参数

Vegetation parameter

数据产品

Data product

分辨率

Resolution （m）

获取时间Time （年-月-日

Year-month-day）

HS-600无人机激光扫描系统CH产品 CH products of HS-600 UAV laser scanning system

0.2

2018-09-11

FVC

HS-600无人机激光扫描系统FVC产品 Fractional vegetation cover products of HS-600 UAV laser scanning system

0.2

2018-09-11

NDVI

搭载MicaSense Red Edge-MX传感器Sense Fly无人机多光谱影像 Multispectral image of Sense Fly UAV with MicaSense Red Edge-MX sensor

0.1

2018-09-11

Fig.3 UAV lidar estimates

Table 2 Mean and standard deviation of CH， FVC and NDVI under different grazing intensities

植被参数 Vegetation parameter	项目 Item	放牧强度 Grazing intensity
植被参数 Vegetation parameter	项目 Item	GI₀	GI₁	GI₃	GI₅
CH （cm）	均值Mean	10.6136	6.6287	4.4974	2.4724
CH （cm）	标准差Standard deviation	4.9968	3.5149	2.5772	1.0140
FVC （%）	均值Mean	78.6755	76.2432	72.1455	61.7160
FVC （%）	标准差Standard deviation	0.8188	3.6008	4.7962	5.7201
NDVI	均值Mean	0.5731	0.5617	0.5699	0.5184
NDVI	标准差Standard deviation	0.5040	0.3990	0.3700	0.4460

Fig.4 Mean variance and confidence interval of CH wavelet under different grazing intensities

Fig.5 Real part of wavelet coefficients of CH under different grazing intensities

Fig.6 Mean variance and confidence interval of FVC wavelet under different grazing intensities

Fig.7 Real part of FVC wavelet coefficients under different grazing intensities

Fig.8 Mean variance and confidence interval of NDVI wavelet under different grazing intensities

Fig.9 Real part of NDVI wavelet coefficients under different grazing intensities

Fig.10 Wavelet variance of grassland canopy height （CH）， fractional vegetation coverage （FVC） and normalized difference vegetation index （NDVI） under different grazing intensities in the three scales

Fig.11 Mean values of the the first principal characteristic scale and the wavelet variance corresponding to the first principal characteristic scale under different grazing intensities of FVC and NDVI

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