干旱区生态环境知识资源中心(Arid): Optimal dates for assessing long-term changes in tree-cover in the semi-arid biomes of South Africa using MODIS NDVI time series (2001-2018)

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DOI	10.1016/j.jag.2019.05.014
	Optimal dates for assessing long-term changes in tree-cover in the semi-arid biomes of South Africa using MODIS NDVI time series (2001-2018)
	Cho, Moses Azong 1,2; Ramoelo, Abel 3,4
通讯作者	Cho, Moses Azong
来源期刊	INTERNATIONAL JOURNAL OF APPLIED EARTH OBSERVATION AND GEOINFORMATION
ISSN	0303-2434
出版年	2019
卷号	81 页码:27-36
英文摘要	The varying proportions of tree and herbaceous cover in the grassland and savanna biomes of Southern Africa determine their capacity to provide ecosystem services. The asynchronous phenologies e.g. annual NDVI profiles of grasses and trees in these semi-arid landscapes provide an opportunity to estimate percentage tree-cover by determining the period of maximum contrast between grasses and trees. First, a 16-day NDVI time series was generated from MODIS NDVI data, i.e. MOD13A2 16-day NDVI composite data. Secondly, percentage tree-cover data for 100 sample polygons (4 x 4) pixels for areas that have not undergone change in tree cover between 2001 and 2018 were derived using high resolution Google Earth imagery. Next, a time series consisting of the coefficients of determination (R-2) for the NDVI/tree-cover linear regression were computed for the 100 polygons. Lastly, a threshold R-2 > 0.5 was used to determine the optimal period of the year for mapping tree-cover. It emerged that the narrow period from Julian day 161-177 (June 10-26) was the most consistent period with R-2 > 0.5 in the region. 18 tree-cover maps (2001-2018) were generated using linear regression model coefficients derived from Julian day 161 for each year. Kendall correlation coefficient (tau) was used to determine areas of significant (p < 0.05 and p < 0.01) increasing or decreasing trend in tree-cover. Areas (polygons) that showed increasing tree-cover appeared to be more widespread in the trend map as compared to areas of decreasing tree-cover. An accuracy assessment of the map of increasing tree-cover was conducted using Google Earth high resolution images. Out of 330 and 200 mapped polygons verified using p < 0.05 and 0.01 thresholds, respectively, 180 (54% accuracy) and 132 (65% accuracy) showed evidence of tree recruitment. Farm abandonment appeared to have been the most important factor contributing to increasing tree-cover in the region.
英文关键词	Tree-cover change MODIS NDVI time series
类型	Article
语种	英语
国家	South Africa
开放获取类型	hybrid
收录类别	SCI-E
WOS记录号	WOS:000472988200003
WOS关键词	FRACTIONAL COVER ; SAVANNA ; VEGETATION ; PHENOLOGY ; RESPONSES ; IMAGERY ; IMPACT ; MAPS ; BAND ; CO2
WOS类目	Remote Sensing
WOS研究方向	Remote Sensing
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/216346
作者单位	1.CSIR, Nat Resources & Environm Unit, POB 395, Pretoria, South Africa; 2.Univ Pretoria, Dept Plant & Soil Sci, Pretoria, South Africa; 3.Univ Limpopo, Limpopo, South Africa; 4.South African Natl Parks, Sci Serv, Dept Conservat Sci, POB 647, Pretoria, South Africa
推荐引用方式 GB/T 7714	Cho, Moses Azong,Ramoelo, Abel. Optimal dates for assessing long-term changes in tree-cover in the semi-arid biomes of South Africa using MODIS NDVI time series (2001-2018)[J],2019,81:27-36.
APA	Cho, Moses Azong,&Ramoelo, Abel.(2019).Optimal dates for assessing long-term changes in tree-cover in the semi-arid biomes of South Africa using MODIS NDVI time series (2001-2018).INTERNATIONAL JOURNAL OF APPLIED EARTH OBSERVATION AND GEOINFORMATION,81,27-36.
MLA	Cho, Moses Azong,et al."Optimal dates for assessing long-term changes in tree-cover in the semi-arid biomes of South Africa using MODIS NDVI time series (2001-2018)".INTERNATIONAL JOURNAL OF APPLIED EARTH OBSERVATION AND GEOINFORMATION 81(2019):27-36.