Vegetation change based on break-point detection in Fu County, Yan’an City
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摘要:
目的 多项生态工程实施以来，陕北黄土高原地区环境明显改善，探究该区域植被的时空变化，为生态环境建设与差异化决策提供依据。 方法 以陕西省延安市富县为研究对象，利用2000—2019年生长季的Landsat TM/ETM+/OLI影像，运用DBEST算法对归一化植被指数(NDVI)时间序列进行断点检测，并提出多阶段趋势分析方法分析富县植被变化时空特征。 结果 富县植被的断点检测结果表明：66.47%的区域断点NDVI变化幅度小于0.2，主要分布在富县西部和东北地区，植被相对稳定，未发生剧烈变化；33.53%的区域断点NDVI变化幅度大于0.2，其中断点数量多于4个的区域仅占5.88%，集中分布于道路、河流沿线，变化频繁，与人为活动有关。当前阶段趋势分析表明：断点NDVI变化幅度大于0.2的区域，改善的面积占总面积的24.57%，退化面积仅占2.12%；开始时间均在2014年之前，时间分布跨度大，空间异质性强，揭示了富县植被变化的多样性及复杂性；富县有林地、疏林地、灌木林地、未成林造林地4种主要林地均趋于改善，改善面积占林地面积的96.23%。 结论 2000—2019年，富县植被整体呈现改善趋势，生态建设工程取得良好的效果；植被变化的时空特征存在差异，后续决策需因地制宜。图6表1参25 -
关键词:
- 归一化植被指数(NDVI) /
- 时间序列 /
- DBEST /
- 变化检测
Abstract:Objective Given the significant environmental improvement after the implementation of ecological projects in the Loess Plateau of northern Shaanxi, this study is aimed to investigate the effect of ecological projects on vegetation improvement so as to provide reference for ecological construction and development countermeasures. Method With the Landsat TM/ETM+/OLI images in the growing season from 2000 to 2019 collected, the DBEST algorithm was used to detect breakpoints in the normalized difference vegetation index (NDVI) time series before a multi-stage trend analysis method was proposed to analyze the temporal and spatial dynamic of the vegetation change in Fu County, Yan’an City, Shaanxi Province. Result Results of break-point detection showed that 66.47% of the breakpoints showed a change magnitude of NDVI lower than 0.2, mainly distributed in the western and northeastern areas and the vegetation was relatively stable without drastic changes; 33.53% of the breakpoints showed a change magnitude of NDVI higher than 0.2 with areas having more than 4 breakpoints accounting for only 5.88% and they were concentrated on roads and rivers with frequent changes in vegetation due to human activities. Results of trend analysis showed that for areas with a break-point change magnitude of NDVI higher than 0.2, the improved area accounted for 24.57% whereas the degraded area only accounted for 2.12%; Featured with a large time distribution span and a strong spatial heterogeneity, the current trends started before 2014, revealing the diversity and complexity of vegetation changes in Fu County; A trend of improvement was detected in all the four main types of forest land in Fu County, namely wood land, sparse wood land, shrub land and young afforested land with the improved area accounting for 96.23% of the total wood land. Conclusion Recent years have witnessed an overall improvement trend of the vegetation in the study area, showing the positive impact exerted by ecological construction projects and further ecological countermeasures should be formulated taking into consideration in accordance the differences in spatial characteristics of vegetation changes in Fu County from 2000 to 2019 as well as local circumstances. [Ch, 6 fig. 1 tab. 25 ref.] -
Key words:
- normalized difference vegetation index (NDVI) /
- time series /
- DBEST /
- change detection
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图 2 2019年富县林地类型与分布示意图
Figure 2 Forest land types and distribution of Fu County in 2019
图 3 富县归一化植被指数变化幅度及其面积占比
Figure 3 Change magnitude and area percent of NDVI in Fu County
图 4 富县不同NDVI变化幅度小于0.2与大于0.2的断点数目及其面积占比
Figure 4 Number of breakpoints and area percent of NDVI (＜0.2 and ＞0.2) in Fu County
图 5 2000—2019年富县NDVI时间序列总体趋势类别及其面积占比
Figure 5 Overall trend level and area percent of NDVI time series in Fu County from 2000 to 2019
图 6 2000—2019年富县NDVI时间序列当前阶段趋势及其面积占比
Figure 6 Current stage trend and area percent of NDVI time series in Fu County from 2000 to 2019
表 1 富县林地类型趋势情况统计
Table 1. Statistics on trend of forest land types in Fu County
林地类型 改善/% 基本不变/% 退化/% 有林地 96.98 0.86 2.16 疏林地 94.32 1.91 3.77 灌木林地 94.41 1.81 3.78 未成林造林地 92.97 1.91 5.12 其他用地 86.66 2.50 10.84 
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