Abstract
Vegetation dynamics is thought to be affected by climate and land use changes. However, how the effects vary after abrupt vegetation changes remains unclear. Based on the Mann-Kendall trend and abrupt change analysis, we monitored vegetation dynamics and its abrupt change in the Yangtze River delta during 1982–2016. With the correlation analysis, we revealed the relationship of vegetation dynamics with climate changes (temperature and precipitation) pixel-by-pixel and then with land use changes analysis we studied the effects of land use changes (unchanged or changed land use) on their relationship. Results showed that: (1) the Normalized Vegetation Index (NDVI) during growing season that is represented as GSN (growing season NDVI) showed an overall increasing trend and had an abrupt change in 2000. After then, the area percentages with decreasing GSN trend increased in cropland and built-up land, mainly located in the eastern, while those with increasing GSN trend increased in woodland and grassland, mainly located in the southern. Changed land use, except the land conversions from/to built-up land, is more favor for vegetation greening than unchanged land use (2) after abrupt change, the significant positive correlation between precipitation and GSN increased in all unchanged land use types, especially for woodland and grassland (natural land use) and changed land use except built-up land conversion. Meanwhile, the insignificant positive correlation between temperature and GSN increased in woodland, while decreased in the cropland and built-up land in the northwest (3) after abrupt change, precipitation became more important and favor, especially for natural land use. However, temperature became less important and favor for all land use types, especially for built-up land. This research indicates that abrupt change analysis will help to effectively monitor vegetation trend and to accurately assess the relationship of vegetation dynamics with climate and land use changes.
Highlights
Vegetation is an important component of terrestrial ecosystems, which plays a vital role in various ecological processes at different scales, reflecting the state of ecosystems [1,2,3]
In 67.2% of the study area, growing season NDVI (GSN) showed an increasing trend and 18.78% showed significant increase and 32.8% of the area suffered a certain degree of vegetation degradation, mainly distributed in the south of the Yangtze River Delta
This indicated that the north-south vegetation trend of the Yangtze River Delta before or after abrupt change was closely related to the land use type
Summary
Vegetation is an important component of terrestrial ecosystems, which plays a vital role in various ecological processes at different scales, reflecting the state of ecosystems [1,2,3]. There are many studies that use NDVI to monitor vegetation dynamics, land degradation and ecosystems status at different scales [5,6,7,8]. Trend detection in NDVI time series can help to identify and quantify the changes in ecosystem properties from local to global scale [9]. The study on vegetation dynamics can help us understand the structure and function of local ecosystems and assess the quality of ecosystems. Vegetation trends may shift after abrupt changes such as from greening to browning or browning to greening. Research on the abrupt change will allow us to monitor vegetation trends more accurately [13,14,15], while how the vegetation trends and the relationship with climate and land use changes varied remains unclear
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