Spatial-temporal changes of ecosystem service values in Xiangxi region based on terrain

To understand the change of land use and ecosystem service value (ESV) on different terrain gradients, this study used remote sensing data, field data and statistic data of Xiangxi region in 1990, 1995, 2000, 2005, 2010 and 2015 to analyze the change of each land use types along the gradients of elevation, slope, aspect and terrain index, which were classified into five levels by quantile method, respectively. The study also evaluated the ESV with XIE Gaodi's method to explore the spatio-temporal change of ESV in Xiangxi region. And R Studio and Pearson correlations were used to analyze correlation between areas changes of different land use types and change of ESV with terrain gradients. The results showed that:1) areas of different land use types were significantly different on different terrain gradients. The human-activity-affected cropland and construction land mainly distributed on low gradients of elevation, slope and terrain index, while the natural systems, such as forestland and grassland, were mainly on high gradients of the three terrain factors. The south and east slopes were with larger areas of each land use type. Forestland occupied about 70% area on every terrain gradient, and the construction land area significantly increased on every terrain gradient over 25 years. 2) ESV decreased first and then increased with increasing elevation. From 1990 to 2015, ESV increased at lower elevation gradient, however, change was slighter at higher elevation, and it even decreased on the highest elevation gradient. ESV increased with slope growth. Over 25 years, ESV increased most on the lowest slope gradient. In a similar way, ESV evenly increased with increasing terrain index gradient. ESV was the lowest in southeast slope, highest in northwest slope, and increased most in east and northwest slopes from 1990 to 2015. 3) Correlations between change of land use types areas and ESV with gradients of elevation, slope, aspect, terrain index were different. On elevation gradient, grassland area change significantly positively correlated with ESV change. On slope gradient, forestland and grassland areas changes both had extremely positive correlation with ESV change. On aspect gradient, cropland and unused land areas changes had extremely negative correlation with ESV change, while forestland had a significant positive correlation. On terrain index gradient, areas changes of forestland and grassland were significantly correlated with change of ESV. In summary, the changes of land use and ESV were obviously different regarding topography. Forestland and grassland were two important land use types for improvement of ESV in mountain area of Xiangxi region.