[Analysis of Urban Vegetation Changes and Drivers in City of Plateau River Valleys].

Abstract

Lanzhou is a typical banded plateau river valley city. This study provides a reference for vegetation restoration， soil and water conservation， and ecological environmental protection of the plateau river valley city. It also supports the sustainable development of Lanzhou. Using remote sensing image data from 2000 to 2020， we analyzed the spatial and temporal trends of vegetation NDVI during the growing season in Lanzhou. We employed the R/S index， Sen slope analysis， MK test， and coefficient of variation to conduct our analysis. Additionally， we used geodetic probes to comprehensively analyze the effects of both natural and anthropogenic factors on the spatial variation of vegetation NDVI. The results indicate that： ① From 2000 to 2020， the vegetation NDVI in the anthropogenic area was mainly of medium grade， with a growth rate of 0.004 8 a^-1. The trends observed were 'insignificant degradation' and 'continuous degradation'. ② The vegetation in the inactive area showed mainly medium-low and low grades of NDVI， with a growth rate of 0.005 8 a^-1， indicating a trend of 'not significantly improved' and 'continuously improved'. The stability of vegetation growth was poor. ③ In Lanzhou， the NDVI of the vegetation in the improvement area accounted for 83.5%， while the degradation area accounted for 16.3%. The high fluctuation change area accounted for 51.1%， and the low fluctuation change area accounted for only 5.7%. ④ Soil type， vegetation type， and precipitation were natural factors that affected vegetation change. Meanwhile， land use type and population density were anthropogenic factors that also had an impact on vegetation change. ⑤ In the factor interaction analysis， vegetation type and precipitation were the main factors affecting the spatial distribution of vegetation NDVI， and slope， slope direction， population density， GDP， agricultural value added， and industrial value added were the indirect factors. ⑥ Based on the analysis of various factors， it is evident that the optimal soil type was drench soil， the preferred land type was woodland， the suitable vegetation type was coniferous forest， and the ideal elevation range was between 3 500 to 3 671 meters. Overall， the NDVI of vegetation in Lanzhou was in the middle to low grade， and the growth stability of the vegetation was relatively poor. However， there is a trend of improvement for the future. In contrast， the vegetation growth stability was higher， and the vegetation NDVI grade was higher in the anthropogenic area， while the non-anthropogenic area had lower vegetation growth stability and NDVI grade. Soil had the greatest influence on vegetation growth， making it a key challenge for ecological management in Lanzhou. This highlights the need to consider human activities when assessing vegetation growth. Anthropogenic factors have a slow but steady impact， surpassing other factors in their influence.