Human activities have an impact on the structure and function of ecosystems. which in turn affects ecosystem service (ES) supply and demand. Based on the four-quadrant model of human activities and ecosystem services, this study evaluated the ecological quality at the county scale on the Qinghai-Tibet Plateau (QTP). Results showed: (1) Human activity intensity (HAI) showed great spatio-temporal variations across the QTP. The mean HAI was low overall and increased by 4% during 2000-2015. HAI in more than 13% of the area of the QTP showed an increasing trend and high HAI levels were mainly distributed in the eastern and central parts. A low HAI level occupied the majority of the study area and declined during the period. (2) The mean ES balance declined during the period and exhibited great spatial variations, with the higher ES balance mainly distributed in the mid-eastern cities of the QTP. The ES balance in approximately 68% of the cities decreased, indicating the ESs were in degradation, with demand exceeding supply. (3) Approximately 98% of the study area, including 205 counties, was in the first, second and fourth quadrant, and only 2% was in the third quadrant, indicating that ecological quality became better overall on the QTP. During 2000-2015, 87.14% of counties were nearly unchangeable-these were distributed in the most regions of the QTP, and only 9.79% and 3.08% of counties were improving and degrading, respectively, mainly distributed in the mid-eastern regions. The change implied that the ecosystems were basically in a stable state and the environment greatly improved on the QTP from 2000 to 2015. This study contributes to exploring the effect of human activity on ecosystem service, thereby providing credible guidance for regional ecosystem management. (C) 2020 Elsevier B.V. All rights reserved.
