Globally, grasslands, covering about 40% of the Earth’s land area, are vital for supporting important ecosystem functions, services, and livelihoods of millions of humans. Currently, grassland degradation is a major threat to the maintenance of ecological services,1 food security, and sustainable development, and directly hinders the global efforts with meeting goals and targets such as the The UN Decade on Ecosystem Restoration and Sustainable Development Goals (SDGs).

Remote sensing approaches have the advantages of spanning large geographical areas with multiple spatial, spectral, and temporal resolutions. In global scale, remote sensing methods used normalized difference vegetation index to determine net primary productivity (NPP), which still is the effective method to indicate grassland conditions. To master the general situation of grassland, we analyzed the global spatial-temporal variation of NPP from 2001 to 2019 at the pixel level across the globe. As presented in Figure 1A, the NPP values of global grasslands showed an obvious variation trend, which indicated a considerable distribution pattern of spatial heterogeneity. The decreasing and increasing trend in grassland NPP covered approximately 25.3% and 74.5% of the total grassland area, respectively. We observed the highest proportion of degradation in Australia (45.5%). Conversely, 73.7% of the total grassland area revealed an increasing NPP trend, especially in Canada (86.4%). These changes are predicted to have huge effects on biodiversity and the livelihoods of approximately 1.5 billion people who rely on grassland ecosystem services and sustainability.

(A) Global trends of grassland degradation and restoration. The significance of the grassland dynamics was determined by the F-test to represent the confidence level of variation. Then, the variation trend in grassland NPP was classified into the following 6 categories based on the F-test: ED (extremely significant degradation, slope < 0, p < 0.01); SD (significant degradation, slope < 0, 0.01 < p < 0.05); LD (light degradation, slope < 0, p > 0.05); LR (light restoration, slope > 0, p > 0.05); SR (significant restoration, slope > 0, 0.01 < p < 0.05); and ER (extremely significant restoration, slope > 0, p < 0.01).

(B) Grassland degradation definitions and grassland sustainability assessment.Different colors represent the focus of different periods of grassland degradation definitions from biotic/abiotic indicators to ecosystem sustainability. Collaborations and mutual relationship of policymaker-performer-evaluator (e.g., government, scientist, rancher). Comprehensive assessment of grassland sustainability from indicators, functions, services, and establish links with climate, soil and grassland conditions, livestock management and trades, herder economics, and effectiveness of policy.