Global degradation trends of grassland and their driving factors since 2000

Grassland is the second largest terrestrial ecosystem and a fundamental land resource for human survival and development.Although grassland degradation is a recognized and crucial ecological problem,there is no consensus on the area,scope,and degree of its global degradation trends,making the implementation of Sustainable Development Goals(SDG)15.3 for achieving a land degradation-neutral world uncertain.This study quantitatively explored global grassland degradation trends from 2000 to 2020 by coupling vegetation growth and its response to climate change.Furthermore,the driving factors behind these trends were analyzed,especially in hotspots.Results show that the improvement in global grassland has been remarkable since 2000,with a 1.92 times larger area than degrading grassland,amounting to 372.47×10^(4) and 193.57×10^(4) km^(2),respectively.Africa and Asia lead in global grassland degradation and improvement,respectively.Globally,the combined effects of climate change and human activities are the main driving factors for grassland degradation and improvement,accounting for 84.72 and 87.76%,respectively.Notably,human activities played a crucial role in reversing the trend of grassland degradation in some hotspots.Finally,this study provides an essential scientific reference and support for realizing SDG 15.3 on global and regional scales.

Dryland agriculture and rangeland restoration priorities in Afghanistan

Afghanistan is threatened by rangeland degradation.A quantitative visual analysis of Google Earth Imagery was used to systematically locate,characterize and quantify the current extent of rangelands in Afghanistan degraded as a consequence of dryland agriculture.Climate data were used in conjunction with dryland agriculture locations to establish a climate envelope comprised by temperature and mean annual precipitation to create a geographical mask known to contain dryland agriculture.Within this mask we created a grid of 100 km2 cells that we analyzed individually to access dryland agriculture extent.Climatic limits to sustainable dryland agriculture and areas of high restoration priority were also assessed as was the distribution of rain-fed agriculture with respect to the location of traditional migration routes for extensive livestock producers.The extents of agriculture in Afghanistan,at both upper and lower elevations,correlated most closely with mean annual temperature（MAT） at the upper elevation limits,and with mean annual precipitation（MAP） at the lower elevation limits.In total,dryland agriculture comprised 38,980 km2 of former native rangeland.Conversion was highest in the northwestern,northern and northeastern provinces of Herat,Badghis,Faryab,Jawzjan,Sar-e-Pul,Samangan,Balkh,Baghlan,Kunduz,Takhar and Badakhshan,with the highest percentage of conversion occurring in Takhar.An MAP value of 〈400 mm is perceived by farmers as the current climatic limit to sustainable dryland agriculture across the northern regions of the country.Uder this MAP value,approximately 27,677 km2 of converted rangeland met the need for restoration priority.Climate projections indicate that Afghanistan will become warmer and drier in the coming decades.One consequence of this trend is that the MAP threshold of 〈400 mm to sustainable dryland agriculture will become obsolete in the coming decades.Restoration of currently converted rangelands is needed to restore critical grazing areas as is the adoption of prudent range management policies to prevent further land degradation and support a vital livestock industry.Food security is at stake as the conversion of rangelands to unsustainable rain-fed agriculture may leave large tracks of land unusable for either agriculture or livestock production.