Fig. 2 The changes of plant height and coverage with gravel content for different plant species. (a), Total coverage; (b), Plant height; (c), Coverage of different plant species; (d), Height of different plant species. Error bars refer to standard deviation. Different lowercase letters indicate significant differences among different gravel soils (p<0.05). Fe, Festuca elata ; Ed,Elymus dahuricus ; Ms, Medicago sativa ; Fe+Ed,Festuca elata plus Elymus dahuricus ; Fe+Ms, Festuca elata plus Medicago sativa ; Ms+Ed, Medicago sativa plus Elymus dahuricus ;Fe+Ms+Ed, Festuca elata plus Medicago sativa plus Elymus dahuricus .