2.2 Experimental design
The experiment was initiated at the Daqinggou Ecological Station in
1992. The single-factor completely randomized design was used for
comparing the three treatments or approaches aimed at restoring degraded
grasslands, namely (1) enclosing the grassland within a shelter belt ofPopulus × beijingensis , referred to as FG, in which the
dominant species were Artemisia scoparia , Setaria viride ,Agropyron cristatum , and Cleistogenes chinensis ; (2)
afforesting small but well-distributed patches within the grassland
using Pinus sylvestris var. mongolica , referred to as MG,
in which the dominant species were Cleistogenes chinensis ,Setaria virides , Artemisia scoparia , andCalamagrostis arundinacea ; and (3) similar afforestation usingUlmus pumila , referred to as UG, in which the dominant species
were Setaria virides , Cleistogenes chinensis ,Temisia scoparia , and Artemisia lavandulaefolia . All the
restoration sites were established in 1992. After tree planting, the
land was left without any intervention or disturbance. A plot of
desertified sandy grassland in which the dominant species wereAgriophyllum squarrosum (Linn.) Moq. and Cenchrus
echinatus Linn. served as a control or a check, referred to as CK,
which was also established in 1992 and has remained unmanaged since
then.