Effect of mowing and grazing on ramet emergence of Leymus racemosus in the inner Mongolia steppe during the spring regreening period

The invasive Leymus racemosus species is mainly established by ramets (or clonal seedling). A field experiment was conducted in the spring of 2004 to investigate the effects on the surface soil temperature caused by mowing, grazing and grazing exclusion, and the influence of these factors on the ramets emergence characteristics. The primary effect of the treatments was significant changes in soil temperature in the grazing plots due to the mulch cover which was removed by sheep, keeping the daily mean soil temperature above 0 degrees C during the period of the experiment. Grazing had positive impacts on the emergence of ramets, and their final cumulative emergence in the grazing plot significantly increased by 77 and 59% when compared to that in the grazing-exclusion and mowing plots. A linear function model was used to describe the correlation between the cumulative ramets emergence percentage and soil thermal time (theta(T)). Variation in theta(T) explained 98% of the observed variation in cumulative emergence; there were no significant differences in the soil thermal requirements for final ramets emergence completion for the other treatments. Both mowing and grazing exclusion had a significant effect on the invasive L. racemosus species ramets recruitment control.