Effects of Exclosure Management on Elm (Ulmus Pumila) Recruitment in Horqin Sandy Land, Northeastern China

Effects of exclosure management on the plant recruitment are not clear yet. To assess the effects of exclosure management on the recruitment of elm, population structure, seed production, and densities of seeds and seedlings of elm were investigated in fenced and grazed pastures in Horqin Sandy Land, northeastern China. The results showed that seed biomass per branch of elm in the grazed plot was significantly higher than in fenced pasture (0.85 +/- 0.27g vs. 0.55 +/- 0.36g, p<0.05), and seed density was higher in grazed pasture (845 +/- 370 seedsm(-2)) than that in fenced pasture (558 +/- 241 seedsm(-2)), indicating that grazing would improve reproductive allocation of elm. However, there was no significant difference of seedling density between grazed and fenced pastures. More important, the elm trees with a height less than 0.5m appeared in the fenced pasture but disappeared in the grazed pasture, indicating the positive effects of exclosure management on the elm recruitment. Our results suggested that the exclosure would favor recruitment of elm through its protection of saplings instead of through increased seed production. This study improves our understanding of the effects of grazing on population dynamics of elm and would contribute to the restoration of degraded sandy land in northern China.