Reproductive effort of Caragana microphylla under long‐term grazing exclusion in a semi‐arid grassland

Abstract

AbstractGrazing exclusion is a commonly used method to protect and recover herbaceous plants in grasslands, and woody expansion is a common phenomenon in grasslands. However, the effects of grazing exclusion on shrub reproduction remain poorly understood. We investigated the effects of long‐term grazing exclusion (0, 8, 30 and 34 years) on reproductive effort of Caragana microphylla in the semi‐arid Inner Mongolia Steppe. Our results showed that the 8‐year grazing exclusion significantly increased the number of flowers, juvenile pods, mature pods and seed (seed number increased 33.5%) of C. microphylla, however, the 30‐ to 34‐year grazing exclusion significantly decreased seed production (seed number decreased 77.9% and 88.1%) of C. microphylla. The 8‐year grazing exclusion had no significant effect on the single flower weight, while the 30‐ to 34‐year grazing exclusion significantly decreased (31.7% and 38.7%) the single flower weight. The grazing exclusion had no significant effect on the seed number per pod. The 8‐year grazing exclusion significantly increased sexual allocation (31.6%), and it had no significant effect on sexual allocation efficiency; however, the 30‐ to 34‐year grazing exclusion significantly decreased the sexual allocation (50.4% and 70.4%) and sexual allocation efficiency (55.5% and 60.1%). The 8‐year grazing exclusion significantly increased seed weight and seed vigor (seed weight increased 18.7%, seed vigor index increased 28.7%), whereas the 30‐ to 34‐year grazing exclusion decreased these indexes (seed weight decreased 14.2% and 21.0%, seed vigor index decreased 9.1% and 14.7%). These results indicated that the 8‐year grazing exclusion increased reproductive effort of C. microphylla, while the 30‐ to 34‐year grazing exclusion sharply decreased the reproductive effort of this shrub species. Our study suggests long‐term grazing exclusion limited the expansion of shrubs in grassland by decreasing sexual reproduction and thus inhibiting population growth of shrubs.