Resilience and community dynamics of understorey vegetation in Mongolian pine plantations at the southeastern edge of the Mu Us Sandy Land, China

Mongolian pine (Pinus sylvestris var. mongolica) is one of the main species introduced on the southeastern edge of the Mu Us Sandy Land. Population of the species shows poor natural regeneration in this region, which reduces the persistence and stability of the plantation. The plant community of Mongolian pine plantation mainly includes tree stand and understorey vegetation. Large areas of the stands are now entering a period of decline, and there is a need to explore whether understorey vegetation community has high enough resilience to effectively assist the degraded stand to maintain the stability of plantation ecosystems. Here, we studied the characteristics of the stands, understorey plant communities and soil seed banks of Mongolian pine plantations 5, 10, 15, 20, 30 and 40 years after afforestation and then analysed the resilience and community dynamics of understorey vegetation. The results confirmed that understorey vegetation degradation occurred, which was indicated by the fact that the plant coverage, species number and Shannon-Wiener diversity index decreased significantly in the plantations 30 and 40 years after afforestation. The degradation trend in the understorey vegetation was mainly related to the stand growth, but aging of the stand within 40 years of afforestation did not promote or stimulate a faster recovery in the understorey vegetation. The soil seed bank with high seed density, dominated by a single annual herb species, did not ensure high resilience of degraded understorey vegetation. Thus, active management measures are urgently needed to accelerate ageing stand rejuvenation and understorey vegetation restoration at the southeastern edge of the Mu Us Sandy Land.