The Study Of Understory Vegetation Of Chinese Fir Plantations And Natural Secondary Forests In Subtropical Forest

Biodiversity is strongly linked to ecosystem functioning important to humanity,and biodiversity conservation is an important goal of sustainable forest management.Understory vegetation,as an important component of plant diversity,promotes nutrient cycling and energy flow.Intensive management is thought to increase the diversity of understory vegetation in the short term,but the long-term impact is still unknown.This study uses the method of space for time substitution by allocating stands of different ages for two forest types: natural regeneration with forest ages 4,8-10,18-20,26-28,36-40 years,and Chinese fir plantation with ages 5,8,21,27,40 years.Statistical methods such as linear models and non-metric multidimensional scaling were used to test the effects of forest type and stand age on understory vegetation cover,diversity,and species composition.Correlation,regression,and redundancy analysis were used to explore possible mechanisms related to understory vegetation dynamics to provide a theoretical basis for the restoration of understory vegetation and forest management.The findings are as follows:(1)Compared with natural secondary forests,the cover of shrub plants in the 4-5 and 8-12-year age classes under Chinese fir plantations was lower,while higher cover of vascular vegetation in 8-12-year age class.Stand age and forest type had no significant effect on the cover of non-vascular species in the herb layer.(2)In the three yonger age classes,the richness of shrub plants in the natural secondary forest was significantly higher than that of Chinese fir plantation,and there was no significant difference in the two older age classes.The species richness of total and vascular vegetation in Chinese fir plantations were significantly higher than those of the natural secondary forest among all age classes,and nonvascular species richness was significantly higher than that of the natural secondary forest only at the 35-40-year age class.(3)Compared with Chinese fir plantations,the evenness of shrub plants and total understory vegetation in natural secondary forests were higher in the 8-12 and 4-5-year age classes,respectively.The vascular species evenness of Chinese fir plantations in the 35-40-year age class was higher than that of natural secondary forests.(4)There were significant differences in species composition under the two forest types.Understory species composition of Chinese fir plantation showed a fair separation from natural secondary forest in ordination space and younger sites were grouped on the left and older sites on the right of axis 1 in ordination space.Indicator species analysis revealed that the species composition under the Chinese fir plantations were mainly species with higher light and nutrient requirements,while the natural secondary forests were mainly species shade-tolerant and low nutrient-tolerant.(5)Stand age significantly affects light quantity,light heterogeneity and the cover of litter,and forest type significantly affects total C,total N,total P,and available N.Regression analysis showed that the cover of shrub vegetation increased with substrate diversity,total C,and total N.The cover of non-vascular vegetation increased with substrate diversity and decreased with litter cover.The richness of shrub plants increased with total C,total N,and litter cover,but decreased with total P.The response of the richness of vascular and shrub plants to total C,total N,total P,and litter cover were opposite.The evenness of the vascular vegetation in the herb layer increased with light heterogeneity and available N,and the evenness of the non-vascular vegetation increased with total P.(6)The species composition of shrub and vascular plants was significantly affected by stand age.In addition,the shrub species composition was also significantly affected by light heterogeneity,vascular species composition was affected by soil total N and light availability,and the non-vascular species composition was affected by soil total C,light availability and substrate diversity.Our study indicated that intense management increased vascular plant richness,but decreased the shrub species cover and richness in the 4-5 and 8-12-year age classes.In addition,more light-and nutrient-demanding herbaceous and less woody plants occurred in Chinese fir plantations.These influences resulted from the alteration of soil nutrients and substrate diversity,and to a lesser extent stand age and light resource conditions.