Characteristics And Community Stability Of Hippophae Rhamnoides In Loess Area Of Northern Shaanxi Province

The Loess Region in Northern Shaanxi is one of the extremely fragile areas in China and the Hippophae rhamnoides has been widely used in the reconstruction of degraded ecosystems in this area due to its good physiological and ecological characteristics.Therefore,clarifying the dominant factors that affect the understory characteristics and the best afforestation model of Hippophae rhamnoides,so as to provide a basis for the formulation of Hippophae rhamnoides nurturing measures and the determination of the direction of Hippophae rhamnoides community transformation,is the current urgent problem to promote the long-term stable development of Hippophae rhamnoides community.In this study,Wuqi County,Shaanxi Province,where a large area of Hippophae rhamnoides was planted,was used as the research area.Based on the comprehensive investigation of the distribution of Hippophae rhamnoides in the study area,a plot survey method was used to study the understory characteristics of Hippophae rhamnoides and evaluate community stability of each afforestation model.(1)The distribution area of Hippophae rhamnoides accounted for 14.18% of the surveyed area,mainly including 6 types of afforestation models: Hippophae rhamnoides pure forest,Hippophae rhamnoides + Robinia pseudoacacia,Hippophae rhamnoides+ Armeniaca sibirica,Hippophae rhamnoides+ Populus hopeiensis,Hippophae rhamnoides+ Pinus tabuliformis,Hippophae rhamnoides+ Platycladus orientalis.Hippophae rhamnoides + Robinia pseudoacacia is the most widely distributed in the study area.The altitude above 1415 m is the dominant terrain for Hippophae rhamnoides planting,and as the altitude increases,the suitability of Hippophae rhamnoides at various altitude levels shows an upward trend.The 15 ° ~ 35 ° is the suitable slope range for Hippophae rhamnoides plantation.Except for Hippophae rhamnoides+ Platycladus orientalis,other Hippophae rhamnoides afforestation models have large distribution areas on shady slope and semi-shady slope,and the suitability of Hippophae rhamnoides planting in various aspect decreases with increasing light intensity.(2)In the Hippophae rhamnoides,74 species of herbaceous plants were investigated,belonging to 24 families and 54 genera,mainly composed of Compositae,Gramineae and Leguminosae.The diversity of herbaceous plants under Hippophae rhamnoides+ Armeniaca sibirica forest is significantly lower than other afforestation models.On sunny slope,The three afforestation models of Hippophae rhamnoides pure forest,Hippophae rhamnoides+ Pinus tabuliformis and Hippophae rhamnoides+ Platycladus orientalis were all higher than Hippophae rhamnoides + Robinia pseudoacacia,Hippophae rhamnoides+ Populus hopeiensis and Hippophae rhamnoides+ Armeniaca sibirica.On shady slope,the herbaceous plant diversity index of the barren grassland is lower than other Hippophae rhamnoides afforestation model except for Hippophae rhamnoides+ Armeniaca sibirica.The biomass of the herb layer in the barren grassland of shady slopes or sunny slopes is the maximum.The biomass of the herb layer in Hippophae rhamnoides pure forest,Hippophae rhamnoides+ Pinus tabuliformis,Hippophae rhamnoides+ Platycladus orientalis is greater than the other three afforestation models.(3)In Hippophae rhamnoides pure forest,the crown width of Hippophae rhamnoides has a greater effect on understory herbaceous plants.The correlation between the density of Hippophae rhamnoides and mixed trees and the diversity index of herbaceous plants in mixed forest of Hippophae rhamnoides is large.With the increase of Hippophae rhamnoides density or mixed tree density,the diversity index of herbaceous plants showed a trend of first increasing and then decreasing.When the tree density exceeded 3000 plants/ha2,the herb plant diversity index of mixed Hippophae rhamnoides forest would decrease accordingly.The growth of trees and Hippophae rhamnoides is the dominant factor affecting the biomass of the herb layer in the community.The biomass of the herb layer decreased rapidly with the growth of trees and shrubs,and then stabilized.(4)The stability of M-Godron in the Hippophae rhamnoides+ Platycladus orientalis herb community is higher,the stability of M-Godron in the Hippophae rhamnoides pure forest herb community is generally low.The evaluation index system of the stability of the mixed Hippophae rhamnoides forest community was established,and the ranking of the stability of the mixed seabuckthorn forest community in different slope directions was Hippophae rhamnoides+ Populus hopeiensis(shady slope)> Hippophae rhamnoides+ Platycladus orientalis(sunny slope)> Hippophae rhamnoides+ Pinus tabuliformis(sunny slope)> Hippophae rhamnoides+ Populus hopeiensis(sunny slope)> Hippophae rhamnoides + Robinia pseudoacacia(shady slope)> Hippophae rhamnoides + Robinia pseudoacacia(sunny slope)> Hippophae rhamnoides+ Pinus tabuliformis(shady slope)> Hippophae rhamnoides+ Platycladus orientalis(shady slope)>Hippophae rhamnoides+ Armeniaca sibirica(shady slope)>Hippophae rhamnoides+ Armeniaca sibirica(sunny slope).The stability of Hippophae rhamnoides+ Armeniaca sibirica community is low on the whole,and the ability to resist external interference is weak.The species composition in the Hippophae rhamnoides+ Armeniaca sibirica community is very susceptible to changes from outside influence.In short,according to the above research results,intermediate cuttings and other measures for Hippophae rhamnoides community can be taken,and the low stability afforestation models such as Hippophae rhamnoides+ Armeniaca sibirica can be transformed to the high stability afforestation models such as Hippophae rhamnoides+ Platycladus orientalis.