Undergrowth Plant Diversity Of Robinia Pseudoac Acia Plantation Community

Robinia pseudoacacia is the tree species with the largest planting area in Northwest China.The healthy development of its community plays an important role in ecological restoration in Northwest China.In order to solve the problem of sparse understory vegetation and declining species diversity of Robinia pseudoacacia plantation community.This study through the investigation of different forest age of acacia pure forest and Robinia pseudoacacia + Platycladus platycladus mixed forests of species composition,ecological diversity and alpha,analyzed the influence of the locust growth of understory plants,locust plantation community at the same time will be compared with native plant communities,This study provided a reference basis for the improvement of species diversity of Robinia pseudoacacia plantation community on the Loess Plateau.The results are as follows:(1)With the increase of stand age,the understory plant species of Robinia pseudoacacia forest decreased gradually;Among them,the species of Compositae first increased and then decreased,the species of Rosaceae first decreased and then increased,and the species of legumes,Moraceae and gramineae decreased.In addition,the similarity coefficient of communities in adjacent stages was higher and decreased,but the proportion of mesophytes in understoreage community increased gradually.The analysis of understory plant community diversity showed that the total α diversity of understory plants decreased with the increase of stand age.The α diversity of herbaceous layer increased first and then decreased,which was positively correlated with litter thickness.The α diversity of shrub layer showed a downward trend.It was positively correlated with soil moisture content and negatively correlated with stand canopy density,crown width,tree height and DBH.(2)With the increase of stand age,the number of plant species under Robinia pseudoacacia + Platycladus platycladus mixed forest increased first and then decreased;Among them,the species of Compositae and legumes decreased gradually.Gramineae decreased first and then increased.Rosaceae increased first and then decreased.In addition,the similarity coefficient of communities in adjacent stages was higher and decreased,but the proportion of mesophytes in understoreage community increased gradually.The analysis of understory plant diversity showed that the total α diversity of understory plants in mixed forest increased first and then decreased with the increase of stand age,and the α diversity of shrub layer and herb layer increased first and then decreased.canopy density and soil moisture content were negatively correlated with shrub diversity.Tree height,canopy density and crown width were negatively correlated with herbaceous diversity.(3)The total α diversity of the understory plants of the four communities was as follows: Robinia pseudoacacia pure forest,Platycladus orientalis pure forest,mixed forest and wild grass forest.The species number of mixed forest and Robinia pseudoacacia pure forest were the same,but the plant species family and genus composition of mixed forest was more complex than that of Robinia pseudoacacia pure forest.According to the analysis of the ecological types and families of the understory plants,the proportion of the understory mesophytes in the four communities was as follows: Robinia pseudoacacia forest> mixed forest> Platycladus orientalis forest > grassland;Among them,Compositae and Gramineae all exist in the four communities.And weeds and other common families of three kinds of forest community forests and only compositae and gramineae,and acacia pure forest and mixed understory plant community similarity is higher,its joint family compositae,gramineae,rosaceae,leguminosae,violet,cyperaceae and 7 kinds of mulberry,arborvitae locust biota orientalis pure forest and mixed forest understory plant community similarity coefficient of the highest,The common family includes 8 species: Compositae,Gramineae,Rosaceae,Leguminosae,Viola,Cyperaceae,Rubiaceae and Apodiaceae.In conclusion,the growth and development of Robinia pseudoacacia have a limiting effect on understory plant diversity of both pure and mixed forests,but the mixed mode can alleviate the problem of species diversity reduction caused by single planting of Robinia pseudoacacia,but it is necessary to strengthen late management to prevent Robinia pseudoacacia crown from oversize to suppress other plants.In addition,Robinia pseudoacacia planting can improve the species diversity of grasslands but has little effect on the understory plant diversity of platycladus orientalis pure forest,but the mixed growth of Robinia pseudoacacia and platycladus orientalis can promote the balanced growth of Robinia pseudoacacia and platycladus orientalis and the healthy and stable development of community.