Study On Community Characteristics And Influencing Factors Of Understory Woody Plants In Robinia Pseudoacacia Plantation

Black locust(Robinia pseudoacacia L.)is the main forest resource in the Loess Plateau,it has made great contributions to the forest vegetation restoration,soil and water conservation and ecological reconstruction in the Loess Plateau.Our study takes the second-generation black locust plantation in Yongshou of Shaanxi Province as the research object,the characteristics of canopy wood and understory woody plants community of 10 black locust plantations were investigated in different site conditions.The specific objectives of our study were to determine the species composition,diversity differences,and the spatial distribution pattern of understory woody plants and the correlation with environmental factors.Simultaneously,based on the comprehensive evaluation of the natural regeneration performance of understory woody plants,the potential alternative species in the canopy were selected,which provided a certain scientific basis for improving the community stability and promoting sustainable development of black locust plantation.The main results are as follows:(1)There were significant differences in species composition and diversity of understory woody plants of black locust plantation under different site conditions.In terms of species and number of plants,the regenerated black locust(19.76%)and Rubus corchorifolius(64.85%)were the most abundant understory tree and shrub species in tableland stands,while Broussonetia papyrifera(6.77%)and Acanthopanax senticosus(37.22%)had an absolute advantage in gully stands.Compared with the tableland plots;the number of tree species in the gully plots was significantly more,but there was no significant difference in the number of shrub species.Meanwhile,we found that the regenerated black locust was generally grew and distributed in the tableland stands,while other understory tree and shrub species were mainly distributed in the gully stands.(2)There were also significant differences in the diversity pattern of understory woody plants.The species richness(S,6.61 vs.14.75),Shannon diversity index(H,0.71 vs.1.72)and evenness index(J,0.39 vs.0.64)of understory woody plants in tableland stands were significantly lower than those of the gully stands.There were significant differences in the density and height growth of understory woody plants among all plots,but the significant difference was the largest in the gully plots.(3)Based on the single objective and comprehensive evaluation,it was found that the renewal ability of the regenerated black locust,Broussonetia papyrifera(Linn.)L’Hér.ex Vent.,Celtis sinensis Pers.and Rhus punjabensis Stewart var.sinica(Diels)Rehd.et Wils.in trees were the best,and the renewal performance of Rubus corchorifolius L.f.,Lonicera hispida Pall.ex Roem.et Schult.,Acanthopanax senticosus(Rupr.Maxim.)Harms.and Celastrus orbiculatus Thunb.were better in shrubs.Therefore,we should focus on the development of the above species in the succession process of gradually replacing black locust plantation in the Loess Plateau.(4)There were significant differences in spatial distribution of understory woody plants of black locust plantation under different site conditions.In the vertical space,the number of height grades of understory woody plants in the gully stands was significantly higher than that in the tableland stands,and the number of shrub species at the same height grade was significantly higher than that of trees.At the same time,understory woody plants in all stands had more seedlings,which shows an overall development trend.(5)For the horizontal spatial pattern,the understory woody plants and understory shrubs mainly presented aggregation distribution,the understory trees mainly presented random distribution on the tableland plots and aggregation distribution on all scales of gully plots.The spatial correlation between understory woody plants and black locust living trees was mainly independent of each other.(6)The results of redundancy analysis showed that all site factors,stand factors and soil factors involved in the study jointly explained 77.57% of the variation of species composition of understory woody plants,The key factors affecting species composition of understory woody plants were shrub coverage,herb coverage,stand age,leaf area index,slope and soil total phosphorus in 10-20 cm soil layer were the main factors.(7)The key factors affected the diversity index of understory woody plants were screened by Akaike information criterion.The results showed that: soil organic carbon in 10-20 cm soil layer and soil total potassium in 0-10 cm soil layer had a significantly impact on species richness(S),Shannon diversity index(H)and evenness index(J)of understory woody plants.Based on the above research results,for the protection and utilization of species diversity under black locust plantations,it is suggested to comprehensively consider site factors,stand factors and their interaction effects,so as to systematically evaluate and clarify the key factors affecting the characteristics and diversity of plant community under black locust plantations.At the same time,measures such as moderate thinning can be considered to reduce the competition among species and increase the living space of other understory species,so as to improve the diversity of understory species and increase the stability of black locust plantations.