| Eucalyptus has made great contributions to the regional economy in China.However,large area development of the trees with short-rotation period also result in decreased biodiversity,degraded soil fertility,lower ecosystem stability,allelopathy and other ecological problems.As one of the most important indicator of ecosystem,biodiversity closely correlated with productivity,stability and nutrient cycling and resistance of forest ecosystem.Understory vegetation was an important component of forest ecosystems and play critical role in the conservation of biodiversity,provision of forest products,and nutrient cycling and energy flow.Previous studies have found that monoculture of Eucalyptus reduced the plant diversity.However,mixed plantations can improve the productivity and stability because of complementary effects among the component trees on physi-biological features,growth,and root distribution.In addition,the mixed effects of various trees are also affected by many factors,such as tree species,forest age,mixed proportion,climate and environment.However,currently,little is known about how eucalyptus artificial mixed forest affects undergrowth plant diversity.Therefore,we took Eucalyptus grandis and fourtypical tree species in Danling region,Sichuan,afforested on arable lands,including Cunninghamia lanceolata,Pinus massoniana,Alnus cremastogyne,Betula mixed and compared with Eucalyptus grandis pure forest,to study the characteristics of species composition,diversity and life forms of understory vegetation in different seasons.We aimed to understand the impact of eucalyptus mixed forests on plant diversity,which will provides theoretical basis for scientific management of Eucalyptus grandis plantation.The results showed that:1)A total of 72 species of plants were recorded,belonging to 45 families.The dominant species include Rosaceae,Poaceae and ammonaceae.The dominant shrub species include Myrsinea fricana,Camellia japonica,Rosa sp.and the dominant herb species include Carex,Dicranopteris dichotoma,Duchesnea indica Bidens pilosa.2)The under vegetation of pure and mixed forests is mostly consist of micro-phanerophytes and nano-phanerophytes.Herb species were mainly consist of hemicryptophytes and therophytes.Among the various life forms,meso-phanerophytes occupied highest ratio in 8-year-old pure stands,micro-phanerophytes have the highest proportions in Eucalyptus+pine stands,which of nano-phanerophytes were highest in Eucalyptus+pine mixed plantations.In herb layers,the proportion of chamaephytes were highest in Eucalyptus mixed with the two evergreen species.The proportion of hemicryptophytes and therophytes were highest in Eucalyptus+alder stands.3)The species richness and diversity of plants were highest in Eucalyptus+alder and Eucalyptus+beech mixed stands in spring,but in summer,which were highest in pure stands and mixed plantations of Eucalyptus and the two broad-leaved tree species.As for the herb species,the richness and density and diversity were highest in Eucalyptus and the two mixed broad-leaved species,but which were highest and similar among pure stands and the two mentioned plantaitons in summer.The species richness and diversity were lowest in Eucalyptus+pine and Eucalyptus +fir mixed plantations.4)The correlationships showed that soil water content,p H value and soil available P were the main factors influencing herb species diveristy.Soil water content,soil organic matter content,soil total N,available P mostly affected the diversity of shrub layers.Therefore he species richness and diversity of plant changed in mixed Eucalyptus and the other four tree species.Shrub species richness and diversity in Eucalyptus+beech plantations were highest,but which of herb species were highest in Eucalyptus+alder plantations.Therefore,alder and beech would be the appropriate component tree species for the mixed Eucalyptus grandis plantations,which will provide the scientific references of the scientific management in Eucalyptus plantations. |
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