Minimal Quadrat Selection For Vegetation Characteristics Investigation In Alpine Meadow On Eastern Qinghai-tibet Plateau And Grass + White Clover Grassland In Northeastern Yunnan

The quadrat sampling method is a traditional method and main means to obtain the quantitative characteristics of grassland plant populations and communities,however,in the investigation of grassland vegetation characteristics,there is no unified standard for setting the size and number of quadrat.Considering the selection of suitable quadrate is extremely critical to the accuracy and sampling efficiency of quantitative traits investigated in grassland vegetation,this study takes the alpine meadow on eastern Qinghai-Tibet Plateau and the grass+white clover grassland in northeastern Yunnan as case,and sets different sizes(0.1 m~2,0.25 m~2 and 0.5 m~2)and numbers(5,10,15 and 20).Based on the survey data of plant population and community characteristics,through the analysis of species diversity,the economic groups biomass,the relationship between species diversity and grassland grading and classification,the aboveground biomass and species number variability of the community,and the species-number curve relationship in different types or communities of grassland,clarify the selection of minimal size or number of quadrat based on species diversity,biomass and species number.The main results are as follows:1)The effect of quadrat size on the plant species diversity of grassland community is greater than that of quadrat number.The species diversity survey of each grassland type or community can reflect the actual situation of the grassland when the quadrat number is more than ten per 0.5 ha,but there is no choice for the quadrat size.2)The effect of quadrat size on the economic group biomass is greater than that of the quadrat number,and the economic group biomass cannot provide guidance for the selection of quadrat in the process of biomass monitoring.The biomass monitoring is more accurate with 0.5 m~2 than 0.1 m~2 and 0.25 m~2.For communities with small vegetation variability,ten quadrats per 0.5 ha can meet the biomass monitoring requirements,while for communities with large vegetation variability,twenty quadrats per 0.5 ha can meet the biomass monitoring requirements.3)The selection of the quadrat number is closely related to the species number in the grassland community and the species number in single quadrat.If the survey goal is only to obtain the dominant species and common species in the community,twenty quadrats per 0.5 ha of 0.1 m~2 can achieve the goal.If it is necessary to objectively reflect the number of all species in the community,the quadrat of 0.1 m~2 is easier to achieve the goal than 0.25 m~2 and 0.5 m~2.The selection of quadrat number of alpine meadow on eastern Qinghai-Tibet Plateau and grass+white clover grassland in northeastern Yunnan is generally 70-100 quadrats per 1.5 ha and 70-110 quadrats per1.5 ha respectively.For the investigation of grassland vegetation characteristics with high heterogeneity,it is recommended to select the quadrat with small size and large number.