Abstract:

[Objective] This study was conducted to explore the quantitative indexes for classifying hazard grade of Stellera chamaejasme L. （S. chamaejasme）, and to provide references for regional poisonous weed control. [Method] Large sample plots were set up in the representative zones with mild, moderate and severe occurrences of S. chamaejasme population respectively to investigate the population characteristics of S. chamaejasme in grassland ecosystems under different hazard grades. Each large sample plot was 100 m×100 m with more than 10 km apart from each other. Four medium quadrats were randomly set up in large sample plot, with an area of 10 m×10 m for each quadrat and more than 10 m apart from each other. The small quadrats with an area of 2 m×2 m for each were randomly arranged in the medium quadrat for each investigation with 5 replicates. The quadrat survey included the height, coverage, density and above ground biomass of the vegetation community and S. chamaejasme population, as well as the individual cluster width and branch number of S. chamaejasme. Statistical analysis was performed to determined the population characteristics of S. chamaejasme in zones with different hazard grades and their relationship with the characteristics of the vegetation community. [Result] The coverage, height, density and above ground biomass of S. chamaejasme population as well as the individual branch number all increased as the hazard grades increased. In the mild, moderate and severe hazard grade zones, the population average coverage was 13.75%, 32.85% and 49.50%, respectively, with significant （P<0.05） differences. The population average height was 21.59 cm and 21.24 cm in the severe and moderate hazard grade zones, respectively, with no significant （P>0.05） difference. But both were significantly （P<0.05） higher than that in the mild hazard grade zone （19.29 cm）. The population average density was 1.95, 3.42 and 7.16 plants/m² in the mild, moderate and severe hazard grade zones, respectively, with significant （P<0.05） differences. The population average above ground biomass was 34.79, 70.73 and 98.39 g/m² in the mild, moderate and severe hazard grade zones, respectively, with significant （P<0.05） differences. The individual average branch number in the severe and moderate hazard grade zones was 34.59 and 32.25, respectively, with no significant （P>0.05） difference. But both were significantly （P<0.05） higher than that in mild hazard grade zone （13.73）. The individual average cluster width was 354.96, 698.95 and 607.10 cm²/plant in the mild, moderate and severe hazard grade zones, respectively, with significant （P<0.05） differences. [Conclusion] The coverage and density could be given priority in quantitative classification for hazard grade of S. chamaejasme in degraded grassland.

Key words: Stellera chamaejasme L., survey, hazard grade, indexes for classification