Characteristics of population structure and community species diversity of an extremely small population of protected Phyllitis scolopendrium

For Phyllitis scolopendrium,a second-class national protected wild plant with extremely small populations,which is distributed in a narrow region of the Changbai Mountains,we analyzed the population size,distribution frequency and density,individual features,and the variation of internal and external populations at 729 and 1008 m above sea level( asl).The plant height,substitute age structure,distribution pattern,community biodiversity,and similarity of various layers were also described. Results showed that P. scolopendrium was a typical occasional species,which showed a patchy distribution pattern. At 729 m asl,the population density was the highest( 91 per 400 m~2),with a distribution frequency of93.75% and highest density of 30/25 m~2. At 1008 m asl,the population density was only 31 per 400 m~2,with a distribution frequency of 43. 75% and highest density of 15/25 m~2. Based on the analyses of morphological features,including plant height,leaf number,sporangium leaf number,maximum leaf length and width,minimum leaf length and width,canopy width,and leaf thickness,we found that the morphological features of the internal population showed the highest variation,indicating a decreasing trend with increasing height/age. Additionally,variations in plant height,mature sporangium leaf number,maximum leaf length and width,canopy width,and leaf thickness all showed significant differences( P < 0.01),indicating that the two populations were from different species types. Plant height showed a double peak pattern. Trough value of type 01 population occurred at 15. 1-20. 0 cm,whereas the trough value of the type 02 population occurred at10.1-15.0 cm. There was a significant update process in both types,and a break of the type 01 population at 40. 1-45.0 cm. We analyzed the age structure of type 01 and 02 populations and found that there were five age classes of the type01 population,which showed a normal distribution pattern,whereas the type 02 population had four age classes,which showed an inverted J distribution pattern. Type 01 and 02 populations were at juvenile and middle age stages,with no trend of senescence. Based on the spatial pattern analysis,we found that P. scolopendrium showed a negative binomial distribution pattern. The diversity indices,including Shannon-Wiener,Pielou,and Margalef,showed that the similarity index of tree,shrub,and herb layers in the two types was low,indicating a low biodiversity status compared with the local climax community. Phy