Analysis of the Population Structure of Broussonetia papyrifera in Suburban of Nanjing

Purpose Broussonetia papyrifera forest was one kind of secondary forests in the suburban of Nanjing, which is the main part of urban forest. The aim of this study is to know the structure and dynamic of the population clearly, in order to provide some useful suggestions for the forest management and the urban construction.

Method Based on the field investigation, setting 20 plots sized 10 m×10 m, the population of B. papyrifera was studied by the methods of age class structure, height class structure, crown class structure, life time, survival curve and time sequence prediction.

Result (1) The age structure of B. papyrifera population exhibited the shape of pyramid in general, which meant that the lower-age populations were more and the mid-age was the main part of the population frame. (2) There was significant correlation between height growth and diameter growth, and the related equation was y=0.597 1+3.412 9lnx. Restricted by the biological characteristics, most individuals of B. papyrifera were less than 10 m height. (3) Most of the crowns were less than 10 m², which was no significant correlation with the height and diameter. (4) Life time indicated that mortality and disappearance rate were high in the stage of II and VI, because it was confined by the environment and population characteristics. (5) The survival curve was a transitional type from Deevey-II to Deevey-III. (6) Ideally, the population would keep stable according to the time sequence. Under disturbance and not-disturbance, population dynamic index were 0.493 and 0.003 respectively, particularly deviating from 0 lightly, which existed the risks of recession potentially.

Conclusion Population of B. papyrifera in the study area was still in stable condition in future, but the population was still in the risk of transitive stage from youth age to mid age. The youth was the most important part for keeping population stably.