A Study of Age structure of Davidia involucrate Population at Different Altitudinal Gradients in Beichuan

The dendrochronology method was used to analyze the age structure of Davidia involucrate trees at different altitudinal gradients in Beichuan. According to the distribution characteristics of Davidia involucrate, three altitudinal gradients were set as the low limit section of altitude (1 400 m~1 500 m),the middle section (1 600 m~1 700 m) and the upper limit section (1 800 m~1 900 m). The result revealed that the age structure of the upper limit section was elder, lacking young seedlings and individuals of 30~40 years old; In the middle section, individuals between 30 and 40 years old had a higher rate, and had stronger ability to compete for more space and resource; In the low limit section, there were more seedlings. Most of the Davidia involucrate trees were distributed at the middle section, and their age was concentrated between 30 and 40 years old, the population characteristics at the low altitude displayed that seedlings was predominated, while at the upper altitude section,seedlings were sparse,which demonstrated that the altitude could significantly influence the age structure of Davidia involucrate.