Abstract:

Su cheng Ecological Reserve is located within the Yuntai Mountains in the coastal region of northeastern Jiangsu Province. Five typical vegetation types, including hardwoods, conifer and bamboo forests have been reported from permanent plots established in this reserve. Pinus densiflora is the dominant species of the conifer forests and reaches its southern-east distribution boundary in China at the Yuntai Mountains, where the vegetation is mainly composed of North-temperate and Pantropic components. A lot of East Shandong species extrend southward to this location. It is reported as being highly susceptible to infestations of the pine wood nematode which is presently causing severe damage in pine forests of China, Japan and other countries.Among canopy trees size class distributions following an inverse J-shaped curve were observed. Nearly 100% mortality of seedlings was observed past the first year following germination. Approximately half the subcanopy and six percent of canopy trees present were dead. Linear regression analysis of the relationship between age and diameter was significant. The model of population age structure shows:

Y = 1. 5829 x 104e-0.0618X

which Y is the number of survivers at time x in stems/0.4ha. X is the age of the population. The use of population age distribution set up the static life table of Pinus densiflora. This information suggests that this population has sustained consistent growth from seedlings recruitment. High mortality of seedlings and young saplings under the closed canopy of this forest indicates that reproduction has been very slow, probably from gap replacement. The present age structure of this stablized population is apparently due to competition within a naturally established forest, in combination with physiographic, edaphic and climatic factors. Absence of nematode infestation is attributed to the high annual precipitation, higher altitude and the relatively low mean annual temperature of the Yuntai Mountains, as well as the disjunct distribution of these populations and relatively different flora components.