<正>以接种松材线虫的1年生抗性黑松苗为实验材料，用感病黑松苗作对照来研究松材线虫在抗性黑松体内的移动及寄主水势变化。结果表明：接种初期，松材线虫在树体内的数量少，移动速度慢；在抗病黑松体内，线虫主要向下移动，且虫体数量明显少于在感病黑松体内的数量；在感病黑松体内线虫自接种点向上、下移动，且向下移动的速度和虫体数量明显大于向上的。随着时间的推移，线虫开始繁殖，扩散能力增强。水势测定结果显示，感、抗病黑松水势变化总趋势是先上升后下降再上升。

Forest statistica! data, agriculture and forestry census data from 1960--19, 95 and mathematical model F/N=a ?exp(p (N/S)), (where F is forest area, N is population, S is city area, a and p are parameters), are employed to predict the urban forest decrease in Kanagawa prefecture Japan. The results show that per capita forest area is decreased because of the increase of population. If the population is increased by 10%, the per capita forest area will be decreased from 1%to 92%. Most of validation coefficients in different cities are over0.9, that means calculation results are very accurate, lnorder to prevent the decrease of urban forest and reduce the preservation cost, based on the deforestation rates and financial status of different governments, we suggest that Japanese governments should purchase the forests, forest land, and monitor the forest land conversion in a long term. These preservation strategies are useful for developing countries, such as P.R. China.