Abstract: Effects of water and heat stress on seedling height growth and biomass of Chinese fir,masson pine,Douglas fir,western redcedar and lodgepole pine seedlings were measured during a threecycle stress period in spring 2001 at the University of British Columbia.The results showed that:(1)Water stress had significant effects on seedling shoot length increment and shoot increment rate.But the level in each of five species was different.The shoot length increment from high to low in five species is masson pine,western redcedar,Chinese fir,Douglas fir and lodgepole pine.And the shoot increment rate is also different,their order from high to low is Chinese fir,masson pine,lodgepole pine,western redcedar and Douglas fir.But the influence is not as strong as water stress.Heat stress had significant effects on seedling shoot length increment and shoot increment rate of western redcedar and Douglas fir,but the influence level in other species is slight,and there is no significant effect on masson pine.(2)Heat stress also had a strong influence on seedling shoot length increment and shoot increment rate.(3)Different levels of water stress treatment in Chinese fir only slightly influenced seedling biomass.There was no significant difference in root dry weight under different level of water stress treatment.The biomass of Chinese fir,however,was dramatically affected under heat stress treatment.All four biomass indexes of Chinese fir had a significant difference a under different levels of heat stress treatment.Masson pine,another subtropical tree,showed a significant difference in all biomass indexes under both water and heat stress treatments except for root/shoot ration(dry weight) under heat stress treatments.It was shown that biomass indexes of Douglas fir were significantly affected by heat stress treatment but not by water stress treatment.The experiment also showed that the heat stress influenced biomass of western redcedar much stronger than water stress did.Lodgepole pine had the similar trend to tolerate heat and water stress treatments as redcedar and Douglas fir.All its biomass indexes had no significant difference under water stress treatment but there are differences observed under heat stress treatment.(4)Of all five experimental species,there is no significant effects on root to shoot ratio under water and heat stress.