Abstract: Studies on the width and density of ring and the length, shrinkage rate and their radial variations of wood fiber of Salix matsudana and Populus pseudo-simonii show that the physical properties of wood are significantly affected by its ring age,and the fiber length of wood is not influenced by ring width.Through synthesizing the radial variation patterns of wood properties,it is suggested that the whole growth period of these two kinds of tree species can be divided into young growth, fast-growing,mature and regeneration stages.The age value of each stage is defined.

Key words: Farm shelterbelts, Wood property, Salix matsudana, Populus pseudo-simonii, fine root, nitrogen use efficiency., bareroot seedling, nitrogen metabolism, gel