Abstract
Forest structure and growth of individual trees were investigated by enumeration survey and stem analysis in the windbreaks established and left free for 15 years in Mu-Us desert in Yinchuan City, Ninxia-Huizu Autonomous Region, China. 40 % of planted Populus alba var. pyramidalis reduced because of self-thinning promoted by severe intra-specific competition for natural resources. Survived trees showed the vigorous growth reaching higher than 12 meters. On the other hand, self-thinning was seldom occurred in both windbreaks of P. Opera and P. hopeiensis. They had a lot of dead branches on their crowns and their annual height growth showed an asymptotic curve to the 7 to 10 meters maximum height. Soil moisture content was lower in P. alba var. pyramidalis forest than in P. Opera and P. hopeiensis forests, because of more water consumption of P. alba var. pyramidalis by great volume of leaf biomass.
