Radial growth characteristics of Ulmus pumila var. sabulosa in Otindag sand land, northern China.

Ulmus pumila var. sabulosa specimens were collected from natural forests located in Baoshaodai and Naritu of Otindag sand land northern China. To provide a basis for the population conservation and natural regeneration of elms in Otindag sand land, tree-ring width, earlywood width and latewood width were measured to study their eccentric growth and radial growth. The results showed that elms in Baoshaodai and Naritu had different degrees of eccentric growth with complicated eccentric forms and irregular shapes. Elms in both Baoshaodai and Naritu had two growth peaks in the ring widths. Tree-ring width and latewood width had a similar double S growth pattern and their growth peaks occurred in exactly the same time. In contrast, earlywood width had little change during the whole growth period. Earlywood width had different growth peaks from annual ring width and latewood width, and the cumulative growth curve of earlywood width was linear. There was no significant difference in average annual growth of elms between Baoshaodai and Naritu, which were 2.25 mm and 2.30 mm respectively. Tree-ring width and latewood width of elms in Baoshaodai had a variation coefficient of 20%, which was much higher than that in Naritu. The first radial growth peak of U. pumila var. sabulosa in Baoshaodai occurred in the year 17 to 21 while that in Naritu occurred in the year 15 to 19. The mature age of U. var. sabulosa in the two places differs by 3 years.