[Growth characteristics of different tree species in shelterbelts in the depression area of Hebei Province, China.].

This research investigated shelterbelt structure indices using the standard sampling method, to study the dynamic changes of different tree species including Ulmus pumila, Populus simonii and Pinus tabuliformis in the depression area in Xiaobazi Township of Fengning County, Hebei Province, China. The results showed that the average age of U. pumila, P. simonii and P. tabuliformis pure forests was 10 years in this area. The average DBH and tree height of P. simonii pure forest were 2.3 times and 3.8 times as those of U. pumila pure forest, as well as, 2.3 times and 3.0 times as those of P. tabuliformis pure forest, respectively. The average DBH, tree height, LAI and height of first live branch of P. simonii pure forest were significantly larger than those of U. pumila pure forest and P. tabuliformis pure forest. Compared with P. simonii mixed forest, the stand density of P. simonii pure forest was 10.8% higher, average DBH of pure forest was 5.2% lower, and average tree height was 11.3% lower. Compared with U. pumila mixed forest, the stand density of U. pumila pure forest was 6.6% higher, average DBH and tree height of pure forest were 7.8% and 14.2% lower. Compared with P. tabuliformis mixed forest, the stand density of P. tabuliformis pure forest was 4.9% larger, but average DBH and tree height were 29.3% and 31.8% lower, respectively. The average DBH, tree height of different forest types showed significant negative correlation with the stand density. Average LAI showed significant positive correlation with density and height of first live branch, and significant negative correlation with the DBH, tree height. There was a significant positive relationship between the average height of first live branch and stand density. The increments of DBH and tree height of coniferous and broad-leaved mixed forest were significantly higher than those of coniferous pure forest. The comprehensive growth potential of the shelterbelts tended to increase, and the lateral growth potential on the whole exhibited a declining trend.