The Forest Structure And Leaf Traits Of Robinia Pseudoacacia In Ansai County

The hilly and gullied Loess Plateau was the main region of implementing the “Grain for Green” project. Located in this region, Ansai County was the first unit for piloting and demonstrating the project. Within the county, we focused on investigating afforestation area and distribution since beginning the project, analyzing characteristics of forest structure of Robinia pseudoacacia along with stand age growth, and understanding the development and leaf traits after 15-year afforestation in abandoned farmland, in order to provide refrences for the health assessment of the 15 years Robinia pseudoacacia stands and effectivenees evalution of “Grain for Green” project in the hilly and gullied Loess Plateau. The main results are as follows:1) The restoration areas of different vegetation types within Ansai County were as follows: trees>shrubs>herbs, and the area of trees accounted for 57%.. The afforestation mode in the early years(1999-2001) was mainly pure plantation. The mixed plantation was implemented since 2002. R. pseudoacacia was the main species of pure stands and its afforestation area was largest relative to other tree species. The area of pure R. pseudoacacia stands was bigger than the mixed R. pseudoacacia stands.2) The height of R. pseudoacacia increased as stand age grew and was subject to stand density. The increment in height was fast at young stand stage(1-10 a) while it tended to be slow prior to mature stand stage(30 a). The increments in diameter at breast height(DBH) at young(1-10 a) and near-mature(15-20 a) stand stages were fast while it tended to be slow afterwards. The distribution of diameter class at maturer stand stages(20-40 a) tended to be asymmetrical. The stand density and canopy density increased as stand matured(10-30 a) but decreased at over-mature stand stage(40 a), while crown breadth increased since stand age grew. Therefore, R. pseudoacacia stopped growing or grew slowly after maturity(about 30 a)at which thinning cutting should be necessary.3) For 15-year R. pseudoacacia within Ansai County, the height and DBH were lower than those in other study areas on the Loess Plateau region, suggesting stunted growth anddevelopment. The growth on sunny slopes was better than that on shady slopes. Excessive stand density would inhibit the growth. The 15-year R. pseudoacacia N content had low, N content, and N:P was less than 14, suggesting N limitation for R. pseudoacacia development.On the whole, the 15 year locust has strong adaptability in arid environment,but poor growth.