干旱区生态环境知识资源中心

The effect and cost-benefit relationships of planted shelterbelts on reducing wind velocity and sand transportation rate (benefit) in relation to shrub height and density (cost) were studied in the Yanchi sandy land in NW China. The species-specific morphology of Salix psammophila C. Wang & Ch.Y. Yang was more effective in wind-breaking than Caragana microphylla Lam. while Tamarix cf. chinensis was least effective. Wind-breaking and reduction of sand transportation increased with shrub height, higher planting density, number of parallel rows in a shelterbelt but was always the greatest near ground. It declined with increasing distance from the lee-side of the belt. Shelterbelts composed of 1.5m tall C. microphylia at 1.5m planting distance in 3 rows per belt exhibited best effects on wind-breaking and sand fixation. In a modelling approach these effects could be generally expressed as manifolds of shrub height rather than absolute distances, and they were correlated to a cost (investment) factor given by shrub height and planting density. The highest benefit-cost relationship is now yielded by planting smallest shrubs in 1 to 2 rows per belt at a larger (optimal) distance between rows and belts. Obviously, the trade-off is more sensitive to costs than to benefits favouring many small shrubs with smaller individual effects rather than fewer larger shrubs with stronger effects. This implies the potential for an appropriate, controlled wood harvesting from these shelterbelts as long as near-ground re-sprouting is not affected, and the use of grasses when planting these belts.