Effects of stand structure on wind speed reduction in a Metasequoia glyptostroboides shelterbelt

In a Metasequoia glyptostroboides coastal forest shelterbelt near Shanghai, China, we studied relationships between stand structure and wind shelter effect. We located 16 plots at intervals of 500 m along the shelterbelt and characterized both horizontal and vertical structure of each plot. Wind speed was measured within each plot and at different distances windward and leeward. We found that wind shelter effects were closely related to stand structure of the studied M. glyptostroboides shelterbelt. Stands with high basal area but intermediate crown index and intermediate proportion of large trees (LT) produced the best shelter effects, with significantly longer shelter distance (d70, shelter distance which the wind speed U does not exceed 70 % of U (0)) and slightly lower minimum relative wind speed (U (m) /U (0)). Simple structural indices that can be easily measured in the field were good predictors of the shelter effect. LT was the best predictor of d70, while basal area at ground level was the best predictor of U (m)/U (0). The relationships between stand structure and shelter effect provides a practical guideline to the design, construction and management of forest shelterbelts. In order to provide the best shelter effects, high basal area of > 50 m(2) ha(-1) at ground level or > 33 m(2) ha(-1) at breast height coupled with an intermediate LT value of about 60 % should be maintained for the studied M. glyptostroboides shelterbelt.