This paper presents a quasi-physically based approach for interactively simulating large-scale dynamic forest scenes under different wind conditions. We introduce theories from the wind engineering, and model the natural wind field as a stationary stochastic process. To reduce the geometry complexities without sacrificing much image quality, we adopt a hybrid geometry/image representation scheme to faithfully model the appearance of trees. Some simplified mechanical rules are employed to compute the movement of such tree models. Three kinds of level of details concerning the scene geometry, the movement of trees and the wind field, are exploited to accelerate the simulation. For forest scenes with tens of thousands of animated trees, our implementation with programable graphics hardware achieves visually plausible results at interactive frame rates on consumer PC platforms.