Decimation and compression of pre-computed deformation data is crucial to synthesize realistic animation of massive plants. In this paper

a motion simplification algorithm is proposed based on the observation that plants are of tree-like hierarchical structure inherently and move in a hierarchical mode. According to the hierarchy of a plant

the motions of its sub-trees in each depth are decomposed into low-frequency motion and high-frequency motion. The former denotes the dominant transformation of the plant within that sub-tree range and the latter contains residual deformation details. By breadth-first traversal of the hierarchy

the motion composed with low-frequency motions of all the sub-trees at a certain depth is the approximation of original motion at that depth. While traversal depth increased

the approximated motion would approach the original motion progressively and become more realistic

which results in a kind of levels of motion detail . The experimental results show that the presented scheme can simplify and compress the plants motions efficiently

and is convenient for the realistic animation of a large-scale forest.