Add Wind to the Model
Wind animation in the SpeedTree modeler will carry over to UE4. The best way to get good settings for your model is to start with the Wind Wizard. This utility will apply wind settings based on your answers to a few simple questions. From there, select the "Fan" object and fine tune the wind behavior by editing the properties.
Of particular importance is the Style property in the Presets group. This property sets the wind complexity and has a direct impact on the vertex shader performance in UE4. Options are detailed below and are ordered from low quality/short shaders to high quality/longer shaders:
None - No wind shader code will be executed in UE4. This is the absolute fastest way to render a SpeedTree model and still get camera facing geometry (should you need it) and smooth LOD transitions.
Fastest - The model will sway back and forth but will not have individual branch or leaf motion.
Fast - The model with sway back and forth and leaves will ripple.
Better - The model will sway, leaves will ripple, and branches will move independently.
Best - The model will sway, leaves will ripple and tumble, and branches will move independently.
Palm - Fronds will whip and move in the direction of the wind (leaves behave like "Best").
You can back the effect down in the UE4 material editor, but you cannot go higher than what you set in the Modeler. It is often a good idea to tune the model using Best or Palm and lower the complexity in UE4 if you need to optimize performance.