I know there is 3 ways of shadowmap reslation enhancement:the layout of 2nd UV, the resolution of 2nd UV,the quality of building light,but how about the dynamic shadow for moving objectS such as plant leaves.
Try playing with the following Console Variables, you can set the in your EngineConfigConsoleVaraibles.ini file.
r.Shadow.FadeResolution - controls how big the light has to be on the screen before it starts to fade out. - Default Value: 64 - Can lower this value to keep shadows from fading out at further distances
r.Shadow.MinResolution - controls how big the light has to be on the screen before it finishes fading out, at which point it no longer has cost. - Default Value: 32 - Lower values seem to increase shadow visibility.
r.Shadow.TexelsPerPixel - Causes a higher resolution to be assigned and then it should fade out less aggressively - Default Value: 1.27324 - Can increase this value to improve shadow rendering visibility & quality
r.Shadow.RadiusThreshold - Default Value: 0.03 - A lower value of 0.02 or 0.01 greatly increases shadow visibility at far camera distances (seems to have the most impact of all the console commands).
Useful Link: https://docs.unrealengine.com/latest/INT/Engine/Rendering/Scalability/ScalabilityReference/index.html