I can see that your Forest object is rotated. Please put the rotation to zero and refresh the Forest object (for example by hitting Update surface data icon). This will solve your issue. Please check screenshots attached.
Please note, that Forest objects are every time while rendering reconstructed based on scene position and coordinates of used splines / surfaces so it shouldn't be transformed or moved. Also we don't recommend to use any modifier over our plug-in to avoid possible issues.
Hope this helps you. Have a nice day.