Hi Jason,
Currently, the UI does not support removing multiple surfaces at the same time. However, you can use the "fp_surface_deleter" script (please see the attached file) to remove any "unused surfaces" from the Forest object. This script checks for unused surfaces and provides an array of assigned surfaces accessible through the .surflist property from maxscript. If necessary, you can clear it by assigning an empty array in the following manner:
$.surflist = #();
I hope this information is helpful.
Best regards,