The two prime suspects when it comes to damage as you describe are deer and rabbits. Do you see either of these species in the area?
Rabbits have a tendency to cleanly cut the woody stem and then feed it into their mouth as they chew with the cut end first. If the piece they cut is more than they eat, they leave the remains.
Deer don't bite off the stems, but break them because they only have front teeth on one jaw. Breakage, as with deer, can sometimes be compared to the clean cut of the rabbit's teeth. Also, if the suspect left a calling card deposit (scat) or tracks, this should help identify the culprit.
Visit the Internet Center for Wildlife Damage Management (Identifying Animal Damage) for more assistance on identifying wildlife damage.
