If you see 'tunnels' under grass, just above the earth then 90% certain you've field voles. They are the most common rodent in the northern hemisphere, and therefore, not endangered.(Except by gardeners!)
They not only take delight in chomping off any plant material they fancy, but cause frustration in then only eating the juciesty bit, leaving the remainder as proof they are around. You will find that they are "friendly" (?), and its not uncommon to feel you are being watched, only to turn and see a pair of voles sitting, just feet away, watching (where you plant? ,no I've become PARANOID!).
Sadly, its difficult to co-exist and some measure of population reduction will help.
Good housekeeping, short grass, nothing laid flat on the ground ;will expose them to natural predators but in enclosed spaces(cold frames, tunnel cloches, polytunnels) the judicious use of little nipper traps baited with a small piece of apple or a single "monkey nut" peanut in shell will account for surprising numbers. It is imperative that you check traps at least daily and bury corpses; they are likely to consume the victims, and leave just a skeletal outline.Also, secure the trap with a strand of thin wire, otherwise the trap is likely to disappear, only to be later found several feet away. The Nipper rat trap is also suitable, on one occasion I found two voles side by side within one such trap.