Chairmen and women are meant to be arbitrators, not perpetrators. They should lead by example and consensus, not aggression and rudeness. If yours behaves unsatisfactorily, then quietly and calmly point this out at the meeting and move for a motion to censure and/or replace him or her.
Working an allotment is supposed to be a pleasure and should be done in a spirit of cooperation with fellow plotholders. It should be a friendly, happy pastime where you can mind you own business but also work with the others to share skills and resources. The committee is there to ensure this happens, not run personal fiefdoms or vendettas.