yes they can and your higher power can be anything you desire. When I first went to AA I did not have one for a long time I used the group as my higher power. it can be a tree if that is what you want it to be. in the steps it says to a god of my understanding so it is your desicion as to what your higher power, it is meant to take control and give it to someone or something else. after all my best thinking got me to AA so I had to give it to someone or something else I used the steps.I used the serinity prayer for everything after all a higher power would know what I would need. I hope this has helped some.