1. a School of Forestry, College of Ecosystem Science and Management , Northern Arizona University , Flagstaff , AZ , 86011-5018 , USA
2. b Merriam-Powell Center for Environmental Research , Northern Arizona University , Flagstaff , AZ , 86011-5064 , USA
3. c Department of Biological Sciences , Northern Arizona University , Flagstaff , AZ , 86011-5640 , USA