1 US Geological Survey, Southwest Biological Science Center, 2290 SW Resource Blvd., Moab, UT 84532, USA.
2 (Author for correspondence: tel +1 435 719 2334; email screed@usgs.gov).
3 International Institute of Tropical Forestry, USDA Forest Service, Jardín Botánico Sur, 1201 Calle Ceiba, Río Piedras, San Juan , 00926-1115, Puerto Rico and Department of Environmental Science, Policy and Management, University of California-Berkeley, 137 Mulford #3114, Berkeley, CA 94209, USA.
4 School of Forest Resources & Environmental Science, Michigan Technological University, 1400 Townsend Dr, Houghton, MI 49931, USA.