1. USDA FS Eastern Forest Environmental Threat Assessment Center RTP NC 27709 USA
2. Nicholas School of the Environment Duke University Durham NC 27708 USA
3. Department of Statistics and Operational Research University of North Carolina Chapel Hill NC 27599 USA
4. Department of Earth & Planetary Sciences University of Tennesse Knoxville TN 37996 USA
5. Key Laboratory of Vegetation Ecology Ministry of Education, and Institute of Grassland Science/School of Environment Northeast Normal University Changchun Jilin 130024 China