School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI, 49931, USA.|School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI, 49931, USA.|School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI, 49931, USA.|Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, 27695, USA.|Statistical Methodology and Applications Branch, Division of Cancer Control and Population Sciences, National Cancer Institute, National Institutes of Health, Rockville, MD, 20850, USA.|NCCWA, USDA ARS, Kearneysville, WV, 25430, USA.|Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, 27695, USA.|School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI, 49931, USA. hairong@mtu.edu.