Average date of first frost and average daily minima for weather stations located near collecting sites of populations from the US and Japan

The date of first frost and annual absolute minimum temperature from 1988-2008 were collected from the National Climatic Data Center (http://www.ncdc.noaa.gov/oa/ncdc.html) and the NOAA National Data Center (http://www7.ncdc.noaa.gov/CDO) for the US and Japan, respectively. For a location in which there were years that did not have a frost, the latest date of first frost across the 20 year data set for that particular population was substituted. For OKI, there was no frost date recorded for the 20 year data set; thus the latest date of first frost for all populations across all years was substituted