a Climatic Classification of Plant Hardiness in the United States and Canada and the Effects of Temperature Fluctuations on the Hardiness of Woody Ornamentals.
A classification that uses maximum and minimum air temperature, precipitation, wind speed, sunshine, relative humidity, growing season length, temperature extremes, growth units and elevation was developed as an improvement to the widely used USDA plant hardiness map. Temperature controlled experiments were also run on two woody ornamental species to determine the effect of temperature fluctuations on the hardiness levels of these plants. The results of these experiments were used in conjunction with the above climatic data in several statistical analyses. In these analyses, the United States and Canada were divided into 1,234 grid boxes. Monthly averages of each of the climatological variables were calculated for each grid box. Since no climatic data were available for some grid boxes, the data for these boxes were reconstructed by taking a distance-weighted-average of the closest stations. Limits were also placed on the difference in elevation between the reconstructed point and the stations used for reconstruction. Principal component analysis was used to reduce the size of the initial data set and eliminate the intercorrelation which existed among the variables. Analyses were run on the original data set, which consisted of 136 variables at the 1,234 grids; subsets of this data set representing temperature, moisture, sunshine and wind related variables and the seven component data set which resulted from the subset analysis. Each of the resulting component data sets were subjected to several different clustering procedures in an attempt to isolate regions which were similar with respect to winter plant hardiness and survival. Twenty-three distinct clusters with sound climatological and horticultural bases were produced by the flexible clustering method. In the east, these clusters were oriented latitudinally and resembled the USDA zones. A distinct cluster which encompassed the southern Appalachian Mountains was also formed. In the central U.S. the orientation of the clusters was influenced by both temperature and precipitation. The clusters were irregular in the mountainous regions and became longitudinally oriented along the Pacific coast. The temperature controlled experiments showed that cell death was not affected when freezing followed a four day warm period. However, a significant increase in cell death occurred when freezing was preceded by a week-long period of temperatures near 19^ circC.
- Pub Date:
- Physics: Atmospheric Science