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Low temperature as it affects the selection of woody ornamentals in British Columbia Rhodes, Hubert Lloyd Joseph

Abstract

Low winter temperature was taken as the most important factor influencing the selection of ornamental trees and shrubs for different areas of British Columbia. The locality around a meteorological station was made the unit of investigation, with the meteorological station as a reference point. Average extreme lowest temperature of the year for each British Columbia meteorological station was calculated from figures compiled for the ten year period 1940-49. Certain methods were used to interpret low temperature information in an original way: the use of the winter rather than the calendar year as the unit in considering low temperature, the application of statistical analysis to express variation in low temperature between winters, and the conversion of statistical estimates to temperatures corresponding to a convenient probability ratio easily understood by practical workers. Average extreme lowest temperature of the winter based on the ten-winter period from 1940-41 to 1949-50, standard deviation, and the ninety percent point were calculated for selected B. C. meteorological stations. The ninety percent point is that temperature above which the extreme lowest temperature of a station will fall in approximately nine out of ten winters, and below which the extreme lowest temperature will fall in approximately one out of ten winters, according to mathematical expectancy based on statistical analysis of temperatures observed over a period of winters. This concept combines the information to be obtained from the average extreme lowest temperature and the standard deviation. The ninety percent point is found by subtracting the standard deviation multiplied by 1.3 from the average extreme lowest temperature of the winter. A survey was conducted to obtain an estimate of the injury to ornamental trees and shrubs in British Columbia following two severe winters. The information was used to test the usefulness of low temperature data as a guide in selecting woody ornamentals for hardiness in a locality, and to get accurate low temperature limits in the Pacific coastal region for a number of ornamental species. Low temperature information was found useful within limitations as an indication of the amount of winter injury to woody ornamentals to be expected in a locality of British Columbia after a severe winter.

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