Effects of Climate on Forage Yields and Tree-ring Widths in British Columbia

Abstract

On forested lands (1954 to 1969) 109 annual forage yields from 12 locations were studied. Very dry springs and unusually low annual precipitation resulted in low forage yields. Dry summer months were associated with superior yields provided the past year had been wet. The relationship was not consistent, however, nor was there a consistent relationship between tree-diameter growth and climate based on monthly or seasonal temperature or precipitation records. Annual forage yields were least on the Dewdrop and highest on the East Mara ranges, 325 and 1017 lb oven dry, respectively. Forage yields on open rangelands (1954 to 1969), although only moderately associated with individual values for seasonal average temperature or total precipitation, could be estimated very well by all weather variables describing a 15-month period. The 190 observations of yield from 16 open rangeland locations averaged 544 lb oven dry, with a minimum of 84 lb in 1967 and a maximum of 616 lb in 1965. Expressed as percentages of 1963 yields, annual forage weights averaged 116% and ranged from 53 to 214%. Such large variations as a result of fluctuations in climate are of obvious importance to graziers, and the possibility that forage yields can be related to long-term variations in tree growth merits further study.