FOREST GROWTH AND GLACIAL CHRONOLOGY IN EASTERN BRITISH COLUMBIA, AND THEIR RELATION TO RECENT CLIMATIC TRENDS

Abstract

Recent activity of Yoho Glacier was determined by botanical and geological dating techniques and from published accounts. Tree growth in four forests adjacent to the end moraine was measured by increment borings of 200 Picea engelmannii. Drawings of increment cores were made in the field, to avoid differential shrinkage with storage. From these drawings, tree growth was calculated in trunk basal area per decade.Corroborating data from three trees indicated that maximum advance of the Yoho Glacier was in 1844. Ice recession increased from 8 m/yr in the mid 1800's to 59 m/yr in 1951–1960 with the greatest rate of increase after 1900. Recession in 1961–1962 was rapid (121 m/yr) because of the warm summer of 1961 and topographic conditions. Total recession 1844–1962 was 2.4 km (ca. 40% of the distance to the Wapta Icefield). Total volume of the lower four-fifths of Yoho Glacier was 7.0 × 10⁶ m³ in 1844, 6.5 × 10⁶ m³ in 1897, and 1.1 × 10⁶ m³ in 1961, for a volume loss of about 85%.Tree ecesis periods for six surfaces of known age ranged from 20 to 43 years (mean 28).The influence of Yoho Glacier in decreasing forest growth was mainly limited to less than 5 meters of the ice margin except in the decade of maximum advance when the influence extended to 30 m. There was no statistical difference in relative trunk growth toward or away from the glacier.Total tree growth was higher from 1581 to 1680, 1761 to 1790, 1851 to 1870, and 1901 to i960 with lower growth intervening. Total growth was positively related to world temperature and sunspot activity and negatively related to world precipitation and glacial activity.Records of glacial activity in Alberta, British Columbia, Washington, and Oregon from 1580 to 1960 showed that two intervals, 1711 to 1724 and 1835 to 1849, contained over one-half of the glacial advances. These intervals followed the two lowest periods of solar activity (1645–1715; 1798–1833) since 1610. Periods of high solar activity showed glacial retreat or stagnation. These results support the solar radiation climatic hypothesis.Résumés of forest growth, glacial activity, climatic regime, and solar activity for 1580–1960 and 800–1950 gave further evidence of a close relation between solar activity and climate. The use of solar activity data in predicting climatic trends and glacial activity was discussed.