Rings of change

The bristlecone pine forests of western North America are notable for individual trees that attain great age and are used in the calibration of the radiocarbon timescale, and provide an element in millennial-scale reconstructions of temperature. But new research suggests that increasing temperature at high altitudes is fuelling a post-1950 growth spurt. Pines close to the treeline have wider annual growth rings for the online in the Proceedings of the National Academy of Sciences). " The unprecedented wide rings of the second half of the twentieth century, unique in the record extending for more than 3,500 years, suggest a relatively recent environmental change in these mountainous regions of western North America that is unmatched during the last 3.5 millennia, " the authors report. Bristlecone pines live for thousands of years on dry, windswept, high-elevation mountain slopes in western America. The researchers collected and analysed tree rings from trees in three mountain ranges in eastern California and Nevada, separated by hundreds of kilometres. Only trees growing within about 150 metres of the treeline showed the surge in growth. These trees were generally at an elevation of 3,300 metres. " We are confident that the large widths of the twentieth century rings are not the result of juvenile growth. Young trees typically grow wider rings than old trees, and at these sites the rings are largest in the first few centuries of a tree's life and become narrower as the tree ages. " At the sites studied, Great Basin bristlecone pine showed radial growth in the second half of the twentieth century that was greater than any time in the last 3,700 years. " We have shown several new lines of evidence that suggest that at the upper forest border bristlecone pine ring widths have responded to temperature in the past and continue to do so, " the authors say. New evidence suggests ancient pines at the treeline have been growing faster over the past half century. Monitors: Ancient bristlecone pines in western North America are showing signs of increased growth at the highest altitude, according to a new study.