Sunday, October 17, 2010

Trails of climate change: bristlecone pine trees

Bristlecone pines can live for thousands of years. Some Great Basin bristlecone pines (Pinus longaeva) are around for over 4,000 years [1]; the record holder is about 4,840 years old [2]. By hiking in areas with stands of bristlecone pines, one easily gets the Methuselah impression by simply looking at the trees, such as the ancient pine shown and photographed a few years ago in the Patriarch Grove of the White Mountains northeast of Owens Valley in California.

Pinus longaeva is found in high-mountains regions from eastern California through south and southeast Nevada to Utah (map on page 3 in [1]). Getting that old, these pines have experienced climate changes long before humans took notes. But the trees keep record—indirectly, at least. The wider an annual growth ring, the faster the growth in that year. Dendrochronologists can thus relate speed of tree growth with time and dates. Further, a significant correlation between tree-ring width and mean air temperature has been found for pines at the tree line [2]. Interestingly, pines at the tree line in California and Nevada developed wider rings during the second half of the 20th century than during any other fifty-year period of the past 3,700 years. Since only pines at the tree line show this pattern, it is difficult to disentangle various factors such as temperature (milder climate), humidity (wetter weather), and carbon dioxide content of the air, which may all contribute to the reported faster growth of the otherwise slow-growing trees. Overall, bristlecone trees seem to benefit from global warming effects and may outlive humans. But the trees are good survivors without global or local warming as well!

Keywords: botany, forests, tree line, longevity, survivability, Pinaceae

References and further reading
[1] Ronald M. Lanner:
The Bristlecone BookA Natural History of the World's Oldest Trees. Mountain Press Publishing Company, Missoula, Montana, 2007.
[2] S.R.:
Fine Times for Pines. Natural History October 2010, 119 (1), page 12.

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