Bald cypress gaining on bristlecone.

Scientists have reconstructed the climate of the Mississippi Valley for the past 450 years using old bald cypress trees from Arkansas swamps, according to a report in the Aug. 8 NATURE. This "paleoclimate reconstruction" is some 150 years longer than any previous reconstruction using tree rings in eastern North America, and it is the first to use swamp trees, says David W. Stahle of the University of Arkansas in Fayetteville.

The reconstruction, which was calibrated and verified against modern climate records, showed smaller fluctuations in moisture between 1650 and 1840 than before or after. The researchers also noted that probably the worst drought in Arkansas in the last 450 years occurred between 1549 and 1577.

Because tree rings from trees in wet places tend not to reflect the effects of droughts or wet periods very well, researchers have traditionally used dry-adapted conifers on very dry sites, says Sthale. The most famous examples of this are the ancient bristlecone pines of the dry western mountains, which have provided tree ring data going back 5,000 years.

The East has no such long-lived dry-adapted trees. But tree ring widths of the bald cypress reflect climate changes very well --an unusual trait in a swamp species, says Stahle. Furthermore, individual bald cypress trees live more than 1,000 years--probably making the species the longest-lived species in the East, he says. When a bald cypress does die, it tends to fall over into the swamp, where it is preserved and eventually fossilized, perhaps making it possible, he says, to extend tree-ring based climate reconstructions of the East back about 5,000 years.