Before elaborate programs of fire suppression were instituted in North America in the 20th century, wildfires occurred frequently and were critical contributors to the health and maintenance of many different ecosystems. Abundant evidence for a link between fires and climate exists for many forested regions, but less attention has been paid to nonboreal environments. The grasslands of the Northern Great Plains, which have replaced the extensive spruce forests that stood there at the start of the Holocene, are one such system.
In order to establish how drought and fire might be related in this region, Brown et al. constructed a 4500-year-long record of charcoal, grass pollen, and soil carbonate at Kettle Lake in North Dakota. They find that charcoal production was highest during moist intervals, when grass cover (fuel) was plentiful, and that fires did not happen at regular intervals. Spectral analysis of the data showed that for much of the late Holocene, fires recurred in cycles with a period of around 160 years, but secular trends, including any evidence of the effects of anthropogenic warming, are more difficult to detect. -- HJS
Proc. Natl. Acad. Sci. U.S.A. 102, 8865 (2005).
