While we are yet unable to predict future climate with certainty, the information locked within trees has become a standard scientific gauge, one used to date mysterious ruins, recall times of insect plagues and centuries-long drought, and chronicle distant volcanic eruptions. And, as if to fulfill Douglass' prophecy, scientists are now using their ability to decode the information in trees to successfully forecast the seasonal conditions that lead to severe episodes of wildfire. The dendrochronologist, says Munro, reads the distinctive patterns of wide and narrow rings which appear in pieces of wood from different trees. It is more than simply a matter of counting rings. Patterns from different trees must be matched to pinpoint the year a tree produced a particular ring, a process known as crossdating.
Trees respond to temperature, rainfall and other environmental conditions by altering growth.
In boom years, the tree adds extra tissue and the ring will be correspondingly thick. During lean years, growth is slowed and rings are thinner. While that sounds like a straightforward way to get at the issue of climate, Munro notes that it is not all that simple. Some trees might respond to changes in overall rainfall, others to the amount of rain during the late summer, and others to the seasonal temperatures that limit the length of the growing season. Other things, like the scars inflicted by fire and plagues of insects, also leave characteristic but indirect clues to climate since widespread forest fires and insect infestations are favored by certain conditions of weather.