Fires that have laid waste to more than 2.4 million hectares of US forest this summer represent a double dose of ecological irony.

Not only have the fires destroyed historic research plots whose increasing concentration of trees over the past 90 years foretold this summer's disaster, but they have also consumed some newly established plots designed to investigate how to prevent such massive fires from flaring up again.

From trees to ash: this ‘Woolsey’ plot in Arizona, established in 1909, was among those destroyed. Credit: DAVID HUFFMAN/NAU

Although ecologists have not yet conducted a full survey of the damage, and the fire season is not yet over, blazes have already damaged or destroyed a third of the so-called Woolsey plots, which are among the oldest research plots in the country.

The plots, named after ecologist T. S. Woolsey, who led US forest-service workers in the early 1900s in counting, measuring and mapping each tree on the 50 plots, ranged from about 2 to 6 hectares in size.

They were surveyed every five years until the 1930s, when they were abandoned. Ecologists rediscovered them in the 1990s, but by then only about 15 remained, many of the others being lost to development.

The plots give ecologists a detailed history of the forest and its changing composition. They also document how the concentration of trees increased when the forest service decided to prevent fires in forests, rather than allow periodic ground fires to remove underbrush and dead trees.

The first time the foresters surveyed the plots there were 30 to 60 trees per hectare. That had risen to 2,000 in the 1990s. But higher concentrations of trees result in more intense fires that can consume even large trees completely, rather than the more desirable ground fires that leave them intact.

At least five of the remaining 15 Woolsey plots were badly damaged this summer. Two in Arizona's Fort Valley Experimental Forest, the oldest US forest-service research station, sustained heavy damage. One portion was “completely consumed”, says David Huffman, a researcher at Northern Arizona University, Flagstaff, who inspected the area after the fires were brought under control.

Plots near Los Alamos and Las Vegas, New Mexico, are also likely to have been at least partly destroyed, although scientists have yet to assess the most remote regions.

The damage hits hard because few plots have detailed records stretching back 100 years. “We've lost a long-term historical record,” says Margaret Moore, professor of forestry at Northern Arizona University.

Fires have also damaged experimental plots in Florida and New Mexico that are part of a larger study of the best methods to restore forests to the conditions documented when the Woolsey plots were established.

The project involves surveying three to four blocks of land at 11 sites around the country. Each block will feature four treatments: control, manual thinning, controlled burning, and thinning and burning. The aim of the project is to find the best ecological approach to reducing the threat of large fires.

In a sense, the project has courted its losses, as the plots are placed in the kinds of forest most threatened by fires. “We are risking losing our experiments to the problems we are trying to measure,” says Jim McIver, the project's director.

⇒ http://www.for.nau.edu/ecorest/woolsey.htm