Wildfire: carbon threat heats up.

Virtually all the studies of trees, forests, and greenhouse gas emissions have focused on two topics - mitigation and adaptation. In plain terms, that means: How can we grow more trees and forests so we can store more carbon and reduce fossil fuel use, and how will we need to manage forests differently if climate change becomes a reality? In some parts of the world there is a third challenge, one we have only recently begun to consider: forests already heavily loaded - or overloaded - with carbon. If not managed differently, those forests inevitably will burn, recycling that carbon.

This is the situation over millions of acres in the western United States, mainly in forests that developed in the presence of frequent, low-intensity wildfires. For example, ponderosa pine was estimated to occupy about 28 million acres in 1992. Historical wildfire frequencies in the five- to 20-year range kept out small trees, brush, and prevented encroachment by other species such as firs. The early western pioneers found many open, savannah-type stands composed of a few large trees per acre and a grassy forest floor.

A century or more of fire suppression caused the forest to change significantly. Tree counts of less than 100 per acre have soared to 500 or more, even as high as 1,200 in some places. Fir thickets have moved in under the large pines, forming a continuous fuel ladder that reaches from the ground into the canopy. This virtually guarantees that any ignition will turn into a hot, lethal crown fire.

AMERICAN FORESTS' Forest Policy Center has been studying the implications of this dangerous wildfire condition in cooperation with the Environmental Protection Agency for the past two years. The study has focused on the Boise National Forest, where since 1989 AMERICAN FORESTS, the USDA Forest Service, the state of Idaho, University of Idaho, and Boise Cascade have been researching forest health conditions. With assistance from Leon Neuenschwander of the University of Idaho, the Boise has developed a state-of-the-art Geographic Information System (GIS) that illustrates hazard and risk conditions facing the forest. Neil Sampson of AMERICAN FORESTS and Neuenschwander have used that model to test possible C[O.sub.2] emissions from the Boise's ponderosa pine forests and evaluate how much a forest-treatment program could affect future emissions.

That model shows an alarming almost 1.2 million acres of the 2.6-million acre forest at risk of major wildfire. The model is based on 1992 satellite imagery that shows that of 378 sub-watersheds in the forest, 152 are ponderosa pine forests with high fuel loadings and a past history of ignitions from lightning or human causes. Adding to that concern is the fact that, over the past 10 years, once a wildfire on the Boise reaches 100 acres in size, it has a 22 percent chance of exceeding 5,000 acres. Using this data, wildfires are expected to affect about 7.5 percent of the at-risk forest annually, an estimate borne out by events since 1992.

The research team then developed estimates of the potential impacts of different land-treatment strategies. Each featured a prescribed fire, given the team's belief that a major management goal is to reintroduce fire to the forest to restore essential and historic ecosystem functions. Most sites will require some kind of fuel reduction, thinning, or mechanical wood removal before they are considered safe to burn. The economic impact of each strategy was estimated, including both wildfire suppression costs, treatment costs, and possible recovery of merchantable timber in the treatment process.

Four treatment options were compared to the option of doing nothing at all: 1. Treat 30,000 acres yearly with no strategic selection; 2. Treat 30,000 acres yearly using a strategy that would treat the highest-risk areas first and those that would intercept large fires and help break up large areas of dangerous fuel conditions; 3. Treat 10,000 acres yearly with strategic selection; 4. Treat 50,000 acres with strategic selection.

Preliminary results indicate that an aggressive forest-health treatment can reduce the Boise's C[O.sub.2] emissions by an average 2 million-3 million tons yearly over the next 20 years [ILLUSTRATION FOR FIGURE 1 OMITTED]. The team also decided it was critical to develop a strategy that treats the worst areas first, saving millions in wildfire costs and losses and cutting air pollution from fire by 30 to 50 percent. Landscape diversity, as shown by Figure 2, would improve dramatically. This diversity, which provides the best possibility of protecting biodiversity, would occur in options 2, 3 and 4, which provide for a mixture of forest structures and ages within the ponderosa pine system. On a variety of measures ranging from climate change to local economics, treating these forests seems like a sensible strategy.