Ecological Restoration vs. Thinning Treatments

The graph produced by the FIRESUM model to project forest densities

A recent study used the FIRESUM model to project forest densities over decades following actual restoration treatments at the G.A. Pearson Natural Area near Flagstaff. Treatment areas were thinned in 1994 to a density that mimicked the presettlement forest density. One treatment area has been burned at 4-year intervals following thinning, while another has not been burned. The FIRESUM model projected that the thinned-only area (the middle, dotted line) would rapidly increase in tree density in the absence of fire, increasing fuel loads and decreasing herbaceous production. After 65 years, its tree density would equal that of the control area (the upper, dashed line). The thinned area treated with prescribed fire at 4- to 10-year intervals (the lower, solid line), meanwhile, would continue to have a low tree density and abundant understory vegetation. Figure 4 from Covington et al. 2001. Reprinted by permission of Blackwell Publishing.

Thinning overly dense forest fuels is a critical step in reducing fire risk and working toward ecological restoration. But though such fuels treatments are an important step toward restoration, they are not the same as restoration.

Mechanical fuels treatments remove ladder fuels in order to reduce the likelihood that a surface fire will become a crown fire. They also reduce the connectivity of tree crowns, making it more difficult for a crown fire to spread throughout the canopy.

Restoration treatments also remove ladder fuels and reduce crown connectivity. But rather than focusing only on altering forest structure, restoration treatments also aim to alter forest functioning, such as the way in which fires move. For that reason, they have the potential to provide a long-term solution to the current wildfire problem, which is really only a symptom of a larger problem—namely, an unhealthy ecosystem.

Forest restoration focuses on reintroducing frequent, low-intensity fires, which provide a number of benefits:

Promoting the growth of herbaceous understory vegetation
Cycling nutrients from needle litter into the soil, where it can be used by plants
Maintaining forest structure by removing most pine seedlings or saplings
Reducing long-term crown fire danger
Enhancing the health of remaining trees by reducing competitive pressures.

Restoration treatments, in other words, provide fire protection and additional benefits. Fuels treatments do reduce fire danger, but only temporarily (see figure), and they do not emphasize these other benefits. In the long term, restoration treatments are likely to be a far more cost-effective and ecologically sustainable solution to the current wildfire problem than fuels treatments alone.

This is a modified version of ERI's publication Working Paper 04: Fuels Treatments and Forest Restoration: An Analysis of Benefits.