What Does a Natural Ecosystem Look Like?


What should be the goal of restoration ecology? Who decides what an ecosystem should look like and how it should function? Most forests that remain in the U.S. are very different in age structure and species composition from their pre-Columbian conditions. Fire suppression as a forest management tool has changed the character of forests, especially those in the Southeast, the Southwest and California. These drier forests evolved in the presence of frequent grass fires started by lightning. Every year or two a grass fire would burn the dry grasses, tree litter, and small trees and brush, effectively clearing out the under- story of the forest of fuels for future fires. These frequent, low intensity fires did not usually burn hot enough or long enough to damage mature trees or the forest soils. Fire scars on cores taken from a 500 year old ponderosa pine for example, have shown that they have lived through as many as 200 low intensity fires. Such fire-adapted forests had a different look from their modern day descendents.

Formerly a ponderosa pine forest in the Southwest would have twenty-five to fifty relatively large old trees per acre; today after 90 years of fire suppression, they typically have 500 trees to the acre, often more. When a forest fire starts in such high fuel loads it will burn hot enough to kill both young and old trees and long enough to damage the soils, killing soil building organisms as well as the roots of the plants. The open, park-like ponderosa pine forest with big trees and open spaces is what restoration ecologists call the reference condition, the goal towards which thinning, logging, fertilizing is aiming.

The National Park Service and to a lesser extent the Forest Service have begun to reintroduce fire or allow natural fires to run through their forests to reduce fuel loads and restore ecological functions. The recent fire that burned 47,000 acres in and around Los Alamos, New Mexico started when a prescribed fire in Bandelier National Monument was pushed by winds in the wrong direction. Humans are not the only organism to modify their environment to better suit their needs, but it is difficult to imagine another group of organisms that have had such an extensive influence on the planet. Restoration ecology is not an exercise in nostalgia, it is not atonement for past mistakes, it is a serious effort to understand how nature organizes living systems. We spoke with Professor Thom Alcoze about his restoration work in the American Southwest.

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