Restoring Fire-Dependent Ponderosa Pine Forests in Western Montana

Abstract

| suppression. M any foresters and ecologists recognize that disruption of the historic pattern of frequent fires in ponderosa pine forests has resulted in major ecological changes, including increasingly severe wildfires and insect and disease epidemics (Weaver, 1943; Covington and Moore, 1992; Mutch and others, 1993; Everett, 1994). In response to this realization, there is increasing interest among natural resource managers, biologists, and the public in restoring ponderosa pine forests to more natural and sustainable conditions (American Forests, 1995). The Intermountain Research Station and the University of Montana’s School of Forestry, in cooperation with the Bitterroot and Lolo National Forests have been testing the effectiveness of different silvicultural and prescribed-fire treatments for restoring ponderosa pine forests, and we will report some observations and initial findings here. But first we will summarize ecological changes that have occurred and describe our restoration treatments. For thousands of years fire shaped the composition and structure of North American forests, favoring species such as ponderosa pine (Pinus ponderosa) that are fireresistant and require fire to regenerate and compete successfully with other species (Pyne, 1982, Agee, 1993). In the inland West, pure ponderosa pine and mixed ponderosa pine-fir types are the most extensive of the fire-dependent forests. Non-fire-dependent species associated with ponderosa pine are interior Douglas-fir (Pseudotsuga menziesii var. glauca), grand fir (Abies grandis), white fir (A. concolor), and incensecedar (Calocedrus decurrens). Pure and mixed ponderosa pine types cover about 40 million acres (16 million hectares) in the western United States, an area equal to that of the state of Washington (van Hooser and Keegan, 1988). Prior to the early 1900s these forests were characterized by frequent lowto moderate-intensity fires, mostly underbums that killed few overstory pines. Historically, fires at intervals averaging five to 30 years in most areas thinned small trees and helped produce open, park-like, fire-resistant stands (Amo, 1988). Today many of these forests have changed dramatically and are experiencing critical health problems as a result of 60-80 years of fire exclusion and logging of overstory pines. For example, more than a million acres in eastern Oregon’s Blue Mountains now consist mostly of dead or dying trees, primarily fir thickets impacted by insect and disease epidemics (Mutch and others, 1993). Also, large stand-destroying wildfires, formerly rare in the open ponderosa pine forests, have become common in the dense stands that have developed as a result of fire exclusion. Dense stands also provide fuel ladders that cause fires to increase in intensity and climb into tree crowns. Severe fires in ponderosa pine made up a large portion of the three million acres that burned in the inland West during 1994. Past logging, which selectively removed large pines and left understory trees has allowed rapid development of conifer thickets (Habeck, 1990). Extensive coni-