Using Fire As a Management Tool in Southwestern Ponderosa Pine1

Using Fire as a Management Tool in Southwestern Ponderosa Pine1 Michael G. Harrington and Stephen S. Sackett2 CHANGING CHARACTERISTICS OF infrequently, rarely accumulated over stagnation has been reported on many sites SOUTHWESTERN PONDEROSA PINE extensive areas. When single or small (Cooper 1960, Schubert 1974), and FORESTS groups of trees fell, they were generally persists where natural or artificial thinning consumed by subsequent fires, creating a has not taken place In addition to stand The ponderosa pine (Pinus ponderosa mineral soil seedbed and reducing grass changes, 75 to 100 years of general fire Laws.) forests of the Southwest have gone competition in microsites, favoring absence has also led to uncharacteristically through extensive structural and ponderosa pine seedling establishment large accumulations of surface and ground compositional changes in the last century. (Cooper 1960). These circumstances fuels (Kallander 1969). Numerous references document the open, created an uneven-aged stand structure Sackett (1979) reported average park-like appearance of historic ponderosa composed of small, relatively even-aged loadings of naturally created fuels at 22 pine stands (Biswell et a1.1973, Brown groups. tons per acre (range 8-48 tons per acre) for and Davis 1973, Cooper 1960), where Change began in the southwestern 62 southwestern ponderosa pine stands. herbaceous vegetation was vigorous and ponderosa pine forests during extensive Harrington (1982) verified the heavy fuel abundant. Fires were a regular feature of livestock grazing in the late 19th century loadings, with an average of 34 tons per these forests, burning the light surface (Faulk 1970). As grazing intensified acre in southeastern Arizona. Another fuels at intervals usually averaging less herbaceous vegetation could not respond, formerly uncommon feature is the than 10 years and as often as every 2 years and its coverage declined drastically. This abundance of large, woody fuels, (Dieterich 1980, Weaver 1951). The decline led to two subsequent changes: averaging about 8 tons per acre. Much of frequency of these fires resulted from the reduced fire spread because of the these down, woody fuels have continuity of grass and pine needle fuels, decrease in fine fuels, and an eventual accumulated in sapling thickets, creating the high incidence of lightning, and the increase in ponderosa pine regeneration an even more severe hazard. A final warm, dry weather common to the because of reduced competition and fire characteristic of current southwestern Southwest. Light surface fuels built up mortality, and more mineral seedbeds ponderosa pine stands is the sparse sufficiently with the rapid resprouting of (Cooper 1960). Beginning in the early understory vegetation, created from thick grasses and the annual pine needle cast. 1900's, forestry practices, including fire forest floor layers and dense pine Large, woody fuels, which fall control, further reduced the spread of canopies, that resulted from fire inevitable fires, leading to unprecedented suppression (Arnold 1950). 1Panel paper presented at the conference, fuel accumulations and stagnation of The changes that have taken place Effects of Fire in Management of Southwestern seedling and sapling thickets. primarily within the last century have Natural Resources (Tucson, AZ. November These human-induced changes have created several undesirable conditions in 14-17.1988). resulted in ponderosa pine forests that the ponderosa pine forests of the 2Research foresters, USDA Forest Service. have little similarity to the presettlement Southwest. The extreme fuel hazard is Harrlngton is with the Intermountain Fire forests. In the uncut or lightly harvested probably most apparent. The combination Sciences Laboratory, Intermountain Forest and stands, old-growth trees still stand. The of heavy forest floor fuel loadings and Range Experiment Station in Missoula MT; open structure is gone, however, as dense dense sapling thickets coupled with the Sackett is at the Forest Fire Laboratory, Pacific Southwest Forest and Range Experiment sapling thickets and small pole groups normally dry climate and frequent Station in Riverside, CA. have developed in the understory. Stand lightning and human-caused ignition 122 potential result in a severe wildfire threat SOUTHWESTERN PONDEROSA PINE reduced by 55% and dead woody fuels (Biswell et al. 1973, Harrington 1982). FUELS were reduced by 64% to 80%. Emphasis Additionally, trees of all sizes have was placed on the consumption of generally poor vigor and reduced growth The deteriorating and hazardous forest thousands of snags and windfalls, which rates (Cooper 1960, Weaver 1951). This conditions described above have greatly lessened the fire hazard. The effect condition is likely due to the reduced contributed to numerous severe wildfires of this burning operation was evident the availability of soil moisture caused by in Arizona and New Mexico. Several following year by a dramatic reduction in intense competition and by moisture examples include the 1951 Escudilla the number of wildfires and in the acreage retention in the thick forest floor (Clary Mountain Fire (19,000 acres) and Gila burned (Weaver 1952). and Ffolliott 1969). The thick forest floor Black Ridge Fire (40,000 acres), the 1956 In a well documented study in 1950, six also indicates that soil nutrients, especially Duddly Lake Fire (21,000 acres), the 1971 small plots were burned under two sets of nitrogen, may be limiting because they are Carrizo Fire (57,000 acres), and the 1977 fuel moisture and weather conditions to bound in unavailable forms (Covington La Mesa Fire (15,000 acres) (Biswell et al. determine fuel consumption and tree and Sackett 1984). 1973, Cooper 1960, USDA 1977). The responses (Gaines et al. 1958). A low In the past, pine regeneration generally need to alleviate the hazards was intensity burn was set at the end of developed in openings in the stand after recognized years ago, but widespread use September, and a high intensity burn was fire had produced a receptive seedbed. of fire under specified conditions to create set in early October with higher air tem- Now, long after tree mortality and the designated results has been adopted peratures and lower fuel moistures, creation of openings, a poor quality, slowly. Reasons for this reluctance include humidities, and winds. The September organic seedbed remains, allowing little a shortage of guidelines for prescription burn resulted in a 57% reduction in opportunity for establishment of pine burning and insufficient information on surface, ground, and aerial fuels. The seedlings. Also, forage production for fire effects. October burn consumed more fuel, but wildlife and livestock is commonly also created new fuel by killing or minimal, because of severe competition Fire Effects on Fuels damaging numerous trees. When the with trees and the physical effect of the newly deadened fuels were added to the deep forest floor (Biswell 1972, Clary et The use of prescribed fire has increased residual fuels, only a 15% reduction was al. 1968). in recent years. Some of the earliest, realized. Ponderosa pine is also found with extensive prescribed burning took place on Another large scale, fuel-reduction burn several other conifers in the higher the Fort Apache Indian Reservation in on the Fort Apache Reservation was elevation mixed-conifer forests. Fire Arizona with about 3,000 acres burned in conducted in November 1956 under cool, occurred less frequently in these more the late 1940's (Kallander 1969). From clear days with a moderately high drought mesic forests. A 22-year average interval 1950 to 1970, over 300,000 acres were index and low rate-of-spread index was found in northeastern Arizona burned, primarily for hazardous fuel (Lindenmuth 1960). Fires were ignited at (Dieterich 1983), but its impact was still reduction. The effectiveness of this specific locations, but allowed to burn un- important for site preparation, species burning program in reducing size and checked for 33 days within project selection, disease and insect distribution, severity of subsequent wildfires has been boundaries. Fire effects were un- and nutrient cycling (Jones 1974). Little documented (Biswell et al. 1973, Knorr documented in fall 1957 (Lindenmuth documentation of fire effects and burning 1963). This burning operation used the 1962). Fuel reduction was deemed prescriptions is available for southwestern cool, dry conditions encountered in late unsatisfactory because fuel consumption mixed-conifer forests, therefore, this fall to moderate fire behavior for initial on 75% of the area was only minimal. In subject will not be addressed here. fuel reduction burns. Burning was not to addition, a large portion. of the area that This paper addresses the use of begin until after November 1, but dry litter had good fuel reduction also had extensive prescribed fire in southwestern ponderosa and duff layers were preferred (Kallander tree mortality or injury. pine forests. From research and 1969). These fires were strategically In central Arizona, a small scale observations, recommendations are made ignited, then allowed to burn, unattended, research burn was conducted on two to apply fire to reduce fuel hazards, thin over vast acreages. In a series of three distinct sites. The first had 75% more fuel dense sapling thickets, and provide burns in 1950, this procedure was used to by depth and weight, and 85% greater conditions for natural regeneration in burn portions of 65,000 acres (Weaver

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