Fuel-Load Reductions Resulting from Prescribed Burning in Grazed and Ungrazed Douglas-fir Stands

Prescribed under-story burning was carried out in both grazed and ungrazed Douglas-fir stands on the University of Idaho Experimental Forest. Burning conditions were moderately cool with IO-hr time-lag fuel moisture varying from 11 to 19%. Preburn and postburn fuel loadings were determined by use of the planar intersect method. Prebum data indicated greater fuel accumulations in grazed stands, 55,460 kg/ha, as compared to ungrazed stands, 44,710 kg/ha. Difficulty in achieving a satisfactory rate-of-spread and llre intensity was encountered due to the combined effects of a very dry summer followed by a wet fall. Moist conditions on the study site, lack of fine fuels, and accumulation of heavy fuels in the grazed portion produced a bum of patchy nature. Fire rate of spread varied from 0 to 183 cm/minute with flame height up to 91 cm. Result was a fuel reduction of 60.2% in the grazed stand and 35.2% in the ungrazed stand. Prolonged grazing in this area had created a dense, overstocked stand with insufficient fine fuels to carry a fire, which severely limited the effectiveness of prescribed burning. Although it has been a practice to utilize livestock to reduce fire hazard in forest areas of the western United States (Adams 1975), little research has been done to determine the validity of this practice. The objective of this paper was to determine the effect of prescribed fire on fuel loading in both grazed and ungrazed Douglas-fir (Pseudotsuga menziesii) stands. In various forested areas of the United States, livestock grazing has been a determining factor in the success of many local economies (Wahlenberg et al. 1939). Since many western ranchers have been dependent upon federal range, numerous areas capable of producing palatable forage have been grazed. Early in this century, it was widely believed that grazing could lessen the number, intensity, and size of fires (Hatton 1920). Foresters allowed heavy grazing to reduce fire hazard and to promote tree growth without consideration for sound range and watershed management principles. Heavy grazing has been distinctly advantageous in lessening the occurrence and intensity of accidental fire, due to the reduction of herbaceous undergrowth and hastened decay of litter by trampling (Ellison 1960). However, heavy grazing has severely damaged palatable species. The amount of understory herbage utilized by grazing animals has been considerably less than the total produced, though the highly palatable plants have been selected first (Froeming 1974). As a result, these species have gradually been replaced, often by highly flammable, unpalatable species. Available research clearly demonstrates that fire has had certain beneficial effects on some forested environments. Complete fire exclusion in many areas has created dangerous fuel accumulations Authors are graduate student and associate professor, College of Forestry, Wildlife and Range Sciences, University of Idaho, Moscow. This research involved a cooperative study with the University of Idaho and the Fire in Multiple-Use Management, Research, Development and Application Program. USDA Forest Service, Intermountain Forest and Range Experiment Station, Northern Forest Fire Laboratory. Missoula, Montana. which have resulted in catastrophic fires, insect and disease buildup, range deterioration, changes in wildlife carrying capacity, and decreased watershed yield (Ahlgren 1974). Where fuels were permitted to accumulate, fires increased in severity and damage, and offered much greater resistance to control (Dodge 1972). For these reasons prescribed burning has been recognized as a valuable land management practice. This practice has been extremely useful in ponderosa pine (Pinus ponderosa) and Douglas-fir ecosystems, with objectives such as (1) reduction of fire hazards after logging, (2) exposure of mineral soil for seedbeds, (3) control of insects and diseases, (4) thinning of dense stands of saplings, (5) increased yield and quality of forage, (6) improvement of big game habitat, and (7) modification of species composition in different plant communities (Habeck and Mutch 1975). Zimmerman (1979) described the study area which is approximately 12 miles northeast of Moscow in Latah County, Idaho, on the East Hatter Creek portion of the University of Idaho Experimental Forest (Fig. 1). The specific area treated by burning was chosen because of the location of natural topographic changes which would have contributed to fire suppression strategies, if necessary, and the size of area which accommodated a concurrent big game study. Plots were located both inside and outside a big game enclosure on the southwest slopes of Basalt Hill, elevation ranging from 853 m to 1006 m. Vegetation of the area was characteristic of the Douglas-fir/ Ninebark (Pseudotsuga menziesii-Physocarpus malvaceus) habitat type, described by Daubenmire and Daubenmire (1968). Stages of vegetational development varied from seral to early climax with ponderosa pine and Douglas-fir equally represented. Zimmerman (1979) studied the effect of grazing on the East Hatter Creek area. He found that grazing in the absence of fire at