FALL RATES OF PRESCRIBED FIRE-KILLED PONDEROSA PINE

The immediate, visible impacts of forest fires can vary from partial c onsumption of the surface litter and minimal plant charring to high co nsumption of all fuel classes and complete mortality of large stands o f trees. When fire passes through a stand, trees can be killed outrigh t if all or a large portion of the foliage, buds, and branches are kil led, or they can be mortally wounded if a smaller portion of the livin g tissue is killed. Trees in this latter group will die over several y ears subsequent to the fire with the mortality rate generally decreasi ng over time. Another category includes trees whose vigor has been red uced by fire injury, thereby permitting successful insect and disease attacks, which commonly result in tree death. Standing dead trees have distinctly different influences on ecosystems than living trees do. I n the first half of this century, snags were primarily thought of as f ire hazards (Dahms 1949; Keen 1955). Management activities at that tim e included felling dead trees in timber sales and along roads. More re cently, managers have realized the economic and ecological value of sn ags. Products with direct economic value include house logs, firewood, and even lumber (Lyon 1977). As decay spreads within the tree, these values diminish and are generally lost when the tree falls. Apart from economics is the value of standing dead trees for wildlife habitat. B irds use such trees to perch, feed, nest, overwinter, and hide (Bull 1 978). Mammals also use snags to nest or den, feed, and overwinter. The value of dead trees for habitat dramatically changes when standing tr ees become fallen logs because bird nest and perch use is greatly redu ced. These logs, however, are important for hiding and thermal cover, feeding, and nesting for ground birds (grouse) and small mammals (rabb its and squirrels) (Thomas and others 1979). As they decay, logs also ameliorate soil moisture and nutrient condition for plant growth (Harv ey and others 1988). Dead trees are also an important forest fuel. The y ignite more easily than live trees and, therefore, represent a highe r potential source of burning embers that can aid wildfire spread. Aft er falling, logs represent a potentially high concentrated heat source causing problems for fire suppression and sometimes resulting in micr osite soil degradation. Knowledge of the transition rate from standing dead trees to fallen logs would be important for those who manage tim ber and soil resources, wildlife habitat, and wildland fuels. Others h ave reported on the fall rate of beetle-killed ponderosa pine (Pinus p onderosa) (Keen 1955; Schmid and others 1985), beetle- and fire-killed Jeffrey pine (Pinus jeffreyi) and white fir (Abies concolor) (Raphael and Morrison 1987), and fire-killed lodgepole pine (Pinus contorta) ( Lyon 1984). This study describes 10 year fall rates of second-growth p onderosa pine following mortality from different levels of crown scorc h sustained in different seasons of prescribed burns.