ill., maps; Final report in partial satisfaction of cooperative agreement CA-9000-8-0007, subagreement 7, National Park Service, Pacific Northwest Region; "Autumn 1988."
EXECUTIVE SUMMARY Previous vegetation and fire history studies of the Panhandle area of Crater Lake National Park showed that nearly 80 years of fire suppression had altered the structure and composition of the mixed conifer forests found there (McNeil and Zobel 1981). A program to restore primeval forest conditions in the Panhandle by use of prescribed fire was begun in 1976 and has continued successfully to the present. Although the program has generally been effective at meeting management objectives, a process of delayed mortality of large ponderosa pine, where fire weakened trees succumb to bark beetle attack, had been observed after some Panhandle burns, as well as in nearby Sun Creek. Park staff requested a study on the level and extent of this type of mortality and the conditions that contributed to it. The research objectives were to: 1) assess mortality of ponderosa pine (>22 cm dbh) relative to tree size, fire severity, timing of burn, and tree vigor, 2) determine duff moisture relationships with National Fire Danger Rating System (NFDRS) moisture estimates, and 3) investigate fire effects after an experimental early season burn. Ponderosa pine mortality was strongly associated with scorch height, depth of char, and early season burning. The death of a high proportion larger diameter trees, which do not normally die from cambial damage, suggest that other factors are involved in addition to fire severity. Fine live roots were concentrated in the forest floor and the upper soil layers; both received lethal temperatures. Also, peak standing crop for fine roots was highest at the time of the experimental burn. Although burning strongly reduced live root biomass, no difference was found in moisture stress between burn and unburned trees in the season following the experimental burn. Observation in following years may detect a difference. Lower duff moisture appears to control consumption of duff and therefore fine root reduction. More data is needed to better define critical levels, but preliminary results suggest that a minimum of 18% fuel moisture for NFDRS-Th should be included in burning prescriptions for early season burns. This restriction would not apply to fall burning in the Panhandle. More research is required to quantify duff moisture and duff reduction relationships, to better predict duff moisture, and to assess longterm mortality patterns. Burning earlier in the spring when duff moisture is higher needs to be examined more thoroughly. The reintroduction of fire alone will not satisfy management objectives. Mortality levels should be monitored to assess burn effects. Lower intensity initial burns and some protective measures for high risk trees are recommended. Keen's tree class system is an effective tool for identifying high risk trees. Forest restoration by prescribed fire is difficult, but remains necessary to maintain primeval ecosystem functions. It is also the most cost effective method for reducing fuel hazards. Without prescribed fire, the open mixed-conifer forests dominated by ponderosa pine will disappear from Crater Lake National Park.
EXECUTIVE SUMMARY Previous vegetation and fire history studies of the Panhandle area of Crater Lake National Park showed that nearly 80 years of fire suppression had altered the structure and composition of the mixed conifer forests found there (McNeil and Zobel 1981). A program to restore primeval forest conditions in the Panhandle by use of prescribed fire was begun in 1976 and has continued successfully to the present. Although the program has generally been effective at meeting management objectives, a process of delayed mortality of large ponderosa pine, where fire weakened trees succumb to bark beetle attack, had been observed after some Panhandle burns, as well as in nearby Sun Creek. Park staff requested a study on the level and extent of this type of mortality and the conditions that contributed to it. The research objectives were to: 1) assess mortality of ponderosa pine (>22 cm dbh) relative to tree size, fire severity, timing of burn, and tree vigor, 2) determine duff moisture relationships with National Fire Danger Rating System (NFDRS) moisture estimates, and 3) investigate fire effects after an experimental early season burn. Ponderosa pine mortality was strongly associated with scorch height, depth of char, and early season burning. The death of a high proportion larger diameter trees, which do not normally die from cambial damage, suggest that other factors are involved in addition to fire severity. Fine live roots were concentrated in the forest floor and the upper soil layers; both received lethal temperatures. Also, peak standing crop for fine roots was highest at the time of the experimental burn. Although burning strongly reduced live root biomass, no difference was found in moisture stress between burn and unburned trees in the season following the experimental burn. Observation in following years may detect a difference. Lower duff moisture appears to control consumption of duff and therefore fine root reduction. More data is needed to better define critical levels, but preliminary results suggest that a minimum of 18% fuel moisture for NFDRS-Th should be included in burning prescriptions for early season burns. This restriction would not apply to fall burning in the Panhandle. More research is required to quantify duff moisture and duff reduction relationships, to better predict duff moisture, and to assess longterm mortality patterns. Burning earlier in the spring when duff moisture is higher needs to be examined more thoroughly. The reintroduction of fire alone will not satisfy management objectives. Mortality levels should be monitored to assess burn effects. Lower intensity initial burns and some protective measures for high risk trees are recommended. Keen's tree class system is an effective tool for identifying high risk trees. Forest restoration by prescribed fire is difficult, but remains necessary to maintain primeval ecosystem functions. It is also the most cost effective method for reducing fuel hazards. Without prescribed fire, the open mixed-conifer forests dominated by ponderosa pine will disappear from Crater Lake National Park.