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Prescribed burning is a management tool used to reduce fuel loads in western interior forests. Following a burn, managers need the ability to predict the mortality of individual trees based on easily observed characteristics. Astudy was established in six stands of mixed-age ponderosa pine (Pinus ponderosa Dougl. ex Laws.) with scattered western junipers at the south end of the Blue Mountains near Burns, Oregon, USA. Stands were thinned in either 1994 or 1995. Three treatments, a fall burn, a spring burn, and an unburned control, were randomly assigned to 12-ha experimental units within each stand. Prescribed burns occurred during mid-October of 1997 or mid-June of 1998 and were representative of operational burns, given weather and fuel conditions. Within each experimental unit, six 0.2-ha plots were established to evaluate responses to the burns. Ponderosa pine plot trees (n =3415) alive 1 month after the burns were evaluated and observed for four growing seasons. Nine fire damage and tree morphological variables were evaluated by logistic regression. A five-factor full model and a two-factor reduced model are presented for projecting probability of mortality. Significant variables in the full model included measures of crown, bole, and basal damage.

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The effects of seasonal prescribed fire on the belowground ectomycorrhizal community and live fine root biomass were investigated before, 1 year after, and 2 years after prescribed underburning. Ectomycorrhizas were sampled from four replications of three treatments (fall underburning, spring underburning, and a nonburned control) in a randomized complete block design. Samples were separated in two subsamples representing the upper 5 cm and lower 5 cm of a soil core. Molecular tools were used to distinguish 140 restriction fragment length polymorphism (RFLP) species of fungi directly from the ectomycorrhizas. Prior to underburning, the number of RFLP species and amount of live root biomass were similar among treatment units and between upper and lower core samples. Fall underburning largely removed live root biomass to a depth of 10 cm and significantly reduced ectomycorrhizal species richness compared with spring underburning and the nonburned control for at least 2 years. RFLP species richness and live root biomass following spring underburning were generally similar to the nonburned treatment. The successful reintroduction of fire to the ecosystem to retain high species diversity of ectomycorrhizal fungi and achieve the desired future condition of large-tree ponderosa pine retention with low fuel loads may require more than underburning in a single season.Résumé : Les effets du brûlage dirigé saisonnier sur la communauté ectomycorhizienne dans le sol et la biomasse de racines fines vivantes ont été étudiés avant, 1 an après et 2 ans après un brûlage dirigé superficiel. Les ectomycorhizes ont été échantillonnées dans les quatre répétitions de trois traitements (brûlage automnal, brûlage printanier et témoin non brûlé) établis selon un dispositif en blocs aléatoires complets. Les échantillons ont été divisés en deux sous-échantillons représentant les parties supérieure (5 cm) et inférieure (5 cm) d'une carotte de sol. Des outils moléculaires ont été utilisés pour distinguer 140 espèces de champignons sur la base des RFLP directement à partir des ectomycorhizes. Avant le brûlage, le nombre d'espèces et la biomasse de racines vivantes étaient similaires entre toutes les parcelles expérimenta-les et entre les parties supérieure et inférieure des carottes de sol. Le brûlage automnal a pratiquement éliminé la biomasse de racines vivantes jusqu'à une profondeur de 10 cm et significativement réduit la richesse en espèces ectomycorhiziennes comparativement au brûlage printanier et au témoin non brûlé pendant au moins 2 ans. La richesse en espèces basées sur les RFLP et la biomasse de racines vivantes à la suite du brûlage printanier étaient généralement semblables au traitement non brûlé. La réintroduction réussie du feu dans l'écosystème dans le but de conserver une grande diversité d'espèces de champignons ectomycorhiziens et de recréer les conditions futures souhaitées pour conserver des pins ponderosa de forte dimension avec une faible quantité de combustibles pourrait exiger plus qu'un brûlage superficiel au cours ...

A study of the effects of season of prescribed burn on tree mortality was established in mixed-age ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at the south end of the Blue Mountains near Burns, Oregon. Each of six previously thinned stands was subdivided into three experimental units and one of three treatments was randomly assigned to each: fall 1997 burn, spring 1998 burn, and no burning (control). Burns were conducted as operational prescribed burns. Trees within six 0.2-ha circular plots on each experimental unit were observed for four post-burn growing seasons to determine fire damage and to detect immediate and delayed mortality and occurrence of black stain root disease (BSRD). There were 5321 tagged ponderosa pines alive at the time of the burns. The percentage of ponderosa pine dying was higher after fall burns than after spring burns. Differences in percentages of fire-caused mortality may be because fall burns are inherently more severe than spring burns. Although present in many trees, BSRD appeared to have little impact on mortality. The lion’s-tail appearance, thought to be a symptom of BSRD, was found to be an unreliable indicator of BSRD in the six test stands.

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