FIRE-INDUCED CHANGES IN THE NUTRITIONAL QUALITY OF LODGEPOLE PINE BARK

Extensive lodgepole pine (Pinus contorta) forests in the Madison River drainage of Yellowstone National Park were burned in 1988. Winter fee ding behavior of 24 radio-collared cow elk (Cervus elaphus) in the Mad ison River drainage indicated widespread consumption of burned lodgepo le pine bark. Following fires, forage availability and composition may be enhanced for ungulates; however, it has not been determined if bur ned vegetation is an important temporary forage. We hypothesized that fire improved the nutritional quality of bark thus creating an additio nal food source for elk. To determine the nutritional quality of bark we analyzed burned and unburned lodgepole pine bark for secondary meta bolites, nutrients, and digestibility. Burned bark was >2 times (P = 0 .049) as digestible as live bark in 96-hour in vitro digestion trials. Overall levels of phenolic glycosides, monoterpenes, and diterpene re sin acids were lower (P < 0.001) in burned bark than in bark from live trees, and burned bark contained more (P < 0.001) crude protein than bark from live trees. Neutral detergent fiber in burned bark was great er-than-or-equal-to 4 times as digestible as that in live trees (P = 0 .107); however, the digestibility of neutral detergent solubles was si milar (P = 0.686) among all barks and lower than predicted. Burned bar k did not diff er (P > 0.05) in its chemical composition or digestibil ity from the bark of dead, unburned trees. Low levels of plant seconda ry metabolites in dead and burned bark may explain why elk and insects preferentially use these trees. Overall, burned bark is a low quality food compared with other winter forages. Consumption of burned bark b y elk may be related more to the efficiency with which they can obtain the bark than to its nutritional quality. We hypothesize that the 198 8 fire removed a barrier to wider use of lodgepole pine by elk by redu cing the levels of plant secondary metabolites in the bark.