Postfire Succession and Disturbance Interactions on an Intermountain Subalpine Spruce-fir Forest

Four general postfire successional pathways leading to a climax Engelmann spruce (Picea engelmmlilii Parry)-subalpine fir (Abies /asiocarpa [Hook] NUll.) forest operate on the T.W. Daniel Experimental Forest in northern Utah. Depending on the successional pathway followed. reestablishment of the prelire climax forest will take 200 to 400 years or more due to a rarity of extreme burning conditions. During the long period between catastrophic stand-replacing fires, a variety of other natural disturbances contribute to the varying structure and composition of vegetation and the fuel mosaic in intennountain subalpine spruce-fir forests. Disturbances may range from chronic and small scale to acute and cataslTophic, resulting in a broad range of vegetative responses. In addition to crown fires. other major abiotic disturbances (Le., landslides. mudflows. severe soil erosion. snow avalanches) and biotic disturbances (i.e.. disease and insect outbreaks) control the availability of sites for the initiation of new stands or accelerated growth of understory plants and subcanopy trees. Understanding the role of natural disturbances in forest ecosystems is key to managing long-return interval fire regimes. This paper explains how the disturbance regime operating in a given landscape inftuences vegetative dynamics and fuel mosaics and how the state of the vegetation in tum influences these natural disturbance agents. Managers must recognize biotic and abiotic agents of disturbance and their interactions to fully understand fire regimes and the effects of fire suppression and prescribed fire. CiTaTion: Jenkins. Michael J., Christopher A. Dicus. and Elizabeth G. Hebertson. 1998. Postfire succession and disturbance interactions on an intennountain subalpine spruce-fir forest. Pages 219-229 in Teresa L. Pruden and Leonard A. Brennan (oos.). Fire in ecosystem management: shifting the paradigm from suppression to prescription. Tall Timbers Fire Ecology Conference Proceedings, No. 20. Tall Timbers Research Station, Tallahassee. FL. INTRODUCTION stock, summer and winter recreational opportunities. and scenic beauty (Alexander 1977). Fire is regarded as the most important mechanism In the spruce-fir zone of the intermountain West, that drives vegetation dynamics in western forest eco­ Engelmarm spruce (Picea engelmannii Parry ex En­ systems (Billings 1969, Loope 1971, Heinselman gel.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) 1973, Romme and Knight 1981, Peet 1988). Long­ typically coexist as dominants in climax. communities return interVal, high-intensity, stand-replacing crown forming extensive stands on cool, moist sites above fires generally occur in the spruce-fir zone due to the 2285 meters to timberline near 3355 meters (Whipple rarity of extreme burning conditions and slow decom­ and Dix 1979, Schimpf et al. 1980, Alexander 1987. position rates that allow fuels to accumulate at high Peet 1988, Long 1994). At the upper-elevationallimits elevations. The primary response of vegetation to this of Engelmann spruce and subalpine fir, forests become kind of fire disturbance is the establishment of new discontinuous, and the two species often grow in stands (Oliver 1981, Veblen et al. 1991). Fire-initiated clumps of small patches within subalpine meadows stands may then follow one of several postfire succes­ (Alexander 1987, Long 1994). On exposed sites at tim­ sional pathways that eventually lead to forests domi­ berline, they may form krummholz (Harlow et al. nated by Engelmarm spruce and subalpine fir (Dicus 1979, Long 1994). Spruce-fir stands may also occur at 1995). lower elevations on north-facing slopes, in cold pock­ During the 300 to 400 or more years between ma­ ets along streams, and in valley bottoms. At lower el­ jor fire events, however, low-intensity surface fires and evations common seral associates include lodgepole other disturbances may occur, including the spruce pine (Pinus contorta Dougl. Ex Loud), Douglas-fir beetle (Dendroctonus rufipennis Kirby (Coleoptera: (Pseudotsuga menziesii (Mirb.) Franco), and aspen Scolytidae) outbreaks, wind, and snow avalanches. (Populus tremuloides Michx)(Alexander 1974, Mauk These may influence vegetative structure. species com­ and Henderson 1984). position, and successional dynamics in spruce-fir com­ According to Alexander (1987), spruce-fir forests munities (Habeck and Mutch 1973, Werner et al. 1977, are suited for multiple use in the central and southern Romme and Knight 1981, Aplet et aL 1988, Baker and Rocky Mountains. They have high commercial value Veblen 1990, Veblen et al. 1991, Veblen et aI. 1994). and provide water, wildlife habitat, forage for IiveAlthough relationships between these disturbances are not completely understood, their interactions likely generate landscape patterns different than those of fire­ Present address: School of ForeslTy, Fisheries and Wildlife, Louisiana State University, Baton Rouge. LA 70803 dependent ecosystems. Resulting landscape patterns