Fire plays a large role in structuring sagebrush ecosystems; however, we have little knowledge of how vegetation changes with time as succession proceeds from immediate postfire to mature stands. We sampled at 38 sites in southwest Montana dominated by 3 subspecies of big sagebrush (Artemisia tridentata Nutt.). At each site we subjectively located 1 sample plot representing the burned area and an unburned macroplot in similar, adjacent, unburned vegetation. Canopy cover of sagebrush was estimated, and plants were counted in 10 microplots. Age and height of randomly chosen sagebrush plants in each size class were determined from 5 microplots. Average postfire time to full recovery of mountain big sagebrush (ssp. vasseyana [Rydb.] Beetle) canopy cover was 32 years, shorter for basin (ssp. tridentata) and much longer for Wyoming (ssp. wyomingensis Beetle & Young) big sagebrush. Height recovered at similar rates. There was no difference in canopy cover or height recovery between prescribed fires and wildfires in stands of mountain big sagebrush. We found no relationship between mountain big sagebrush canopy cover recovery and annual precipitation, heat load, or soil texture. Nearly all unburned sagebrush macroplots were uneven-aged, indicating that recruitment was not limited to immediate postfire conditions in any of the subspecies. Average canopy cover of three-tip sagebrush (A. tripartita Rydb.) did not increase following fire, and many three-tip sagebrush plants established from seed instead of sprouting. Our results suggest that the majority of presettlement mountain big sagebrush stands would have been in early to midseral condition in southwest Montana assuming a mean fire interval of 25 years. Only long firereturn intervals will allow stands dominated by Wyoming big sagebrush to remain on the landscape in our study area. We speculate that effects of site-specific factors conducive to sagebrush recovery are small compared to stochastic effects such as fire. Resumen El fuego jugó un gran papel en estructurar los ecosistemas de ''Sagebrush''; pero, tenemos poco conocimiento de cómo la vegetación cambia con el tiempo conforme la sucesión se desarrolla, desde el momento inmediato despue´s del fuego hasta las poblaciones maduras. Muestreamos 38 sitios en el suroeste de Montana dominados por tres subespecies de ''Big sagebrush'' (Artemisia tridentata Nutt.). En cada sitio, localizamos subjetivamente una parcela representando el área quemada y una macroparcela adyacente de vegetación similar sin quemar. La cobertura de copa del ''Sagebrush'' fue estimada y las plantas se contaron en 10 microparcelas. En cinco microparcelas, se determinó la edad y altura de plantas de ''Sagebrush'' elegidas aleatoriamente dentro de cada categoría de tamañ o. El tiempo promedio para la recuperación total de la copa del ''Mountain big sagebrush'' (ssp. vasseyana [Rydb.] Beetle) despue´s del fuego fue de 32 añ os, periodo más corto que para el ''Basin'' (ssp. tridentata) y mucho más largo que el del ''Wyoming (ssp. wyomingensis Beetle & ...

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Bill Volk from the Montana BLM State Office was instrumental in initiating and supporting this project. We are very grateful to Roxanne Falise and Teresa Hanley, also at the State Office, for their support. Robert Mitchell, Louise de Montigny, Dale Tribby, and others at the BLM Miles City Field Office helped us with logistics and their considerable local knowledge. Bob Leinard and Sue Noggles from the NRCS gave freely of their time to help us better understand ecological sites. In our office, we are grateful for the help Allan Cox gave us with maps and Pam Chriske with production of the final report.

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