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Increased wildfire size and frequency pose major challenges to rangeland conservation. A common strategy for mitigating fire risk in sagebrush-dominated rangelands is to use fuel treatments that alter the amount and structure of burnable material, resulting in lower fire intensity, and creating access points for fire suppression resources. For fuel treatments to be practical in management, durability (lasting effectiveness) is critical. We present 15 years of data on fuel accumulation and resultant modeled fire behavior through time in prescribed fire, mechanical, herbicide, and control plots using data from the Sagebrush Steppe Treatment Evaluation Project (SageSTEP). In shrub-dominated plots ('shrubland network'), fire and mechanical treatments reduced fuel beds by up to 49%, resulting in modeled flame lengths that were significantly lower than untreated control plots. In sagebrush systems experiencing conifer expansion ('woodland network'), however, treatments increased surface fire spread rate by 15-21 times that of untreated areas due to increased herbaceous fuels. However, treatments also completely removed the risk of canopy fire spread. By 15 years post-treatment, durability was limited in shrubland systems, though prescribed fire and mechanical treatments continued to perform better than herbicide or untreated control treatments through year 10. In woodland plots, the infilling and growth of trees began to limit durability by post-treatment year 15. An improved understanding of fuel treatment effectiveness and durability will allow natural resource managers to evaluate tradeoffs and synergies in conserving rangeland ecosystems and reducing the potential for fast spreading and high intensity wildfire.