Managers masticate fuels to reduce extreme fire hazards, but the impact on fire behavior within the resulting compact fuelbeds is poorly understood. We burned 54 laboratory-based fuelbeds one and two growing seasons after mastication and 75 masticated fuelbeds in prescribed fires one growing season after treatment in three replicate Pinus ponderosa stands. Mastication treatments reduced density of trees >5cm by 30-72% resulting in total fuel depth of 6.9-13.7cm and surface woody fuel loading of 1.0-16.0kg m-2. Flame length and rate of spread were low and similar for coarse and fine mastication treatments and controls. Smoldering combustion lasted 6-22h in prescribed fire experiments where fuelbeds included duff and were well-mixed by machinery, compared to <2h in the lab with varying fuel moisture. Compared to fine mastication treatments, coarse treatments took less time to implement and were more cost-effective. Tree mortality was nil, and post-fire diameter growth of ponderosa pine trees was greater following low intensity surface fires, similar to unburned and greater than trees where masticated fuels were burned with moderate intensity surface fires. Density of resin ducts in the wood, an indicator of tree defense against insect damage, increased following non-lethal surface fires burning in masticated fuels. While lab experiments expand our understanding of burning masticated fuels under controlled conditions, they did not readily translate to prescribed burning conditions where fuels, weather, and ignition patterns were more variable. This highlights the need for more lab experiments and in-situ research that together can be used to develop much needed, scalable predictive models of mastication combustion.