Fire frequency in low-elevation coniferous forests in western North America has greatly declined since the late 1800s. In many areas, this has increased tree density and the proportion of shade-tolerant species, reduced resource availability, and increased forest susceptibility to forest insect pests and high-severity wildfire. We investigated how low-intensity fire affects tree defenses and whether fuel treatments in ponderosa pine forests impact resistance to a mountain pine beetle outbreak using a combination of sampling in natural stands for which we had multi-century fire histories and an experimental design of four thinning and burning treatments. Fire stimulated tree resin duct defenses and areas with long-term fire exclusion showed lower defenses. Trees surviving mountain pine beetle attack produced larger and more resin ducts than trees that died from beetle attack. In the experimental treatments, ponderosa pine mortality from the insect outbreak was 50% in the denser, untreated control and 39% in the burn-only, compared to almost no mortality in the thin-only and thin-burn treatments. This study suggests that fuel and restoration treatments designed to reduce fire intensity in fire-dependent ponderosa pine forests can also function to increase resistance to mountain pine beetle outbreaks.