Management of aquatic resources in fire-prone areas requires understanding not only of fish species’ response to wildfire, but also an understanding of the intermediate and long-term consequences of these disturbances. We examined rainbow trout populations in nine headwater streams a decade after a major wildfire: three with no history of severe wildfire, three severely burned throughout most of their watersheds, and three also severely burned, immediately followed by channel-reorganizing events scouring the stream channel and destroying streamside vegetation. Prior study of this system suggested the primary lasting effects of this wildfire history on headwater stream habitat were differences in canopy cover and solar radiation, leading to higher summer stream temperatures. Despite these differences, trout were present throughout burned streams. Older age classes were least abundant in burned and reorganized streams; individuals older than one year were most abundant in unburned streams. Wildfire history corresponded with fast growth, low lipid content, and early maturity of rainbow trout. We used an individual-based model of rainbow trout growth and demographic patterns to determine if temperature interactions with rainbow trout bioenergetics and competition among individuals could lead to observed phenotypic and ecological differences among rainbow trout populations in the absence of other plausible mechanisms. Modeling suggested that moderate warming associated with wildfire and channel disturbance history leads to faster individual growth, which exacerbates competition for limited food, leading to decreases in population densities. The inferred mechanisms from this modeling exercise suggest the transferability of ecological patterns to a variety of temperature warming scenarios.