How fire interacts with an ecosystem is driven by forest structure, fuel bed heterogeneity, topography, and weather. The juxtaposition of two distinct vegetation types with divergent properties can further influence the effects of fire on an ecosystem. In the southeastern United States, pine flatwoods and hardwood–cypress swamps are distinct ecosystems that can be geographically intermixed as a function of elevation, affecting how fires move across the landscape. We sought to understand the consequence of extreme fire weather on landscape wildfire severity and biomass accumulation taking into consideration the spatial configuration of the two ecosystems and fuels reduction management strategies. We used a spatially explicit growth and succession model at the landscape scale to simulate a suite of management activities employed at the Osceola National Forest (Florida, USA), which are aimed at mitigating severe wildfire, maintaining ecosystem function, and producing wood fiber. We found that with extreme fire weather, hardwood–cypress swamps were more available to burn because of drier and hotter conditions, increasing the risk of high‐severity fire in the adjacent pine flatwoods. This reduced landscape aboveground biomass stability relative to contemporary fire weather, with an end‐of‐simulation range from 59.2 to 69.2 Mg C/ha. When we incorporated targeted mechanical thinning and prescribed burning into the simulations under extreme fire weather, the landscape showed higher aboveground biomass stability, with an end‐of‐simulation range of 70.9-72.8 Mg C/ha. We found that targeting mechanical thinning treatments to the interface of the hardwood–cypress swamps and maintaining the pine flatwoods with prescribed burning constrained the spread of high‐severity wildfire at the landscape scale. These results highlight the importance of understanding how changes to fire weather severity may alter fire regimes and consequently carbon stability of these highly interspersed yet functionally dissimilar ecosystems.