The effect of a pine invasion on the fuel characteristics was studied to predict fire behaviour and hypothesize potential changes on fire regime. Subalpine Andean forests, fire-prone environments, in the Malalcahuello Reserve in south-central Chile were invaded by the non-native Pinus contorta affecting the native endangered trees Araucaria araucana and Nothofagus antarctica communities. Several fuel components were evaluated by studying different variables, such as fuel load, vertical and horizontal continuity, and flammability of native and invasive tree species. The survey was conducted in five stand conditions: A. araucana and N. antarctica stands, each with and without invasion of P. contorta, and stands with only P. contorta (invasion source). The invasion of P. contorta increased the vertical fuel continuity in the Araucaria forest. The flammability analysis showed that P. contorta is a species highly flammable in comparison to the native trees. The invasion of P. contorta in the Malalcahuello Reserve is under progression and if the process of invasion continues the effects on fuel characteristics will increase. These results suggest that wildfires will be more intense and severe, and that the type of fires of the Malalcahuello Reserve will change from a mixed fire regime to a crown fire regime. These changes will affect plant regeneration, and a positive feedback that favours the P. contorta invasion could emerge. Long-term studies to understand the effect of invasive woody plants on the fire regime are essential for the control of these invasions, especially for the conservation of biodiversity and ecosystem processes in the Araucaria-Nothofagus ecosystems is the Chilean and Argentinean Patagonia.