After a wildfire, the flames may fade, but the danger does not. A new study by UBC researchers reveals that burned landscapes remain vulnerable for years, with large areas still bare and at risk of invasion by fast-growing, fire-prone grasses.
The research, one of the largest vegetation trajectory studies in the world, monitored landscapes two years after major wildfires in interior B.C. While some native plants returned, recovery was slower and more fragile than expected.
One of the most pressing concerns is invasive grasses, which germinate early in spring, dry out during the hottest months, and act as dry runways that spread flames at highway speed—a dynamic that contributed to the 2023 Lahaina fire in Maui and is increasingly likely in B.C.'s Interior.
"Areas that looked like post-apocalyptic ground right after the fire are now blanketed in cheatgrass. Once you can see the invasion, the opportunity for rapid response may already be gone," said Dr. Jennifer Grenz, senior author and restoration ecologist and a member of Lytton First Nation.
Published in Fire Ecology , the study examined vegetation recovery two years after the 46,000-hectare McKay Creek wildfire near Lillooet, conducted in partnership with six Northern St'át'imc communities on whose territory the fire burned. It was made possible by years of pre-fire invasive plant monitoring collected by the Lillooet Regional Invasive Species Society in collaboration with the BC Provincial Invasive Plant Program and local Indigenous communities—rare baseline data that allowed the team to test long-held assumptions about post-fire invasion.
Elevation plays a critical role in recovery
The analysis showed a clear elevation trend in post-fire plant recovery. At lower elevations, where conditions are hotter, drier and more accessible to human activity, drought-tolerant invasive species quickly gain a foothold. Heavy traffic from hikers, ATVs, hunters and road maintenance equipment continually introduces new seeds, giving invaders like cheatgrass little competition in the valley bottoms.
Moving upslope, cooler temperatures and lingering moisture create less favourable conditions for invasive species. Here, native shrubs are beginning to regenerate, slowing the advance of non-native plants. Recovery is still slow, but native vegetation is re‑emerging where roots survived the fire.
"In a new era of mega-fires, understanding where and how vegetation recovers could determine the intensity of the next wildfire," said Dr. Grenz.
Controlling invasive plants
With post-fire restoration resources limited, the researchers highlight three actions that could substantially reduce risk: vehicle and boot washing stations at fire access points to slow seed spread; targeted seeding or planting of native species along roads and high-risk corridors; and early herbicide treatment of small infestations before they expand.
The team plans to continue tracking recovery trends to help communities and land managers make informed decisions.
"A landscape left to invasive grasses after one fire becomes more likely to burn again," said Virginia Oeggerli, a PhD student in Dr. Grenz's lab who led the study. "Recovery is part of prevention."
Interview languages: English (Grenz, Oeggerli)
