Anticipating fire-mediated impacts of climate change using a demographic framework

Climate change indirectly affects forest ecosystems through changes in the frequency, size, and/or severity of wildfires. In addition to its direct effects prior to fire, climate also influences immediate postfire recruitment, with consequences for future vegetation structure and fire activity. A major uncertainty, therefore, is if, when and where vegetation shifts will occur. With an emphasis on species traits, we use a demographic framework to examine how the interaction of changing climate and fire will affect postfire woody vegetation recruitment and the likelihood of vegetation shifts. Each demographic stage – adult mortality, propagule availability, seed germination, seedling establishment, and seedling survival – serves as a filter through which a species must pass for establishment and recovery to occur. We apply this framework to case studies in western North American forests, including boreal and southwestern U.S. Pinus ponderosa forests, to help understand the mechanisms behind recent postfire vegetation changes. The case studies highlight how changes in climate and fire properties will make it increasingly difficult for some species to pass through each demographic filter in the future. As climate warming continues, we expect increased dominance of species that resprout following fire, maintain canopy or soil seed banks, have long distance seed dispersal, produce drought-tolerant seedlings, and/or reach reproductive maturity quickly. The persistence of postfire vegetation shifts will depend the on ratio of recovery time to disturbance interval(s). An advantage of the demographic-filter framework is that it places emphasis on mechanisms, thus improving our ability to anticipate future vegetation shifts. As such, it highlights the clear need for more mechanistic studies of postfire recruitment to disentangle the relative effects of multiple drivers in postfire environments. A plain language summary is available for this article.