Tree survival scales to community-level effects following mixed-severity fire in a mixed-conifer forest

Identifying the drivers of tree mortality and survival is critical to developing conceptual and predictive models of fire effects on forest communities and landscapes. Individual tree characteristics (a function of species traits and tree size) govern tree- and community-scale mortality following fire, but mortality can also depend on tree density and effects arising from instantaneous extreme fire behavior. However, the relative importance and interaction of these factors are not well understood, especially for mixed-severity fire regimes. We sampled burned mixed-conifer forests dominated by western larch (Larix occidentalis) in the Bob Marshall Wilderness of Montana, U.S.A. We combined these field measurements with a remotely-sensed estimate of initial burn severity (dNBR) to test predictions about drivers of fire effects that produce heterogeneous post-fire tree and stand-level mortality. Tree survival 8-13 years after fire depended on complex interactions between species, size, and initial burn severity. Western larch experienced much higher survival than other tree species across tree sizes. Predictably, less fire-tolerant species experienced much lower survival than western larch. These tree-level probabilities in survival scale up to govern community-level mortality through variability in species composition. Greater relative abundance of fire-tolerant larch was associated with reduced levels of mortality at community scales. Interestingly, higher tree densities were either uncorrelated with community-level mortality or associated with lower community-level mortality. Our results show that traits of individuals can govern fire effects from trees to communities, and give rise to highly variable fire effects characteristic of mixed-severity fire. (C) 2015 Elsevier B.V. All rights reserved.