The influence of pre-fire growth patterns on post-fire tree mortality for common conifers in western US parks

Fire severity in forests is often defined in terms of post-fire tree mortality, yet the influences on tree mortality following fire are not fully understood. Pre-fire growth may serve as an index of vigour, indicating resource availability and the capacity to recover from injury and defend against pests. For trees that are not killed immediately by severe fire injury, tree growth patterns could therefore partially predict post-fire mortality probabilities. Here, we consider the influence of multiple growth patterns on post-fire tree mortality for three common conifer species in the western USA. Using observations from 1 to 9 years following prescribed fires in USA national parks across five western states, we show that post-fire conifer mortality was related not only to fire-caused injuries (crown scorch and bole char), but also to average growth rate and long-term (25 years) growth patterns (counts of abrupt growth declines and possibly growth trends). Our results suggest that pre-fire conditions affecting tree vigour may influence post-fire tree mortality probabilities. Environmental conditions (such as rising temperatures and moisture stress), independent of fire intensity, may thus cause expressed fire severity to increase in western forests.