Fire Intensity / Burn Severity
Forested ecosystems cover nearly one-third of Earth’s land surface and can perform an essential function as one of the globe’s largest terrestrial carbon sinks, absorbing more carbon than they release, lowering the concentration of carbon dioxide in the atmosphere. Wildfire affects the carbon cycle through direct carbon emissions during combustion and tree mortality, potentially impairing the ability of surviving trees to sequester carbon and limiting the photosynthesis of surviving saplings. While studies have demonstrated that increases in fire intensity can lead to reductions in post-fire net primary productivity (hereafter: productivity), wildfires have largely been assumed to either cause tree mortality, or conversely, cause no physiological impact. With increasing fire activity, lower fuel moisture projected as a result of climate change and limited resources for post-fire rehabilitation, it has never been more important to understand the longer-term effects of wildfire on the surviving vegetation.
Researchers at the University of Idaho set out to understand how fire intensity affects post-fire net primary productivity in conifer-dominated forested ecosystems in the western United States on the scale of large wildfires. Fires were chosen to represent forest stands ranging from those dominated by fire-resistant species (that typically survive low-intensity fires) to those dominated by fire-susceptible species (that do not). Forests dominated by fire-resistant species were typically composed of Pseudotsuga menziesii, Pinus ponderosa, Larix occidentalis, and lesser quantities of Abies grandis. Forests dominated by fire-susceptible species were typically composed of Picea engelmannii, Abies lasiocarpa, Pinus contorta, and lesser quantities of Pinus albicaulis.