Reduce the risk of tree mortality from biological or climatic stressors in fire-prone systems

The complex interactions and feedbacks between climate, vegetation, and tree insect pests on fire occurrence and behavior have global consequences for atmospheric carbon concentrations (Sommers et al. 2014). Extensive tree mortality due to drought, insect pests and pathogens, weather extremes, or other climate-related disturbances greatly increases fuel loads and the risk of wildfire. Fire risk may respond over short timeframes if vegetation mortality occurs quickly, such as when windthrow occurs, or have a time-lagged response due to interactions between multiple stressors (Reichstein et al. 2013). Management actions that reduce susceptibility of forest stands to drought-, insect-, or disturbance-induced tree die-offs may reduce susceptibility to these threats.

Natural disturbance events—including insect pests and diseases, damage from wind and ice, drought, and wildfire—typically reduce near-term forest carbon stocks while initiating long-term and gradual recovery. These disturbances are both a major causes of carbon loss in forests (Williams et al. 2016) and influence future sequestration rates through impacts on species composition, ecosystem structure, rates of photosynthesis and respiration, and flows through various carbon pools (Noormets et al. 2015). While forest regrowth offsets carbon losses following human and natural disturbances over time allowing U.S. forests to remain a net carbon sink (Pan et al. 2011), enhanced disturbance frequency, severity, or extent from climate change may enhance large-scale forest carbon release (Peterson et al. 2014). Shifting climatic conditions, including earlier snowmelt, low precipitation, and warmer temperatures contribute to increases in fire size, frequency, and the area burned annually in the U.S. (Littell et al. 2009; Westerling et al. 2006). Impacts of wildfire on forest carbon sequestration can be long lasting and profound, particularly when they occur outside of the historical fire regime. Not only do wildland fires emit carbon stored in trees that have been burned, but mineral soils and forest floor carbon stocks can also be reduced significantly (Nave et al. 2011; Pellegrini et al. 2018). Additionally, carbon sequestration rates can be lowered in burned areas because of negative impacts on vegetation productivity following severe fire (Hicke et al. 2013). While many actions associated with this strategy can result in a short-term, low magnitude, or fine-scale forest carbon loss, this strategy aims to avoid or reduce long-term, large magnitude, or broad-scale carbon losses through management actions intended to decrease natural disturbance frequency, extent, intensity, or severity.