Potential wildfire and carbon stability in frequent‐fire forests in the Sierra Nevada: trade‐offs from a long‐term study

Abstract

Forests are the largest terrestrial carbon stock, and disturbance regimes can have large effects on the structure and function of forests. Many dry temperate forests in the western United States are adapted to a regime of frequent, low‐to‐moderate severity fire. The disruption of this disturbance regime over the last century has shifted forest conditions, making them more susceptible to high‐severity fire. Fuel treatments have been shown to effectively reduce wildfire hazard, often with co‐benefits to ecological values. However, the effects of fuel treatments on forest carbon are complex, often characterized by direct costs (e.g., carbon emissions from prescribed fire) and wildfire‐contingent benefits (increased resistance of live tree carbon to wildfire). In this study, we employ risk‐sensitive carbon accounting and empirical data from a replicated field experiment to evaluate the stand‐scale carbon effects of four management regimes over a 14‐yr period in a historically frequent‐fire adapted forest. All three active treatment regimes immediately increased stable live tree carbon stocks over no‐treatment controls. In most contexts examined, mechanical‐only or no‐treatment controls will maximize expected total carbon stocks when incorporating wildfire risk and the carbon stability of live biomass, dead biomass, and offsite forest products, although we acknowledge our wildfire modeling may underestimate C losses, particularly in the control stands. Undoubtedly, many other ecosystem and social values besides carbon will be important factors that influence fuel and restoration treatments.

Adapting western North American forests to climate change and wildfires: 10 common questions

“…Forested landscapes across much of western North America (wNA) are significantly departed from historical structure, species composition, and wildland fire regime characteristics (Hagmann et al 2021), and as such, their resilience and resistance to rapidly changing wildfire and climatic regimes are compromised (Stephens et al 2020, Hessburg et al 2021. Through a variety of causes, including curtailment of Indigenous burning practices, livestock grazing, and modern fire suppression, fire frequency in the 20th century decreased in many wNA forests (Marlon et al 2012, Hessburg et al 2019.…”

“…Nonetheless, adaptive strategies prompt managers to define a set of historical and future reference conditions that can be used to discern the direction and magnitude of changes from the current conditions and continuing trends to develop metrics of success (e.g., see Keane et al 2009, Safford and). An evidenced-based approach built on data and the scientific method is the most promising path to promote resilience in forests subject to future wildfires and climate change (Stephens et al , 2020. Given the historical role of Indigenous land stewardship on many wNA landscapes, combining western science and Indigenous knowledge systems is foundational to intentionally restoring and adapting western forest ecosystems (Kimmerer and Lake 2001, Lake et al 2017, Roos et al 2021.…”

Commentary: Large Trees Dominate Carbon Storage in Forests East of the Cascade Crest in the United States Pacific Northwest

“…For instance, deferring harvest or increasing rotation ages in mesic forests currently below their carbon storage capacity has tremendous potential for offsetting emissions (Hudiburg et al, 2009). But relying on seasonally dry, fire-prone stands that are currently well above historical levels of aboveground tree carbon is likely to destabilize carbon stocks and forfeit the multiple ecological benefits associated with restoration treatments, especially as the climate warms (Hurteau et al, 2016;Liang et al, 2018;Foster et al, 2020;Stephens et al, 2020). We urge policy makers to rely on comprehensive and accurate accounts of carbon dynamics when crafting policy for dry forests.…”

Probability-based accounting for carbon in forests to consider wildfire and other stochastic events: synchronizing science, policy, and carbon offsets

“…• Forest carbon. Increase in stored carbon on the designated landscape (project area) over time, particularly in larger, more fire-resistant trees (Foster et al 2020;Hurteau and North 2010;Stephens et al 2009). This results from reducing individual wildfire severity and potentially size on both the directly treated areas and untreated areas through fuel limitation (Collins et al 2008).…”

“…Forest restoration treatments including mechanical thinnings and prescribed fire can restore forests to desired ecological conditions and fire regimes (Goodwin et al 2020;Jeronimo et al 2019;Schoennagel et al 2017;North 2012;Noss et al 2006). The goal is to increase stored carbon in trees that are larger and more resistant to wildfire, drought, or insects (Foster et al 2020;Hurteau and North 2010;Stephens et al 2009; see Box 1). These treatments stabilize forest carbon by retaining a larger share of forest carbon stocks in the live carbon pool and maintaining continuous sequestration potential.…”