Managing nature-based solutions in fire-prone ecosystems: Competing management objectives in California forests evaluated at a landscape scale

Abstract

California’s cap-and-trade compliance offset market incentivizes forest managers to maintain elevated carbon stocks. It provides these incentives without enforcing standardized fire mitigation practices despite many projects being located in fire prone regions. Here, we evaluated the difference between management actions in California forests that participated in the carbon offset market versus those that engaged with state programs to reduce wildfire risk via fuel reduction treatments. Using remotely sensed data from the California Forest Observatory and the Moderate Resolution Imaging Spectroradiometer, we compared the vertical forest structure and vegetation canopy trends on forest offsets with forests that are receiving fuel treatment. We found California forests managed for carbon under the Improved Forest Management (IFM) program by the California Air Resources Board had higher levels of biomass than forests managed for fire risk reduction as indicated by 2016 lidar-estimated fuel loads. In addition, IFM-participating forests did not reduce their fuel loads between 2016 and 2020, whereas lands receiving grants for fuel management did, indicating that on average, the IFM projects were not engaging in fuel reduction efforts. However, despite the differences in fuel management between IFM projects and active fuel treatments, we found that both types of management saw a declining trend in vegetation greenness between 2015 and 2021. While declining greenness is expected of active fuel treatments associated with vegetation removal, such a trend in the case of IFM indicates additional wildfire risk. Managing forests for long-term carbon storage and sequestration requires consideration of fire risk mitigation. Given the little evidence of fuel reduction in the first decade of IFM projects implementation we question whether the century-long duration of carbon stocks in these offsets is realistic. We recommend that policymakers reevaluate the incentives directed at carbon stock preservation or expansion to better encompass the growing wildfire risk in California.

Comprehensive review of carbon quantification by improved forest management offset protocols

“…Larger buffer pool deductions along with regularly updating the protocols based on the latest science would help to address this issue. Protocols may also consider incentivizing, and avoid dis-incentivizing, practices that reduce carbon in the short run but increase resilience in the long-run, like thinning and fuels treatments that reduce the risk of catastrophic wildfire (Hurteau et al, 2011;North and Hurteau, 2011;Herbert et al, 2022).…”

“…If possible, reversal risk should be defined in a spatially explicit way to reflect the fact that different types of risks vary tremendously depending on the location, species composition, and stand structure (Anderegg et al, 2020). Further, existing protocols give minimal incentive to reduce disturbance hazards and could be updated to more actively reward management activities like prescribed burning, species selection, and thinning that increase resistance to reversals (Stephens et al, 2020;Herbert et al, 2022). New time accounting frameworks have been proposed to clarify the value of shorter project terms.…”

“…Peer-reviewed and non-peer-reviewed studies of IFM offset projects and protocols have shown evidence of over-crediting and non-conservative methodological rules. Studies of the California Air Resources Board (ARB) forest offset protocol found that the protocol is likely to significantly over-generate credits due to its methods for assessing project baselines (Badgley et al, 2022b;Coffield et al, 2022), leakage (Haya, 2019), and risk of reversal (Anderegg et al, 2020;Badgley et al, 2022a), as well as to create incentives counter to long term carbon stability in fire-prone areas (Herbert et al, 2022). Several peer reviewed and investigative case study analyses of projects using different IFM protocols identified substantial over-crediting (van Kooten et al, 2015;Elgin, 2020;Koberstein and Applegate, 2021).…”

Remotely sensing the effects of managed wildfire programs on Sierra Nevada meadows

“…This departure from historic fire regimes has had several consequences for the composition of California's forests. One of these consequences is that the state's forests currently support 2.75 times more trees per acre than historic averages, a change that has led in many mixed-conifer stands to trees becoming drought-stressed and more likely to burn at high stand-replacing severity levels (Steel et al 2015, Herbert et al 2022. This increased density exists primarily in the form of small-diameter trees, and large trees in California forests have actually declined by over 50% from the 1930s to the 2000s (Bernal et al 2022).…”

“…Accepting a certain level of type conversion due to the presence of fire may be a difficult proposition for the state's decisionmakers to accept, due (among other concerns) to the high level of importance that mixed-conifer forests play in the state's carbon sequestration goals. Recent research suggests, however, that current forest carbon offset programs in the state may not only be unreliable as a tactic to reach net zero emission but may also be having adverse effects on 2 forest ecosystem health and resiliency (Herbert et al 2022, Williams et al 2022. There is, additionally, potential for unexpected benefits from forest conversion in the form of post-fire increases in ecologically valuable non-forest vegetation.…”