Climate mitigation potential of natural climate solutions and clean energy on The Nature Conservancy properties in California, USA

The Nature Conservancy, California chapter would need to consider implementing NCS on properties with conservation easements or identifying future land protection deals with car- bon rich ecosystems or high impact NCS to reach their goal. This finding is consistent with emerging science suggesting that land conservation and changes to forest management have a bigger climate mitigation impact than other NCS activities. The chapter is also balancing tra- deoffs between maximizing climate mitigation and biodiversity conservation objectives, as illustrated at the Staten Island property. Our work provides a simple and generalizable approach to estimating CO2e reduction from feasible NCS and clean energy transitions that large landowner’s can use to understand the climate mitigation potential of their lands. Supporting information S1 Table. Stewardship and science team survey. The survey addressed whether it was feasible, and it made sense to implement an individual NCS activity on The Nature Conservancy, Cali- fornia fee or conservation easement properties. Scores were: (1) strongly disagree, (2) disagree, (3) neither agree nor disagree, (4) agree, and (5) strongly agree. (DOCX) S2 Table. Emission factors used to calculate clean energy CO2e reduction potential. (DOCX) S3 Table. Search terms for the literature review. Science Direct was the second review and we did not include repeat articles from the Google Search. (DOCX) S4 Table. Sequestration rates based on past studies. Studies that reported MgC per hectare

were converted using the equation: MgC/ha x (44g/mole CO2)/(12 g/mole C) = MTCO2e/ha. We used low and high sequestration rates based on the low mean and high mean when multi- ple studies available for an activity. When only one study available the standard error or 95% confidence interval used to represent the low and high sequestration rate. (DOCX) S1 Fig. Feasibility survey. (DOCX) Acknowledgments Thank you especially to Dick Cameron for motivated this study and helping to shape the study design. Thanks also to Molly Powell, who conducted the feasibility survey of stewardship and science staff at the Nature Conservancy, California chapter while working as an intern. There were several staff from The Nature Conservancy who made this study possible. The steward- ship and science teams provided important feedback on which natural climate solutions were possible to pursue and consideration of tradeoffs with biodiversity conservation. Adriana Gar- cia compiled feasibility scores from the online survey. Charlotte Stanley provided information on The Nature Conservancy’s land ownership compared to other private landowners in the state. Dr. Sophie Parker and Dr. Sarah Skikne offered comments on an early draft of the manuscript. Author Contributions Conceptualization: Kristen N. Wilson, Michelle C. Passero. Data curation: Daniel W. Salzer. PLOS ONE Climate mitigation potential of natural climate solutions and clean energy: The nature conservancy, California PLOS ONE | https://doi.org/10.1371/journal.pone.0311195 October 21, 2024 12 / 14