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

protecting, restoring, or improving land management [1]. NCS include protecting existing ecosystems from conversion, restoring ecosystems, and improving agricultural or forest man- agement. While NCS show great promise at global [2], national [1], and state-level scales [3–5], they have not been widely implemented to date. Most NCS projects have involved tree planting and reforestation, primarily in places where mitigation funds exist to pay for activities or where action is taken by private sector corporations [6]. Opportunities for NCS projects on large, contiguous swaths of public lands may be rela- tively easy to envision, if not to enact. On private lands, however, coordinated implementation of NCS, as with any cohesive land management, may be hampered by small and fragmented parcels and the presence of many landowners with various needs and interests. To make prog- ress towards NCS implementation, The Nature Conservancy, California chapter which is the largest private conservation land manager in the state including 72,439 ha held in fee as the landowner and 140,831 ha in conservation easements as of 2020, set a goal that year to reduce net emissions and increase sequestration in the state using NCS by 720,000 metric tons of car- bon dioxide-equivalents (MTCO2e) by 2030 [Dick Cameron, personal communication]. The basis for the 2030 goal was that ten percent of lands owned in fee by The Nature Con- servancy in California (7,244 ha) would have NCS implemented, specifically restoration and

changes to agricultural activities, with an assumed 10 MTCO2e ha-1 year -1 sequestered for an annual rate of 72,000 MTCO2e year -1 over a decade. The Nature Conservancy, California chapter set this goal based on fee-owned lands because it is much easier to implement NCS and clean energy as a landowner compared to implementing these activities on a conservation easement. A conservation easement is a voluntary, legal agreement between a landowner and an organization, typically a land trust or government agency, to protect conservation values by limiting the landowner’s rights to develop or use their property. The landowner, and any future landowners, can use the property within the limits of the easement terms. While conser- vation easement can be a helpful legal instrument to implement and create incentives for NCS, the easement terms were already executed at a time when the climate benefits of NCS were not contemplated. Any future implementation of NCS with a conservation easement or on a prop- erty with an existing conservation easement would require the landowner’s consent. Implementation of NCS on 10% of The Nature Conservancy’s fee-owned lands seemed like a reasonable target to aim for over a decade, and the sequestration rate was based on science at the time showing �10 MTCO2e year –1 for four out of five NCS restoration activities [3]. The goal did not include two NCS activities, changes to forest management or avoided conversion (i.e. land protection), because these activities apply to new property deals, not existing proper-

ties. Changes to forest management, specifically shifting from even aged to selective harvest, are made by default when the chapter acquires industrial timberland property or sets easement terms to conserve biodiversity alongside timber harvest. To date, The Nature Conservancy, California chapter has implemented or been associated with three NCS projects. The first offset project was the Garcia River Forest property, where changes to redwood timber harvest commenced in 2004. The Conservation Fund, another environmental non-profit, owns and manages the 9,623-ha timberland. The Nature Conser- vancy helped acquire the property and holds a conservation easement which specified that The Conservation Fund had to gain certifications from the Forest Stewardship Council and Sus- tainable Forest Initiative Standard and establish a timber Management Plan. The Conservation Fund sells carbon credits in the regulatory marked for forest harvest practices that increase carbon storage, and the recent 2020–2022 reduction rate was on average 147,749 MTCO2e year-1 [7]. The second project is Childs Meadow, a wetland restoration project funded by Cap- and-Trade Greenhouse Gas Reduction Funds implemented in 2016 that sequesters 38 MTCO2e year-1 across 7.5 hectares [8]. The third project at Staten Island in the California 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 2 / 14