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

period, to not limit the area available for NCS activities, under an RCP 8.5 emissions trajectory and the CanESM2 ‘average’ climate model. We further refined the area of riparian restoration on the fourteen properties identified by using aerial imagery to delineate riparian buffers based on existing riparian corridors that were visible upstream or downstream. We did this to avoid limiting the treatment areas based on a set 30 m riparian buffer width being applied to streams of different sizes. Agroforestry covered 148 ha, cover cropping 4,292 ha, and riparian restoration 723 ha on The Nature Conservancy, California chapter lands. Urban tree restoration was possible in developed areas and developed open space [16], not including impervious areas, in places where the area for planting was >90 m2 [17]. This NCS activity covered 97 ha. Freshwater wetland restoration areas consisted of herbaceous vegetation [18] and nonperennial croplands not including rice fields [19] with historic hydric soils indica- tive of wetlands [20] and excluding existing wetlands [21]. Tidal wetland restoration areas were Table 1. Natural climate solutions included in the feasibility survey. Descriptions of the activities are the same as presented in the survey. Compost application was deemed not feasible because of possible conflicts with biodiversity conservation and woodland restoration is not included as we did not find any studies on the sequestra- tion rate for oak restoration. Activity Activity Description Spatial Data Source Spatial Data Description

Agroforestry Plant trees along field boundaries. [5, 14] Margins of agricultural land, Central Valley only. Cover cropping Plow under cover crop prior to cash crop planting. [5, 14] Agricultural land. Rice BMPs Farming practices to reduce emissions. [15] Rice fields. Riparian restoration Establishing forest cover along streams. [5, 14] Agricultural land and grasslands adjacent to major waterways. Existing forest cover masked out within stream buffer. Urban tree reforestation Planting trees. [17] Urban canopy cover in areas >90 m2, excluding impervious surfaces. Wetland restoration Cultivated to freshwater wetland Restoration of lands that were formerly peatland back to wetlands. [17–21] Hydric soils, herbaceous vegetation and nonperennial croplands, not including rice fields or existing wetlands Pasture to freshwater wetland Cultivated to tidal wetland Restoration of tidal wetlands. [22] Undeveloped upland wetland habitat projected to be inundated by sea level rise or adjacent o vulnerable coastal habitat. Pasture to tidal wetland https://doi.org/10.1371/journal.pone.0311195.t001 Table 2. Feasible natural climate solutions applied to specific vegetation types. Vegetation Type Agroforestry Cover cropping Riparian restoration Annual Grassland X Barren X Blue Oak Woodland X Cropland X X X Deciduous Orchard X X Dryland Grain Crops X X X Irrigated Grain Crops X X X Irrigated Hayfield X X X Irrigated Row and Field Crops X X X Pasture X Perennial Grassland X Rice X Vineyard X X https://doi.org/10.1371/journal.pone.0311195.t002 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 4 / 14