Carbon Sequestration in Degraded Intermountain West Rangelands, United States

Abstract

Rangelands are often ignored in the discussion of using management to sequester carbon; however, demonstrating that carbon storage could be paid by carbon credit markets would be a significant advancement for rangeland conservation. The additional amount and cost of carbon sequestered was quantified by simulating seeding perennial grass and shrub species in sagebrush shrublands dominated by non-native annual grass and forb species (NNAGF) compared with doing nothing in a 485 623 km2 area of interest (AOI) centered around Nevada, United States. Using Sentinel-2 satellite imagery, NNAGF cover was mapped across the AOI to locate areas dominated by NNAGFs. Spatial state-and-transition simulation models with a carbon stock-and-flow submodel simulated the seeding of perennial species in NNAGF-dominated sagebrush shrublands in the Columbia Plateau ecoregion (IL Ranch, Nevada), north-central Great Basin ecoregion outside the North American Monsoon (TS-Horseshoe Ranch, Nevada), and the southeastern Great Basin ecoregion within the North American monsoon (PVMH landscape, Utah). The net biome productivity (NBP) and cost per unit area of sagebrush shrublands was quantified by simulating restoration of NNAGF to perennial vegetation over a 25-yr period. The unseeded PVMH landscape, IL Ranch, and TS-Horseshoe Ranch were sinks of carbon (i.e., positive NBP) at 84 g, 9 g, and 11 g C·m−2·yr−1, respectively. About 58−90% of NBP was stored in the soil. The IL Ranch required only small levels of seeding and was a small sink of C at 0.71 ± 0.65 g C·m−2·yr−1, whereas the additional NBP for the seeded PVMH landscape was 19.9 ± 10.6 g C·m−2·yr−1. Across the AOI, the most and least carbon stored, respectively, was in Utah (136 132 metric ton·yr−1, cost: $287M) and the central Great Basin (3 196 metric ton·yr−1, cost: $23M). Positive NBP values reported here showed that carbon sequestration in sagebrush shrublands compares favorably with those of more productive systems in the United States and worldwide.