Carbon Storage in Southwestern Riparian Ecosystems: Impacts of Climate Change, Human Modifications, and Restoration Strategies for Climate Mitigation

Riparian ecosystems in the American Southwest store disproportionate amounts of carbon relative to their limited extent, yet their capacity is poorly quantified and threatened by climate and land-use change. We synthesize current knowledge of riparian carbon dynamics in Arizona and New Mexico and combine this with spatial datasets to estimate potential and current carbon storage. We review how climate, hydrology, geomorphic setting, and biota interact to control carbon stored in biomass, large wood, and floodplain soils. Using the national riparian basemap and hydroclimatic data, we map more than 3.5 million hectares of riparian area across Arizona and New Mexico and classify them into "warm & dry" and "cool & dry" climate classes. Applying carbon stock values from a global meta-analysis, we estimate that intact riparian ecosystems could store nearly 400 million Mg C, with National Forest System lands accounting for roughly 10% of this potential. We then use existing vegetation maps to show that only about 56% of mapped riparian extent currently supports riparian vegetation, and that riparian areas on National Forests and Grasslands store about 57% of their potential capacity, with substantial variation among forests. Finally, we report how climate change, water management, land use, livestock grazing, biological invasions, and fire jointly influence carbon pools, and we highlight restoration strategies that could increase or maintain carbon storage in southwestern riparian ecosystems. Together, our synthesis and spatial analysis demonstrate that restoring and conserving riparian ecosystems represents a high-leverage, yet underutilized, opportunity for climate mitigation and adaptation in the American Southwest.