Can the Carbon Storage Function of a Degraded Mountain Wet Meadow Be Restored?

Abstract

Sierra Nevada meadows experienced intense livestock grazing in the 19th century, resulting in a shift from deep-rooted highly productive perennial clonal sedges to short-lived and shallow-rooted plants. The current meadow vegetation contains >20% bare ground and <10% cover of highly productive clonal sedges and rushes. We hypothesized that the existing vegetation was insufficiently productive to have formed or to maintain the 2000-year-old carbon-rich meadow soils. We established a multiyear experiment (2016–2019) to determine if planting Carex scopulorum seedlings into Tuolumne Meadows in Yosemite National Park could reverse the impacts of legacy grazing and restore the soil carbon storage function. Planted C. scopulorum had a high 4-year survival rate (75.2%) with slow but significantly increasing belowground biomass production (1.34 g plant⁻¹ yr ⁻¹). Field-measured and gap-fill modeled carbon fluxes indicate an annual average ecosystem respiration (ER) of 0.96 kg C m⁻² yr⁻¹ and gross primary production (GPP) of 0.59 kg C m⁻² yr⁻¹, resulting in a net ecosystem exchange loss of 0.37 kg C m⁻² yr⁻¹. This represents an annual loss of 1.3% of the 29.4 kg C m⁻² of soil organic carbon (SOC). The transplanted sedges would need to increase meadow GPP by 63%, or ER decreases by 39%, to achieve a net annual storage of SOC to reestablish the processes that formed the organic rich soil. Active planting to increase the currently sparse high-productivity plant species is a good option to boost GPP, but climate change could accelerate ER and increase net ecosystem carbon loss.