Droughting a megadrought: Ecological consequences of a decade of experimental drought atop aridification on the Colorado Plateau

Authors: FINGER-HIGGENS, REBECCA - Us Geological Survey; BISHOP, TARA - Us Geological Survey; BELNAP, JAYNE - Us Geological Survey; GELGER, ERIKA - Us Geological Survey; GROTE, EDMUND - Us Geological Survey; Hoover, David; REED, SASHA - Us Geological Survey; DUNIWAY, MICHAEL - Us Geological Survey

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2023
Publication Date: 3/15/2023
Citation: Finger-Higgens, R., Bishop, T., Belnap, J., Gelger, E., Grote, E., Hoover, D.L., Reed, S., Duniway, M. 2023. Droughting a megadrought: Ecological consequences of a decade of experimental drought atop aridification on the Colorado Plateau. Global Change Biology. Article gcb.16681. https://doi.org/10.1111/gcb.16681.
DOI: https://doi.org/10.1111/gcb.16681

Interpretive Summary: Drylands are threated by climate change through increased aridifcation and drought. In this study, we imposed experimental droughts over a decade across diverse rangeland communities of the Colorado Plateau to explore the impacts on plants, soils, and nutrient availability. An ongoing megadrought in the region compounded these experimental effects, leading to large declines in all plant types. Natural and experimental drought also lead to increased nitrogen availability, which could help facilitate plant recovery from drought. These results highlight the complex ecosystem responses to drought in dryland ecosystems.

Technical Abstract: The stability of global dryland vegetation communities remains unclear as ongoing drought conditions shift regional climates towards a more arid future. Dryland aridification can impact plant and ground cover, biogeochemical cycles, and plant-soil feedbacks, yet it remains unclear how and when crucial ecosystem components will respond to drought intensification. Using a long-term precipitation reduction experiment (30% reduction) conducted across the Colorado Plateau and spanning ten years into a regional megadrought, we explored how vegetation cover, soil conditions, and growing season nitrogen (N) availability are impacted by multifaceted drying climate conditions. Likely due to ongoing regional megadrought conditions, we observed large declines for all dominant plant functional types (C3 and C4 grasses and C3 and C4 shrubs) across measurement period, both in the drought treatment and control plots. In experimental drought plots, we observed less plant cover, less biological soil crust cover, warmer and drier soil conditions, and more soil N compared to the control plots. Observed increases in soil N availability were best explained by a negative correlation with plant cover regardless of treatment, suggesting that declines in vegetation N uptake may be driving increases in available soil N. In fluctuating drought conditions, this could lead to times when increased soil resources sustain post-drought recovery. However, in ecosystems experiencing long-term aridification, increased N availability may ultimately result in N losses if soil moisture is consistently too dry to support plant and microbial N immobilization and ecosystem recovery. These results show dramatic, worrisome declines in plant cover with long-term drought. Additionally, this study highlights that more plant cover losses are possible with further drought intensification, and underscore that, in addition to large drought effects on aboveground communities, drying trends drive significant changes to critical soil resources such as N availability, all of which could have long-term ecosystem impacts for dryland ecosystems.