Legacy earthen berms influence vegetation and hydrologic complexity in the Altar Valley, Arizona

Authors: Nichols, Mary; Duke, Sara; Holifield Collins, Chandra; THOMPSON, L. - University Of Arizona

Submitted to: International Soil and Water Conservation Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2023
Publication Date: 1/25/2023
Citation: Nichols, M.H., Duke, S.E., Holifield Collins, C.D., Thompson, L. 2023. Legacy earthen berms influence vegetation and hydrologic complexity in the Altar Valley, Arizona. International Soil and Water Conservation Research. https://doi.org/10.1016/j.iswcr.2023.01.005.
DOI: https://doi.org/10.1016/j.iswcr.2023.01.005

Interpretive Summary: Across the American Southwest water development has played a critical role in managing rangelands. One common method for controlling surface runoff is the construction of earthen berms to intercept the runoff and allow it to soak into the soil. However, if runoff is captured in one area, another area can be starved. Research was conducted to quantify the impact of berms on vegetation and bare soil patterns in the Altar Valley in southern Arizona where hundreds of berms have been constructed. We analyzed remotely sensed images to quantify grass, shrubs, and bare soil. For berms that are intact, grass and shrub cover are higher upslope in comparison with cover downslope. Correspondingly, the amount of bare soil was higher downslope of berms. This study points to the importance of considering the impacts of prior conservation work when making management decisions.

Technical Abstract: Across the American Southwest water development has played a critical role in managing rangelands. Soil and water conservation structures such as earthen berms constructed to intercept surface runoff and increase local vegetation can also be effective for reducing erosion. However, altered runoff patterns can be considered a disturbance that affects broader scale vegetation patterns. A supervised classification of grass, shrubs, and bare soil was performed using orthographic imagery taken in June 2016 to quantify the effects of 181 earthen berms in the uplands and floodplain of the Altar Valley in Southern Arizona, US. For berms that are intact, grass and shrub cover are higher upslope in comparison with cover in proximal downslope runoff shadows. Correspondingly, the amount of bare soil was higher downslope of berms. The statistical significance of these differences depends on soil type. This study points to the role conservation structures in adding additional complexity to already heterogeneous landscapes by creating patchwork assemblages of vegetation and bare soil proximal to earthen runoff and erosion control berms.