Expansion of piñon (Pinus spp.) and juniper (Juniperus spp.) trees into semi‐arid sagebrush steppe may cause these systems to pass a biotic threshold into weed dominance and recurrent fire, as well as pass an abiotic threshold of accelerated soil erosion. To determine effects of chaining to reduce trees and seeding to increase vegetation cover, we measured runoff and sediment after natural precipitation on 10 m2 intercanopy runoff plots on untreated and treated areas over a 5‐year period. The former sagebrush steppe study site was in an advanced phase of tree infilling before treatment and is underlain by lacustrine sediments with clay loam soils on moderate steep slopes. These characteristics, and the potential for high‐intensity thundershowers, make this site one of high soil erosion potential. Chaining‐seeding greatly increased vegetation cover from 4.5% on untreated plots to 23.5% on chained‐seeded plots by the first year after treatment. These cover increases were associated with runoff that was reduced from 44.2 to 9.4 L and sediment from 557.9 to 53.9 g from runoff plots, averaged over the 5 years. Piecewise regression indicated significant threshold decreases in runoff and sediment when vegetation cover exceeded 12 and 11%. High annual precipitation (53 cm) supported successful revegetation on this site in association with chaining and produced sufficient intercanopy cover to reverse an abiotic threshold of soil loss that is associated with advanced tree infilling. Tree reduction and restoration of intercanopy vegetation may have significant hydrologic benefits on sites with high erosion potential where piñon–juniper has expanded into sagebrush steppe.

ABSTRACT. Off-road vehicle (ORV)