Runoff and sediment response to tree control and seeding on a high soil erosion potential site in Utah: evidence for reversal of an abiotic threshold

Abstract

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.

Long‐term evidence for fire as an ecohydrologic threshold‐reversal mechanism on woodland‐encroached sagebrush shrublands

“…Similar results were reported by Pierson et al (2007) following tree removal by cutting in a western juniper (J. occidentalis Hook.) The studies noted here demonstrate tree removal can be effective at recruiting understory cover and reversing the soil erosion feedback but that responses can be prolonged for substantially degraded cover conditions depending on the method of treatment (Pierson et al, 2007;Roundy et al, 2017;. Pierson et al (2007) reported increased intercanopy perennial herbaceous cover and litter cover 10 years after cutting juniper on a sagebrush shrubland in the later stages of woodland encroachment.…”

“…However, our study does demonstrate tree removal on late-succession woodlands can effectively re-establish a "resource-conserving" vegetation structure and reverse the soil erosion feedback. In another Great Basin study, Roundy et al (2017) found that pinyon and juniper removal by chaining paired with a seeding treatment increased intercanopy vegetation cover from 5% to 24% 1 year after treatment and to more than 40% 3 years after treatment. woodland in the northwestern portion of the Great Basin.…”

“…In this conceptual model, fire-induced mortality of trees frees up soil water for herbaceous vegetation (e.g., Bates, Miller, & Svejcar, 2000;Bates, Svejcar, & Miller, 2002;. Tree removal is commonly employed to retain or re-establish sagebrush vegetation and the associated ecohydrologic function Pierson et al, 2015;Pierson et al, 2014;Pierson, Bates, Svejcar, & Hardegree, 2007;Roundy et al, 2017;Williams, Pierson, Al-Hamdan, et al, 2014;Williams, Pierson, Spaeth, et al, 2016), but results can vary substantially depending on the phase (vegetation conditions) of woodland encroachment at the time of treatment and initial impacts on vegetation during treatment application (Bates et al, 2014;Miller et al, 2005;Miller et al, 2013). Williams, Pierson, Al-Hamdan, et al, (2014) demonstrated that fire-induced mortality of western juniper (J. occidentails Hook.)…”

“…Williams, Pierson, Al-Hamdan, et al, (2014) demonstrated that fire-induced mortality of western juniper (J. occidentails Hook.) Mechanical treeremoval practices are also often used to reduce pinyon and juniper tree cover on woodland-encroached sagebrush sites (Bates et al, 2000;Bybee et al, 2016;Cline et al, 2010;Pierson et al, 2007;Pierson et al, 2013;Pierson et al, 2015;Miller et al, 2014;Roundy et al, 2017; , but these practices can leave numerous residual juvenile trees that re-establish tree dominance over time Bates, Svejcar, Miller, & Davies, 2017;Miller et al, 2005;Miller et al, 2013;Tausch & Tueller, 1997). That study spanned a period of two years postfire, and the authors acknowledged that the short-term nature of the study limited inferences on fire as a long-term ecohydrologic threshold-reversal mechanism on late-succession woodlands.…”

Effect of soil properties and hydrologic characteristics on plants in a restored calcareous quarry under a transitional arid to semiarid climate

“…A second step for ecological restoration is revegetation. This decreases water erosion by intercepting rainfall (Roundy et al, 2017;Tromble, 1987), increases water infiltration (Huang, Zhang, Hu, & Zhao, 2015;King, Franz, & Caylor, 2012;Piñol, Lledó, & Escarré, 1991), and promotes soil regeneration. Revegetation in quarry restoration is expected to enhance the establishment and survival of other new species through facilitation, which is an important mechanism of succession improvement in exposed soil surfaces (Clemente et al, 2004;Maestre & Cortina, 2004;Pugnaire, Haase, Incoll, & Clark, 1996).…”