Can wildfire serve as an ecohydrologic threshold‐reversal mechanism on juniper‐encroached shrublands

Abstract

Woody plant encroachment on water-limited lands can induce a shift from biotic (plant)-controlled resource retention to abiotic (physical)-driven losses of critical soil resources. The biotic-to-abiotic shift occurs where encroachment propagates connectivity of runoff processes and amplified cross-scale erosion that, in-turn, promote ecohydrologic resilience of the post-encroachment community. We investigated these relationships for woodland-encroached sagebrush steppe in the Great Basin, USA, and evaluated wildfire as a mechanism to reverse the post-encroachment soil erosion feedback. We measured vegetation, soil properties, and runoff/ erosion from experimental plots on burned and unburned areas of a late-succession woodland 1 and 2 years post-fire. Our findings suggest that the biotic-to-abiotic shift and amplified cross-scale erosion occur where encroachment-induced bare ground exceeds 50-60% and bare gaps between plant bases frequently extend beyond 1 m. The trigger for amplified cross-scale erosion is formation of concentrated flow within the degraded intercanopy between trees. Burning in this study decreased ecohydrologic resilience of the latesuccession woodland through herbaceous recruitment 2 years post-fire. Increased intercanopy herbaceous productivity decreased connectivity of bare ground, improved infiltration, and reduced erosion, but the study site remained vulnerable to runoff and erosion from high-intensity rainfall. We conclude that burning can reduce woodland ecohydrologic resilience and that woodland encroachment-induced structural and functional ecohydrologic attributes may persist during high-intensity storms for an undetermined period post-fire. We cannot conclude whether wildfire reverses the woodland-induced soil erosion feedback on sagebrush rangelands. However, our results suggest that wildfire may provide a restoration pathway for sagebrush steppe by reducing woodland ecohydrologic resilience over time. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Evaluating rehabilitation efforts following the Milford Flat Fire: successes, failures, and controlling factors

“…Second, and most importantly, disturbing a post-fire landscape can result in accelerated soil erosion (Pierson et al 2009, Miller et al 2012. Wildfires typically negatively impact surface soil quality through loss of organic matter and exacerbation of hydrophobicity effects (Pierson et al 2014, Williams et al 2014a, resulting in reduced infiltration capacity, increased run-off, and generally poor seed germination (Pierson et al 2002, Ravi et al 2006, 2007, Pierson et al 2011. However, the loss of vegetation cover from wildfire leaves these soils exposed to erosion by wind and water (Pierson et al 2009), and disturbing these soil surfaces further during post-fire rehabilitation can greatly increase soil erodibility (Williams et al 2014b).…”

Cover Estimations Using Object-Based Image Analysis Rule Sets Developed Across Multiple Scales in Pinyon-Juniper Woodlands

“…Similarly, prescribed fire on hillslopes of encroached woodlands caused a sharp increase in runoff in the short term, especially within the coppices formerly occupied by trees ). Yet, leaving the trees in place renders the interspaces between trees vulnerable to loss of surface soil, which may eventually lead to the crossing of an irreversible threshold Williams et al 2014). Leaving trees remaining in the vegetation community, either by design or because of an incomplete treatment, also resulted in a landscape that was unsuitable for use by sagebrush-obligate birds (Knick et al 2014).…”

“…In terms of runoff and erosion, the rapidity of response of the herbaceous vegetation will in turn be the key to recovery of more desirable hydrological function in burned plots. Two years after prescribed fire, erosion in intercanopy areas had already declined due to enhanced herbaceous production, which impeded overland flow Williams et al 2014). Longer-term impacts on runoff and erosion will depend on persistence of enhanced intercanopy vegetation and how effectively vegetation occupies former tree coppices ).…”

Effects of Turfgrass Thatch on Water Infiltration, Surface Runoff, and Evaporation

“…Turfgrass thatch is assumed to be comparable to vegetation litters at forest floors and in grasslands due to their similar biological characteristics. Vegetation litters can intercept rainfall and maintain the water input up to their maximum water holding capacity [6] [7] [8]. For instance, the rainfall interception by grassland litters was 5.3 to 6.6 mm annually in Northeastern China [9].…”

“…The presence of a soil surface cover thus delays the initiation of infiltration and increases infiltration depths by allowing for a longer infiltrating time [5] [16]. The improvement in infiltration could be attributed to the reduced impact of raindrops on the surface soil, improve soil structure by increased porosity and organic matter content, and a relatively rougher microtopography [8] [17] [18]. A soil surface cover of plant tissues also impedes overland flow and reduces the occurrence and quantities of surface runoff [14] [17] [19].…”