Ecological site‐based assessments of wind and water erosion: informing accelerated soil erosion management in rangelands

Abstract

Accelerated soil erosion occurs when anthropogenic processes modify soil, vegetation, or climatic conditions causing erosion rates at a location to exceed their natural variability. Identifying where and when accelerated erosion occurs is a critical first step toward its effective management. Here we explored how erosion assessments structured in the context of ecological sites (a land classification based on soils, landscape setting, and ecological potential) and their vegetation states (plant assemblages that may change due to management) can inform systems for reducing accelerated soil erosion in rangelands. We evaluated aeolian horizontal sediment flux and fluvial sediment erosion rates for five ecological sites in southern New Mexico, USA, using monitoring data and rangeland‐specific wind and water erosion models. Across the ecological sites, plots in shrub‐encroached and shrub‐dominated vegetation states were consistently susceptible to aeolian sediment flux and fluvial sediment erosion. Both processes were found to be highly variable for grassland and grass–succulent states across the ecological sites at the plot scale (0.25 ha). We identified vegetation thresholds that define cover levels below which rapid (exponential) increases in aeolian sediment flux and fluvial sediment erosion occur across the ecological sites and vegetation states. Aeolian sediment flux and fluvial erosion in the study area could be effectively controlled when bare ground cover was <20% of a site or the cover of canopy interspaces >100 cm in length was less than ∼35%. Land use and management activities that alter cover levels such that they cross thresholds, and/or drive vegetation state changes, may increase the susceptibility of areas to erosion. Land use impacts that are constrained within the range of natural variability should not result in accelerated soil erosion. Evaluating land condition against the erosion thresholds identified here will enable identification of areas susceptible to accelerated soil erosion and the development of practical management solutions.

Grazing impacts on the susceptibility of rangelands to wind erosion: The effects of stocking rate, stocking strategy and land condition

“…5). The importance of this variability has been demonstrated elsewhere for wind erosion assessments in the United States, supporting the case that land type and soil degradation influences on vegetation responses to grazing underpin management impacts on wind erosion (Ash et al, 1994;Webb et al, 2014). The modelled land erodibility responses to different land management follows expected patterns for the land types given their plant growth characteristics and local climate variations.…”

“…This trend, also described by Li et al (2005), and indicates that the rate of change in land erodibility is related to ecological and geomorphic changes within landscapes which affect their erodibility (Sasaki et al, 2008;Peters et al, 2004Peters et al, , 2007. In particular, a change in plant composition from perennial to annual dominated systems and shrub encroachment can significantly increase land erodibility (Okin et al, 2006;Ravi et al, 2011;Webb et al, 2014). Annual plants are sensitive to drought conditions and their presence can result in low vegetation cover levels and greater soil exposure, both seasonally and during extended drought (Ash et al, 1994;Scanlon et al, 2005).…”

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

“…Wind erosion models form a key part of our understanding of sediment transport dynamics on partly vegetated surfaces, and are crucial for assessing the potential vulnerability of dryland regions to soil degradation [11,27,33,135]. The mobility potential of vegetated dunes over long timescales has been successfully modelled using wind-based indices that combine precipitation, temperature and wind data [8,9].…”

“…Since the Okin model uses relatively simple spatial inputs, as opposed to the structural parameters of roughness elements needed for traditional shear stress partitioning models, data can be collected easily in the field using standardized measurement methods (e.g., [135,153]), and at the landscape scale using high resolution (<5 m) remote sensing techniques (e.g., [152,154,155]). As remote sensing approaches to estimating the precise spatial configuration of surface roughness are yet to be established at moderate spatial resolutions (e.g., 30-500 m), alternative data and models are needed to represent the heterogeneous effects of vegetation on aeolian sediment transport at regional to global scales.…”

Elevated aeolian sediment transport on the Colorado Plateau, USA: The role of grazing, vehicle disturbance, and increasing aridity

“…These consistently large q values measured at some of the heavily grazed sites, even after some reduction in cattle numbers in 2005, suggest that soil stabilization in these areas has not yet been achieved, especially when compared with the light/not grazed locations (all q measurements <2.0 g m -2 day -1 ). Areas that have been pushed into such degraded ecological states are often unable to recover biotic and hydrological functioning autogenically, necessitating active management intervention (Bestelmeyer et al, 2009;Miller et al, 2011;Webb et al, 2014;Fick et al, 2016) (Figure 5). These degraded states (termed 'annualized-bare' by Miller et al (2011)) are characterized by decreased ecosystem function due to loss of protective biological soil crusts, increased bare ground exposure, large decreases in perennial native vegetation, exotic plant invasions, high q, wind pedestalling, and, in more extreme cases, dune mobilization and gullying Draut et al, 2012;Duniway et al, 2016; T.W.…”