Small‐scale barriers mitigate desertification processes and enhance plant recruitment in a degraded semiarid grassland

Abstract

Citation: Fick, S. E., C. Decker, M. C. Duniway, and M. E. Miller. 2016. Small-scale barriers mitigate desertification processes and enhance plant recruitment in a degraded semi-arid grassland. Ecosphere 7(6):e01354. 10.1002/ecs2.1354Abstract. Anthropogenic desertification is a problem that plagues drylands globally; however, the factors which maintain degraded states are often unclear. In Canyonlands National Park on the Colorado Plateau of southeastern Utah, many degraded grasslands have not recovered structure and function >40 yr after release from livestock grazing pressure, necessitating active restoration. We hypothesized that multiple factors contribute to the persistent degraded state, including lack of seed availability, surficial soilhydrological properties, and high levels of spatial connectivity (lack of perennial vegetation and other surface structure to retain water, litter, seed, and sediment). In combination with seeding and surface raking treatments, we tested the effect of small barrier structures ("ConMods") designed to disrupt the loss of litter, seed and sediment in degraded soil patches within the park. Grass establishment was highest when all treatments (structures, seed addition, and soil disturbance) were combined, but only in the second year after installation, following favorable climatic conditions. We suggest that multiple limiting factors were ameliorated by treatments, including seed limitation and microsite availability, seed removal by harvester ants, and stressful abiotic conditions. Higher densities of grass seedlings on the north and east sides of barrier structures following the summer months suggest that structures may have functioned as artificial "nurse-plants", sheltering seedlings from wind and radiation as well as accumulating windblown resources. Barrier structures increased the establishment of both native perennial grasses and exotic annuals, although there were species-specific differences in mortality related to spatial distribution of seedlings within barrier structures. The unique success of all treatments combined, and even then only under favorable climatic conditions and in certain soil patches, highlights that restoration success (and potentially, natural regeneration) often is contingent on many interacting factors.

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.…”

“…In addition, the rangeland spatial models also captured areas of offhighway vehicle use (both in designated areas as well as unsanctioned off-road activity). Even though grazing has been excluded from these parks for >50 years, vegetation and biological soil crusts in many areas impacted by historical cattle use have not recovered and as a result may still be erosion prone if not actively restored Fick et al, 2016). It is notable that these sand dunes mark the leading edge of a large series of sand dunes in the San Rafael Desert to the southwest that may reflect a trend towards desertification in the region and warrant further study.…”

“…History provides examples of the risks posed by aeolian transport in dryland ecosystems by soil disturbing land-use activities during drought (Yao et al, 2006;Peters et al, 2007;Bestelmeyer et al, 2011;Miller et al, 2012) as well as new policy and associated management changes that have shown success in mitigating wind erosion (e.g. Areas in persistent annualized-bare ecological states may need more active restoration such as planting of vegetation, biological soil crust remediation, and other erosion control measures (Field et al, 2010;Fick et al, 2016). There is evidence that reductions in wind erosion in our study region were achieved following the Taylor Grazing Act (1934), but it also appears that wind erosion rates still have not returned to those estimated for pre-Anglo colonization (Neff et al, 2008).…”

Restoration islands: a tool for efficiently restoring dryland ecosystems?

“…Slow plant growth may also lead managers to rely on novel methods to spur successful establishment and thus prevent erosion. For example, erosion barriers have been used in drylands both in Kenya and in the Colorado Plateau in the Western United States to establish islands of vegetation that spread over time and reduce the connectivity of bare ground (Fick et al ; Kimiti et al ). In many drylands, biological soil crusts also stabilize soils and protect against erosion (Belnap ; Chiquoine et al ), and thus, restoring these crusts may offer additional stabilization.…”

Abiotic processes are insufficient for fertile island development: A 10‐year artificial shrub experiment in a desert grassland

“…Consequently, the relative importance of biotic and abiotic processes in the development of soil resource heterogeneity is still unknown. With the recent advent and use of abiotic barriers for restoration of arid and semiarid systems [Rachal et al, 2015;Fick et al, 2016], an understanding of the longer-term effects of these types of interventions is critically needed.…”