Search

Many important ecological phenomena occur on large spatial scales and/or are unplanned and thus do not easily fit within analytical frameworks that rely on randomization, replication, and interspersed a priori controls for statistical comparison. Analyses of such large‐scale, natural experiments are common in the health and econometrics literature, where techniques have been developed to derive insight from large, noisy observational data sets. Here, we apply a technique from this literature, synthetic control, to assess landscape change with remote sensing data. The basic data requirements for synthetic control include (1) a discrete set of treated and untreated units, (2) a known date of treatment intervention, and (3) time series response data that include both pre‐ and post‐treatment outcomes for all units. Synthetic control generates a response metric for treated units relative to a no‐action alternative based on prior relationships between treated and unexposed groups. Using simulations and a case study involving a large‐scale brush‐clearing management event, we show how synthetic control can intuitively infer treatment effect sizes from satellite data, even in the presence of confounding noise from climate anomalies, long‐term vegetation dynamics, or sensor errors. We find that accuracy depends on the number and quality of potential control units, highlighting the importance of selecting appropriate control populations. Although we consider the synthetic control approach in the context of natural experiments with remote sensing data, we expect the methodology to have wider utility in ecology, particularly for systems with large, complex, and poorly replicated experimental units. [ABSTRACT FROM AUTHOR]

In dryland ecosystems, natural recovery of biological soil crusts (biocrusts) following disturbance may be slow or inhibited, necessitating active restoration practices. While biocrusts can be readily propagated under environmentally controlled conditions, rehabilitation in the field is complicated by environmental stresses which may be particularly acute in degraded, destabilized soils with harsh climatic conditions at the soil surface. In this study, we first present the results of a field trial at a severely degraded rangeland site examining the stabilizing effects of various soil amendments (polysaccharide glues and polyacrylamides) in combination with biocrust inoculum. We found that a psyllium compound was the only amendment to maintain effectiveness after 19 months, and the only treatment that maintained biocrust inoculum throughout the trial. In a subsequent short‐term experiment where plots were shaded and watered, we examined how biocrust inoculation rate (0, 20, and 40% initial cover) and the psyllium‐based amendment affected biocrust growth. After 4 months, visible biocrust cover in inoculated plots was greater than in controls, but only chlorophyll a exhibited a dosage‐response to inoculum application rate, indicating preferential establishment of cyanobacteria. Psyllium did not affect biocrust development but did improve soil stability. Shade and watering buffered against temperature extremes (up to 15°C) and increased the duration of moist surface conditions necessary for biocrust growth by up to 30%, mimicking conditions more common in the fall and winter months. Our results suggest that inducing early successional biocrusts on a highly degraded site is possible with suitable microclimate conditions. [ABSTRACT FROM AUTHOR]

A 'resilient' forest endures disturbance and is likely to persist. Resilience to wildfire may arise from feedback between fire behaviour and forest structure in dry forest systems. Frequent fire creates fine‐scale variability in forest structure, which may then interrupt fuel continuity and prevent future fires from killing overstorey trees. Testing the generality and scale of this phenomenon is challenging for vast, long‐lived forest ecosystems. We quantify forest structural variability and fire severity across >30 years and >1000 wildfires in California's Sierra Nevada. We find that greater variability in forest structure increases resilience by reducing rates of fire‐induced tree mortality and that the scale of this effect is local, manifesting at the smallest spatial extent of forest structure tested (90 × 90 m). Resilience of these forests is likely compromised by structural homogenisation from a century of fire suppression, but could be restored with management that increases forest structural variability. [ABSTRACT FROM AUTHOR]

Inducing biological soil crust (biocrust) development is an appealing approach for dust mitigation in drylands due to the resistance biocrusts can provide against erosion. Using a portable device, we evaluated dust emissions from surfaces either inoculated with biocrust, amended with a plant‐based soil stabilizer, or both at varying wind friction velocities. Four months after application, emissions from all treatments were either indistinguishable from or greater than controls, despite evidence of biocrust establishment. All treatments had greater surface roughness and showed more evidence of entrapment of windblown sediment than controls, factors which may have been partially responsible for elevated emissions. There was a synergistic effect of inoculation and stabilizer addition, resulting in a nearly two‐fold reduction in estimated emissions compared to either treatment alone. Stepwise regression analysis indicated that variables associated with surface crust strength (aggregate stability, penetration resistance) were negatively associated with emissions and variables associated with sediment supply (sand content, loose sediment cover) were positively associated with emissions. With more time to develop, the soil‐trapping activity and surface integrity of biocrust inoculum and soil stabilizer mixtures is expected to increase with the accumulation of surface biomass and enhancement of roughness through freeze–thaw cycles. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Colorado Plateau is one of North America's five major deserts, encompassing 340,000 km2 of the western United States, and offering many opportunities for restoration relevant to researchers and land managers in drylands around the globe. The Colorado Plateau is comprised of vast tracts of public land managed by local, state, and federal agencies that oversee a wide range of activities (e.g., mineral and energy extraction, livestock grazing, and recreation). About 75% of the Plateau is managed by federal and tribal agencies and tens of millions of people visit the Plateau's public lands each year. However, even in the face of this diverse use, our knowledge of effective ways to restore Plateau ecosystems remains relatively poor. Further, the multiple agencies on the Plateau have mandates that differ greatly in allowable practices, restoration needs, and desired outcomes. The Colorado Plateau is also expected to undergo ecosystem shifts in the face of climate change, further complicating management decisions and potentially limiting some options while creating others. Here, we explore the current state of Colorado Plateau restoration science and underscore key challenges and opportunities for improving our capacity to maintain the myriad of services provided by these desert ecosystems. We highlight past research efforts and future needs related to restoration concepts, including consideration and design of novel ecosystems, mitigation for and adaptation to climate change, use of genetically diverse seed adapted for current and future conditions, and the value of strong multi‐agency and stakeholder collaborations in restoring systems on the Colorado Plateau and beyond. [ABSTRACT FROM AUTHOR]

Historical reconstructions of plant community distributions are useful for biogeographic studies and restoration planning, but the quality of insights gained depends on the depth and reliability of historical information available. For the Central Valley of California, one of the most altered terrestrial ecosystems on the planet, this task is particularly difficult given poor historical documentation and sparse relict assemblages of pre-invasion plant species. Coastal and interior prairies were long assumed to have been dominated by perennial bunchgrasses, but this hypothesis has recently been challenged. We evaluated this hypothesis by creating species distribution models (SDMs) using a novel approach based on the abundance of soil phytoliths (microscopic particles of biogenic silica used as a proxy for long-term grass presence) extracted from soil samples at locations statewide. Modeled historical grass abundance was consistently high along the coast and to a lesser extent in higher elevation foothills surrounding the Central Valley. SDMs found strong associations with mean temperature, temperature variability, and precipitation variability, with higher predicted abundance in regions with cooler, equable temperatures and moderated rainfall, mirroring the pattern for modern perennial grass distribution across the state. The results of this study strongly suggest that the pre-Columbian Central Valley of California was not dominated by grasses. Using soil phytolith data as input for SDMs is a promising new method for predicting the extent of prehistoric grass distributions where alternative historical datasets are lacking. [ABSTRACT FROM AUTHOR]

ABSTRACT We created a new dataset of spatially interpolated monthly climate data for global land areas at a very high spatial resolution (approximately 1 km2). We included monthly temperature (minimum, maximum and average), precipitation, solar radiation, vapour pressure and wind speed, aggregated across a target temporal range of 1970-2000, using data from between 9000 and 60 000 weather stations. Weather station data were interpolated using thin-plate splines with covariates including elevation, distance to the coast and three satellite-derived covariates: maximum and minimum land surface temperature as well as cloud cover, obtained with the MODIS satellite platform. Interpolation was done for 23 regions of varying size depending on station density. Satellite data improved prediction accuracy for temperature variables 5-15% (0.07-0.17 °C), particularly for areas with a low station density, although prediction error remained high in such regions for all climate variables. Contributions of satellite covariates were mostly negligible for the other variables, although their importance varied by region. In contrast to the common approach to use a single model formulation for the entire world, we constructed the final product by selecting the best performing model for each region and variable. Global cross-validation correlations were ≥ 0.99 for temperature and humidity, 0.86 for precipitation and 0.76 for wind speed. The fact that most of our climate surface estimates were only marginally improved by use of satellite covariates highlights the importance having a dense, high-quality network of climate station data. [ABSTRACT FROM AUTHOR]

The outcomes of restoration efforts are contingent on the specifics of the restoration practices utilized, but also on uncontrolled contingencies such as site effects and year effects. Although restoration practitioners have long been aware that the successes of their projects vary from site to site and from year to year, there have been few direct experimental tests of these contingencies., We established grassland restoration plots identically across three sites in northern California, in each of four establishment years (for 12 site-year combinations)., The resulting plant communities differed significantly across sites and across establishment years. As a consequence of these community differences, there were 'forb years' and 'grass years', although these sometimes differed among sites. Multivariate analysis identified mean annual temperature and total precipitation as likely drivers of some of these differences., Synthesis and applications. Our results not only confirm the idiosyncratic nature of the results of restoration efforts (and ecological experiments in general) but also demonstrate that some of this variation can potentially be related to measurable environmental conditions. Understanding the drivers of this variability can ultimately aid restoration practitioners by allowing them to focus restoration efforts on years and sites most likely to yield desired outcomes. [ABSTRACT FROM AUTHOR]

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 soil-hydrological 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 wind-blown 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. [ABSTRACT FROM AUTHOR]

In dryland ecosystems, land degradation and erosion pose severe threats to ecosystem productivity and human well‐being. Bio‐inoculation of degraded soils with native biological soil crusts ("biocrusts") is a promising yet relatively untested means to improve soil stability and hydrological function (i.e., increase infiltration and reduce run‐off). In a degraded semiarid grassland on the Colorado Plateau, we studied the establishment and hydrological function (via simulated rainfall) of induced biocrusts grown with and without an organic soil stabilizer (psyllium, derived from Plantago sp.), after a period of 4 months. We found evidence of biocrust establishment, including significantly higher biocrust cover, chlorophyll a, and exopolysaccharides in inoculated plots compared with controls. Plots inoculated with biocrust had higher run‐off and sediment yields than controls during rainfall simulation. However, this effect was mitigated in plots where stabilizer was added, resulting in greater soil aggregate stability and higher levels of infiltration (reduced total run‐off). The time to ponding was significantly greater than control for all inoculated plots, suggesting that induced biocrusts may be most effective at improving infiltration under low‐intensity, smaller precipitation events. Notably, the biocrusts in this study lacked rough surface microtopography, which is common in well‐developed biocrusts regionally and likely instrumental in slowing overland flow and increasing infiltration for larger rain events. These results highlight the temporal lag that may exist between apparent and functional restoration of biocrusts. In addition, the simultaneous additions of stabilizing amendments with biocrust inoculum may work collectively to achieve both short‐ and long‐term restoration targets. [ABSTRACT FROM AUTHOR]

Erosion by wind is one of the principal processes associated with land degradation in drylands and is a significant concern to land managers and policymakers globally. In the drylands of North America, millions of tons of soil are lost to wind erosion annually. Of the 60 million ha in the United States identified as most vulnerable to wind erosion (arid and dominated by fine sandy soils), 64% are managed by federal agencies (37 million ha). Here we review the drivers and consequences of wind erosion and dust emissions on drylands in the United States, with an emphasis on actionable responses available to policymakers and practitioners. We find that while dryland soils are often relatively stable when intact, disturbances including fire, domestic livestock grazing, and off‐highway vehicles can increase horizontal eolian flux by an order of magnitude, in some cases as much as 40‐fold. A growing body of literature documents the large‐scale impacts of deposited dust changing the albedo of mountain snow cover and in some cases reducing regional water supplies by ~5%. Predicted future increases in aridity and extreme weather events, including drought, will likely increase wind erosion and consequent dust generation. Under a drier and more variable future climate, new and existing soil‐ and vegetation‐disturbing practices may interact in synergistic ways, with dire consequences for environments and society that are unforeseen to many but fairly predictable given current scientific understanding. Conventional restoration and reclamation approaches, which often entail surface disturbance and rely on adequate moisture to prevent erosion, also carry considerable erosion risk especially under drought conditions. Innovative approaches to dryland restoration that minimize surface disturbance may accomplish restoration or reclamation goals while limiting wind erosion risk. Finally, multidisciplinary and multijurisdictional approaches and perspectives are necessary to understand the complex processes driving dust emissions and provide timely, context‐specific information for mitigating the drivers and impacts of wind erosion and dust. [ABSTRACT FROM AUTHOR]