Matthew Alan Bowker

Dryland ecosystems cover much of Earth’s terrestrial surface and are increasingly affected by climate warming, land-use change, and biological invasion. The Sonoran Desert of western North America, a biodiversity hotspot that historically experienced infrequent fire, exemplifies how these global-change processes are driving ecosystem transformation through the emergence of novel disturbance regimes. Using records of more than 73,000 wildland fire events, we quantified anthropogenic and environmental controls on fire ignition, size, and spread across the Sonoran Desert. Human-caused ignitions accounted for 95.5% of all recorded fires since the early 1990s and were concentrated near roads, buildings, and other areas of human activity, particularly during late spring. In contrast, lightning-caused ignitions were rare within the Sonoran Desert and occurred primarily in adjacent montane forests during late summer months. Consistent with broader trends across the western United States, fires were typically largest when they ignited far from roads, where access is limited, and fire management often relies on indirect attack strategies. Pre-fire annual and perennial herbaceous vegetation both promoted fire spread, with detectable effects at cover values as low as 5%, while bare ground reduced fuel connectivity and constrained fire growth. Rather than exhibiting a distinct threshold response, fire spread increased linearly with herbaceous cover, suggesting that even modest increases in fine fuels can alter fire behavior in this historically fuel-limited ecosystem. Together, our results illustrate that human ignitions determine where fires occur, whereas herbaceous fuels determine whether those ignitions spread, driving fire-regime transformation across an iconic North American desert. Managing and adapting to this novel fire regime will require coordinated efforts to reduce human-caused ignitions, limit invasive herbaceous fuels, maintain bare-ground interspaces, and rapidly suppress fires. More broadly, our findings identify the mechanisms controlling fire regime change in dryland ecosystems and provide a framework for anticipating ecosystem transformation under ongoing global change.

Non-native grass invasion, human ignitions and expanding land use pressures in the Sonoran Desert, result in loss of vegetation, destabilized soils and slow ecosystem recovery. Biological soil crusts (biocrusts) – thin, coherent soil surface layers, created and inhabited by biota such as cyanobacteria, lichens and mosses – play a critical role in stabilizing soils and supporting ecosystem resilience, yet their potential as active restoration catalysts in post-fire drylands remains underexplored. This study evaluated two biocrust restoration strategies at a fire-affected site in the Tonto National Forest: application of intact strips of farmed biocrusts (sods) and dispersal of gel capsules containing biocrust material, native seeds and diatomaceous earth. Late-successional biocrust cover was eight-fold higher on sod treatments compared to the control and soil stability also increased nearby sods. Capsule treatments produced over 3x higher late-successional biocrust cover than controls in the last season. Seeded plots also supported successful seedling establishment of Baileya multiradiata. Together, these results demonstrate that cultivated biocrust applications can accelerate biocrust recovery, especially for late-successional taxa and increased soil stability in post-fire desert landscapes, offering a nature-based solution to reduce dryland degradation.

Climate change and land use (e.g., grazing, solar farms, mining) contribute to the loss of biological soil crusts (biocrusts) and associated ecosystem degradation. Biocrusts are composed of mosses, lichens, liverworts and cyanobacteria, alone or in any combination at the soil surface. Cultivating biocrusts for reintroductions into degraded ecosystems could support restoration efforts, but effective methods are still emerging. We built a fog chamber to test cultivation of two mosses ( Homalothecium aureum and Syntrichia ruralis ) and two lichens ( Peltigera rufescens and Cladonia spp.) common in intermountain west biocrust communities. Each taxon was tested in intact and disaggregated forms. We hypothesized that disaggregated samples would grow better than the intact ones, and the mosses would grow faster than lichens. Results showed that disaggregated mosses and lichens produced a minimum of 50% more healthy tissue than intact mosses and lichens, but lichens failed to grow well in either condition. Fog cultivation may be a promising method for mosses, but not for lichens under these conditions.

Wind erosion and sand and dust storms are a global challenge. While many management practices to mitigate sources of wind erosion and sand and dust storms have been documented, existing guidance largely emphasizes what practices are available, with limited information on where and under what ecological conditions they should be applied. As a result, mitigation efforts can be ineffective or can exacerbate erosion when implemented without regard to local ecological context. Land potential, or the inherent capacity of land to support vegetation, soil stability, and productivity, provides a basis for aligning mitigation practices with a site's resistance and resilience to erosion. Here, we present a land potential‐based framework to improve the selection, implementation, and evaluation of wind erosion and sand and dust storm source mitigation practices across diverse landscapes. The framework uses land potential assessment with agroecological state concepts to guide decision‐making through the following steps: (1) characterize land potential by soils, topography, and climate to identify resistance and resilience to erosion; (2) identify agroecological states that capture vegetation–soil configurations, thresholds, and feedbacks determining erosion dynamics; (3) identify and monitor wind erosion risk and sand and dust storm source areas; (4) define mitigation targets and benchmarks that guide decision‐making; (5) identify and implement practices to avoid, reduce, reverse, or accept wind erosion; and (6) evaluate mitigation outcomes and adapt management. By linking local‐scale land assessments with mitigation practices, this framework increases the likelihood of successful mitigation and provides scalable decision support for advancing Land Degradation Neutrality and sustainable land management.

Biological soil crusts (biocrusts) – thin, coherent soil surface layers aggregated and inhabited by communities of tiny photoautotrophic and heterotrophic organisms – support ecosystem functioning in drylands and influence the Earth system. Biocrust loss due to disturbance, global change and land use leads to altered hydrological function, susceptibility to erosion and diminished biogeochemical cycling, with consequences extending to regional and global environmental quality and ecosystem service provisioning. To restore degraded drylands, specific techniques could inform how to 1. produce biocrust biota ex situ for use as an inoculum in degraded environments and then 2. encourage the establishment of the inoculum in high-stress environments. To re-establish lost biocrusts, a promising pathway could be the integration of adding biocrust biota (inoculation), ensuring that it stays where applied (retention) and softening environmental stresses and limitations (amelioration) at approximately the same time. Several techniques, most of them developed in only the past few years, demonstrate this integration: biocrust sods, cloths, pellets, capsules and slurries. Biocrust sods are fabric-reinforced patches of biocrust growing on soil, produced in farms and transported to and deployed intact in field sites. Biocrust cloths are fabrics and sheets with biocrust biota grown directly on their surface in greenhouse-based fog chambers that can be attached to soil in the field. Biocrust pellets are small, protective pieces of a binder material (often clay) infused with biocrust inoculum. Biocrust capsules are biodegradable gel capsules filled with biocrust inoculum, often with protective substances. Both pellets and capsules are broadcast over degraded soils. Biocrust slurries are semi-liquid suspensions of biocrust inoculum and other solids that are sprayed or spread in degraded sites. Emerging techniques like these have the potential to restore highly functional drylands and their ecosystem services. Potential applications include ecological restoration of dryland areas disturbed by fire, overgrazing, agriculture, mining and other factors or environmental engineering in other contexts such as cultural heritage sites, croplands or human infrastructure. The next-generation techniques for biocrust restoration described here are tools that could be applied to solve small- to medium-scaled challenges now and with increased production efficiency and informed, strategic use of the products, large-scaled challenges in the future.

Gypsum-rich soils have unusual characteristics that make them a haven for rare and endemic species and a target for disturbance, such as mining. To restore habitat and determine best practices for native plant reestablishment, we conducted a factorial, randomized complete block experiment in disturbed areas with gypsum-rich soils in the Mojave Desert, testing the interactive effect of seeding endemic plant species, out-planting shrubs grown with or without live native soil, biocrust inoculum and psyllium husk as a soil stabilizer. Biocrust inoculation and seeding were both needed treatments to increase the abundance of native biota, increasing biocrust cover in inoculated plots 13 times more than in uninoculated plots, and there was no passive recovery of the vascular plants; however, these factors had no interactive effect after 3 years. Soil stability generally increased across all treatments through time, though soil resistance to shear stress was reduced by biocrust, and soil aggregate stability was increased by psyllium. Shrub planting was unsuccessful, with near total mortality. Both seeding and biocrust inoculation were vital to increase the cover of perennial plants and biocrust organisms. This work reinforces the need for active restoration techniques in degraded dryland ecosystems.

Drylands are increasingly degraded by livestock grazing, mining, recreation, off-road vehicles and wildfire. These disturbances damage biological soil crusts (biocrusts) that stabilize soil, cycle nutrients, and store carbon. Farming biocrust as transplantable “sods” offers a promising restoration approach, but invasive plants colonizing sods risk contaminating restoration areas. Manually removing invasives is labor-intensive and unreliable. To determine the viability of herbicide control of weeds while cultivating biocrust, we tested four herbicide treatments, hand-cutting and untreated controls on biocrust sods seeded with the rapidly invading Oncosiphon pilulifer (stinknet) and, later, native plants. We measured biocrust and stinknet cover, native seedling establishment and treatment costs. Late-successional biocrust (lichens, mosses and dark cyanobacteria) grew best under all herbicide treatments compared to controls. Post-emergent herbicides (aminopyralid and glyphosate) effectively controlled stinknet while allowing later native seedling establishment. Preemergent indaziflam prevented both stinknet and native plant establishment. Preemergent aminopyralid was less effective against stinknet. Post-emergent aminopyralid and preemergent indaziflam were most cost-effective and suitable for promoting or preventing native recruitment, respectively. Herbicide application to biocrust sods represents a significant advancement in making biocrust farming economically viable by reducing manual labor, while providing critical information for combating an emerging invasive species threat.

Ecological restoration often requires exotic invasive plant control. In many ecosystems, reestablishment of biological soil crusts (biocrusts) is a desired restoration outcome because biocrusts enhance ecosystem function and may favor native plants over exotics. We sought to pair exotic plant suppression with biocrust restoration using a novel restoration material: biocrust‐covered weed barriers. We tested five different barriers, including three biodegradable weed barriers, one synthetic weed barrier commonly used in the study area, and burlap cloth, because it has previously been shown to be useful in biocrust establishment. We grew biocrust moss over the surface of each barrier type in a fog chamber. Each barrier type was attached to the ground in the field with moss on the underside of the barrier (moss‐down), the top, or not present. We monitored the establishment of moss biocrusts and exotic plants and the durability of the barriers. The most successful barrier type for biocrust establishment was burlap, but one biodegradable weed barrier made of maize‐derived polylactic acid (corn) promoted biocrusts, especially in the moss‐down position. Only the synthetic weed barrier suppressed exotic plants for two growing seasons. The corn barrier only partially suppressed exotic plants for one growing season. Less durable weed barriers were less able to suppress exotic plants. Though we failed to identify a biodegradable barrier that both stimulates biocrust recovery and suppresses exotic plants beyond one growing season, our results suggest that our goal may be attainable if more durable biodegradable weed barriers were used or created.

Increases in the abundance of woody species have been reported to affect the provisioning of ecosystem services in drylands worldwide. However, it is virtually unknown how multiple biotic and abiotic drivers, such as climate, grazing, and fire, interact to determine woody dominance across global drylands. We conducted a standardized field survey in 304 plots across 25 countries to assess how climatic features, soil properties, grazing, and fire affect woody dominance in dryland rangelands. Precipitation, temperature, and grazing were key determinants of tree and shrub dominance. The effects of grazing were determined not solely by grazing pressure but also by the dominant livestock species. Interactions between soil, climate, and grazing and differences in responses to these factors between trees and shrubs were key to understanding changes in woody dominance. Our findings suggest that projected changes in climate and grazing pressure may increase woody dominance in drylands, altering their structure and functioning.