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  1. This dataset contains weights of windblown dust collected by BSNE collectors at long-term observation plots that are part of the Jornada Basin LTER Cross-Scale Interaction Study (CSIS) located at the Jornada Experimental Range. There are 15 experimental blocks (or sites) in this study. Within each block, there are 4 plots with different experimental treatments: 1 control, 1 with mesquite herbicide applied, 1 with connectivity modifiers (Conmods) installed, and 1 with Conmods AND mesquite herbicide applied. The intent of Conmods is to decrease gap size between perennial vegetation. The plots are 8 x 8 meters and have an 8 x 8 meter buffer zone on both the upwind and downwind sides of the plot. There are two BSNE (aeolian dust collector) stands per experimental plot positioned at the edge of the upwind and downwind 8m x 8m buffers. Each stand has 3 collectors positioned at heights of 10 cm, 30 cm, and 50 cm, and all collector openings face the prevailing wind direction. Upwind BSNEs collected the amount of dust entering the plot, and the downwind BSNEs collected the amount of dust moving off the plot. These collectors estimate the effectiveness of the plot surface in obstructing wind blown dust. This study is ongoing with data collected quarterly each year. 
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  2. Abstract

    Janus is the Roman god of transitions. In many environments, state transitions are an important part of our understanding of ecological change. These transitions are controlled by the interactions between exogenous forcing factors and stabilizing endogenous feedbacks. Forcing factors and feedbacks are typically considered to consist of different processes. We argue that during extreme events, a process that usually forms part of a stabilizing feedback can behave as a forcing factor. And thus, like Janus, a single process can have two faces. The case explored here pertains to state change in drylands where interactions between wind erosion and vegetation form an important feedback that encourages grass‐to‐shrub state transitions. Wind concentrates soil resources in shrub‐centered fertile islands, removes resources through loss of fines to favor deep‐rooted shrubs, and abrades grasses' photosynthetic tissue, thus further favoring the shrub state that, in turn, experiences greater aeolian transport. This feedback is well documented but the potential of wind to act also as a forcing has yet to be examined. Extreme wind events have the potential to act like other drivers of state change, such as drought and grazing, to directly reduce grass cover. This study examines the responses of a grass‐shrub community after two extreme wind events in 2019 caused severe deflation. We measured grass cover and root exposure due to deflation, in addition to shrub height, grass patch size, and grass greenness along 50‐m transects across a wide range of grass cover. Root exposure was concentrated in the direction of erosive winds during the storms and sites with low grass cover were associated with increased root exposure and reduced greenness. We argue that differences between extreme, rare wind events and frequent, small wind events are significant enough to be differences in kind rather than differences in degree allowing extreme winds to behave as endogenous forcings and common winds to participate in an endogenous stabilizing feedback. Several types of state change in other ecological systems in are contextualized within this framework.

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  3. Abstract Aims

    Grassland-to-shrubland transition is a common form of land degradation in drylands worldwide. It is often attributed to changes in disturbance regimes, particularly overgrazing. A myriad of direct and indirect effects (e.g., accelerated soil erosion) of grazing may favor shrubs over grasses, but their relative importance is unclear. We tested the hypothesis that topsoil “winnowing” by wind erosion would differentially affect grass and shrub seedling establishment to promote shrub recruitment over that of grass.


    We monitored germination and seedling growth of contrasting perennial grass (Bouteloua eriopoda,Sporobolus airoides, andAristida purpurea) and shrub (Prosopis glandulosa,Atriplex canescens, andLarrea tridentata) functional groups on field-collected non-winnowed and winnowed soils under well-watered greenhouse conditions.


    Non-winnowed soils were finer-textured and had higher nutrient contents than winnowed soils, but based on desorption curves, winnowed soils had more plant-available moisture. Contrary to expectations, seed germination and seedling growth on winnowed and non-winnowed soils were comparable within a given species. The N2-fixing deciduous shrubP. glandulosawas first to emerge and complete germination, and had the greatest biomass accumulation of all species.


    Germination and early seedling growth of grasses and shrubs on winnowed soils were not adversely nor differentially affected comparing with that observed on non-winnowed soils under well-watered greenhouse conditions. Early germination and rapid growth may giveP. glandulosaa competitive advantage over grasses and other shrub species at the establishment stage in grazed grasslands. Field establishment experiments are needed to confirm our findings in these controlled environment trials.

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  4. Abstract

    Southern California is a biodiversity hotspot and home to over 23 million people. Over recent decades the annual wildfire area in the coastal southern California region has not significantly changed. Yet how fire regime will respond to future anthropogenic climate change remains an important question. Here, we estimate wildfire probability in southern California at station scale and daily resolution using random forest algorithms and downscaled earth system model simulations. We project that large fire days will increase from 36 days/year during 1970–1999 to 58 days/year under moderate greenhouse gas emission scenario (RCP4.5) and 71 days/year by 2070–2099 under a high emission scenario (RCP8.5). The large fire season will be more intense and have an earlier onset and delayed end. Our findings suggest that despite the lack of a contemporary trend in fire regime, projected greenhouse gas emissions will substantially increase the fire danger in southern California by 2099.

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  5. With rapid innovations in drone, camera, and 3D photogrammetry, drone-based remote sensing can accurately and efficiently provide ultra-high resolution imagery and digital surface model (DSM) at a landscape scale. Several studies have been conducted using drone-based remote sensing to quantitatively assess the impacts of wind erosion on the vegetation communities and landforms in drylands. In this study, first, five difficulties in conducting wind erosion research through data collection from fieldwork are summarized: insufficient samples, spatial displacement with auxiliary datasets, missing volumetric information, a unidirectional view, and spatially inexplicit input. Then, five possible applications—to provide a reliable and valid sample set, to mitigate the spatial offset, to monitor soil elevation change, to evaluate the directional property of land cover, and to make spatially explicit input for ecological models—of drone-based remote sensing products are suggested. To sum up, drone-based remote sensing has become a useful method to research wind erosion in drylands, and can solve the issues caused by using data collected from fieldwork. For wind erosion research in drylands, we suggest that a drone-based remote sensing product should be used as a complement to field measurements. 
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  6. Abstract. Fire causes abrupt changes in vegetation properties and modifies fluxexchanges between land and atmosphere at subseasonal to seasonal scales. Yetthese short-term fire effects on vegetation dynamics and surface energybalance have not been comprehensively investigated in the fire-coupledvegetation model. This study applies the SSiB4/TRIFFID-Fire (the SimplifiedSimple Biosphere Model coupled with the Top-down Representation of InteractiveFoliage and Flora Including Dynamics with fire) model to studythe short-term fire impact in southern Africa. Specifically, we aim toquantify how large impacts fire exerts on surface energy throughdisturbances on vegetation dynamics, how fire effects evolve during the fireseason and the subsequent rainy season, and how surface-darkening effectsplay a role besides the vegetation change effects. We find fire causes an annual average reduction in grass cover by 4 %–8 %for widespread areas between 5–20∘ S and a tree cover reductionby 1 % at the southern periphery of tropical rainforests. The regionalfire effects accumulate during June–October and peak in November, thebeginning of the rainy season. After the fire season ends, the grass coverquickly returns to unburned conditions, while the tree fraction hardlyrecovers in one rainy season. The vegetation removal by fire has reduced theleaf area index (LAI) and gross primary productivity (GPP) by 3 %–5 % and5 %–7 % annually. The exposure of bare soil enhances surface albedo andtherefore decreases the absorption of shortwave radiation. Annual meansensible heat has dropped by 1.4 W m−2, while the latent heat reductionis small (0.1 W m−2) due to the compensating effects between canopytranspiration and soil evaporation. Surface temperature is increased by asmuch as 0.33 K due to the decrease of sensible heat fluxes, and the warmingwould be enhanced when the surface-darkening effect is incorporated. Ourresults suggest that fire effects in grass-dominant areas diminish within1 year due to the high resilience of grasses after fire. Yet fire effectsin the periphery of tropical forests are irreversible within one growingseason and can cause large-scale deforestation if accumulated for hundredsof years. 
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  7. A combination of drought and high temperatures (“global-change-type drought”) is projected to become increasingly common in Mediterranean climate regions. Recently, Southern California has experienced record-breaking high temperatures coupled with significant precipitation deficits, which provides opportunities to investigate the impacts of high temperatures on the drought sensitivity of Mediterranean climate vegetation. Responses of different vegetation types to drought are quantified using the Moderate Resolution Imaging Spectroradiometer (MODIS) data for the period 2000–2017. The contrasting responses of the vegetation types to drought are captured by the correlation and regression coefficients between Normalized Difference Vegetation Index (NDVI) anomalies and the Palmer Drought Severity Index (PDSI). A novel bootstrapping regression approach is used to decompose the relationships between the vegetation sensitivity (NDVI–PDSI regression slopes) and the principle climate factors (temperature and precipitation) associated with the drought. Significantly increased sensitivity to drought in warmer locations indicates the important role of temperature in exacerbating vulnerability; however, spatial precipitation variations do not demonstrate significant effects in modulating drought sensitivity. Based on annual NDVI response, chaparral is the most vulnerable community to warming, which will probably be severely affected by hotter droughts in the future. Drought sensitivity of coastal sage scrub (CSS) is also shown to be very responsive to warming in fall and winter. Grassland and developed land will likely be less affected by this warming. The sensitivity of the overall vegetation to temperature increases is particularly concerning, as it is the variable that has had the strongest secular trend in recent decades, which is expected to continue or strengthen in the future. Increased temperatures will probably alter vegetation distribution, as well as possibly increase annual grassland cover, and decrease the extent and ecological services provided by perennial woody Mediterranean climate ecosystems as well. 
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