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Warm drylands represent 19% of land surfaces worldwide and host ca. 1100 tree species. The risk of decline due to climate aridification of this neglected biodiversity has been overlooked despite its ecological and societal importance. To fill this gap, we assessed the risk of decline due to climate aridification of tree species in warm drylands based on spatialized occurrence data and climate models. We considered both species vulnerability and exposure, compared the risk of tree species decline across five bioregions and searched for phylogenetic correlates. Depending on the future climate model, from 44% to 88% of warm drylands' tree species will undergo climate aridification with a high risk of decline even under the most optimistic conditions. On a regional scale, the rate of species that will undergo climate aridification in the future varies from 21% in the Old World North, to 90% in Australia, with a risk of decline confirming the high level of risk predicted at the global scale. Using generalized linear mixed models, we found that, species more exposed to climate aridification will be more at risk, but also that species vulnerability is a key driver of their risk of decline. Indeed, the warm drylands specialist species will be less at risk due to climate aridification than species being marginal in warm drylands. We also found that the risk of decline is widespread across the main clades of the phylogeny and involves several evolutionary distinct species. Estimating a high risk of decline for numerous tree species in all warm drylands, including emblematic dryland endemics, our work warns that future increase in aridity could result in an extensive erosion of tree biodiversity in these ecosystems., (© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

AbstractClimate change is altering species' habitats, phenology, and behavior. Although sexual behaviors impact population persistence and fitness, climate change's effects on sexual signals are understudied. Climate change can directly alter temperature-dependent sexual signals, cause changes in body size or condition that affect signal production, or alter the selective landscape of sexual signals. We tested whether temperature-dependent mating calls of Mexican spadefoot toads ( Spea multiplicata ) had changed in concert with climate in the southwestern United States across 22 years. We document increasing air temperatures, decreasing rainfall, and changing seasonal patterns of temperature and rainfall in the spadefoots' habitat. Despite increasing air temperatures, spadefoots' ephemeral breeding ponds have been getting colder at most elevations, and male calls have been slowing as a result. However, temperature-standardized call characters have become faster, and male condition has increased, possibly due to changes in the selective environment. Thus, climate change might generate rapid, complex changes in sexual signals with important evolutionary consequences.

Historical population contraction and expansion events associated with Pleistocene climate change are important drivers of intraspecific population structure in Australian arid-zone species. We compared phylogeographic patterns among arid-adapted Dasyuridae ( Sminthopsis and Planigale ) with close phylogenetic relationships and similar ecological roles to investigate the drivers of phylogeographic structuring and the importance of historical refugia. We generated haplotype networks for two mitochondrial (control region and cytochrome b) and one nuclear (omega-globin) gene from samples distributed across each species range. We used Φ ST to test for a genetic population structure associated with the four Pilbara subregions, and we used expansion statistics and Bayesian coalescent skyline analysis to test for signals of historical population expansion and the timing of such events. Significant population structure associated with the Pilbara and subregions was detected in the mitochondrial data for most species, but not with the nuclear data. Evidence of population expansion was detected for all species, and it likely began during the mid-late Pleistocene. The timing of population expansion suggests that these species responded favorably to the increased availability of arid habitats during the mid-late Pleistocene, which is when previously patchy habitats became more widespread. We interpret our results to indicate that the Pilbara region could have acted as a refugium for small dasyurids.

Long-term observations of ecological communities are necessary for generating and testing predictions of ecosystem responses to climate change. We investigated temporal trends and spatial patterns of soil fauna along similar environmental gradients in three sites of the McMurdo Dry Valleys, Antarctica, spanning two distinct climatic phases: a decadal cooling trend from the early 1990s through the austral summer of February 2001, followed by a shift to the current trend of warming summers and more frequent discrete warming events. After February 2001, we observed a decline in the dominant species (the nematode Scottnema lindsayae) and increased abundance and expanded distribution of less common taxa (rotifers, tardigrades, and other nematode species). Such diverging responses have resulted in slightly greater evenness and spatial homogeneity of taxa. However, total abundance of soil fauna appears to be declining, as positive trends of the less common species so far have not compensated for the declining numbers of the dominant species. Interannual variation in the proportion of juveniles in the dominant species was consistent across sites, whereas trends in abundance varied more. Structural equation modeling supports the hypothesis that the observed biological trends arose from dissimilar responses by dominant and less common species to pulses of water availability resulting from enhanced ice melt. No direct effects of mean summer temperature were found, but there is evidence of indirect effects via its weak but significant positive relationship with soil moisture. Our findings show that combining an understanding of species responses to environmental change with long-term observations in the field can provide a context for validating and refining predictions of ecological trends in the abundance and diversity of soil fauna., (© 2018 by the Ecological Society of America.)

Climate change will result in reduced soil water availability in much of the world either due to changes in precipitation or increased temperature and evapotranspiration. How communities of mites and nematodes may respond to changes in moisture availability is not well known, yet these organisms play important roles in decomposition and nutrient cycling processes. We determined how communities of these organisms respond to changes in moisture availability and whether common patterns occur along fine-scale gradients of soil moisture within four individual ecosystem types (mesic, xeric and arid grasslands and a polar desert) located in the western United States and Antarctica, as well as across a cross-ecosystem moisture gradient (CEMG) of all four ecosystems considered together. An elevation transect of three sampling plots was monitored within each ecosystem and soil samples were collected from these plots and from existing experimental precipitation manipulations within each ecosystem once in fall of 2009 and three times each in 2010 and 2011. Mites and nematodes were sorted to trophic groups and analyzed to determine community responses to changes in soil moisture availability. We found that while both mites and nematodes increased with available soil moisture across the CEMG, within individual ecosystems, increases in soil moisture resulted in decreases to nematode communities at all but the arid grassland ecosystem; mites showed no responses at any ecosystem. In addition, we found changes in proportional abundances of mite and nematode trophic groups as soil moisture increased within individual ecosystems, which may result in shifts within soil food webs with important consequences for ecosystem functioning. We suggest that communities of soil animals at local scales may respond predictably to changes in moisture availability regardless of ecosystem type but that additional factors, such as climate variability, vegetation composition, and soil properties may influence this relationship over larger scales., (© 2014 John Wiley & Sons Ltd.)

Questions: Rapid climate change has profoundly altered the spatial distribution of terrestrial plants especially in arid and semi‐arid biomes. However, it remains poorly documented how climate shapes the current and future patterns of plant diversity within and across these vulnerable vegetation types. Location: Parts of Mongolia, southeastern Russia, and northern China (94.78°–126.78°E, 34.60°–54.27°N). Methods: Using a random forest model trained by a comprehensively compiled database on vascular plant species richness (i.e., the number of species within a defined plot area) and corresponding climate variables, soil conditions and vegetation types (forest, grassland, desert), we assessed the current pattern of vascular plant species richness across a typical forest–grassland–desert transect in East Asia. We further predicted future changes in vascular plant species richness under three climate scenarios (SSP1‐2.6, SSP3‐7.0, and SSP5‐8.5). Results: Vascular plant species richness generally showed a decrease from northeast to southwest across the transect, mainly explained by spatial variations in growing‐season precipitation and the minimum temperature of the coldest month. More than half of the transect area will likely experience a loss in vascular plant species richness in 2041–2070 under all three scenarios. The decrease in vascular plant species richness will likely occur in a smaller area under the low‐emission scenario (SSP1‐2.6). We also predict distinct changes in vascular plant species richness for different vegetation types, including a slight increase in forests but an overall decrease in both grasslands and deserts. Conclusions: Our findings suggest a dominant role of growing‐season precipitation in shaping the spatiotemporal patterns of vascular plant species richness across the forest–grassland–desert transect and highlight a risk of plant diversity loss in the regional dryland ecosystems in response to future climate change. [ABSTRACT FROM AUTHOR]

Rodents are one of the most abundant and diverse groups of mammals in arid zones. Their population and community dynamics are closely linked to climatic factors and pulses of primary productivity activation. In the future, climatic conditions in arid ecosystems could become more extreme as a consequence of climate change, which could affect the species that inhabit these regions. In this paper, we review the literature on the ecological response of rodents in the world's arid zones, at the population and community levels, to climatological factors (temperature and precipitation), climatic events and the possible impact of climate change. We used the PRISMA protocol to systematically search the literature, and the “vote‐counting” method to count positive, null or negative responses of the rodents. At the population level, rodent density and abundance responded positively to precipitation, while biomass responded negatively and reproduction responded positively to increasing temperature. At the community level, rodent density, biomass and diversity increased after rainfall. El Niño events were positively related to rodent population increases. In contrast, intense storms affected the survival of some species. Rodents with physiological adaptations suited to living in arid areas, for example, the heteromyids, responded positively to precipitation and could suffer fewer negative ecological consequences in the future when exposed to increased temperature and changes in precipitation. [ABSTRACT FROM AUTHOR]

Climate change can affect species' geographical range in several ways, leading to species' geographical range expansion and contraction. Amphibians are the most threatened vertebrate class, and deterioration is due, in part, to the loss of suitable habitat. This taxonomic group is especially sensitive because of their biphasic life cycles (aquatic and terrestrial) and microhabitat requirements. Herein, we propose a combined approach, which uses biological and life history information to understand species' sensitivity to climate change. The goals of our study were to (1) identify the contribution of environmental variables to the broad-scale distribution of amphibians in drylands of the southwestern United States and Mexico, (2) describe how the habitat suitability of amphibians can potentially respond to a range of climate change scenarios across drylands, and (3) identify amphibian traits related to increased vulnerability and adaptation to the specific pressures and mechanisms of climate change projected for the dryland areas. Results show that climate strongly influences the geographic distribution of amphibian diversity in drylands and that most amphibians are expected to lose habitat in the upcoming decades. This study also shows that areas with the greatest loss of high habitat suitability are related to temperature increases and precipitation reductions. Our results build a framework that will significantly improve the current state of knowledge on the drylands' biogeography while providing comprehensive information and analyses for decision-makers to conserve and protect endangered and threatened amphibian species and their habitats.

Ants (Hym., Formicidae) have been recognized as vital components of arid ecosystems. Determining the diversity patterns of ants and the ecological factors behind these patterns is expected to improve our understanding of the functioning of arid ecosystems. Here, we explored patterns of ant species diversity and community composition along an elevational gradient (800 to 2800 m) in the arid area of Central Iran. The elevational gradient in ant diversity and the effects of environmental factors on various indices of ant diversity and species composition were investigated using generalized linear mixed models and variance partitioning analysis. We recorded 34 ant species of 12 genera and 8 tribes from 120 surveyed quadrats. Climate variables were the most important predictors of ant community structure. Indices of ant alpha diversity including Hill numbers and taxonomic diversity increased with elevation. Hill numbers were negatively influenced by temperature, while they were positively affected by precipitation. The observed diversity pattern could be explained by the diversity-productivity hypothesis. In our study area, the maximum primary productivity and consequently the maximum species diversity occurred at high elevations, where precipitation is high and temperature is lower than the extremes that could limit plant productivity. Ant assemblages are expected to become increasingly composed of warm-tolerant species in response to warmer and drier conditions driven by climate change. The distribution of species with lower heat tolerance will be limited to high-elevation areas in Central Iran. These areas could act as refuges for ants and should be considered priorities for conservation. [ABSTRACT FROM AUTHOR]

Background: Understanding coupled human-environment factors which promote Aedes aegypti abundance is critical to preventing the spread of Zika, chikungunya, yellow fever and dengue viruses. High temperatures and aridity theoretically make arid lands inhospitable for Ae. aegypti mosquitoes, yet their populations are well established in many desert cities. Methods: We investigated associations between socioeconomic and built environment factors and Ae. aegypti abundance in Maricopa County, Arizona, home to Phoenix metropolitan area. Maricopa County Environmental Services conducts weekly mosquito surveillance with CO2-baited Encephalitis Vector Survey or BG-Sentinel traps at > 850 locations throughout the county. Counts of adult female Ae. aegypti from 2014 to 2017 were joined with US Census data, precipitation and temperature data, and 2015 land cover from high-resolution (1 m) aerial images from the National Agricultural Imagery Program. Results: From 139,729 trap-nights, 107,116 Ae. aegypti females were captured. Counts were significantly positively associated with higher socioeconomic status. This association was partially explained by higher densities of non-native landscaping in wealthier neighborhoods; a 1% increase in the density of tree cover around the trap was associated with a ~ 7% higher count of Ae. aegypti (95% CI: 6–9%). Conclusions: Many models predict that climate change will drive aridification in some heavily populated regions, including those where Ae. aegypti are widespread. City climate change adaptation plans often include green spaces and vegetation cover to increase resilience to extreme heat, but these may unintentionally create hospitable microclimates for Ae. aegypti. This possible outcome should be addressed to reduce the potential for outbreaks of Aedes-borne diseases in desert cities. [ABSTRACT FROM AUTHOR]

In the context of global climate change, changes in precipitation patterns will have profound effects on desert plants, particularly on shallow-rooted plants, such as ephemeral plants. Therefore, we conducted an experiment on artificial control of precipitation for four dominant ephemeral plants, Erodium oxyrhinchum, Alyssum linifolium, Malcolmia scorpioides, and Hyalea pulchella, in the southern edge of Gurbantunggut Desert. We measured the importance value and some growth parameters of the four species under increased or decreased precipitation and constructed trait correlation networks for each of the four species. We also compared the response of increased or decreased precipitation to vegetation coverage. The results show that drought significantly reduced the survival rate, seed production and weight, and aboveground biomass accumulation of ephemeral plants. The four ephemeral plants showed different tolerance and response strategies to precipitation changes. E. oxyrhinchum and M. scorpioides can avoid drought by accelerating life history, and E. oxyrhinchum, A. linifolium, and H. pulchella can alleviate the negative effects of drought by adjusting leaf traits. However, the response of different species to the wet treatment was not consistent. Based on the results of the trait correlation network, we consider A. linifolium belongs to the ruderal plant, E. oxyrhinchum and M. scorpioides belong to the competitive plants, and H. pulchella belongs to the stress-tolerant plant. The outstanding trait coordination ability of E. oxyrhinchum makes it show absolute dominance in the community. This indicate that ephemeral plants can adapt to precipitation changes to a certain extent, and that distinct competitive advantages in growth or reproduction enabled species coexistence in the same ecological niche. Nevertheless, drought significantly reduces their community cover and the ecological value of ephemeral plants. These findings established the basis to predict vegetation dynamics in arid areas under precipitation changes. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change and ecosystem disturbances can detrimentally affect habitats and species. Areas with concentrated biodiversity, such as aridland riparian zones, often yield the greatest number of vulnerable species. A better understanding of ecological and environmental relationships can guide more effective conservation strategies. We used both visual transects and external (tape) radio telemetry to study the behavioral and spatial ecology of black-necked gartersnakes (Thamnophis cyrtopsis; n = 81)--a dietary generalist yet aquatic habitat specialist--in a heterogenous aridland riparian zone of lower Sabino Canyon, Tucson, Arizona, between 2018 and 2021. Our objectives were to (1) understand how extrinsic conditions influence population ecology dynamics, including immediately prior to and after major disturbances and environmental extremes; (2) analyze behavioral activity and microhabitat usage in relation to environmental factors; and (3) assess the efficacy of a less-invasive telemetry strategy. Between late spring 2020 and early summer 2021, ecosystem disturbances included near-record heat and drought, wildfire, and low overwinter precipitation. Many aquatic habitats either completely dried or were spatially disjunct; gartersnake prey species were noticeably sparse. Extreme drought rapidly shifted to excessive flooding during the 2021 monsoon that brought above-average streamflow magnitude and duration. Between 2019 and 2021, we observed a dramatic decline in T. cyrtopsis; odds of detection reduced by 92.8% (CI [56.0-99.1%]). Strong spatiotemporal links relative to the extent and timing of available surface water appear important. Prior to the onset of monsoonal stream recharge in early summer, shallow and drying aquatic habitats are used as parturition sites and foraging grounds; all age classes took advantage to corral fishes trapped in isolated and shrinking pools. Ambient conditions had varying effects on gartersnake behaviors. Variation in microhabitat assemblages occurred with distance from water, activity level, and developmental age class. Interestingly, associations remained consistent across seasons and years, which suggests a reliance on heterogenous habitat structure. Sampling techniques complemented each other, however, bioclimatic parameters rendered limitations and should be considered in methodological decisions. Overall, disadvantageous responses to major disturbances and climatic extremes by a presumably adaptable generalist like T. cyrtopsis are concerning. Insights from long-term monitoring of responses by common yet environmentally sensitive species such as T. cyrtopsis may serve to more broadly highlight demographic challenges that other taxa with similar semi-aquatic life histories may face in changing systems. Such information could inform more effective conservation management strategies in warming and drying ecosystems. [ABSTRACT FROM AUTHOR]

In recent history, built environment practices have accepted a paradigm which underlines the land's static quality, prioritizes immediate utility, and consequently adopts design processes that inevitably accelerate assimilation. With the capitalist propensity to obtain control and enhance efficiency, those processes nevertheless privilege certain cultures while rejecting other forms of knowledge or living specific to the land. The design discourse, confronted with the rising pressure of global climate challenges and environmental inequity, suggests a shift of design pattern from static to responsive as a means to an end that is part of nature's transformation. Located amid the semi-arid playa of Nevada in the USA, Fly Ranch sits on land remote yet crisscrossed by industrial activity, with extreme climatic conditions yet teeming with life and traditions. Working with these contradictions, "Lodgers," the project to be constructed in Fly Ranch, is grounded in three key approaches to challenging contemporary architectural practice. Firstly, prioritize the well-being of all plants and animals species, including humans, by creating cohabitation spaces. Secondly, utilize local or nearby building resources to minimize waste, maintain ecological balance, and rebuild the material cycle. Finally, integrate Traditional Ecological Knowledge with modern building practices and employ low-tech construction techniques to encourage community participation. As a pilot project goes into construction, the authors offer critical reflection on contemporary architecture practice, the design process, and the meaning of "unbuilding" as a response to climate challenge. [ABSTRACT FROM AUTHOR]

Intermittent and ephemeral streams in dryland environments support diverse assemblages of aquatic and terrestrial life. Understanding when and where water flows provide insights into the availability of water, its response to external controlling factors, and potential sensitivity to climate change and a host of human activities. Knowledge regarding the timing of drying/wetting cycles can also be useful to map critical habitats for species and ecosystems that rely on these temporary water sources. However, identifying the locations and monitoring the timing of streamflow and channel sediment moisture remains a challenging endeavor. In this paper, we analyzed daily conductivity from 37 sensors distributed along 10 streams across an arid mountain front in Arizona (United States) to assess spatiotemporal patterns in flow permanence, defined as the timing and extent of water in streams. Conductivity sensors provide information on surface flow and sediment moisture, supporting a stream classification based on seasonal flow dynamics. Our results provide insight into flow responses to seasonal rainfall, highlighting stream reaches very reactive to rainfall versus those demonstrating more stable streamflow. The strength of stream responses to precipitation are explored in the context of surficial geology. In summary, conductivity data can be used to map potential stream habitat for water‐dependent species in both space and time, while also providing the basis upon which sensitivity to ongoing climate change can be evaluated. [ABSTRACT FROM AUTHOR]

Tenebrionids represent a conspicuous component of the fauna of Mediterranean coastal dunes showing particular adaptations to the extreme climatic conditions of these environments (high temperature and aridity). These adaptations involve, for example, distinct morphological traits (such as long legs and subelytral cavity), finely tuned life cycles, ecological specialization, and diel and seasonal activity patterns that vary in response to temperature changes. Although these species are able to cope with high temperature and water scarcity, the ongoing climatic change may represent a serious threat. Increases in average temperatures and in frequency and severity of extreme events may affect profoundly species that already live close to their upper climatic tolerance limits. Tenebrionids in Mediterranean sand dunes are also flightless: although flightlessness is advantageous in this type of environment, it reduces substantially dispersal capabilities, and hence the possibility of tracking suitable climatic conditions. In fact, because of their adaptations to sand substrates and the limited extension of sandy shores, these animals are strictly confined to environments that are experiencing a dramatically fast increase in average temperature with no possibility to escape. [ABSTRACT FROM AUTHOR]

This paper reports on the most ancient unusual morphological trait of the apertures of Poaceae pollen found in archaeological layers. In Poaceae, high levels of hybridization, polyploidy, apomixis, and multiporate pollen are often related. Multiple genomes in polyploids are critical for the adaptation of plant species to stresses and could be revealed by anomalies in pollen development. Therefore, the paleoenvironmental research can gain great benefits from identifying polyploids in past contexts by observing anomalous pollen morphology during pollen counts. The occurrence of multiporate pollen in Poaceae has also been related to special features of the ecology of the species showing this anomaly, as well as to climatic and environmental stresses experienced by Poaceae living in a given region. Multiporate and bi- or tri-porate instead of monoporate pollen grains have been observed in samples taken from Takarkori rockshelter, an archaeological site in southwestern Libya (central Sahara) that has been occupied between ~10,200 and ~4650 cal BP. Multiporate pollen was found in organic sands and coprolites of ovicaprines. On the basis of archaeobotanical research, this work aims to investigate whether the presence of supernumerary pores in Poaceae pollen may be an effect of both climatic/hydrological changes and continued anthropogenic pressure on the wild grasses living in the region. The presence of multiporate pollen reveals that Poaceae that lived in central Sahara tackled several kinds of stress during the early and middle Holocene. The Takarkori pollen record suggests that climate change could have played a major role in the early Holocene, while human pressure became stronger during the middle Holocene. The change in environmental conditions determined adaptive responses of polyploid grasses even in the form of multiporate pollen. [ABSTRACT FROM AUTHOR]

As an Indigenous community of Algeria and the broader Sahel, the Tuareg hold unique ecological knowledge, which might contribute to broader models of place‐based climate change impacts. Between January and April 2019, we carried out semi‐structured interviews (N = 23) and focus group discussions (N = 3) in five villages of the province of Illizi, Algeria, to document the local Tuareg community's timeline and ecological calendar, both of which are instruments used to understand place‐based reports of climate change impacts. The livelihoods of the Tuareg of Illizi are finely tuned to climate variability as reflected in changes reported in the cadence of events in their ecological calendar (marked by cyclical climatic and religious events). Participants reported rain and temperature irregularities and severe drought events, which have impacted their pastoral and semi‐pastoral livelihoods. These reports are aligned with scientifically measured climate observations and predictions. Paradoxically, although participants recall with detail the climatic disasters that happened in the region over the last century, the Tuareg do not explicitly report decadal trends in the frequency of extreme events. The differential perception of climate change impacts across scales can have important implications for undertaking climate change adaptation measures. Plain Language Summary: Climate change impacts are perceived by communities across the world. The Tuareg of Illizi (Algeria) have animal rearing livelihoods relying on local resources and have deep knowledge of the desert environment and its climatic conditions. Here, we discuss that Tuareg communities perceive a diversity climate change impacts (on climate, vegetation, and fauna) affecting yearly cyclical activities, but they do not explicitly recognize climate change trends happening over decades. This may hamper adaptation as these trends are predicted to continue or even worsen in the future. Key Points: The Tuareg of Illizi (Algeria) report on multiple climate change impacts including temperature irregularities and severe drought eventsThese reports are aligned with scientifically omeasured climate observations and predictionsThe Turaeg do not explicitly report on decadal trends, which has implications for their ability to adapt to such changes [ABSTRACT FROM AUTHOR]

Global deserts occupy one-third of the Earth's surface and contribute significantly to organic carbon storage, a process at risk in dryland ecosystems that are highly vulnerable to climate-driven ecosystem degradation. The forces controlling desert ecosystem degradation rates are poorly understood, particularly with respect to the relevance of the arid-soil microbiome. Here we document correlations between increasing aridity and soil bacterial and archaeal microbiome composition along arid to hyperarid transects traversing the Atacama Desert, Chile. A meta-analysis reveals that Atacama soil microbiomes exhibit a gradient in composition, are distinct from a broad cross-section of nondesert soils, and yet are similar to three deserts from different continents. Community richness and diversity were significantly positively correlated with soil relative humidity (SoilRH). Phylogenetic composition was strongly correlated with SoilRH, temperature, and electrical conductivity. The strongest and most significant correlations between SoilRH and phylum relative abundance were observed for Acidobacteria, Proteobacteria, Planctomycetes, Verrucomicrobia, and Euryarchaeota (Spearman's rank correlation [rs] = >0.81; false-discovery rate [q] = ≤0.005), characterized by 10- to 300-fold decreases in the relative abundance of each taxon. In addition, network analysis revealed a deterioration in the density of significant associations between taxa along the arid to hyperarid gradient, a pattern that may compromise the resilience of hyperarid communities because they lack properties associated with communities that are more integrated. In summary, results suggest that arid-soil microbiome stability is sensitive to aridity as demonstrated by decreased community connectivity associated with the transition from the arid class to the hyperarid class and the significant correlations observed between soilRH and both diversity and the relative abundances of key microbial phyla typically dominant in global soils. IMPORTANCE We identify key environmental and geochemical factors that shape the arid soil microbiome along aridity and vegetation gradients spanning over 300 km of the Atacama Desert, Chile. Decreasing average soil relative humidity and increasing temperature explain significant reductions in the diversity and connectivity of these desert soil microbial communities and lead to significant reductions in the abundance of key taxa typically associated with fertile soils. This finding is important because it suggests that predicted climate change-driven increases in aridity may compromise the capacity of the arid-soil microbiome to sustain necessary nutrient cycling and carbon sequestration functions as well as vegetative cover in desert ecosystems, which comprise one-third of the terrestrial biomes on Earth.

AbstractThe Pacific coastal Peruvian landscapes are dominated by desert and dry-forest biomes, which have undergone shifts in extent and floral composition in response to Plio–Pleistocene climatic fluctuations. Within this context, the coastal Lomas develop as seasonal vegetation patches, renowned for their high endemism, rich floral diversity, and essential ecosystem services. Despite growing within the desert biome, the Lomas exhibit characteristic elements and vegetation structure typical of a dry-forest biome, evidencing an active species migration between xeric biomes. However, assessing the historical evolution of this arid flora and, by extension, the coastal desert landscape, presents challenges. The scarcity of continental sedimentary records and a lack of extended and well-described palynological references impede these efforts. In response to this, our study offers a thorough morphological review of the Lomas palynoflora, encompassing over 194 genera from 76 families, representing approximately 80% of the known Lomas flora. Our review includes at least one species per reviewed genus, featuring 37 palynomorphs from endemic species (18.5% of the studied flora). This palynological characterization is intended to serve as accessible reference material for investigating the historical and long-term evolution of the coastal dry flora. Furthermore, these findings facilitate the analysis of honeys and bee floral foraging patterns, as well as the study of animal–plant or human–plant interactions from middens and archaeological remains. [ABSTRACT FROM AUTHOR]

The Asian summer monsoon (ASM) margin of northwest China is a critical region for studying Asian monsoon variability during the Holocene. However, the pattern of precipitation variations and migration of the ASM northern boundary in arid regions during the Holocene remains unclear. In this study, we analyzed oxygen isotopes of 70 calcareous root tube (CRT) samples from the desert hinterlands in the ASM margin of northwest China, including the Badain Jaran, Tengger, Ulan Buh, and Kubuqi deserts. The CRT samples were analyzed to reconstruct millennial‐scale precipitation variation patterns during the Holocene and further explored the location of the ASM northwestern boundary during the middle Holocene. Our results demonstrated that the δ18O values of CRTs during the late Holocene (4.0–1.0 cal kyr BP) were all less negative than those during the middle Holocene (8.0–4.0 cal kyr BP), which revealed that the precipitation decreased from the middle Holocene to the late Holocene. Moreover, an increase in δ18O values from the southeast to northwest revealed that the precipitation decreased. We argued that the Holocene millennial‐scale precipitation changes in this region were influenced by the migrations in the ASM northern boundary. During the middle Holocene, due to the strong summer solar radiation and reduced ice sheets, the ASM northern boundary in the arid region advanced by at least 250 km to the northwest, which resulted in increased precipitation. During the late Holocene, the ASM northern boundary retreated southeastward, resulting in decreased precipitation. Plain Language Summary: The pattern of precipitation variations remains controversial in the Asian summer monsoon (ASM) margin of northwest China. Especially in the desert hinterlands, sedimentary records are scarce. Therefore, it is difficult to accurately determine the spatial distribution of precipitation in the ASM margin of northwest China, and further discuss the migration in the ASM northern boundary during the Holocene. In this study, we attempt to analyze the oxygen isotopes of pedogenic carbonates within calcareous root tube (CRT) samples from deserts in this region to reconstruct the millennial‐scale precipitation variations during the Holocene. Our results showed that precipitation decreased from the middle Holocene (8.0–4.0 cal kyr BP) to the late Holocene (4.0–1.0 cal kyr BP) and decreased from southeast to northwest in this region. Moreover, precipitation was influenced by migrations in the ASM northern boundary in the ASM margin of northwest China. During the middle Holocene, due to strong summer solar radiation and reduced ice sheets, the ASM northern boundary in the arid region advanced by at least 250 km to the northwest, which resulted in an increase of precipitation in this region. During the late Holocene, the ASM northern boundary retreated southeastward, resulting in decreased precipitation. Key Points: Holocene millennial‐scale precipitation variations of deserts in the Asian summer monsoon margin of northwest China were reconstructedPrecipitation decreased from the middle Holocene to the late Holocene and accompanied by decreasing from southeast to northwestDuring the middle Holocene, the Asian summer monsoon northern boundary in the arid region advanced by at least 250 km to the northwest [ABSTRACT FROM AUTHOR]

Globally, the impacts of anthropogenic climate change can displace species into more favourable climates. Semi‐arid desert specialists, such as the sandhill dunnart, Sminthopsis psammophila, are typically susceptible to rainfall deficits, wildfires and extreme temperatures caused by anthropogenic climate change. We first used maximum entropy (MaxEnt) species distribution models (SDMs) to predict the current distribution of S. psammophila. Between 2016 and 2018, we ground validated the model's predictions throughout Western Australia, confirming S. psammophila in 18 locations in which it was predicted to occur. The predicted distribution of S. psammophila appears mostly constrained to within its known range. However, S. psammophila was verified 150 km north of its range in Western Australia and connectivity between the South Australian populations was correctly predicted. In 2019, we used updated occurrence data to project SDMs for S. psammophila during the mid‐Holocene, present day and under two future representative concentration pathways (RCPs) of RCP 4.5 (an optimistic emissions scenario) and RCP 8.5 ("business as usual") for 2050 and 2070. By 2050 (RCP 8.5), almost all Western Australian Great Victoria Desert (WAGVD) habitat is predicted to be unsuitable for S. psammophila. By 2070 (RCP 8.5), the climates of the WAGVD and Yellabinna Regional Reserve populations are predicted to become unsuitable, and the species' geographical range is predicted to contract in Australia by 80%. However, the 2070 (RCP 4.5) scenario predicts that this contraction could be halved. As a sandy desert specialist, the distribution of S. psammophila is geographically limited at its southern bounds due to the cessation of suitable spinifex (Triodia spp.) habitats, and so further extension of the range southwards is not possible. Sympatric desert species may be similarly affected, and we suggest that SDMs will be a useful tool in helping to predict the effects of climate change on their distributions. [ABSTRACT FROM AUTHOR]

This paper reports on the most ancient unusual morphological trait of the apertures of Poaceae pollen found in archaeological layers. In Poaceae, high levels of hybridization, polyploidy, apomixis, and multiporate pollen are often related. Multiple genomes in polyploids are critical for the adaptation of plant species to stresses and could be revealed by anomalies in pollen development. Therefore, the paleoenvironmental research can gain great benefits from identifying polyploids in past contexts by observing anomalous pollen morphology during pollen counts. The occurrence of multiporate pollen in Poaceae has also been related to special features of the ecology of the species showing this anomaly, as well as to climatic and environmental stresses experienced by Poaceae living in a given region. Multiporate and bi- or tri-porate instead of monoporate pollen grains have been observed in samples taken from Takarkori rockshelter, an archaeological site in southwestern Libya (central Sahara) that has been occupied between ~10,200 and ~4650 cal BP. Multiporate pollen was found in organic sands and coprolites of ovicaprines. On the basis of archaeobotanical research, this work aims to investigate whether the presence of supernumerary pores in Poaceae pollen may be an effect of both climatic/hydrological changes and continued anthropogenic pressure on the wild grasses living in the region. The presence of multiporate pollen reveals that Poaceae that lived in central Sahara tackled several kinds of stress during the early and middle Holocene. The Takarkori pollen record suggests that climate change could have played a major role in the early Holocene, while human pressure became stronger during the middle Holocene. The change in environmental conditions determined adaptive responses of polyploid grasses even in the form of multiporate pollen.

Understanding the causes of spread of overabundant species plays a key role in deciphering their invasion mechanisms, while providing managers with targeted management actions to control their spread. The objective of this research was to quantify the spread of Hooded Crow (Corvus cornix) in Israel and to elucidate the causes of its spread. Long-term occurrence data of Hooded Crow sightings were used to analyze the species range expansion rate. This dataset was analyzed with a range of climatic, normalized difference vegetation index (NDVI), and land-use variables. Analysis of opportunistic presence-only data, corrected for possible sampling biases, illustrated traveling waves of eastward expansion, from the Mediterranean coast into Israel's central mountain range, and a star-like pattern of spread southward into the northwestern Negev desert. A diffusion equation model revealed an expansion rate of 1.60 km year-1. Land-use analysis revealed an affinity of sighted individuals toward urban and low vegetation land types. Hooded Crow sightings were positively correlated with annual precipitation, with the remaining variation being negatively correlated with precipitation during the wettest quarter. Species distribution modeling suggested that the species has established new populations and is currently expanding its range. The slow rate of dispersal is consistent with a neighborhood diffusion pattern, corresponding to the species life-history traits. Human-managed environments, including low-cover agricultural fields, provide constant available food and nesting trees, allowing the Hooded Crow to thrive all year-round. Precipitation may aid in enhancing Hooded Crow tolerance toward other unfavorable physical conditions. In light of these new findings, management plans ought to recognize centers of Hooded Crow activity as indicators of highly disturbed native wildlife communities. Also, our findings emphasize the need to establish agri-environmental schemes (AES) in such areas, which would raise community resistance to overabundant species. As AES are currently not in place on a national scale, and since their creation has the power to improve landscape connectivity of native species, this last component is especially necessary. [ABSTRACT FROM AUTHOR]

Environmental temperatures are increasing worldwide, threatening desert ectotherms already living at their thermal limits. Organisms with flexible thermoregulatory behaviours may be able to mitigate the effects of extreme temperatures by moving among microhabitats, yet little work has tracked movement patterns of desert ectotherms in the wild over diurnal scales or compared behaviour among seasons. Here, we used camera traps to track the thermoregulatory behaviour and microhabitat choices of 30 desert lizards (Messalina bahaldini) in custom, outdoor arenas that provided access to open, rock, and bush microhabitats. We found that in the summer, lizards preferred to move to the shaded microhabitats and remain there under warmer conditions. During winter, however, lizards' activity was not related to temperature, and lizards mostly chose to remain in the open habitat. Interestingly, in both seasons, lizards tended to remain in their current microhabitat and moved infrequently between certain combinations of microhabitats. Our study shows that thermoregulation (shade-seeking behaviour) is a major factor during summer, helping lizards to avoid extreme temperatures, but not during winter, and shows a novel effect of current microhabitat on movement, suggesting that other biotic or abiotic factors may also drive microhabitat choice. Understanding the complex factors at play in microhabitat choice is critical for developing conservation programs that effectively mitigate the negative impacts of climate change on desert animals. • We tracked desert lizards in semi-natural arenas using camera traps. • Lizards mailny stayed in their initial microhabitats, suggesting high movement costs. • In winter, lizards preferred open habitats, unaffected by temperature. • In summer, lizards sought and stayed in shade as temperatures rose. • Movement costs and microclimate conditions significantly influence lizard behavior. [ABSTRACT FROM AUTHOR]

The adaptation of crops to saline stress conditions generated by changes in rainfall and the current production systems is essential for maintaining many of them and minimizing possible damage or reductions in their productivity. The use of microorganisms to improve the conditions of plants from extreme environments, increasing their resilience, appears to be a possible alternative. In this work, we isolated strains from samples obtained in extreme environments, such as the Atacama Desert and Sahara Desert, and evaluated their capacity to promote the growth of plants directly and under stress conditions. We studied their ability to grow under salinity, and we selected some of these strains for their capacity to improve plant resilience.

The spatio-temporal characteristics and driving mechanisms of the Asian summer monsoon (ASM) during the early and middle Holocene remain unclear. Moreover, the timing of maximum monsoon precipitation in the Asian monsoon margin of northwest China during this period is also a subject of considerable debate. Herein, we analyzed phytolith assemblages within 55 calcareous root tube (CRT) samples from the hinterland of the Tengger Desert to quantitatively reconstruct Holocene millennial-scale precipitation changes and discuss the potential forcing mechanisms. Our results revealed that the mean annual precipitation (MAP) was 138 ± 53 to 149 ± 18 mm during 10.0–7.0 cal kyr BP, 179 ± 26 to 192 ± 26 mm during 7.0–5.0 cal kyr BP, and 129 ± 20 to 161 ± 13 mm during 5.0–1.0 cal kyr BP. The quantitative reconstruction results suggested that precipitation in this area was low in the early Holocene, then increased to a maximum in the middle Holocene (30% higher precipitation than present), and gradually decreased in the late Holocene. Maximum monsoon precipitation did not occur until the middle Holocene in this area because the northernmost margin of the ASM reached its northernmost latitude lagging behind its maximum monsoon intensity suppressed by high-northern latitude ice volume forcing during the early Holocene despite high summer insolation. In addition to quantifying the Holocene millennial-scale precipitation changes in the northwestern margin of the ASM, this study also provides new evidence for spatial and temporal variations of the ASM during the Holocene. [ABSTRACT FROM AUTHOR]

Over the past decade, a growing interest has developed on the archaeology, palaeontology, and palaeoenvironments of the Arabian Peninsula. It is now clear that hominins repeatedly dispersed into Arabia, notably during pluvial interglacial periods when much of the peninsula was characterised by a semiarid grassland environment. During the intervening glacial phases, however, grasslands were replaced with arid and hyperarid deserts. These millennial-scale climatic fluctuations have subjected bones and fossils to a dramatic suite of environmental conditions, affecting their fossilisation and preservation. Yet, as relatively few palaeontological assemblages have been reported from the Pleistocene of Arabia, our understanding of the preservational pathways that skeletal elements can take in these types of environments is lacking. Here, we report the first widespread taxonomic and taphonomic assessment of Arabian fossil deposits. Novel fossil fauna are described and overall the fauna are consistent with a well-watered semiarid grassland environment. Likewise, the taphonomic results suggest that bones were deposited under more humid conditions than present in the region today. However, fossils often exhibit significant attrition, obscuring and fragmenting most finds. These are likely tied to wind abrasion, insolation, and salt weathering following fossilisation and exhumation, processes particularly prevalent in desert environments. [ABSTRACT FROM AUTHOR]

The soil sink of molecular hydrogen is the largest and most uncertain term in the global atmospheric H2 budget. Lack of information about the mechanisms regulating this sink limits our ability to predict how atmospheric H2 may respond to future changes in climate or anthropogenic emissions. Here we present the results from a series of laboratory experiments designed to systematically evaluate and describe the temperature and soil moisture dependence of H2 uptake by soils from boreal forest and desert ecosystems. We observed substantial H2 uptake between −4°C and 0°C, a broad temperature optimum between 20°C and 30°C, a soil moisture optimum at approximately 20% saturation, and inhibition of uptake at both low and high soil moisture. A sigmoidal function described the temperature response of H2 uptake by soils between −15°C and 40°C. Based on our results, we present a framework for a model of the soil H2 sink.

Oasification is a complex oasis expansion and ecological processes caused by climate changes and human activities under available water supply in arid and semiarid regions. The process can effectively improve soil productivity, vegetation cover, and biomass production in fighting against land degradation, such as desertification and soil erosion. However, the significance of oasification has not yet reached the general cognition compared to desertification, which is regarded as one of the most severe global eco-environmental issues. This paper identifies desertification and oasification processes and their perspectives in cognition. The implication of oasification in combating desertification and controlling land degradation is emphasized by the justification between desertification and oasification processes. As opposite process of desertification, the oasification is an unable evasive process that can provide positive environmental effects in the control of desertification, ecological restoration, and land rehabilitation. According to the interaction of climatic variations and human activities, the oasification processes is classified into six main forms: natural oasis evolution process, engineering forest construction, conversion of natural landforms into farmlands, urban encroachment, constructed environments, and coupled ecosystems. These processes gradually modify the productive capacity of soils, increase vegetation cover for restoring degraded lands, and improve the living environment for human settlement and sustainability of an oasis ecosystem. Moreover, an overview of oasification research is detailed, and Northwest China as an example is used to illustrate the progress of the oasification research in recent decades. Currently, the oasification process and its mechanistic research still remain less concern in the arid and semiarid regions. A new science framework of the oasification research is proposed to effectively deal with ecological and environmental issues in the arid and semiarid regions. • Desertification and oasification and their perspectives are identified. • Implication of oasification is emphasized in comparison with desertification. • Oasification processes are classified into six main forms. • Overview of oasification research is detailed and illustrated in Northwest China. • A new science framework of the oasification research is proposed. [ABSTRACT FROM AUTHOR]

Premise of Study: Mechanisms by which invasive species succeed across multiple novel environmental contexts are poorly understood. Functional traits show promise for identifying such mechanisms, yet we lack knowledge of which functional traits are critical for success and how they vary across invaded ranges and with environmental features. We evaluated the widespread recent invasion of Sahara mustard (Brassica tournefortii) in the southwestern United States to understand the extent of functional trait variation across the invaded range and how such variation is related to spatial and climatic gradients. Methods: We used a common garden approach, growing two generations of plants in controlled conditions sourced from 10 locations across the invaded range. We measured variation within and among populations in phenological, morphological, and physiological traits, as well as performance. Key Results: We found nine key traits that varied among populations. These traits were related to phenology and early growth strategies, such as the timing of germination and flowering, as well as relative allocation of biomass to reproduction and individual seed mass. Trait variation was related most strongly to variation in winter precipitation patterns across localities, though variations in temperature and latitude also had significant contributions. Conclusions: Our results identify key functional traits of this invasive species that showed significant variation among introduced populations across a broad geographic and climatic range. Further, trait variation among populations was strongly related to key climatic variables, which suggests that population divergence in these traits may explain the successful colonization of Sahara mustard across its invaded US range. [ABSTRACT FROM AUTHOR]

Abstract: Questions: Is there evidence of recent altitudinal range shifts in a hyper‐arid Middle Eastern desert mountain flora? How do the directions of shift for upper and lower altitudinal range limits of plants vary? Location: Hyper‐arid mountain desert, St Katherine Protectorate, South Sinai, Egypt. Method: We tested for shifts in both upper and lower altitudinal range limits by comparing a 1970s data set of recorded species’ limits with recent surveys using altitudinal transects across 36 sites. Altitudinal limits between 63 paired upper‐limit and 22 paired lower‐limit values from the 1970s and 2014 were compared using paired t‐tests; binomial tests were used to indicate the dominant direction of change. The upper and lower limits of 22 species were considered together to allow assessment of overall altitudinal range size changes. In order to avoid the potential effect of yearly environmental fluctuations on the distributions of annual species, subsets of upper and lower limit shifts were taken for perennials, and for trees and shrubs. Results: Our results show significant overall up‐slope shifts in mean upper altitudinal limits and significant overall down‐slope shifts in mean lower altitudinal limits. A majority of assessed species expanded their altitudinal ranges, but the responses of individual species varied. Conclusions: Since perennial herbs/graminoids, as well as trees and shrubs, show strong patterns of change, we suggest there has been a long‐term shift in altitudinal range in South Sinai's mountain flora. More research effort needs to be focussed on the drivers of range shift responses in arid regions. [ABSTRACT FROM AUTHOR]

ABSTRACT Global deserts occupy one-third of the Earth’s surface and contribute significantly to organic carbon storage, a process at risk in dryland ecosystems that are highly vulnerable to climate-driven ecosystem degradation. The forces controlling desert ecosystem degradation rates are poorly understood, particularly with respect to the relevance of the arid-soil microbiome. Here we document correlations between increasing aridity and soil bacterial and archaeal microbiome composition along arid to hyperarid transects traversing the Atacama Desert, Chile. A meta-analysis reveals that Atacama soil microbiomes exhibit a gradient in composition, are distinct from a broad cross-section of nondesert soils, and yet are similar to three deserts from different continents. Community richness and diversity were significantly positively correlated with soil relative humidity (SoilRH). Phylogenetic composition was strongly correlated with SoilRH, temperature, and electrical conductivity. The strongest and most significant correlations between SoilRH and phylum relative abundance were observed for Acidobacteria, Proteobacteria, Planctomycetes, Verrucomicrobia, and Euryarchaeota (Spearman’s rank correlation [rs] = >0.81; false-discovery rate [q] = ≤0.005), characterized by 10- to 300-fold decreases in the relative abundance of each taxon. In addition, network analysis revealed a deterioration in the density of significant associations between taxa along the arid to hyperarid gradient, a pattern that may compromise the resilience of hyperarid communities because they lack properties associated with communities that are more integrated. In summary, results suggest that arid-soil microbiome stability is sensitive to aridity as demonstrated by decreased community connectivity associated with the transition from the arid class to the hyperarid class and the significant correlations observed between soilRH and both diversity and the relative abundances of key microbial phyla typically dominant in global soils. IMPORTANCE We identify key environmental and geochemical factors that shape the arid soil microbiome along aridity and vegetation gradients spanning over 300 km of the Atacama Desert, Chile. Decreasing average soil relative humidity and increasing temperature explain significant reductions in the diversity and connectivity of these desert soil microbial communities and lead to significant reductions in the abundance of key taxa typically associated with fertile soils. This finding is important because it suggests that predicted climate change-driven increases in aridity may compromise the capacity of the arid-soil microbiome to sustain necessary nutrient cycling and carbon sequestration functions as well as vegetative cover in desert ecosystems, which comprise one-third of the terrestrial biomes on Earth.

We assessed the effects of temperature differences on gene expression using whole-transcriptome microarrays and cuticular hydrocarbon variation in populations of cactophilic Drosophila mojavensis. Four populations from Baja California and mainland Mexico and Arizona were each reared on two different host cacti, reared to sexual maturity on laboratory media, and adults were exposed for 12 hr to 15, 25, or 35°C. Temperature differences influenced the expression of 3,294 genes, while population differences and host plants affected >2,400 each in adult flies. Enriched, functionally related groups of genes whose expression changed at high temperatures included heat response genes, as well as genes affecting chromatin structure. Gene expression differences between mainland and peninsular populations included genes involved in metabolism of secondary compounds, mitochondrial activity, and tRNA synthases. Flies reared on the ancestral host plant, pitaya agria cactus, showed upregulation of genes involved in metabolism, while flies reared on organ pipe cactus had higher expression of DNA repair and chromatin remodeling genes. Population × environment (G × E) interactions had widespread effects on the transcriptome where population × temperature interactions affected the expression of >5,000 orthologs, and there were >4,000 orthologs that showed temperature × host plant interactions. Adults exposed to 35°C had lower amounts of most cuticular hydrocarbons than those exposed to 15 or 25°C, including abundant unsaturated alkadienes. For insects adapted to different host plants and climatic regimes, our results suggest that temperature shifts associated with climate change have large and significant effects on transcriptomes of genetically differentiated natural populations. [ABSTRACT FROM AUTHOR]

The soil seed bank is a major component of plant communities. However, long-term analyses of the dynamics of the seed bank and the ensuing vegetation are rare. Here, we studied the dynamics in plant communities with high dominance of annuals in Mediterranean, semiarid, and arid ecosystems for nine consecutive years. For annuals, we hypothesized that the density of the seed bank would be more stable than the density of the standing herbaceous vegetation. Moreover, we predicted that differences in temporal variability between the seed bank and the vegetation would increase with aridity, where year-to-year rainfall variability is higher. We found that the temporal variability at the population level (assessed as the standard deviation of the log e -transformed density) of the nine dominant annuals in each site did not differ between the seed bank and the ensuing vegetation in any of the sites. For the total density of annuals, patterns depended on aridity. In the Mediterranean site, the temporal variability was similar in the seed bank and the vegetation (0.40 vs. 0.40). Still, in the semiarid and arid sites, variability in the seed bank was lower than in the vegetation (0.49 vs. 1.01 and 0.63 vs. 1.38, respectively). This difference between the population-level patterns and the total density of annuals can be related to the lower population synchrony in their seed bank. In contrast, for the herbaceous perennials (all species combined), the seed bank variability was higher than in the vegetation. Overall, our results highlight the role of the seed bank in buffering the annual vegetation density with increasing climatic uncertainty typical in aridity gradients. This role is crucial under the increasing uncertainty imposed by climatic change in the region. • The ecological theory highlights the role of the seed bank in stabilizing plant communities, but empirical studies are rare. • We investigated patterns of density dynamics in the vegetation and seed bank in three sites along a rainfall gradient. • The total density of annual plants was more stable than the vegetation, and these differences increased with aridity. • For perennial herbs, the vegetation was more stable than the seed bank. • Our results highlight the role of the seed bank in buffering the annual vegetation density with increasing uncertainty. [ABSTRACT FROM AUTHOR]

Woody plant encroachment and overall declines in perennial vegetation in dryland regions can alter ecosystem properties and indicate land degradation, but the causes of these shifts remain controversial. Determining how changes in the abundance and distribution of grass and woody plants are influenced by conditions that regulate water availability at a regional scale provides a baseline to compare how management actions alter the composition of these vegetation types at a more local scale and can be used to predict future shifts under climate change. Using a remote-sensing-based approach, we assessed the balance between grasses and woody plants and how climate and topo-edaphic conditions affected their abundances across the northern Sonoran Desert from 1989 to 2009. Despite widespread woody plant encroachment in this region over the last 150 years, we found that leguminous trees, including mesquite ( Prosopis spp.), declined in cover in areas with prolonged drying conditions during the early 21st century. Creosote bush ( Larrea tridentata) also had moderate decreases with prolonged drying but was buffered from changes on soils with low clay that promote infiltration and high available water capacity that allows for retention of water at depth. Perennial grasses have expanded and contracted over the last two decades in response to summer precipitation and were especially dynamic on shallow soils with high clay that have large fluctuations in water availability. Our results suggest that topo-edaphic properties can amplify or ameliorate climate-induced changes in woody plants and perennial grasses. Understanding these relationships has important implications for ecosystem function under climate change in the southwestern USA and can inform management efforts to regulate grass and woody plant abundances. [ABSTRACT FROM AUTHOR]