In desert environments, infrequent but intense rainfall events drive ephemeral flows that shape the landscape, influence vegetation patterns, and sustain biodiversity. However, despite their ecological and hydrological importance, ephemeral flows are poorly mapped and assessed, hindering effective study, management, and conservation. To address this gap, we developed and validated a high-resolution surface hydrology dataset for the Borrego Springs Subbasin in California, USA, using a 1-m digital elevation model (DEM) and the ArcGIS Hydrology Toolset. The dataset includes detailed outputs illustrating water movement across the landscape, including flow direction, flow accumulation, flow networks, and distance to the nearest flow path for each cell in the subbasin. Validation was conducted using satellite imagery following a significant monsoon rainfall event, which revealed visible water flow and wet soil. Leveraging this dataset, we present a novel framework for examining the relationship between flow proximity and vegetation productivity, using the mean growing season normalized difference vegetation index (NDVI) as a proxy for vegetation productivity and cover. Our findings reveal a strong decrease in NDVI values with increasing distance from flow paths. Dense, highly productive vegetation (NDVI > 0.5) was restricted to areas within 40 m of ephemeral flow paths, while the highest NDVI (NDVI > 0.75) was confined to within 10 m. These findings underscore the central role ephemeral flows play in structuring desert vegetation by generating consistent spatial patterns of productivity at the meter scale. However, we also found that urban development in the central subbasin has significantly disrupted natural flow networks, reducing hydrologic connectivity and altering the distribution of surface water resources. When viewed in the context of finer scale soil moisture dynamics and broader geomorphic processes, these patterns offer insight into the multiscale physical drivers shaping arid landscapes. By validating the dataset and exploring its ecological applications, this study provides essential insights into the ecohydrological interactions that govern arid regions and offers a valuable tool for managing and conserving desert ecosystems.

During community assembly, species' traits interact with environmental conditions and influence biotic interactions. Learning how traits of non-native species enable them to successfully navigate these interacting biotic and abiotic filters informs invasion dynamics. Here we test how plant traits relate to invasion resistance under differing degrees of abiotic stress based on slope aspect in a large restoration project in Southern California. The site was dominated by non-native annual plants but was restored to coastal sage scrub and grassland with mixtures of native shrubs, grasses, and forbs on two different slope aspects. Abiotic filters may be stronger than biotic filters on slopes exposed to greater solar radiation (S-facing at our study site) resulting in decreased soil moisture and increased abiotic stress. We measured subsequent establishment and performance by the three most abundant non-native species (Brassica nigra in year 1, Salsola tragus and Sonchus oleraceus in year 3) on N- and S-facing slopes to investigate relationships between traits, abiotic environment, native community composition, and invasibility in the context of community assembly. We evaluated which measures of community functional diversity best predicted invader performance and tested whether relationships between invader performance and community-weighted trait values varied by slope aspect. Plots with slow-growing native shrubs contained less of the fast-growing invasive, Brassica nigra. Invasibility was greatest in native communities restored with native grass and on N-facing slopes. Correlations among individual species traits indicated strong biotic filtering, but only in certain environments. For instance, the abundance of Phacelia cicutaria, a native annual with traits similar to Brassica nigra, was negatively correlated with that invasive on N-facing slopes. Community-weighted trait metrics were also related to invasibility and differed by slope aspect, though relationships varied based on specific functional trait, community-weighted trait measure (mean or dispersion), and invader. The native functional group most effective at preventing invasion (native shrubs) was different from the species that most prevented invasion (native forb). In restoration planning, functional groups and individual native species traits may be more predictive of invasion resistance than community-weighted trait metrics. Combining perennials with an under-story of fast-growing annuals worked well to prevent invasion by non-native annuals. Understanding the role of lifespan effects in biotic filtering is essential for interpreting complex community-weighted trait responses to environmental variation across space and time.

Ecosystems are experiencing changing global patterns of mean annual precipitation (MAP) and enrichment with multiple nutrients that potentially colimit plant biomass production. In grasslands, mean aboveground plant biomass is closely related to MAP, but how this relationship changes after enrichment with multiple nutrients remains unclear. We hypothesized the global biomass-MAP relationship becomes steeper with an increasing number of added nutrients, with increases in steepness corresponding to the form of interaction among added nutrients and with increased mediation by changes in plant community diversity. We measured aboveground plant biomass production and species diversity in 71 grasslands on six continents representing the global span of grassland MAP, diversity, management, and soils. We fertilized all sites with nitrogen, phosphorus, and potassium with micronutrients in all combinations to identify which nutrients limited biomass at each site. As hypothesized, fertilizing with one, two, or three nutrients progressively steepened the global biomass-MAP relationship. The magnitude of the increase in steepness corresponded to whether sites were not limited by nitrogen or phosphorus, were limited by either one, or were colimited by both in additive, or synergistic forms. Unexpectedly, we found only weak evidence for mediation of biomass-MAP relationships by plant community diversity because relationships of species richness, evenness, and beta diversity to MAP and to biomass were weak or opposing. Site-level properties including baseline biomass production, soils, and management explained little variation in biomass-MAP relationships. These findings reveal multiple nutrient colimitation as a defining feature of the global grassland biomass-MAP relationship.

Humans have facilitated the spread and evolution of invasive species, a pattern that has accelerated with the globalisation of trade and societal development. Consequently, the invasiveness of a species may be determined not only by how many propagules and which genotypes are introduced, but also by its evolutionary history and how humans have interacted with it. Here, we document the population structure and movement of Sahara mustard (Brassica tournefortii) within its native range and its invaded U.S. and Australian ranges. We evaluated 312 individuals spanning 31 sites. We found that Sahara mustard has likely undergone substantial mixing within its native range, with genotypes from Egypt potentially representing a human-created connection between North African, European and West Asian genotypes. Our results suggest Egypt-and perhaps closely related populations in Morocco and France-as the likely origin of invasive U.S. populations. Australian accessions appear most closely related to those from Qatar and may have acted as a bridgehead and potential source of the most-recently introduced U.S. population. Further, agricultural varieties from Pakistan and India represent a mix of genotypes from the western part of the species' native range and the eastern site in Qatar. We also identified evidence of mixing of some accessions of crop wild relatives. Nearly all populations sampled display excess heterozygosity and negative inbreeding coefficients, likely indicative of selection and potential admixture with other cultivated Brassica species. Overall, we reconstructed the probable invasion history of Sahara mustard, inferring significant human-mediated movement of the species within and beyond its native distribution.

The rapidly expanding demand for avocado production places significant strain on agricultural communities and associated ecosystems. As temperature increases and water scarcity worsens, the avocado, a high-water demanding crop, faces declining yields and increased tree mortality. Deforestation, monoculture farming, and pesticide use further threaten interconnected landscapes, reducing biodiversity, degrading soil quality, and devaluing natural capital. Michoacan, Mexico, the largest producer of avocados worldwide, with production expected to reach 9.2 million tonnes per year by 2028, now faces additional pressures to keep up with market demand in a changing climate. To meet such demands, production workers are exposed to high levels of pesticides that are harmful for workers' physical and mental health. In addition to chemical exposures, increasing labor demands pose additional threats for workers who face elevated risks for depression and anxiety. Through semi-structured, in-depth interviews with 3 avocado growers and 1 supervisory personnel, and following principles of a knowledge-action network, we develop recommendations to achieve socio-ecological outcomes within the avocado system that emphasize plant and human health. Here, we draw attention to an urgent need to address these complex environmental and social challenges associated with avocado production. We provide and discuss trade-offs of 4 recommendations emphasizing governance, science, and policy: (1) targeted policy intervention, (2) inclusive and equitable social initiatives, (3) a comprehensive science program, and (4) fostering transparency through open-access data sharing. These measures can strengthen the interconnected agricultural, ecological, and human systems associated with this key crop, improving their capacity to adapt and endure over time.

Removal of non-native plants is known to increase overall native cover within degraded communities that contain at least a small percentage of native plant cover. We investigated the mechanisms behind this pattern, asking whether removal of non-native annual species increases the density and species richness of the native community through increased seedling recruitment or through the growth of established native shrubs. We also investigated whether the effectiveness of non-native removal was influenced by region (coastal versus inland) and whether there was a threshold of native cover required for invasive removal to be effective. We established 13 study sites (7 coastal and 6 inland) located throughout the Nature Reserve of Orange County, CA, USA. Each degraded site contained four paired plots corresponding to a range of existing native plant cover: low 20–29%, medium-low 30–39%, medium-high 40–49%, and high cover 50–59% with one plot per pair subjected to non-native removal. We collected plant density, species richness, and established native shrub volume measurements to clarify the effectiveness of non-native removal. Non-native plant removal reduced non-native annual recruitment, increased that of native shrub seedlings, but had no impact on native forb recruitment. Non-native removal increased the number and reduced mortality of established native shrubs but did not influence shrub size. Native seedling density, species richness, and established native shrub number were highest inland, but coastal sites had larger adult shrubs. We found that non-native removal was most effective for increasing native density and species richness for degraded inland sites with less than 40% of existing native cover. The initial native cover did not affect established shrub volume or number. Our results confirm the importance of non-native plant removal in areas with medium-low or low native cover to increase native recruitment, species richness, adult shrub number, and to reduce established shrub mortality, especially during extreme drought.

The disruptive effects of tertiary species on otherwise positive pairwise species interactions (e.g. context-dependent parasitism in pollinator syndromes) is well-known. However, few-if any-studies have investigated how invasive plants affect interactions between facilitative plants and their native plant communities. Further, if tertiary invasive species can change interactions among native species from positive to negative, then a tertiary native should be capable of the same phenom for pairwise interactions between natives and invasives. Our previous research indicates invasive black mustard (Brassica nigra) changes interaction signs for otherwise positive species interactions between the dominant, native facilitator California buckwheat (Eriogonum fasciculatum) and its co-dominant beneficiary California sagebrush (Artemisia californica) in semi-arid California coastal sage scrub habitat. Here, E. fasciculatum and A. californica seedlings increased B. nigra shoot growth in pairwise species interactions in the greenhouse. However, in three-way species interactions, E. fasciculatum and A. californica together reduced B. nigra SLA, height, and reproductive potential while not increasing shoot DW. In three-way species interactions, B. nigra did not significantly reduce E. fasciculatum facilitation of A. californica. Also surprisingly, light competition with B. nigra resulted in an increase in A. californica height, which reduced the negative effects of A. californica light competition on shade-intolerant E. fasciculatum. In an additive field experiment, A. californica protected E. fasciculatum from facilitating germination and growth of B. nigra when water competition was minimized. Taken together, this study demonstrates the importance of studying species interactions between competitive, native perennials in the current ecological context of invaded ecosystems.

Global change threatens plant diversity and disrupts its interrelationship with ecosystem structure and function. This disruption in turn undermines confidence in the knowledge ecologists produce, and whether it will translate into multidisciplinary research settings or guide the effective management of natural lands. To address this challenge, ecology needs to consider the interactions between different levels of biological hierarchy, especially how they feedback on, and are mediated by, plant diversity. Doing so will require conducting empirical work and developing theory that simultaneously considers multiple disciplinary perspectives and units of study. Here we advocate the use of common gardens to integrate ecology, evolutionary biology and ecosystem science through an explicit focus on simultaneous measurement of response variables at multiple levels of biological organization. This approach will provide opportunities to evaluate assumptions important to prediction, such as space‐for‐time substitution, and tackle the integration of physicochemical and eco‐evolutionary foundations to understanding plants and ecosystems. Synthesis . We summarize the large body of research on Sonoran Desert winter annuals to demonstrate how experimental designs that employ common gardens to integrate processes across scales hold special promise. This includes refining trait‐based theories of plant strategies, providing insight into ecosystem responses to global change and collaborating effectively with other scientific disciplines.

Climate models predict that, in the coming decades, many arid regions will experience increasingly hot conditions and will be affected more frequently by drought. These regions are also experiencing rapid vegetation change, notably invasion by exotic grasses. Invasive grasses spread rapidly into native desert ecosystems due, in particular, to interannual variability in precipitation and periodic fires. The resultant destruction of non-fire-adapted native shrub and grass communities and of the inherent soil resource heterogeneity can yield invader-dominated grasslands. Moreover, recurrent droughts are expected to cause widespread physiological stress and mortality of both invasive and native plants, as well as the loss of soil resources. However, the magnitude of these effects may differ between invasive and native grasses, especially under warmer conditions, rendering the trajectory of vegetated communities uncertain. Using the Biosphere 2 facility in the Sonoran Desert, we evaluated the viability of these hypothesized relationships by simulating combinations of drought and elevated temperature (+5°C) and assessing the ecophysiological and mortality responses of both a dominant invasive grass (Pennisetum ciliare or buffelgrass) and a dominant native grass (Heteropogan contortus or tanglehead). While both grasses survived protracted drought at ambient temperatures by inducing dormancy, drought under warmed conditions exceeded the tolerance limits of the native species, resulting in greater and more rapid mortality than exhibited by the invasive. Thus, two major drivers of global environmental change, biological invasion and climate change, can be expected to synergistically accelerate ecosystem degradation unless large-scale interventions are enacted.

While models of species coexistence largely focus on how competition defines biological communities, over recent decades, a number of studies show positive plant–plant species interactions (facilitation) can also promote stable coexistence. The long‐lived, co‐dominant shrubs California buckwheatEriogonum fasciculatumand California sagebrushArtemisia californicashare a well‐documented positive association at the habitat level in their native California coastal sage scrub ecosystem, but mechanisms underlying their interactions remain unclear at finer spatial scales. Here, a hypothesis thatE. fasciculatumacidifies CSS's alkaline soils and facilitatesA. californicathrough amelioration of alkalinity stress is tested in a greenhouse experiment and association tests in the field. Greenhouse results demonstrate facilitation at early growth stages. In late growth stages, water competition is known to determine the shrubs' interactions with each other, but here, field observations of the shrubs in late growth stages show positive associations betweenA. californicaandE. fasciculatumthat have a positive linear relationship to increasing soil pH. These results highlight the importance of understanding lifecycle‐long interactions among species in evaluating facilitation's impacts on community structure.

Dryland ecosystems cover large regions of the Earth and have important impacts on global biogeochemistry and the carbon cycle. The plant species that occupy dryland environments have traits that enable them to withstand harsh environmental conditions, and some researchers have hypothesized that dryland vegetation may be comparatively resilient to changing climate, while others have pointed out that dryland vegetation often operates close to the physiological limits of many species, implying a possible vulnerability to warming. Here we use the Landsat archive to analyze vegetation dynamics for part of the Sonoran Desert and adjacent mountains in southern California. We show that large decreases in vegetation cover occurred over the last 34 years (1984–2017), especially across the xeric portions of our study region, where we observed a normalized difference vegetation index (NDVI) decline of 1.1 ± 0.3% yr −1 . Changes in precipitation explain most of the year‐to‐year variation but are unable to fully explain the observed long‐term decline in NDVI. Statistical models that combined summer temperature and mean annual precipitation explained more of the spatial and temporal structure of NDVI trends and implicate climate warming as an important driver of declining vegetation cover. The impact of warming contributed to a change in the precipitation‐vegetation relationship through time for this desert region, indicating a structural change in ecosystem function during the study period. These results suggest that recent climate change has already had significant impact on these drylands and highlight the potential for future warming to increase risks for dryland ecosystems in other regions.

As Southern California becomes hotter and dryer, wildfires are becoming more frequent and severe. At the same time, the suburbanization of poverty and immigration are making the region increasingly - albeit unevenly - diverse. This paper synthesizes insights from planning and ecology to address the following questions: how do burned areas differ from the rest of the region in terms of poverty, race, and housing values; how has this changed since 1980; and what are the implications for environmental justice? Typically, low-income urban communities of color are disproportionately vulnerable to climate impacts. However, this study finds that the wildland-adjacent neighborhoods most impacted by wildfire have remained predominantly white and affluent, even as Southern California has become increasingly diverse. Moreover, housing in burned areas is increasingly more expensive. These results indicate that home ownership in a fire-prone, wildland-adjacent neighborhood is a profitable investment for those who can afford it. This situation is likely creating perverse incentives for continued development of the wildland-urban interface, leading to both continued ecological disturbance and affluent residents continuing to subject themselves to more physical danger than they have acknowledged.

Tropical forests may be vulnerable to climate change1–3 if photosynthetic carbon uptake currently operates near a high temperature limit4–6. Predicting tropical forest function requires understanding the relative contributions of two mechanisms of high-temperature photosynthetic declines: stomatal limitation (H1), an indirect response due to temperature-associated changes in atmospheric vapour pressure deficit (VPD)7, and biochemical restrictions (H2), a direct temperature response8,9. Their relative control predicts different outcomes—H1 is expected to diminish with stomatal responses to future co-occurring elevated atmospheric [CO2], whereas H2 portends declining photosynthesis with increasing temperatures. Distinguishing the two mechanisms at high temperatures is therefore critical, but difficult because VPD is highly correlated with temperature in natural settings. We used a forest mesocosm to quantify the sensitivity of tropical gross ecosystem productivity (GEP) to future temperature regimes while constraining VPD by controlling humidity. We then analytically decoupled temperature and VPD effects under current climate with flux-tower-derived GEP trends in situ from four tropical forest sites. Both approaches showed consistent, negative sensitivity of GEP to VPD but little direct response to temperature. Importantly, in the mesocosm at low VPD, GEP persisted up to 38 °C, a temperature exceeding projections for tropical forests in 2100 (ref. 10). If elevated [CO2] mitigates VPD-induced stomatal limitation through enhanced water-use efficiency as hypothesized9,11, tropical forest photosynthesis may have a margin of resilience to future warming. Photosynthesis in tropical forests shows an apparent sensitivity to temperature. This Letter teases apart the effects of temperature and correlated atmospheric water demand on ecosystem productivity.

Understanding the nature of biological invasions is an important grand challenge, and we share Prof. Hedrick's concern for developing good theory and mechanistic understanding of the ecological and evolutionary dynamics of invasion (Hedrick, 2020). We understand the concern that FIS cannot be calculated from the expected and observed heterozygosity values provided in the table 1 of Winkler et al. (2019) and acknowledge this discrepancy exists because of the different ways subpopulations and loci were handled by our analytical methods. Specifically, FIS was calculated using the heterozygosity estimate HS, calculated as

The specific mechanisms that result in the success of any species invasion case are difficult to document. Reproductive strategies are often cited as a primary driver of invasive success, with human activities further facilitating invasions by, for example, acting as seed vectors for dispersal via road, train, air, and marine traffic, and by producing efficient corridors for movement including canals, drainages, and roadways. Sahara mustard (Brassica tournefortii) is a facultative autogamous annual native to Eurasia that has rapidly invaded the southwestern United States within the past century, displacing natives, and altering water-limited landscapes in the southwest. We used a genotyping-by-sequencing approach to study the population structure and spatial geography of Sahara mustard from 744 individuals from 52 sites across the range of the species' invasion. We also used herbaria records to model range expansion since its initial introduction in the 1920s. We found that Sahara mustard occurs as three populations in the United States unstructured by geography, identified three introduction sites, and combined herbaria records with genomic analyses to map the spread of the species. Low genetic diversity and linkage disequilibrium are consistent with self-fertilization, which likely promoted rapid invasive spread. Overall, we found that Sahara mustard experienced atypical expansion patterns, with a relatively constant rate of expansion and without the lag phase that is typical of many invasive species.

Phylogenetically informed trait comparisons across entire communities show promise in advancing community ecology. We use this approach to better understand the composition of a community of winter annual plants with multiple decades of monitoring and detailed morphological, phenological and physiological measurements. Previous research on this system revealed a physiological trade-off among dominant species that accurately predicts population and community dynamics. Here we expanded our investigation to 51 species, representing 96% of individual plants recorded over 30 years, and analysed trait relationships in the context of species abundance and phylogenetic relationships. We found that the functional-trait trade-off scales to the entire community, albeit with diminished strength. It is strongest for dominant species and weakens as progressively rarer species are included. The trade-off has been consistently expressed over three decades of environmental change despite some turnover in the identity of dominant species.

Plant phenology-the timing of cyclic or recurrent biological events in plants-offers insight into the ecology, evolution, and seasonality of plant-mediated ecosystem processes. Traditionally studied phenologies are readily apparent, such as flowering events, germination timing, and season-initiating budbreak. However, a broad range of phenologies that are fundamental to the ecology and evolution of plants, and to global biogeochemical cycles and climate change predictions, have been neglected because they are "cryptic"-that is, hidden from view (e.g., root production) or difficult to distinguish and interpret based on common measurements at typical scales of examination (e.g., leaf turnover in evergreen forests). We illustrate how capturing cryptic phenology can advance scientific understanding with two case studies: wood phenology in a deciduous forest of the northeastern USA and leaf phenology in tropical evergreen forests of Amazonia. Drawing on these case studies and other literature, we argue that conceptualizing and characterizing cryptic plant phenology is needed for understanding and accurate prediction at many scales from organisms to ecosystems. We recommend avenues of empirical and modeling research to accelerate discovery of cryptic phenological patterns, to understand their causes and consequences, and to represent these processes in terrestrial biosphere models.

Summary Seasonal dynamics in the vertical distribution of leaf area index (LAI) may impact the seasonality of forest productivity in Amazonian forests. However, until recently, fine‐scale observations critical to revealing ecological mechanisms underlying these changes have been lacking. To investigate fine‐scale variation in leaf area with seasonality and drought we conducted monthly ground‐based LiDAR surveys over 4 yr at an Amazon forest site. We analysed temporal changes in vertically structured LAI along axes of both canopy height and light environments. Upper canopy LAI increased during the dry season, whereas lower canopy LAI decreased. The low canopy decrease was driven by highly illuminated leaves of smaller trees in gaps. By contrast, understory LAI increased concurrently with the upper canopy. Hence, tree phenological strategies were stratified by height and light environments. Trends were amplified during a 2015–2016 severe El Niño drought. Leaf area low in the canopy exhibited behaviour consistent with water limitation. Leaf loss from short trees in high light during drought may be associated with strategies to tolerate limited access to deep soil water and stressful leaf environments. Vertically and environmentally structured phenological processes suggest a critical role of canopy structural heterogeneity in seasonal changes in Amazon ecosystem function.