Joshua Tree Research Articles

Shifting Baselines: Visualizing Climate Change in America’s National Parks

This visual essay highlights four national parks where the impacts of climate change are well-documented and visually compelling (Everglades, Mesa Verde, Joshua Tree, and Mount Rainier). In drawing attention to these visible climate impacts and effectively interpreting the changes in situ, the park service can play a key role in clarifying the issue of climate change for the American public. Park managers and other park professionals have undoubtedly identified locations in their own management units offering similar opportunities to engage visitors in the science of climate change (either through on-site signage or ranger-led programs). The photographs comprising this visual essay, taken over eight weeks of fieldwork from 2017 to 2024, are intended to spark ideas and move the conversation forward.

Reconstructing 120 years of climate change impacts on Joshua tree flowering.

Quantifying how global change impacts wild populations remains challenging, especially for species poorly represented by systematic datasets. Here, we infer climate change effects on masting by Joshua trees (Yucca brevifolia and Y. jaegeriana), keystone perennials of the Mojave Desert, from 15 years of crowdsourced observations. We annotated phenophase in 10,212 geo-referenced images of Joshua trees on the iNaturalist crowdsourcing platform, and used them to train machine learning models predicting flowering from annual weather records. Hindcasting to 1900 with a trained model successfully recovers flowering events in independent historical records and reveals a slightly rising frequency of conditions supporting flowering since the early 20th Century. This reflects increased variation in annual precipitation, which drives masting events in wet years-but also increasing temperatures and drought stress, which may have net negative impacts on recruitment. Our findings reaffirm the value of crowdsourcing for understanding climate change impacts on biodiversity.

Description of new micro-colonial fungi species Neophaeococcomyces mojavensis, Coniosporium tulheliwenetii, and Taxawa tesnikishii cultured from biological soil crusts.

Black yeasts and relatives comprise Micro-Colonial Fungi (MCFs) which are slow-growing stress-tolerant micro-eukaryotes that specialize in extreme environments. MCFs are paraphyletic and found in the Orders Chaetothyriales (Eurotiomycetes) and Dothideales (Dothidiomycetes). We have isolated and described three new MCFs species from desert biological soil crusts (BSCs) collected from two arid land regions: Joshua Tree National Park (Mojave Desert) and UC Natural Reserve at Boyd Deep Canyon (confluence of Mojave and Sonoran Deserts). BSCs are composite assemblages of cyanobacteria, eukaryotic algae, fungi, lichens, and bryophytes embedded into the surface of desert soils, providing a protective buffer against the harsh desert environment. Our work focused on one type of desert BSC, the cyanolichen crust dominated by Collema sp. Using culture-dependent protocols, three MCFs were axenically isolated from their respective samples along with the extracted DNA. Their genomes were sequenced using Illumina and Nanopore, and finally assembled and annotated using hybrid assembly approaches and established bioinformatics pipelines to conduct final taxonomic phylogenetic analysis and placement. The three species described here are unique specimen from desert BSCs, here we introduce, Neophaeococcomyces mojavensis (Chaetothyriales), Cladosporium tulheliwenetii (Dothideales), and Taxawa tesnikishii (Dothideales).

Uplifting Community and Incorporating Reuse in Conservation Planning for the Noah Purifoy Outdoor Desert Art Museum of Assemblage Sculpture

ABSTRACT In 2023 the Noah Purifoy Foundation received a Mellon Foundation Grant to develop, with conservators, an innovative and thoughtful conservation plan for the over 100 sculptures at the Noah Purifoy Outdoor Desert Art Museum of Assemblage Sculpture. Located in the high desert of Joshua Tree, California, USA, it encompasses four hectares of rural art space where Purifoy lived and worked from 1989 until his death in 2004. Although Purifoy was a trained artist, his works also draw from his time as a US Navy Seabee and the tradition of Black self-taught artists from the American South. His artworks were never complete, but alive, and in an ongoing conversation among him, nature, and material. Amidst the physical challenges of addressing found material assemblage in a challenging landscape, the project also requires bringing stakeholders and knowledge bearers into conversation to determine an appropriate ‘patina’ of weathering for the works. To achieve this, the project involves identifying Purifoy's definition of community, reuse, and interaction with the natural landscape into the conservation plan. The project also included drone mapping as a documentation tool alongside condition surveys and photographic documentation. Being led by a group of racially diverse conservators who are centering community involvement in the work helps the team mimic Purifoy’s own commitment to community engagement. This project has the potential to act as a model for the development of conservation plans for other sites of contemporary sculpture, especially those in remote locations or those focused on African American artists.

TINY HOUSE IN THE DESERT: A study in indoor comfort using moveable insulation and thermal storage

A tiny house for seasonal rangers was designed for the extreme climate and diurnal temperature fluctuations of Joshua Tree National Park. The challenging climate conditions resulted in an extensive investigation of the building envelope to act as a passive thermal storage system to naturally cool and heat the house. The north wall was designed as a “cold battery,” which uses a dynamic internal and external insulation system with a high-mass concrete wall to achieve coolth absorption at night as part of a thermal management system and to achieve indoor thermal comfort under extreme desert climates. A combination of opening an exterior insulation system at night to absorb coolth, closing the exterior insulation system when the temperature rises, and opening the interior insulation system to release coolth was attempted. The goal was to achieve a comfortable indoor temperature without the use of HVAC systems. Several software programs were tested for their capabilities to simulate time lag in concrete and thermal storage including Opaque and IES VE. The design of the north wall was carried out for different conditions such as different modulating profiles, locations and thicknesses of insulation, and the data were collected and analyzed again. IES VE was able to successfully simulate the effects of moving interior and exterior insulation twice a day on different sides of a concrete wall. In consideration of the special occupancy type, the expansion of the comfort zone for seasonal rangers is achieved by the specification of a comfortable temperature range from 65°F to 85°F. In a standard year, consisting of 8,760 hours, simulations were conducted on the entire residence, primarily during the months when seasonal rangers were present, to investigate thermal comfort conditions. These assessments encompassed various aspects, including ventilation (2,941 comfort hours), the north wall (4,653 comfort hours), the base model (2,883 comfort hours), and enhancements to the south wall (5,543 comfort hours) and the east and west glazed facade (6,137 comfort hours). The culmination of these findings significantly contributed to an enhanced overall comfort experience within the tiny house design, specifically tailored to accommodate the needs of seasonal rangers at Joshua Tree National Park. Natural ventilation proved to be a good strategy.

Unprecedented distribution data for Joshua trees (Yucca brevifolia and Y. jaegeriana) reveal contemporary climate associations of a Mojave Desert icon

IntroductionForecasting range shifts in response to climate change requires accurate species distribution models (SDMs), particularly at the margins of species' ranges. However, most studies producing SDMs rely on sparse species occurrence datasets from herbarium records and public databases, along with random pseudoabsences. While environmental covariates used to fit SDMS are increasingly precise due to satellite data, the availability of species occurrence records is still a large source of bias in model predictions. We developed distribution models for hybridizing sister species of western and eastern Joshua trees (Yucca brevifolia and Y. jaegeriana, respectively), iconic Mojave Desert species that are threatened by climate change and habitat loss.MethodsWe conducted an intensive visual grid search of online satellite imagery for 672,043 0.25 km2 grid cells to identify the two species' presences and absences on the landscape with exceptional resolution, and field validated 29,050 cells in 15,001 km of driving. We used the resulting presence/absence data to train SDMs for each Joshua tree species, revealing the contemporary environmental gradients (during the past 40 years) with greatest influence on the current distribution of adult trees.ResultsWhile the environments occupied by Y. brevifolia and Y. jaegeriana were similar in total aridity, they differed with respect to seasonal precipitation and temperature ranges, suggesting the two species may have differing responses to climate change. Moreover, the species showed differing potential to occupy each other's geographic ranges: modeled potential habitat for Y. jaegeriana extends throughout the range of Y. brevifolia, while potential habitat for Y. brevifolia is not well represented within the range of Y. jaegeriana.DiscussionBy reproducing the current range of the Joshua trees with high fidelity, our dataset can serve as a baseline for future research, monitoring, and management of this species, including an increased understanding of dynamics at the trailing and leading margins of the species' ranges and potential for climate refugia.

The reference genome assembly of the bright cobblestone lichen, Acarospora socialis.

Acarospora socialis, the bright cobblestone lichen, is commonly found in southwestern North America. This charismatic yellow lichen is a species of key ecological significance as it is often a pioneer species in new environments. Despite their ecological importance virtually no research has been conducted on the genomics of A. socialis. To address this, we used long-read sequencing to generate the first high-quality draft genome of A. socialis. Lichen thallus tissue was collected from Pinkham Canyon in Joshua Tree National Park, California and deposited in the UC Riverside herbarium under accession #295874. The de novo assembly of the mycobiont partner of the lichen was generated from Pacific Biosciences HiFi long reads and Dovetail Omni-C chromatin capture data. After removing algal and bacterial contigs, the fungal genome was approximately 31.2 Mb consisting of 38 scaffolds with contig and scaffold N50 of 2.4 Mb. The BUSCO completeness score of the assembled genome was 97.5% using the Ascomycota gene set. Information on the genome of A. socialis is important for California conservation purposes given that this lichen is threatened in some places locally by wildfires due to climate change. This reference genome will be used for understanding the genetic diversity, population genomics, and comparative genomics of A. socialis species. Genomic resources for this species will support population and landscape genomics investigations, exploring the use of A. socialis as a bioindicator species for climate change, and in studies of adaptation by comparing populations that occur across aridity gradients in California.

Johansenicoccus eremophilus gen. et sp. nov., a novel evolutionary lineage in Chlorophyceae with unusual genomic features

Background – Green algae are a diverse group of photosynthetic eukaryotes, yet are still vastly understudied compared to land plants. For many years, green algae were characterized based on their morphology and life cycles. More recently, phylogenetic and genomic analyses have been added to the phycological toolkit for a better understanding of algal biodiversity and evolutionary history. Material and methods – A desert strain of green algae was isolated from Joshua Tree National Park (JTNP) in southern California as part of a larger biodiversity survey. The alga’s nuclear rRNA genes as well as the chloroplast genome were sequenced, annotated, and analysed in addition to a morphological assessment. Results – Morphologically this strain is especially similar to Pseudomuriella and Rotundella, and its lipid profile resembles that of other soil algae, but phylogenomic analyses demonstrate that it is a distinct evolutionary lineage in Chlorophyceae. The alga exhibits several unusual genomic features, the most remarkable being its highly derived yet apparently functional nuclear rRNA genes, 18S and 28S. Both genes are GC-rich and bear many compensatory base changes to maintain a similar secondary structure to that of other green algae. The chloroplast genome has a distinct gene order and repeat arrangement from other published green algal plastomes, but contains the expected genes and also provides phylogenetically informative data. Conclusion – We conclude that the strain be placed into a new species and genus in the class Chlorophyceae, and propose the name Johansenicoccus eremophilus for this new taxon. Johansenicoccus eremophilus exemplifies science’s insufficient understanding of the range of genomic variations among inconspicuous soil algae.

Assisted Species Migration of Joshua Trees

The Joshua tree evolved in a complex way with its environment, pollinator, and seed dispersers over millions of years. Its survival as a species is now imminently threatened by climate change. Many factors prevent it from migrating to a cooler range quickly enough to keep up with the planet’s current rate of warming. This paper explores the viability of assisted migration for the Joshua tree, where humans help it move to escape extinction. Several studies are examined. One persuasively shows that the Joshua tree had a range contraction when the climate warmed at the end of the Ice Age and that present warming will cause a similar, drastic range reduction. Other studies look at factors such as soil, CO2, pollinator mutualism, and seed longevity to determine if assisted migration would be successful. The ethics of assisted migration is also explored. This paper concludes that humans must try to assist the Joshua tree to migrate but that it will be difficult given the complexities of its evolution, its relationship to its environment, and a migration lag that is not completely understood.

Titanite Petrochronology Records Secular Temperature and Fluid Evolution During Ductile Deformation: An Example From Late Cretaceous Shear Zones in the Eastern Transverse Ranges

AbstractQuantifying the timing and conditions of ductile deformation is essential for quantitative models of lithospheric deformation. Yet, directly constraining these variables and documenting how they change during a single deformation event remain difficult. We present titanite microstructural, zoning, trace‐element, and U‐Pb data from <m‐scale mylonitic shear zones in the Eastern Transverse Ranges, CA (Joshua Tree National Park) that record (a) the timing and conditions of ductile deformation and (b) the evolution of deformation conditions within a single, punctuated ductile deformation event. Titanite grains in sheared plutonic rocks yield a bimodal distribution of dates (∼151 and ∼75 Ma) interpreted as the independently constrained pluton crystallization and shear zone deformation ages, respectively. Synkinematic titanite neocrystallization at ∼75 Ma documents early deformation at ∼640–710°C under hydrous fluid conditions. Recrystallized titanite rims with ∼75 Ma dates indistinguishable from the neocrystallized titanite record Zr‐in‐titanite temperatures of 600–610°C and higher F contents, suggesting that the fluid became a more halogen‐rich brine as deformation progressed and the system cooled. Chemical zoning related to fluid‐driven recrystallization occurs in tandem with lattice misorientations and partially to fully reset U‐Pb dates in bent titanite, implying that reactive fluid flow is the ultimate mechanism by which dates are reset in titanite deformed by dislocation creep. These data document a punctuated (e.g., ∼1–3 Myr) phase of high‐temperature deformation that accompanied local pluton emplacement and demonstrate that titanite petrochronology can capture multiple, discrete reactions associated with crustal weakening and variables that affect the rheological evolution of ductile shear zones.

How ‘green energy’ is threatening biodiversity, human health, and environmental justice: An example from the Mojave Desert, California

In recent years, the Mojave Desert, which is known for its unique and endemic plant and animal diversity, has become a preferred area for renewable energy developments. However, an environmental impact that is not calculated into the production of green energy has emerged that not only puts an additional burden on already endangered species but also affects the quality of life for residents living in disadvantaged and underserved communities. Using the example of just another solar farm to be built on 2,300 acres of pristine desert land, we point out the negative impacts of unsustainable land development on community health and environmental justice, driven by the administration of Kern County, which promotes and prioritizes economic growth over residents’ concerns. In the eyes of the local population, several promises by the County to the community, as documented in the 2017–2020 County of Kern Strategic Goals, were broken. This study investigates the effects of unsustainable land development, particularly the threat to iconic Joshua trees (Yucca brevifolia), the increase in PM10 pollution, and the risk of contracting Valley fever for residents of two small desert communities, Boron, and Desert Lakes, in Kern County, California. This study focused on environmental justice issues due to the implementation of an ambitious renewable energy transition plan supported by the administration. This is the first study that documented the presence of the causative agent of Valley fever in soils to be disturbed for ambitious renewable energy development in eastern Kern County using a molecular, culture-independent, approach.

Understanding Paleoclimate Through Southern California’s Packrat Middens

Documenting how ecosystems responded to climate change in the past can inform models for the future relevant to conservation decision-making. Packrat middens, or giant nests consisting of gathered plant material made by rodents of the genus Neotoma, represent one of the best data sources for understanding how plant communities change over time. These nests can be preserved for thousands of years, spanning episodes of glacial-interglacial variation, such as the Pleistocene-Holocene transition, or more recent fluctuations, such as the Little Ice Age and Medieval Warm Period. We used the USGS-NOAA paleoclimate open-access database to develop spatiotemporal reconstructions of plant species in Southern California, incorporating more than 242 individual middens with a total of 193 available radiocarbon dates spanning around 44,493 years cal BP. As a result, 374 plant species were identified within the SoCal middens, with Joshua Tree (Yucca brevifolia), Joint Pine (Ephedra species), and California Juniper (Juniperus californica) being the most abundant. We then applied these data to reconstruct past vegetation communities and contextualize a recently discovered asphaltic midden recovered from the La Brea Tar Pits (Los Angeles, California). The La Brea midden represents both the oldest and most coastal midden in our dataset in California and contains vegetation spanning Marine Isotope Stages 2-3. Ultimately, this research allows us to paint a picture of changing vegetation over time as a baseline for palaeoecological food web studies and can be compared with present day packrat nests found in this urban biodiversity hotspot. These data will be curated through the Conservation Paleobiology Network’s urban vegetation working group (based in Los Angeles, California) and made available for use by conservation and management projects throughout the region. With this information, CPN can implement habitat restoration projects in SoCal.

Swainson’s Hawk Nesting Population in the Antelope Valley of the Western Mojave Desert, California

The Swainson’s Hawk (Buteo swainsoni) has a long history of breeding in California, but a severe decline in the statewide breeding population was identified in 1979, when in all of southern California only two pairs were found, one in the Antelope Valley of the western Mojave Desert. That area was little studied until we began banding Swainson’s Hawks there in 1997. Over 20 breeding seasons between 1979 and 2022, we documented in the Antelope Valley 124 attempts to nest, in which the mean clutch and brood sizes were 2.49 and 2.37, respectively. From 2004 through 2006, we observed two to four breeding pairs annually; from 2009 through 2022, three to 14 breeding pairs. The rate of success of the 91 nests revisited to determine if any young fledged was 64%. Nest trees consisted of 81.5% non-native species, 13.7% native species, including Joshua trees (Yucca brevifolia), and 4.8% unidentified deciduous trees. Between 1997 and 2022, in 50 nests, we recorded 170 vertebrate prey items, of which 90 were gophers (Thomomys bottae). Though the Antelope Valley population has grown since 1980, its nesting and foraging habitat now face multiple threats. To conserve occupied nesting territories, we recommend creation of nesting and foraging habitat reserves that include both native desert and cultivated alfalfa close to existing conserved land.

Optimizing Wilderness Search and Rescue: Discovery and Outcome

This article is a follow-up to a 2019 analysis that applied Bayesian probability techniques to the search for a missing hiker in Joshua Tree National Park. In February 2022, that hiker was found. Here, we compare the location of his remains with the results of our prediction model and discuss further implications for optimizing wilderness search and rescue. KEY WORDS: Wilderness Search and Rescue, Lost Persons, Bayesian Analysis, Resource Optimization

Science and Public Engagement in National Parks: Examples and Advice from Young Scientists

Science and Public Engagement in National Parks: Examples and Advice from Young Scientists

Dust storms ahead: Climate change, green energy development and endangered species in the Mojave Desert

The Mojave Desert contains the hottest, driest regions in North America and is also one of the most ecologically intact regions in the contiguous United States. However, a confluence of factors including urbanization, climate change, and energy development are rapidly transforming this ecoregion. As a result of these growing threats, even common, widespread Mojave Desert endemics are at risk of being driven to extinction by the end of the 21st century. Ironically, renewable energy development that could delay or even reverse the effects of climate change in the region is also a potentially significant source of habitat loss for these same organisms. Protecting the Mojave therefore presents difficult choices about how to select among different conservation priorities. We argue that these choices will necessarily involve compromises in which protections for some habitats will have to be prioritized while allowing development in other areas. We review the state of conservation in the Mojave and use the Mojave Desert's iconic Joshua trees (Yucca brevifolia and Y. jaegeriana) as a case study to describe a framework for identifying habitats that should be given the highest levels of protection to ensure climate change resilience. Finally, using existing spatial data, we evaluate land use and conservation status in the Mojave. The result identifies considerable scope for compromise between conservation and renewable energy development. Although our examples are specific to the Mojave, we argue that these recommendations apply broadly to many biological communities threatened by climate change.

Like a shark in the ocean: the semiotics of extreme precarity in Joshua Tree rock climbing

Abstract During the mid-1970s the extraordinarily dangerous style of free solo climbing (climbing without protection) emerged in the collective practice of a small community of “Stonemaster” climbers actively developing new climbing routes and the new “free” style of roped climbing in what is now Joshua Tree National Park, California. While its emergence might be interpreted as an affectively-driven, macho embodied social semiotic or ethnomotricity, in actuality the evolution of free soloing in the case of Stonemaster-era climbing at Joshua Tree may be more accurately understood as the logical consequence of an intensive regime of practice in which climbers developed a near absolute bodily familiarity with certain climbing routes. Eventually, the reasonableness of climbing with little and even no protection on a subset of these routes became self-evident and conventional. Free soloing, in the semiotic perspective of the later Peirce, manifested as a Normal Logical Interpretant in the Joshua Tree landscape. It embodied the living definition of self-controlled conduct, and the Symbols it cultivated testified persuasively to the growth of a creative corporeal intelligence actualizing near absolute degrees of free will.

Distribution, morphology, and karyotype of San Joaquin pocket mice from the western Mojave Desert

The San Joaquin pocket mouse (Perognathus inornatus) is endemic to California and currently includes three subspecies (P. i. inornatus, neglectus, and psammophilus). P. inornatus from the western Mojave Desert have been assigned to the subspecies neglectus based on similar morphology. During the course of live-trapping projects between 1990 and 2017, we captured P. inornatus at several locations in the Mojave Desert and gathered information on habitat associations, relative abundance, seasonal activity, and field identification. P. inornatus was found at elevations ranging from 668–1,109 m above mean sea level in creosote bush scrub, allscale scrub, Joshua tree woodland, rubber rabbitbrush scrub, spinescale scrub, and California juniper woodland. The capture locations and our review of museum specimens indicate that, at a minimum, the species’ range in the Mojave Desert encompasses approximately 7,000 km2 primarily in the Antelope Valley, extending at least as far north as the Rand Mountains, east to the vicinity of Hinkley, south to Palmdale, and west to near Gorman. P. inornatus capture rates were typically low relative to other nocturnal rodents, and it was not found consistently at localities at which it had been captured previously. Adults were sexually dimorphic, with males significantly larger than females. P. inornatus was significantly larger than the sympatric little pocket mouse (P. longimembris) for length of head-body, total length and body mass, and possessed a relatively shorter tail. We collected 15 specimens of P. inornatus from nine localities in the western Mojave Desert for cytogenetic analysis and each possessed the same karyotype, characterized by a diploid complement of 52 chromosomes, which has not been previously described for the genus. We argue that the 52-chromosome form should be considered distinct for conservation purposes, because it occupies a relatively small geographic area that is being subjected to increasing habitat loss and fragmentation due to residential, commercial, and renewable energy development.

From coral reefs to Joshua trees: What ecological interactions teach us about the adaptive capacity of biodiversity in the Anthropocene.

The pervasive loss of biodiversity in the Anthropocene necessitates rapid assessments of ecosystems to understand how they will respond to anthropogenic environmental change. Many studies have sought to describe the adaptive capacity (AC) of individual species, a measure that encompasses a species’ ability to respond and adapt to change. Only those adaptive mechanisms that can be used over the next few decades (e.g. via novel interactions, behavioural changes, hybridization, migration, etc.) are relevant to the timescale set by the rapid changes of the Anthropocene. The impacts of species loss cascade through ecosystems, yet few studies integrate the capacity of ecological networks to adapt to change with the ACs of its species. Here, we discuss three ecosystems and how their ecological networks impact the AC of species and vice versa. A more holistic perspective that considers the AC of species with respect to their ecological interactions and functions will provide more predictive power and a deeper understanding of what factors are most important to a species’ survival. We contend that the AC of a species, combined with its role in ecosystem function and stability, must guide decisions in assigning ‘risk’ and triaging biodiversity loss in the Anthropocene.This article is part of the theme issue ‘Ecological complexity and the biosphere: the next 30 years’.

Addressing the raven food subsidy challenge by engaging restaurants to close their dumpsters.

Ravens have benefitted from resource subsidies provided by humans so much that their population has increased by over 800% in the western Mojave desert over the last 50 years. Our food waste is an especially large subsidy. Raven predation is one of the greatest threats to desert tortoise survival in the California desert. We sought to create and evaluate a behavioral change program among restaurants in Yucca Valley and Twentynine Palms, California in the western Mojave with elevated raven populations. Half of the 60 restaurants in these two communities received an intervention encouraging them to close their dumpsters while the other half served as controls with no intervention. Treatment restaurants received two in-person visits to discuss the manifold importance of dumpster closure and laminated information signs to display and extend communication to staff. We surveyed all dumpsters for open/closed status five times before the intervention and five times again 3 months after the intervention. We found a significant increase in closure rates among treatment restaurants due to the interventions, with an average of 9.5% increase toward maximum possible lid closure. Restaurants achieving 80%+ closure received "Gold Star Awards" to further stimulate community-wide behavior change by publicly recognizing and encouraging desired behaviors. We summarize dumpster closure rates from similar interventions in nearby Joshua Tree and across the Coachella Valley to illustrate how local social norms may influence behavior.