Geology topics

Research about New Mexico

Source-linked reports with geographic coverage including New Mexico.

At least 55 records · Page 3Linked to original sources

USGS2025

Drone-based radiometric surveys provide high-resolution mine waste characterization

Airborne radiometric surveys use passive geophysical techniques to characterize geochemical variations at or near earth’s surface. These methods have been used for a variety of mapping applications, including mineral resource evaluation. However, detailed characterization of smaller geologic targets, including mine waste features, requires flying at lower altitudes and with tighter line spacing than is feasible with traditional aircraft. Here, a small uncrewed aircraft system (sUAS) equipped with a radiometric sensor was used to acquire high-resolution gamma-spectrometry over small mine waste features and a low-grade stockpile in southwestern New Mexico. The sUAS radiometric system mapped local variability within each survey area and revealed ~2–10 m wide zones where radioelements K, Th, and U may be elevated 2–10× the surrounding material. Additionally, the sUAS radiometric data revealed radioelement variability across survey sites, which correlated reasonably well with variability seen in geochemical samples at each survey site, even though samples collected from individual sites showed high local variability. The sUAS data characterized local heterogeneity within mine waste and other small geologic targets at scales of a few meters to tens of meters, which is not possible with traditional crewed aircraft, and with continuity of coverage that is not possible with ground surveys, thus filling a key gap in geophysical survey spatial resolution.

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USGS2025

Inferring Brown-Capped Rosy-Finch demography and breeding distribution trends from long-term wintering data in New Mexico

The three North American Rosy-Finch species (Brown-capped [ Leucosticte australis ], Black [ L. atrata ], and Gray-crowned [ L. tephrocotis ]) are among the most climate-threatened species in the United States. New Mexico is an important location for investigating the effects of climate change because it is the southernmost location in which Brown-capped Rosy-Finches breed and the southernmost location where all three Rosy-Finch species co-occur during winter. In the context of climate change, this range boundary is important to study because it is the first part of the range anticipated to cross a threshold of unsuitability for these species with increasing temperatures. Rosy-Finches are difficult to study during the breeding season due to the high elevation and remoteness of their breeding grounds; therefore, winter studies may lend insight into population trends and provide direction for conservation actions based on knowledge of the breeding origins of wintering birds. The goals of our study were to investigate long-term survival and migration trends from wintering Brown-capped Rosy-Finches in New Mexico and evaluate the efficacy of radio frequency identification (RFID)-equipped artificial feeders to monitor population trends. As of May 2025, we have conducted a robust design survival analysis on 22 years of mark-recapture data from a particular wintering site in New Mexico, assessed patterns in the breeding origins of individuals captured at this site using stable isotope analysis, and examined patterns in data collected via RFID. Our main findings from this study are that annual survival probability of Rosy-Finches wintering in New Mexico is low compared to that of other migratory passerines, that Brown-capped Rosy-Finches wintering in New Mexico likely originate from a variety of locations across their breeding range, and that RFID monitoring is useful in improving survival estimates in Rosy-Finches, particularly in short-term studies.

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USGS2025

Tracing fluid evolution during batholith and deposit formation: In-situ and bulk rock Mo isotopes from the Questa porphyry Mo deposit, New Mexico, USA

The Oligocene Questa porphyry Mo deposit, located in New Mexico, USA, is a well-characterized system that formed over 400 kyr, punctuating the 8 Myr formation of the Questa-Latir batholith. Detailed sampling of the intrusions and minerals associated with magmatichydrothermal mineralization, as well as bookending barren intrusions, allows for examination of the Mo isotope record of the deposit and its host batholith. Through this established chronologic framework, such data can yield insights into the metallogenesis of deposit formation and long-term magma genesis evolution for upper crustal magmatism. The Mo isotopic compositions of barren intrusions yield a younging trend towards lighter δ 98 Mo. However, intrusions associated with Mo deposit formation yield heavier δ 98 Mo relative to barren magmatism, by up to 2.0‰. This indicates that they were affected by an isotopically heavy and Mo-rich fluid. The in-situ data from molybdenite covers the range observed in mineralized bulk rocks. However, individual samples consistently yield Mo isotopic variations of 0.4‰ to 0.5‰. The consistency of the δ 98 Mo variation in in-situ analyses of molybdenite within hand samples and individual mineral grains is likely the result of MoS 2 crystallization in a closed system and reflects an almost complete precipitation of Mo.

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USGS2024

Effects of Mycoplasma ovipneumoniae, abundance, and environmental conditions on bighorn sheep lamb:ewe ratios and adult survival in New Mexico

Mycoplasma ovipneumoniae is a primary causative agent responsible for initiating polymicrobial pneumonia in bighorn sheep ( Ovis canadensis ). Infections of bighorn sheep populations are typically characterized by initial all-age epizootics followed by long-term periods of repressed juvenile (lamb) survival. Populations of bighorn sheep in New Mexico, USA, were thought to be free of this pathogen prior to 2017 but recent infection of multiple herds raised concerns regarding impacts on population size and juvenile:female ratios. Using aerial survey, survival, and disease sampling data in an exploratory framework, we (1) characterize age-related differences in M. ovipneumoniae prevalence and seroprevalence, (2) quantify differences in lamb:ewe ratios pre- and post- M. ovipneumoniae detection, and (3) investigate differences in survival between previously exposed and naïve individuals. From 2007 to 2022, we sampled 466 bighorn sheep across 19 populations in New Mexico for M. ovipneumoniae exposure. While the timing of initial herd infections varied across populations, one population sustained active infections for over 15 years. We found reduced juvenile:female ratios post M. ovipneumoniae exposure for both desert ( O. c. mexicana ) and Rocky Mountain ( O. c. canadensis ) bighorn sheep populations. Post-exposure ratio declines ranged from 20% to 69%. Evaluation of population size and environmental condition effects on juvenile:female ratios indicated varying impacts for each subspecies. Notably, population size was negatively related to Rocky Mountain juvenile:female ratios only after populations were exposed to M. ovipneumoniae . Additionally, climatic conditions in the previous lambing season and pre-parturition time frame were associated with juvenile:female ratios for Rocky Mountain populations, while juvenile:female ratios of desert bighorn appeared to only be affected by pre-parturition climatic conditions. Kaplan–Meier survival estimation of previously exposed, but putatively recovered, individuals ( n = 31) and naïve individuals ( n = 70) revealed lower (75%; 95% CI: 62%–93%) but not statistically significant ( p = 0.2) 1-year survival rates for individuals that were seropositive but not actively infected, when compared to seronegative individuals (88%; 95% CI: 81%–97%). These results collectively suggest that following M. ovipneumoniae introduction, bighorn sheep populations in New Mexico could be limited by lamb survival.

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USGS2024

Dryland fungi are spatially heterogeneous and resistant to global change drivers

Fungi are considered particularly important in regulating the structure and function of dryland ecosystems, yet the response of dryland fungal communities to global change remains notably understudied. Without a clear understanding of how fungi respond to global change drivers, mitigation plans—required for biodiversity and ecosystem service conservation and restoration—are impossible to develop. In this study, we asked the following: (1) How does the fungal community respond to the individual and interactive effects of physical disturbance and drought in a heterogeneous dryland landscape comprised of drought-adapted shrubs separated by adjacent open areas of soil? (2) What are the larger scale impacts of this response? We assessed fungal communities (using fungal-specific DNA metabarcoding analyses) of surface soil samples in an in situ global change experiment that included disturbance and drought in a full factorial design in the northern extent of the Chihuahuan Desert. We found that the fungal community was spatially heterogenous and remarkably resistant to disturbance and drought. We also show that dryland soils harbor high shares of facultative pathogenic and obligately pathogenic fungal taxa, with several concerning taxa reaching high relative abundances under drought. Our results suggest that the fungal community is highly influenced by microclimatic conditions associated with the presence or absence of vegetation. Moreover, our results imply that the fungal community in our experiment was already adapted to the magnitude of stress imposed by two years of experimental disturbance and drought treatments. Overall, our study shows that the fungal community is spatially heterogeneous and resistant to global change drivers and houses many fungal species known for being stress tolerant and pathogenic.

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USGS2024

Combining past and contemporary species occurrences with ordinal species distribution modeling to investigate responses to climate change

Many organisms leave evidence of their former occurrence, such as scat, abandoned burrows, middens, ancient eDNA or fossils, which indicate areas from which a species has since disappeared. However, combining this evidence with contemporary occurrences within a single modeling framework remains challenging. Traditional binary species-distribution modeling reduces occurrence to two temporally coarse states (present/absent), so thus cannot leverage the information inherent in temporal sequences of evidence of past occurrence. In contrast, ordinal modeling can use the natural time-varying order of states (e.g. never occupied versus previously occupied versus currently occupied) to provide greater insights into range shifts. We demonstrate the power of ordinal modeling for identifying the major influences of biogeographic and climatic variables on current and past occupancy of the American pika Ochotona princeps , a climate-sensitive mammal. Sampling over five years across the species' southernmost, warm-edge range limit, we tested the effects of these variables at 570 habitat patches where occurrence was classified either as binary or ordinal. The two analyses produced different top models and predictors – ordinal modeling highlighted chronic cold as the most-important predictor of occurrence, whereas binary modeling indicated primacy of average summer-long temperatures. Colder wintertime temperatures were associated in ordinal models with higher likelihood of occurrence, which we hypothesize reflect longer retention of insulative and meltwater-provisioning snowpacks. Our binary results mirrored those of other past pika investigations employing binary analysis, wherein warmer temperatures decrease likelihood of occurrence. Because both ordinal- and binary-analysis top models included climatic and biogeographic factors, results constitute important considerations for climate-adaptation planning. Cross-time evidences of species occurrences remain underutilized for assessing responses to climate change. Compared to multi-state occupancy modeling, which presumes all states occur in the same time period, ordinal models enable use of historical evidence of species' occurrence to identify factors driving species' distributions more finely across time.

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USGS2024

Biological feasibility of introducing bighorn sheep to the Jicarilla Apache Nation

The biological feasibility of introducing Rocky Mountain bighorn sheep ( Ovis canadensis canadensis ) to the Dulce area of the Jicarilla Apache Nation (JAN) depends on availability and condition of potential habitat and the potential for disease risk, as pneumonia is the largest current threat to wild sheep populations. We modeled quality and quantity of potential bighorn sheep habitat incorporating the three most recent fire scars around Dulce, determined potential winter range within preferred habitat, assessed on the ground vegetation characteristics, and examined potential for disease transmission via risk of contact with domestic sheep and goats. Most of the area of interest for this study has a suitability value ≥ 50%, with approximately 23-29% of the study area considered preferred, or high-quality habitat for bighorn sheep. High-quality habitat for Rocky Mountain bighorn sheep is defined as being within 300 m of escape terrain, within 1.6 km of water, and containing ≤ 30% shrub and tree cover. Of this, approximately 43-56% of potential preferred habitat qualifies as winter range, which is mostly concentrated in the narrow valley bottoms where roads are commonly located and the south-facing slopes surrounding valleys. Analysis of field-collected vegetation data indicate most of the existing forage within the surveyed area to be of moderate or high forage value to bighorn sheep, but horizontal visibility, predominantly in the form of shrubs, is more obscured than what bighorn sheep prefer for most of the area of interest. Maximum shrub and tree cover is also the most limiting factor in the suitability model, primarily due to the prevalence of dense shrub regeneration, particularly Gambel oak, which occurs after high severity burns. The largest quantities of high-quality potential bighorn sheep habitat within the study area occur in unburned areas or those burnt by the predominantly low-moderate severity Amargo fire in 2021. Relative to risk of contact with domestic sheep and goats that can transmit lethal pneumonia-causing pathogens, potentially causing an introduction effort to fail, there is high risk because of the proximity to two hobby-subsistence herds (< 3 km away).

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USGS2024

Patterns and drivers of cottonwood mortality in the middle Rio Grande, New Mexico, USA

Riparian ecosystems are some of the most valuable and vulnerable on the planet. Riparian tree mortality is increasing in the western United States, where altered streamflows are combining with warming climate. Between 2011 and 2013, one third of an extensive stand of Populus deltoides var. wislizeni (Rio Grande cottonwood) died along the middle Rio Grande on the Pueblo of Santa Ana in New Mexico. Mortality coincided with a severe drought that followed a decade of decreasing streamflow, but it was heterogeneous, with adjacent patches of dead and live trees. The goal of this research was to determine the drivers of mortality to provide insights into future risks of die-off and potential management interventions. We compared tree age, competition, tree-ring widths, sediment particle size and climate influences between live and dead forest patches in a nested plot design. Live and dead trees had similar age, stand density and particle sizes of shallow sediments. Tree-ring widths had the highest correlations with July–September streamflow (1932–2013). All trees had declining ring growth since 1992, coinciding with declining late summer streamflow. An accelerated decline in growth began in 2002, corresponding to recent warmer droughts. Trees that died had lower ring growth 3 years prior to death and in the mid-1900s. Dead trees also had coarser deep sediments 2.4–3.7 m below ground, suggesting that reduced water holding capacity was an important factor for mortality. Water management to increase streamflow during the late summer, especially during times of extended drought, could reduce mortality risk in the face of projected increasingly warm droughts.

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USGS2024

Onset and tempo of ignimbrite flare-up volcanism in the eastern and central Mogollon-Datil volcanic field, southern New Mexico, USA

The Cenozoic ignimbrite flare-up (40–18 Ma) generated multiple volcanic fields in the southwestern United States and northern Mexico resulting from asthenospheric mantle upwelling after removal of the Farallon slab. The correlation of tuffs to one another and to source calderas within these volcanic fields is essential for determining spatiotemporal patterns in volcanism and magma geochemistry, which have been used to deduce migration of the Farallon slab at depth and associated mantle melting. However, the correlation of Eocene–Oligocene tuffs in the southwestern U.S. is difficult because of post-emplacement erosion and faulting. This study focuses on spatiotemporal patterns of the initial episode of ignimbrite flare-up activity (ca. 36.5–33.8 Ma) in the Mogollon-Datil volcanic field in south-central New Mexico, USA. We show that alkali feldspar major and trace element geochemistry is an effective tool for correlating tuffs when combined with high-precision, single-crystal 40 Ar/ 39 Ar geochronology and bulk-rock geochemistry. Using these data, we correlate several tuff units and differentiate other tuffs that have the same eruption age but very different geochemistry, and we conclude that there was a broadly northwestward migration in volcanism over time. The new tuff correlations are used to investigate spatiotemporal variations in magma geochemistry, erupted volumes, and recurrence intervals during the initial episode of Mogollon-Datil volcanic field volcanism. Early-erupted tuffs restricted to the eastern Mogollon-Datil volcanic field share similarities with western U.S. topaz rhyolites, which suggests that the silicic magmas were generated by partial melting of mafic lower crustal rocks. We also find differences in the compositions, crystallinities, and mineral assemblages between the early- and late-erupted tuffs. The early-erupted tuffs tend to have single-feldspar mineralogies, lower feldspar Or contents, large negative Eu anomalies, and low-whole–rock Ba concentrations. Conversely, late-erupted tuffs have two feldspar plus quartz assemblages, lesser Eu anomalies, higher whole-rock Ba concentrations, and feldspars have higher Or contents. Thus, we suggest that for some of the early eruptions, after magmas underwent crystal fractionation in the crust, the silicic melt largely separated from the crystalline mush prior to eruption, whereas late-erupted tuff magmas underwent crystal fractionation at near the eutectic minimum and were remobilized and erupted with a larger proportion of their crystalline mush. Using our new ages, correlations, and previously published data, we find that the initial phase of Mogollon-Datil volcanic field volcanism produced at least 15 eruptions between 36.5 Ma and 33.8 Ma, with a minimum total erupted volume of ~1350 km 3 and an average recurrence interval of 170 k.y. However, eruptions were generally smaller in volume (most <15 km 3 ) than in other coeval fields, and most eruptions (n = 11) occurred in the first 1.2 m.y. (ca. 36.5–35.3 Ma) of activity. Altogether, our work sheds new light on variations in the composition, timing, and migration of volcanism during the initial phase of Mogollon-Datil volcanic field activity and highlights the utility of feldspar geochemistry in both “fingerprinting” tuffs and elucidating magma evolution.

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USGS2024

Three-dimensional geologic framework model of the Rio San Jose groundwater basin and adjacent areas, New Mexico

As part of a U.S. Geological Survey study in cooperation with the Bureau of Reclamation and the Pueblo of Acoma, New Mexico, and the Pueblo of Laguna, New Mexico, a digital three-dimensional geologic framework model was constructed for the Rio San Jose and its surface-water drainage basin in west-central New Mexico. This three-dimensional model defines the altitude, thickness, and extent of 18 geologic units for use in a regional numerical hydrologic model. The model included an undifferentiated Proterozoic basement layer, 13 consolidated Paleozoic and Mesozoic rock units, and 4 Cenozoic units. Model input data were compiled from published cross sections, well data, structure contour maps, selected geophysical data, and data derived from geologic maps and structural features in the study area. These data were used to construct faulted surfaces that represent the upper and lower subsurface geologic unit boundaries. The digital three-dimensional geologic framework model combines faults, the altitude of the tops of each geologic unit, and boundary lines depicting the subsurface extent of each geologic unit. The digital three-dimensional geologic model described in this report and the corresponding data release represents the generalized geometry of the subsurface geologic units; it reproduces with reasonable accuracy the input geologic data and is consistent with previously published subsurface conceptualizations of the region. The geologic framework model is at a scale and resolution appropriate for use as the foundation for a numerical hydrologic model of the study area.

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USGS2024

Pre-fire assessment of post-fire debris flow hazards in the Santa Fe Municipal Watershed

Background Wildfires are increasing in size and severity due to climate change combined with overstocked forests. Fire increases the likelihood of debris flows, posing significant threats to life, property, and water supplies. Aims We conducted a debris-flow hazard assessment of the Santa Fe Municipal Watershed (SFMW) to answer two questions: (1) where are debris flows most likely to occur; and (2) how much debris might they produce? We also document the influence of fuel treatments on fire severity and debris flows. Methods We modelled post-fire debris-flow likelihood and volume in 103 sub-basins for 2-year, 5-year, and Probable Maximum Precipitation rainfalls following modelled low-, moderate-, and high-severity wildfires. Key results Post-fire debris-flow likelihoods were >90% in all but the lowest fire and rain scenarios. Sub-basins with fuel treatments had the lowest burn severities, debris-flow likelihoods, and sediment volumes, but treatment effects decreased with increased fire severity and rain intensity. Conclusions Post-fire debris flows with varying debris volumes are likely to occur following wildfire in the SFMW, but fuel treatments can reduce likelihood and volume. Implications Future post-fire debris flows will continue to threaten water supplies, but fuel reduction treatments and debris-flow mitigation provide opportunities to minimise effects.

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USGS2024

Redistribution of debris-flow sediment following severe wildfire and floods in the Jemez Mountains, New Mexico, USA

Severe fire on steep slopes increases stormwater runoff and the occurrence of runoff-initiated debris flows. Predicting locations of debris flows and their downstream effects on trunk streams requires watershed-scale high-resolution topographic data. Intense precipitation in July and September 2013 following the June 2011 Las Conchas Fire in the Jemez Mountains, New Mexico, led to widespread debris flows in the watershed of Rito de los Frijoles. We differenced lidar Digital Elevation Models (DEMs) collected in 2010 and 2016 to map subwatersheds experiencing debris flows and changes in elevation of the trunk stream. Debris flow occurrence was well predicted by previous assessments of debris-flow hazard; debris flows occurred in 7 of 9 sub-basins where the debris-flow hazard was above 60% for the 25-year rainfall event, and in 0 of 21 basins where debris flow hazard was less than 60%. Debris flows resulted in fan deposition at the confluence with the trunk stream followed by transport during three documented floods. The bed of the 22 km trunk stream increased in elevation by a mean of 0.29 m, but the local change in thalweg elevation was controlled by inputs of water and sediment and longitudinal variation in gradient. Downstream of the mouths of tributaries with debris flows, the thalweg of the trunk stream rose as much as 2 m. Downstream of the mouths of tributaries without debris flows the thalweg of the main stem degraded by as much as 2 m, mobilizing sediment that was then deposited further downstream where the gradient of the trunk stream decreases. In conclusion, the transport of sediment generated by debris flows was predictably related to spatial variation in sediment supply, discharge and gradient.

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USGS2024

The geochronology of White Sands Locality 2 is resolved

Rhode et al. (2024) allege that there are many “unresolved issues” with the geochronology of White Sands National Park (WHSA) Locality 2. They suggest there are substantial age offsets due to hard-water effects in the aquatic plants that were dated and that radiocarbon ages of pollen may be anomalously old due to reworking. In their view, the luminescence ages are likely to be maximum ages because of the probable presence of partially bleached quartz grains, overestimation of water content, and stratigraphic position of the samples. They also assert the ages of the footprint trackways are not as internally consistent as suggested and can be interpreted in various ways. We review each of these issues and show they are without merit, often irrelevant, at odds with first principles, and stem from a lack of firsthand understanding of the studies we conducted at WHSA Locality 2.

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USGS2024

Movement patterns of a small-bodied minnow suggest nomadism in a fragmented, desert river

Background Unfettered movement among habitats is crucial for fish to access patchily distributed resources and complete their life cycle, but many riverscapes in the American Southwest are fragmented by dams. The federally endangered Rio Grande silvery minnow ( Hybognathus amarus , RGSM) persists in a fragmented remnant of its former range (ca. 95% range reduction), and its movement ecology is understudied. Methods We tracked movements of hatchery-reared RGSM, tagged with passive integrated transponder tags, using stationary and mobile antennas from 2019–2022. We quantified probability of movement and total distance moved by RGSM released above and below a dam. We then assessed how well two prevailing riverine movement theories (i.e., restricted movement paradigm [RMP] and colonization cycle hypothesis [CCH]) explained RGSM movement patterns. Results We detected 36.8% of released RGSM (n = 37,215) making at least one movement. Movements were leptokurtic and substantially greater than expected based on the RMP for both stationary (1.7–5.9 m) and mobile (30.3–77.8 m) individuals. On average, RGSM were detected at large for 75 days and moved a total of 12.2 rkm within a year. The maximum total distance moved by RGSM was 103 rkm. Similarly, we observed a multimodal distribution of detected range sizes with a mean detected range of 2.4 rkm and a maximum detected range of 78.2 rkm. We found little support for an upstream movement bias, as expected under the CCH, and most movements (74%) were directed downstream. Conclusions Our data suggest RGSM are highly mobile, with the ability to make long-distance movements. Neither movement theory adequately described movement patterns of RGSM; instead, our findings support a nomadic movement pattern and an apparent drift paradox matching recent studies of other pelagic-broadcast spawning minnows who persist upstream despite experiencing downstream drift as larvae. Resolution of the drift paradox may be achieved through further, targeted studies into different aspects of the species’ life history. Quantification of RGSM movement provides crucial insights into the species’ movement ecology and may help define the appropriate scale of recovery efforts.

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USGS2024

The LTAR Grazing Land Common Experiment at the Jornada Experimental Range: Old genetics, new precision technologies, and adaptive value chains

Rangelands and the supply chains connected to them are central to the agrifood systems of the Southwestern United States. Local ranchers are simultaneously arid lands managers, herd managers, and marketing managers. To stay in business, they must constantly adapt to unpredictable forage resources and markets while conserving soils and vegetation resources for the long term. As climate warming and drying exacerbate the complexity and difficulty of day-to-day production, producers and policy-makers are seeking alternatives to “business as usual”. To meet this need, the LTAR-Jornada team has developed a package of strategies to help producers adapt to the local and inter-regional challenges. The package includes heritage cattle, precision ranching systems, and adaptive value chains. Five ranches across the Southwest have adopted different combinations of the strategies and are partnering to measure their benefits and drawbacks in real-world conditions. Opportunities for controlled experimentation differ among the ranches, so we use LTAR’s indicator system to assess and compare results. Even as we invest in co-producing knowledge about these three strategies, we recognize that progressive aridification and urbanization of Southwestern rangelands create challenges for which a single “silver bullet” agricultural innovation is unlikely to provide durable solutions. We are learning from our customers and stakeholders about ways to adjust the development of new options.

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USGS2024

A semi-mechanistic model for partitioning evapotranspiration reveals transpiration dominates the water flux in drylands

Popular evapotranspiration (ET) partitioning methods make assumptions that might not be well-suited to dryland ecosystems, such as high sensitivity of plant water-use efficiency (WUE) to vapor pressure deficit (VPD). Our objectives were to (a) create an ET partitioning model that can produce fine-scale estimates of transpiration (T) in drylands, and (b) use this approach to evaluate how climate controls T and WUE across ecosystem types and timescales along a dryland aridity gradient. We developed a novel, semi-mechanistic ET partitioning method using a Bayesian approach that constrains abiotic evaporation using process-based models, and loosely constrains time-varying WUE within an autoregressive framework. We used this method to estimate daily T and weekly WUE across seven dryland ecosystem types and found that T dominates ET across the aridity gradient. Then, we applied cross-wavelet coherence analysis to evaluate the temporal coherence between focal response variables (WUE and T/ET) and environmental variables. At yearly scales, we found that WUE at less arid, higher elevation sites was primarily limited by atmospheric moisture demand, and WUE at more arid, lower elevation sites was primarily limited by moisture supply. At sub-yearly timescales, WUE and VPD were sporadically correlated. Hence, ecosystem-scale dryland WUE is not always sensitive to changes in VPD at short timescales, despite this being a common assumption in many ET partitioning models. This new ET partitioning method can be used in dryland ecosystems to better understand how climate influences physically and biologically driven water fluxes.

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USGS2024

Delineating draft inventory analysis units for National Scenic and Historic Trails inventory, assessment, and monitoring programs

As of 2024, there are 32 National Scenic and Historic Trails (NSHTs) in the system administered by the Bureau of Land Management (BLM), National Park Service, and U.S. Department of Agriculture Forest Service. The BLM administers, manages, and protects 19 of these trails as part of its system of national conservation lands. Various laws, regulations, and policies require that the BLM conduct and maintain an inventory to protect trail-related resources, qualities, values, associated settings, and primary use or uses. There are set procedures for conducting inventory, assessment, and monitoring (IAM) of NSHTs, as outlined in volumes 1 and 2 of BLM Technical Reference 6280-1. One of the first steps in the IAM process is deciding the area along a trail to inventory. However, volumes 1 and 2 of BLM Technical Reference 6280-1 do not specify how the land area to be inventoried should be delineated. The BLM calls these focus areas for IAM efforts “inventory analysis units” (IAUs), which are defined as the geospatial boundary for the location of an inventory along a trail. This report reviews the approach used to delineate the IAUs for an inventory effort and identifies best practices for creating initial IAUs, termed “draft IAUs.” Draft IAUs would provide standardization across multiple management jurisdictions by applying the same parameters for their delineation. These draft IAUs would provide trail managers with an area surrounding NSHTs that would trigger the need for an inventory if a project were proposed within it and are meant to be refined during localized inventory efforts. The best practices herein are for creating draft IAUs using standard parameters for performing a viewshed analysis to identify a proxy of land to include in an initial inventory effort.

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USGS2024

Multi-decadal vegetation transformations of a New Mexico ponderosa pine landscape after severe fires and aerial seeding

Wildfires and climate change are having transformative effects on vegetation composition and structure, and post-fire management may have long-lasting impacts on ecosystem reorganization. Post-fire aerial seeding treatments are commonly used to reduce runoff and soil erosion, but little is known about how seeding treatments affect native vegetation recovery over long periods of time, particularly in type-converted forests which have been dramatically transformed by the effects of repeated, high-severity fire. In this study, we analyze and report on a rare long-term (23-year) dataset that documents vegetation dynamics following a 1996 post-fire aerial seed treatment and subsequent 2011 high-severity reburn in a dry conifer forest of northern New Mexico in the southwestern United States. Repeated surveys between 1997 – 2019 of 49 permanent transects were used to test for differences in vegetation cover, richness, and diversity between seeded and unseeded areas, and to characterize the development of seeded and unseeded vegetation communities through time and across gradients of burn severity, elevation, and soil-available water capacity. Post-fire seeding led to a clear and sustained divergence in herbaceous community composition. Seeded plots had much higher cover of non-native graminoids, primarily Bromus inermis , a likely contaminant in the seed mix. High-severity reburning in all plots in 2011 reduced native graminoid cover by half at seeded plots compared to both pre-fire levels and to plots that were unseeded following the initial 1996 fire. In addition, increased fire severity was associated with increased non-native graminoid cover and reduced native graminoid cover, native species richness, and species diversity. This study documents a fire-driven ecosystem transformation from a former conifer forest into a shrub-grass system, reinforced by aerial seeding of grasses and high-severity reburning. This unique long-term dataset illustrates that post-fire seeding carries significant risk of unwanted non-native species invasions that persist through subsequent fires – indicating that alternative post-fire management actions merit consideration to better support native ecosystem resilience in the face of emergent climate change and increasing disturbance. Lastly, this study highlights the importance of long-term monitoring of post-fire vegetation dynamics, as short-term assessments will miss key elements of the full complexity of ecosystem responses to fire and post-fire management actions.

New Mexico↗