Geology topics

Kiona Ogle

Publications and source records attributed to Kiona Ogle.

10 recordsLinked to original sources

USGS2026

James Buttle Review: A synthesis of riparian plant water use over two decades in North American drylands

Assessing riparian ecosystem water use, particularly transpiration from vegetation and evaporation from soils (‘plant water use’, hereafter), is key to developing sound water management approaches. In western North America, a multidecadal drought is reducing water availability and increasing the use of detailed water budgets. Questions related to both removal of vegetation for water salvage and budgeting water to maintain valuable riparian areas have led to a wealth of studies on riparian plant water use across dryland river systems in North America. Towards evaluating broad patterns in riparian plant water use, we synthesise results from over two decades of research, with the goal of informing water management policies and planning. This study asks: (1) Do some riparian plant communities exhibit lower plant water use than others? (2) Do riparian plant communities have higher water use under hotter climates? (3) Can statistical models based on existing data, plant communities and climate data be used to predict water use for unmeasured locations? Using hierarchical Bayesian models to synthesise data on annual and daily-scale plant water use, we show that marshes, cottonwood-willow stands and tamarisk not impacted by biocontrol use larger amounts of water at the annual scale than other vegetation communities. All plant communities have higher annual water use in hotter climates, which is likely related to a longer growing season and higher evaporative demand. Statistical models based on existing water-use data, plant communities and climate provide bounds on plant water use that can be applied to unmeasured locations and used to evaluate the effects of plant community change on water use. This synthesis produces the most complete summary of riparian plant water use in North American drylands to date and provides water use predictions across different climate and community scenarios that can be used for current and future conditions.

Arizona, California, Colorado, Idaho, Nevada, New ↗

USGS2025

Precipitation pulse dynamics are not ubiquitous: A global meta-analysis of plant and ecosystem carbon- and water-related pulse responses

Ecosystem responses to precipitation pulses (“pulse responses”) exert a large control over global carbon, water, and energy cycles. However, it is unclear how the timing and magnitude of pulse responses will vary across ecosystems as precipitation regimes shift under accelerating climate change. To address this issue, this study evaluates how plants and ecosystems respond to precipitation pulses and explores potential implications of altered precipitation regimes for the carbon and water cycles. In particular, we conducted a global meta-analysis to quantify the magnitude and timing of plant and ecosystem carbon-related ( A net , NPP, GPP, R eco , R bg ) and water-related (ET, T, Ψ, g s ) responses to 587 precipitation pulses. By analyzing pulse-response metrics published in the primary literature, we evaluated the characteristics of those pulse responses. We assessed whether precipitation pulses lead to a classic pulse response (i.e., a hump-shaped response as described by the pulse-reserve framework), a linear pulse response, a combination of classic and linear, or a lack of a pulse response. If a pulse response occurred, we explored the factors that drove its timing, magnitude, and speed. Our meta-analyses revealed that the classic, hump-shaped response is not ubiquitous, as it only accounted for 52% of the pulse responses. However, when a pulse response did occur, carbon-related responses to precipitation pulses were larger in magnitude (e.g., larger peak) than water-related pulse responses at relatively arid sites. However, at relatively mesic sites, this relationship reversed (i.e., water-related responses to precipitation pulses were larger than carbon-related responses). Additionally, larger precipitation pulse amounts increased water-related response magnitudes more than carbon-related response magnitudes across both arid and mesic sites. Therefore, under future precipitation intensification, carbon-related responses to precipitation pulses may become more decoupled from water-related pulse responses in wetter biomes but more coupled to water-related pulse responses in drier biomes.

Global Change Biology↗

USGS2025

Filling the gaps: A Bayesian mixture model for imputing missing soil water content data

Soil water content (SWC) data are central to evaluating how soil moisture varies over time and space and influences critical plant and ecosystem functions, especially in water-limited drylands. However, sensors that record SWC at high frequencies often malfunction, leading to incomplete timeseries and limiting our understanding of dryland ecosystem dynamics. We developed an analytical approach to impute missing SWC data, which we tested at six eddy flux tower sites along an elevation gradient in the southwestern United States. We impute missing data as a mixture of linearly interpolated SWC between the observed endpoints of a missing data gap and SWC simulated by an ecosystem water balance model (SOILWAT2). Within a Bayesian framework, we allowed the relative utility (mixture weight) of each component (linearly interpolated vs. SOILWAT2) to vary by depth, site and gap characteristics. We explored “fixed” weights versus “dynamic” weights that vary as a function of cumulative precipitation, average temperature, and time since the start of the gap. Both models estimated missing SWC data well (R2 = 0.70–0.88 vs. 0.75–0.91 for fixed vs. dynamic weights, respectively), but the utility of linearly interpolated versus SOILWAT2 values depended on site and depth. SOILWAT2 was more useful for more arid sites, shallower depths, longer and warmer gaps and gaps that received greater precipitation. Overall, the mixture model reliably gap-fills SWC, while lending insight into processes governing SWC dynamics. This approach to impute missing data could be adapted to accommodate more than two mixture components and other types of environmental timeseries.

New Mexico↗

USGS2025

Hotter temperatures alter riparian plant outcomes under regulated river conditions

Climate change and river regulation alter environmental controls on riparian plant occurrence and cover worldwide. Simultaneous changes to river flow and air temperature could result in unanticipated plant responses to novel environmental conditions. Increasing temperature could alter riparian plant response to hydrology and other factors, while river regulation may exacerbate environmental stress through novel flows like those resulting from power generation. Further, plant establishment and growth may require differing conditions, which may be decoupled by novel conditions. Using a large dataset that spans a natural 5°C mean annual temperature (MAT) gradient and a Bayesian model that integrates plant occurrence and cover, we address four questions: (1) Does hotter MAT modify plant response to hydrology, substrate composition, topography, and cover of co-occurring plant species? (2) Does the timing of hydropower tides benefit some species over others? (3) Does dam-induced erosion hinder riparian species more than upland species? (4) Do occurrence and cover respond to different environmental variables, allowing for decoupling of life history processes? We addressed these questions with data collected along 364 km of the Colorado River downstream of Glen Canyon Dam, Arizona, United States of America. Occurrence and cover class were recorded in >10,000 plots from 2016 to 2020, along with environmental covariates that repeat across the climate gradient. For 36 species, plant occurrence and cover were modeled with respect to MAT, hydrology, substrate, topography, other plant cover, and their interactions with MAT. There were four key results. (1) Increasing MAT will not only directly influence plants but will mediate their responses to the environment, including greater dependence on stable water supplies. (2) The timing of hydropower tides shapes plant community composition. (3) Dam-related erosion has an outsized effect on riparian species, which could lead to a loss of regionally unique plant species. (4) For all species, the most important covariates driving occurrence differed from those for cover, suggesting the potential for these life stages to be decoupled. Not only will climate change and river regulation independently alter plant distributions, interactions among hotter temperature, dam-controlled flow patterns, and limited fine sediments will determine which species flourish or perish under future conditions.

Arizona↗

USGS2025

Beyond optimality: Dryland ecosystems infrequently use water efficiently for carbon gain

Optimality theory assumes plants maximize carbon gain per unit water lost and is often implemented to scale leaf-level carbon gain and water use to regional and global scales. Optimality theory is often mathematically represented by assuming plant water-use efficiency (WUE) scales with VPD k , where k = ½ represents expected optimal behavior. It is unclear, however, if this relationship holds in arid and semi-arid ecosystems that are strongly impacted by soil and atmospheric moisture status. We used data from seven flux tower sites along an aridity gradient in New Mexico to answer: how does the relationship between WUE and VPD compare to expectations based on optimality theory? To address this question, we integrated the Dynamic Evapotranspiration Partitioning Approach for Rapid Timescales with a stochastic antecedent model to estimate ecosystem-level WUE (GPP/T) and the net sensitivity of WUE to VPD, or k Dynamic , which we compare to the theoretical optimal sensitivity of k = ½. Our results show that optimality theory is not always appropriate, and k Dynamic often deviates from ½, especially at some of the more arid sites or during periods of low soil moisture. At less arid, higher elevation sites, k Dynamic is most consistent with optimality theory at moderate VPD levels, but not at high VPD. In general, the sensitivity of WUE to VPD is highly variable such that k Dynamic exhibits notable daily and seasonal variability, suggesting highly dynamic stomatal behavior. These results emphasize that representing plant water-use strategies as dynamic in time and space is critical to improving large-scale estimates of plant water use.

New Mexico↗

USGS2024

Restoration treatments enhance tree growth and alter climatic constraints during extreme drought

The frequency and severity of drought events are predicted to increase due to anthropogenic climate change, with cascading effects across forested ecosystems. Management activities such as forest thinning and prescribed burning, which are often intended to mitigate fire hazard and restore ecosystem processes, may also help promote tree resistance to drought. However, it is unclear whether these treatments remain effective during the most severe drought conditions or whether their impacts differ across environmental gradients. We used tree-ring data from a system of replicated, long-term (>20 years) experiments in the southwestern United States to evaluate the effects of forest restoration treatments (i.e., evidence-based thinning and burning) on annual growth rates (i.e., basal area increment; BAI) of ponderosa pine ( Pinus ponderosa ), a broadly distributed and heavily managed species in western North America. The study sites were established at the onset of the most extreme drought event in at least 1200 years and span much of the climatic niche of Rocky Mountain ponderosa pine. Across sites, tree-level BAI increased due to treatment, where trees in treated units grew 133.1% faster than trees in paired, untreated units. Likewise, trees in treated units grew an average of 85.6% faster than their pre-treatment baseline levels (1985 to ca. 2000), despite warm, dry conditions in the post-treatment period (ca. 2000–2018). Variation in the local competitive environment promoted variation in BAI, and larger trees were the fastest-growing individuals, irrespective of treatment. Tree thinning and prescribed fire altered the climatic constraints on growth, decreasing the effects of belowground moisture availability and increasing the effects of atmospheric evaporative demand over multi-year timescales. Our results illustrate that restoration treatments can enhance tree-level growth across sites spanning ponderosa pine's climatic niche, even during recent, extreme drought events. However, shifting climatic constraints, combined with predicted increases in evaporative demand in the southwestern United States, suggest that the beneficial effects of such treatments on tree growth may wane over the upcoming decades.

Arizona, Colorado, Nevada, New Mexico, Texas↗

USGS2023

Provenance, genotype, and flooding influence growth and resource acquisition characteristics in a clonal, riparian shrub

Premise Riparian plants can exhibit intraspecific phenotypic variability across the landscape related to temperature and flooding gradients. Phenotypes that vary across a climate gradient are often partly genetically determined and may differ in their response to inundation. Changes to inundation patterns across a climate gradient could thus result in site-specific inundation responses. Phenotypic variability is more often studied in riparian trees, yet riparian shrubs are key elements of riparian systems and may differ from trees in phenotypic variability and environmental responses. Methods We tested if individuals of a clonal, riparian shrub, Pluchea sericea , collected from provenances spanning a temperature gradient differed in their phenotypes and responses to inundation and to what degree such differences were related to genotype. Plants were subjected to different inundation depths and a subset genotyped. Variables related to growth and resource acquisition were measured and analyzed using hierarchical, multivariate Bayesian linear regressions. Results Individuals from different provenances differed in their phenotypes, but not in their response to inundation. Phenotypes were not related to provenance temperature but were partially governed by genotype. Growth was more strongly influenced by inundation, while resource acquisition was more strongly controlled by genotype. Conclusions Growth and resource acquisition responses in a clonal, riparian shrub are affected by changes to inundation and plant demographics in unique ways. Shrubs appear to differ from trees in their responses to environmental change. Understanding environmental effects on shrubs separately from those of trees will be a key part of evaluating environmental change impacts on riparian ecosystems.

American Journal of Botany↗

USGS2022

What drought means for southwestern landscapes

Introduction Each year, more than 20,000 people raft the Grand Canyon, many of whom will experience this iconic landscape for the first and only time. Visitors to our region for their once-in-a-lifetime Grand Canyon experience might be surprised to see forests and wetlands in addition to deserts. While locals are seeing changes to the Colorado Plateau woodlands, many visitors may not be able to distinguish between our normal desert landscapes (we have cactus!) and the increasingly dry and hot conditions we have experienced in recent decades. Helping visitors see these drought impacts could help communicate that climate change is not a problem for future generations but something affecting us now. The southwestern US (“Southwest”) is one of many dry regions around the world located within about 30 degrees of the equator. As global temperatures rise, these dry zones are getting drier and are likely expanding1. Dryland expansion and aridification alters water availability, which touches our lives and ecosystem health in the Southwest. This essay focuses on drought impacts on ecosystems across the Four-Corners region and Grand Canyon, with particular attention to the forests and woodlands that contribute, in part, to Colorado River flows.

Arizona, California, Nevada↗

USGS2021

Riverine complexity and life history inform restoration in riparian environments in the southwestern U.S.

Riparian habitat in the southwestern USA has undergone substantial degradation over the past century, prompting extensive management and restoration of these critical ecosystems. Most restoration efforts, however, do not account for life history traits or riverine complexity that may influence genetic diversity and structure. Here, we use simple sequence repeat (SSR) markers in four southwestern riparian species ( Populus fremontii, Salix gooddingii, S. exigua, and Prosopis glandulosa ) that occupy a geographically complex region to address four questions: 1) How is river connectivity related to genetic diversity and structure? 2) How do mating systems and dispersal mechanisms influence gene flow? 3) Is genetic diversity influenced by unidirectional water flow? 4) How do unregulated tributary and regulated river flows affect clonality and associated diversity? Our results identify five findings: 1) Patterns of genetic diversity and structure vary substantially across different species; 2) species with geographic distributions that include a large, perennial river exhibit the least genetic structure; 3) mating system, clonality, and seed dispersal are related to genetic structure; 4) genetic diversity is variable among species and populations, but does not increase or decrease unidirectionally; and 5) clonality and associated diversity does not differ along a regulated river relative to unregulated tributaries. Our multispecies approach to understanding how riverine complexity and life history traits influence genetic diversity and structure could be incorporated into management efforts to more closely match riparian species with their unique environments, thereby facilitating restoration success.

Arizona↗

USGS2020

Pervasive shifts in forest dynamics in a changing world

Forest dynamics arise from the interplay of environmental drivers and disturbances with the demographic processes of recruitment, growth, and mortality, subsequently driving biomass and species composition. However, forest disturbances and subsequent recovery are shifting with global changes in climate and land use, altering these dynamics. Changes in environmental drivers, land use, and disturbance regimes are forcing forests toward younger, shorter stands. Rising carbon dioxide, acclimation, adaptation, and migration can influence these impacts. Recent developments in Earth system models support increasingly realistic simulations of vegetation dynamics. In parallel, emerging remote sensing datasets promise qualitatively new and more abundant data on the underlying processes and consequences for vegetation structure. When combined, these advances hold promise for improving the scientific understanding of changes in vegetation demographics and disturbances.

Science↗