Greg Barron-Gafford

Greg Barron-Gafford
The University of Arizona | UA · School of Geography and Development / Biosphere 2, College of Science

Ph.D, Univeristy of Arizona

About

163
Publications
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Introduction
I am a Biogeographer, an Ecosystem Ecologist, and a Plant Physiologist. I work across disciplines to study the interactive effects of vegetation and climate change on plant and ecosystem function to inform forecasting and decision makers. Learn more at my website: http://www.barrongafford.org/

Publications

Publications (163)
Article
Full-text available
While photovoltaic (PV) renewable energy production has surged, concerns remain about whether or not PV power plants induce a “heat island” (PVHI) effect, much like the increase in ambient temperatures relative to wildlands generates an Urban Heat Island effect in cities. Transitions to PV plants alter the way that incoming energy is reflected back...
Article
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Current understanding of the dynamic and slow flow paths that support streamflow in mountain headwater catchments is inhibited by the lack of long-term hydrogeochemical data and the frequent use of short residence time age tracers. To address this, the current study combined the traditional mean transit time and the state-of-the-art fraction of you...
Article
Mounting evidence indicates dryland ecosystems play an important role in driving the interannual variability and trend of the terrestrial carbon sink. Nevertheless, our understanding of the seasonal dynamics of dryland ecosystem carbon uptake through photosynthesis [gross primary productivity (GPP)] remains relatively limited due in part to the lim...
Article
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Plant canopy temperature (Tc) is partly regulated by evaporation and transpiration from the canopy surface and can be used to infer changes in stomatal regulation and vegetation water stress. In this study, we used a thermal Unmanned Aircraft Systems in conjunction with eddy covariance, sap flow, and spectral reflectance data to assess the diurnal...
Article
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Explicit representations of microbial processes in soil organic carbon (SOC) decomposition models have received increasing attention, because soil heterotrophic respiration remains one of the greatest uncertainties in climate‐carbon feedbacks projected by Earth system models (ESMs). Microbial‐explicit models have been developed and applied in site‐...
Article
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 interan...
Preprint
Full-text available
Current understanding of the dynamic flow paths and subsurface water storages that support streamflow in mountain catchments is inhibited by the lack of long-term hydrologic data and the frequent use of single age tracers that are not applicable to older groundwater reservoirs. To address this, the current study used both multiple metrics and trace...
Article
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Hydraulic redistribution is the transport of water from wet to dry soil layers, upward or downward, through plant roots. Often in savanna and woodland ecosystems, deep‐rooted trees, and shallow‐rooted grasses coexist. The degree to which these different species compete for or share soil‐water derived from precipitation or groundwater, as well as ho...
Article
Tracking wood formation in semi-arid regions during the seasonal march of precipitation extremes has two important applications. It can provide 1) insight into the adaptive capacities of trees to drought, and 2) a basis for a richer interpretation of tree-ring data, assisting in a deeper understanding of past and current climate. In the southwester...
Article
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Catchment‐scale response functions, such as transit time distribution (TTD) and evapotranspiration time distribution (ETTD), are considered fundamental descriptors of a catchment's hydrologic and ecohydrologic responses to spatially and temporally varying precipitation inputs. Yet, estimating these functions is challenging, especially in headwater...
Article
Transition from historic grasslands to woody plants in semiarid regions has led to questions about impacts in soil functioning, where microorganisms play a primary role. Understanding the relationship between microbes, plant diversity and soil functioning, is relevant to assess such impacts. We evaluate the effect that plant type change in semiarid...
Article
Intraspecific competition among parasites should, in theory, increase virulence, but we lack clear evidence of this from nature.1-3 Parasitic plants, which are sessile and acquire carbon-based resources through both autotrophy (photosynthesis) and heterotrophy (obtaining carbon from the host), provide a unique opportunity to experimentally study th...
Article
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Anticipating the ability of ecosystems to maintain functional integrity across predicted altered precipitation regimes remains a grand ecohydrological challenge. Overstory trees and understory grasses within semiarid savannas vary in their structure and sensitivity to environmental pressures, underscoring the need to examine the ecohydrological imp...
Article
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At the seasonal timescale, daily photochemical reflectance index (PRI) measurements track changes in photoprotective pigment pools as plants respond to seasonally variable environmental conditions. As such, remotely‐sensed PRI products present opportunities to study seasonal processes in evergreen conifer forests, where complex vegetation dynamics...
Article
Knowing how evapotranspiration (ET) is mediated by abiotic and biotic pathways is essential to understanding how water affects ecosystem productivity. Recent studies have investigated the average transpiration fraction (T/ET) across sites and biomes, but the temporal variability of the partitioning and its controls are less understood. Here, we exa...
Article
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Land-atmosphere interactions at different temporal and spatial scales are important for our understanding of the Earth system and its modeling. The Landscape Evolution Observatory (LEO) at Biosphere 2, managed by the University of Arizona, hosts three nearly identical artificial bare-soil hillslopes with dimensions of 11 × 30 m2 (1 m depth) in a co...
Article
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High-elevation montane forests are disproportionately important to carbon sequestration in semi-arid climates where low elevations are dry and characterized by low carbon density ecosystems. However, these ecosystems are increasingly threatened by climate change with seasonal implications for photosynthesis and forest growth. As a result, we levera...
Article
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Climate change is dramatically restructuring agriculture and damaging crops, food security, and human health, especially in deserts. To radically redesign food systems to buffer against climatic disruptions, we focus on agroecological function, human health, and community well‐being. Using arid North America (“Aridamerica”) as a laboratory for the...
Article
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Semiarid forests in the southwestern United States are generally restricted to mountain regions where complex terrain adds to the challenge of characterizing stand productivity. Among the heterogeneous features of these ecosystems, topography represents an important control on system-level processes including snow accumulation and melt. This basic...
Article
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We used the weighted wavelet method to perform spectral analysis of observed long-term precipitation, streamflow, actual evapotranspiration, and soil water storage at a sub-humid mountain catchment near Tucson, Arizona, USA. Fractal scaling in precipitation and the daily change in soil water storage occurred up to a period of 14 days and correspond...
Article
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“Sky islands” are characteristic of sequential mountain-valley terrain where mountains form an island archipelago rising from surrounding valleys of desert “sea”. At high elevations in the Madrean sky islands of the southwestern United States (USA) and Mexico, mixed evergreen conifer forests occur near the latitudinal extent of their distribution....
Article
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Ecosystem carbon flux partitioning is strongly influenced by poorly constrained soil CO2 efflux (Fsoil). Simple model applications (Arrhenius and Q10) do not account for observed diel hysteresis between Fsoil and soil temperature. How this hysteresis emerges and how it will respond to variation in vegetation or soil moisture remains unknown. We use...
Article
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Ecosystem carbon flux partitioning is strongly influenced by poorly constrained soil CO 2 efflux (F soil). Simple model applications (Arrhenius and Q 10) do not account for observed diel hysteresis between F soil and soil temperature. How this hysteresis emerges and how it will respond to variation in vegetation or soil moisture remains unknown. We...
Article
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Hybrid-poplar tree plantations provide a source for biofuel and biomass, but they also increase forest isoprene emissions. The consequences of increased isoprene emissions include higher rates of tropospheric ozone production, increases in the lifetime of methane, and increases in atmospheric aerosol production, all of which affect the global energ...
Article
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This study coupled long‐term hydrometric and stable water isotope data to identify links between subsurface water storage and vegetation in a subhumid mountain catchment in Arizona, USA. Specific observations included catchment‐scale hydrologic fluxes and soil water storage, and stable water isotopes from stream water, soil water, groundwater, and...
Article
Understanding the hydrologic and carbon cycling consequences of precipitation variability in dryland ecosystems requires improved appreciation and accounting of how above- and belowground biophysical processes differ in their response to rainfall. Our objective was to contrast the sensitivity of dryland ecosystem evapotranspiration (ET), gross ecos...
Article
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Predicting fluid biogeochemistry in the vadose zone is difficult because of time‐dependent variation in multiple controlling factors, such as temperature, moisture, and biological activity. Furthermore, soils are multicomponent, heterogeneous porous media where manifold reactions may be affecting solution chemistry. We postulated that ecosystem‐sca...
Article
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The vulnerabilities of our food, energy and water systems to projected climatic change make building resilience in renewable energy and food production a fundamental challenge. We investigate a novel approach to solve this problem by creating a hybrid of colocated agriculture and solar photovoltaic (PV) infrastructure. We take an integrative approa...
Article
Critical Zone Science (CZS) represents a powerful confluence of research agendas, tools, and techniques for examining the complex interactions between biotic and abiotic factors located at the interface of the Earth’s surface and shallow subsurface. Earth’s Critical Zone houses and sustains terrestrial life, and its interacting subsystems drive mac...
Article
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Bayesian inference of microbial soil respiration models is often based on the assumptions that the residuals are independent (i.e., no temporal or spatial correlation), identically distributed (i.e., Gaussian noise), and have constant variance (i.e., homoscedastic). In the presence of model discrepancy, as no model is perfect, this study shows that...
Article
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Soil CO2 efflux (Fsoil) is a major component of the ecosystem carbon balance. Globally expansive semiarid ecosystems have been shown to influence the trend and interannual variability of the terrestrial carbon sink. Modeling Fsoil in water-limited ecosystems remains relatively difficult due to high spatial and temporal variability associated with d...
Article
High elevation mountain catchments are often subject to large climatic and topographic gradients. Therefore, high density hydrogeochemical observations are needed to understand water sources to streamflow and the temporal and spatial behavior of flow paths. These sources and flow paths vary seasonally, which dictates short‐term storage and the flux...
Article
Full-text available
Bayesian inference of microbial soil respiration models is often based on the assumptions that the residuals are independent (i.e. no temporal or spatial correlation), identically distributed (i.e. Gaussian noise) and with constant variance (i.e. homoscedastic). In the presence of model discrepancy, since no model is perfect, this study shows that...
Article
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This paper defines a new scoring rule, namely relative model score (RMS), for evaluating ensemble simulations of environmental models. RMS implicitly incorporates the measures of ensemble mean accuracy, prediction interval precision, and prediction interval reliability for evaluating the overall model predictive performance. RMS is numerically eval...
Article
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Soil CO2 efflux (Fsoil) is commonly considered equal to soil CO2 production (Rsoil), and both terms are used interchangeably. However, a non-negligible fraction of Rsoil can be consumed in the subsurface due to a host of disparate, yet simultaneous processes. The ratio between CO2 efflux/O2 influx, known as the apparent respiratory quotient (ARQ),...
Chapter
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Understanding the process interactions and feedbacks among water, porous geological media, microbes, and vascular plants is crucial for improving predictions of the response of Earth’s critical zone to future climatic conditions. However, the integrated coevolution of landscapes under change is notoriously difficult to investigate. Laboratory studi...
Article
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Most land surface models (LSMs) used in Earth System Models produce a lower ratio of transpiration (T) to evapotranspiration (ET) than field observations, degrading the credibility of Earth System Model-projected ecosystem responses and feedbacks to climate change. To interpret this model deficiency, we conducted a pair of model experiments using a...
Article
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A major challenge in critical zone science is to understand and predict the interaction between above-ground and below-ground ecohydrologic processes. One process that facilitates this connection is hydraulic redistribution, a phenomenon by which roots serve as preferential pathways for water movement from wet to dry soil layers. We use a multilaye...
Article
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Earth's future carbon balance and regional carbon exchange dynamics are inextricably linked to plant photosynthesis. Spectral vegetation indices are widely used as proxies for vegetation greenness and to estimate state variables such as vegetation cover and leaf area index. However, the capacity of green leaves to take up carbon can change througho...
Data
Mean, median, and standard deviation of R2 values based on proportion of data used for training the PLSR model. The mean, median, and standard deviation in R2 of 100 PLSR models per training proportion are represented. (DOCX)
Data
Variance of R2 values based on proportion of data used for training the PLSR model. Each point represents the r-squared between predicted and actual Vcmax/Jmax values from PLSR using a random sample corresponding to the designated proportion of training data (each proportion was sampled 100 times). (TIF)
Article
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Soil-mantled pole-facing hillslopes on Earth tend to be steeper, wetter, and have more vegetation cover compared to adjacent equator-facing hillslopes. These and other slope aspect controls are often the consequence of feedbacks among hydrologic, ecologic, pedogenic, and geomorphic processes triggered by spatial variations in mean annual insolation...
Article
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Widespread, high levels of tree mortality, termed forest die-off, associated with drought and rising temperatures, are disrupting forests worldwide. Drought will likely become more frequent with climate change, but even without more frequent drought, higher temperatures can exacerbate tree water stress. The temperature sensitivity of drought-induce...
Article
The net ecosystem exchange (NEE) is the difference between ecosystem CO2 assimilation and CO2 losses to the atmosphere. Ecosystem respiration (Reco), the efflux of CO2 from the ecosystem to the atmosphere, includes the soil-to-atmosphere carbon flux (i.e., soil respiration; Rsoil) and aboveground plant respiration. Therefore, Rsoil is a fraction of...
Article
Full-text available
Across much of western North America, forests are predicted to experience a transition from snow- to rain-dominated precipitation regimes due to anthropogenic climate warming. Madrean sky island mixed conifer forests receive a large portion of their precipitation from summertime convective storms and may serve as a lens into the future for snow-dom...
Article
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Widespread tree mortality associated with drought has been observed on all forested continents and global change is expected to exacerbate vegetation vulnerability. Forest mortality has implications for future biosphere-atmosphere interactions of carbon, water and energy balance, and is poorly represented in dynamic vegetation models. Reducing unce...
Article
A long-standing ambition in ecosystem science has been to understand the relationship between ecosystem community composition, structure and function. Differential water use and hydraulic redistribution have been proposed as one mechanism that might allow for the coexistence of overstory woody plants and understory grasses. Here, we investigated ho...
Article
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Climate change is increasing the frequency and extent of high-severity disturbance, with potential to alter vegetation community composition and structure in environments sensitive to tipping points between alternative states. Shrub species display a range of characteristics that promote resistance and resilience to disturbance, and which yield dif...
Article
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2017. Prototype campaign assessment of disturbance-induced tree loss effects on surface properties for atmospheric modeling. Ecosphere 8(3): Abstract. Changes in large-scale vegetation structure triggered by processes such as deforestation, wild-fires, and tree die-off alter surface structure, energy balance, and associated albedo—all critical for...
Conference Paper
Brush management activities have traditionally been undertaken to reduce woody cover in an effort to improve forage production on managed rangelands encroached by woody plants. Yet, economic analyses suggest that this sole focus is often financially unjustified. Quantification of the long-term effects on other ecosystem services (ESs) (forage produ...
Article
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Basalt weathering is a key control over the global carbon cycle, though in situ measurements of carbon cycling are lacking. In an experimental, vegetation-free hillslope containing 330 m(3) of ground basalt scoria, we measured real-time inorganic carbon dynamics within the porous media and seepage flow. The hillslope carbon flux (0.6-5.1 mg C m(-2)...