Kiona Ogle

Northern Arizona University | NAU · School of Informatics Computing and Cyber Systems

Trees are long‐lived organisms, exhibiting temporally complex growth arising from strong climatic “memory.” But conditions are becoming increasingly arid in the western USA. Using a century‐long tree‐ring network, we find altered climate memory across the entire range of a widespread western US conifer: growth is supported by precipitation falling...

Changing climatic conditions suggest that forests will be altered at unprecedented rates over the course of this century. In forests experiencing drought-induced dieback, declining trees may exhibit altered climate memory, likely reflecting their lower buffering capacity and shorter leaf lifespan. This study evaluates the effects of past climate co...

The vegetation's response to climate change is a significant source of uncertainty in future terrestrial biosphere model projections. Constraining climate–carbon cycle feedbacks requires improving our understanding of both the immediate and long-term plant physiological responses to climate. In particular, the timescales and strength of memory effe...

Spatial patterns of precipitation in the southwestern United States result in a complex gradient from winter-to-summer moisture dominance that influences tree growth. In response, tree growth exhibits seasonal-to-annual variability that is evident in the growth of whole tree rings, and in sub-annual sections such as earlywood and latewood. We evalu...

Warming temperatures and droughts are driving widespread forest dieback and growth decline worldwide. In forests experiencing dieback, declining trees may exhibit altered climate memory of growth, indicative of physiological impairment. Thus, we evaluated climate-growth responses of trees in four drought-disturbed forests dominated either by gymnos...

The Allometrically Constrained Growth and Carbon Allocation (ACGCA) model is an individual-based model of tree growth and mortality, and it is a unique tool for investigating how tree functional traits influence growth and mortality. Several studies have used the ACGCA model to investigate tree traits, but the model is not readily accessible to the...

Legacies of past climate conditions and historical management govern forest productivity and tree growth. Understanding how these processes interact and the timescales over which they influence tree growth is critical to assess forest vulnerability to climate change. Yet, few studies address this issue, likely because integrated long-term records o...

Trees are long-lived organisms that integrate climate conditions across years or decades to produce secondary growth. This integration process is sometimes referred to as ‘climatic memory.’ While widely perceived, the physiological processes underlying this temporal integration, such as the storage and remobilization of non-structural carbohydrates...

In trees, large uncertainties remain in how non-structural carbohydrates (NSCs) respond to variation in water availability in natural, intact ecosystems. Variation in NSC pools reflects temporal fluctuations in supply and demand, as well as physiological coordination across tree organs in ways that differ across species and NSC fractions (e.g., sol...

Despite a long history of discussion of ‘non‐stationarity’ in dendrochronology, researchers and modellers in diverse fields commonly rely on the implicit assumption that tree growth responds to climate drivers in the same way at any given time. Synthesising recent work on drought legacies and other climate‐related phenomena, we show tree growth res...

Water and CO2 flux responses (e.g., evapotranspiration [ET] and net ecosystem exchange [NEE]) to environmental conditions can provide insights into how climate change will affect the terrestrial water and carbon budgets, especially in sensitive semiarid ecosystems. Here, we evaluated sensitivity of daily ET and NEE to current and antecedent (past)...

BACKGROUND: Forest dynamics arise from the interplay of chronic drivers and transient disturbances with the demographic processes of recruitment, growth, and mortality. The resulting trajectories of vegetation development drive the biomass and species composition of terrestrial ecosystems. Forest dynamics are changing because of anthropogenic-drive...

Shifting forest dynamics Forest dynamics are the processes of recruitment, growth, death, and turnover of the constituent tree species of the forest community. These processes are driven by disturbances both natural and anthropogenic. McDowell et al. review recent progress in understanding the drivers of forest dynamics and how these are interactin...

Ecologists are increasingly familiar with Bayesian statistical modeling and its associated Markov chain Monte Carlo (MCMC) methodology to infer about or to discover interesting effects in data. The complexity of ecological data often suggests implementation of (statistical) models with a commensurately rich structure of effects, including crossed o...

Non‐structural carbohydrates (NSC) are necessary for plant growth and affected by plant water status, but the temporal dynamics of water stress impacts on NSC are not well understood. We evaluated how seasonal NSC concentrations varied with plant water status (predawn xylem water potential, Ψ) and air temperature (T) in the evergreen desert shrub L...

How do antecedent (past) conditions influence land‐carbon dynamics after those conditions no longer persist? In particular, quantifying such memory effects associated with the influence of past environmental (exogenous) and biological (endogenous) conditions is crucial for understanding and predicting the carbon cycle. Here we show, using data from...

Plant species are characterized along a spectrum of isohydry to anisohydry depending on their regulation of water potential (Ψ), but the plasticity of hydraulic strategies is largely unknown. We evaluated the role of environmental drivers in the hydraulic behavior in Larrea tridentata, a drought tolerant desert shrub that withstands a wide range of...

Despite widespread interest in drought legacies—multi‐year impacts of drought on tree growth—the key implication of reported drought legacies remains unaddressed: as impaired growth and slow recovery associated with drought legacies are pervasive across forest ecosystems, what is the impact of more frequent drought conditions? We investigated the a...

We use a high-resolution time series of plant water potential to evaluate whether environmental drivers control the iso/anisohydry of Larrea tridentata, a common desert shrub.

1.Ecologists increasingly use hierarchical Bayesian (HB) models to estimate group‐level parameters that vary by, e.g., species, treatment level, habitat type, or other factors. Group‐level parameters may be compared to infer differences among levels. We would conclude a non‐zero pairwise difference, separately, for each pair in the group, when the...

While we often assume tree growth‐climate relationships are time‐invariant, impacts of climate phenomena such as the El Niño Southern Oscillation (ENSO) and the North American Monsoon (NAM) may challenge this assumption. To test this assumption, we grouped ring‐widths (1900‐present) in three southwestern US conifers into La Niña periods (LNP) and o...

Plant water potential Ψ is regulated by stomatal responses to atmospheric moisture demand D and soil water availability W, but the timescales of influence and interactions between these drivers of plant Ψ are poorly understood. Here, we quantify the effects of antecedent D and W on plant Ψ in the desert shrub Larrea tridentata. Repeated measurement...

Background/Question/Methods Tree rings are often analyzed to reconstruct past climate or disturbances, but there is much to be learned about tree growth responses from tree rings. Traditional approaches to inferring climate from tree rings involve a series of steps to remove age effects, long-term trends that could mask the climate signal, and auto...

The flux of CO2 from the soil to the atmosphere (soil respiration, Rsoil) is a major component of the global carbon (C) cycle. Methods to measure and model Rsoil, or partition it into different components, often rely on the assumption that soil CO2 concentrations and fluxes are in steady state, implying that Rsoil is equal to the rate at which CO2...

When standing dead trees (snags) fall, they have major impacts on forest ecosystems. Snag fall can redistribute wildlife habitat and impact public safety, while governing important carbon (C) cycle consequences of tree mortality because ground contact accelerates C emissions during deadwood decay. Managing the consequences of altered snag dynamics...

Detailed description of model simplification procedure. (DOCX)

The predicted proportion of snags standing closely corresponds to the observed proportion of snags standing when aggregated within 151 1.7°x1.7° spatial grid cells. Symbol diameter is scaled by the abundance of snags per grid cell. (PDF)

Snags occurring in physiographic settings with loose or disturbed soils are significantly more likely to fall compared to snags in settings with standing water. The final column indicates subsets of the data where the 95% CI for the effect excluded 0. (DOCX)

BUGS language code for the simplified snag fall model. (DOCX)

The predicted proportion of snags standing closely corresponds to the observed proportion of snags standing when aggregated by 205 species. Symbol diameter is scaled by species abundance. (PDF)

The predicted proportion of snags standing closely corresponds to the observed proportion of snags standing when aggregated within 16 physiographic classes. Symbol diameter is scaled by the abundance of snags per physiographic class. (PDF)

Model selection criteria applied to all first-order non-hierarchical models for snag persistence in every subset of the data. The set of parameters selected via backwards elimination from the fully hierarchical model is indicated in bold. (XLSX)

Snags of intermediate decay class are less likely to fall in locations with faster average wind speeds. Thick central curve corresponds to the posterior mean for the effect of average wind speed at 10m on decay class 2 snag persistence and the transparent curve overlay represents uncertainty by showing 100 curves drawn from the posterior distributi...

R code for the simple forest C model. (DOCX)

Compilation of wood durability estimates for species in the eastern United States drawn from various sources. The least resistant category was set as 0 and the most resistant category as 4. Sources that used ambiguous designations (e.g. non-resistant or slightly resistant) were given the average numeric score of the corresponding categories (i.e. 0...

Inferences about subsurface CO2 fluxes often rely on surface soil respiration (Rsoil) estimates because directly measuring subsurface microbial and root respiration (collectively, CO2 production, STotal) is difficult. To evaluate how well Rsoil serves as a proxy for STotal, we applied the nonsteady state DEconvolution of Temporally varying Ecosyste...

Future droughts are expected to become more severe and frequent under future climate change scenarios, likely causing widespread tree mortality in the western USA. Coping with an uncertain future requires an understanding of long-term ecosystem responses in areas where prolonged drought is projected to increase. Tree-ring records are ideally suited...

Plant functional traits research has revealed many interesting and important patterns among morphological, physiological, and life-history traits and the environment. These are exemplified in trade-offs between groups of traits such as those embodied in the leaf and wood economics spectra. Inferences from empirical studies are often constrained by...

Evapotranspiration (ET) is an important water loss flux in ecosystem water cycles, and quantifying the spatial and temporal variation of ET can improve ecohydrological models in arid ecosystems. Plant neighbor interactions may be a source of spatial and temporal variation in ET due to their effects on the above- and belowground microclimate and inc...

Variation in antecedent (past) climate conditions is likely to govern tree growth over long periods of time. Antecedent conditions are rarely considered in models of tree growth, representing a weakness in quantitative understanding of forest responses to climate variations. 2.We applied the stochastic antecedent modelling (SAM) framework to 367 In...

Determining whether the terrestrial biosphere will be a source or sink of carbon

Non-steady state chambers are often employed to measure soil CO2 fluxes. CO2 concentrations (C) in the headspace are sampled at different times (t), and fluxes (f) are calculated from regressions of C versus t based a limited number of observations. Variability in the data can lead to poor fits and unreliable f estimates; groups with too few observ...

Little is known about the ecological impacts of permafrost degradation on water fluxes in boreal ecosystems, such as those in Interior Alaska. Low plant water stress suggests a reliance on a diversity of water sources. In addition to rainfall, we hypothesize that deep soil water derived from thawing seasonal ground ice (TSGI) supports plants during...

Vertical root distributions (‘profiles’) influence plant water use and productivity, and the differentiation of root profiles between neighbouring species can indicate the degree of plant interactions and niche partitioning. However, quantifying multiple species' root distributions in the field can be labour intensive and highly destructive to the...

Understanding impacts of drought on tree growth and forest health is of major concern given projected climate change. Droughts may become more common in the Southwest due to extreme temperatures that will drive increased evapotranspiration and lower soil moisture, in combination with uncertain precipitation changes. Utilizing ~1.3 million tree-ring...

Vessel length is an important but understudied dimension of variation in angiosperm vascular anatomy. Among other traits, vessel length mediates an important tradeoff between hydraulic efficiency and safety that could influence how plants respond to extreme weather with climate change. However, the functional significance of vessel length variation...

Terrestrial plant and soil respiration, or ecosystem respiration (Reco), represents a major CO2 flux in the global carbon cycle. However, there is disagreement in how Reco will respond to future global changes, such as elevated atmosphere CO2 and warming. To address this, we synthesized six years (2007-2012) of Reco data from the Prairie Heating An...

Isotopic methods offer great potential for partitioning trace gas fluxes such as soil respiration into their different source contributions. Traditional partitioning methods face challenges due to variability introduced by different measurement methods, fractionation effects, and end-member uncertainty. To addresses these challenges, we describe a...

Stomata simultaneously regulate plant carbon gain and water loss, and patterns of stomatal conductance (g s) provide insight into water use strategies. In arid systems, g s varies seasonally based on factors such as water availability and temperature. Moreover, the presence and species identity of neighboring plants likely affects g s of the focal...

The role of time in ecology has a long history of investigation, but ecologists have largely restricted their attention to the influence of concurrent abiotic conditions on rates and magnitudes of important ecological processes. Recently, however, ecologists have improved their understanding of ecological processes by explicitly considering the eff...

This report describes accomplishments for the two-year project investigating temporal dynamics of glacial ice and snow meltwater, rainfall and base flow contributions to stream flow of Dinwoody Creek in the Wind River Range of western Wyoming. The primary objectives were to 1) characterize diurnal, seasonal and interannual variation in the isotopic...

Deep snow in sub-alpine ecosystems may reduce or eliminate soil freezing, thus contributing to the potential for winter soil respiration to account for a significant fraction of annual CO2 efflux to the atmosphere. Quantification of carbon loss from soils requires separation of respiration produced by roots and rhizosphere organisms from that produ...

Background/Question/Methods In arid systems, the plant root profile indicates a plant’s potential to utilize different sources of water (e.g. deep vs shallow soil water) and is useful for understanding water use strategies. Interactions between plant neighbors may affect root profiles directly through allelopathy or indirectly by altering soil wa...

The effect of thawing permafrost on boreal ecosystem water cycling represents a significant knowledge gap of how climate change will affect northern landscapes. Evapotranspiration, particularly transpiration, may be changing in response to changes in permafrost conditions, vegetation, and climate. This study focuses on the effect of permafrost thaw...

Recent meta-analyses have revealed that plant traits and their phylogenetic history influence decay rates of dead wood and leaf litter, but it remains unknown if decay rates of wood and litter covary over a wide range of tree species and across ecosystems. We evaluated the relationships between species-specific wood and leaf litter decomposability,...

Carbon dioxide is the main greenhouse gas inducing climate change. Increased global CO2 emissions, estimated at 8.4 Pg C yr(-1) at present, have accelerated from 1% yr(-1) during 1990-1999 to 2.5% yr(-1) during 2000-2009 (ref. 1). The carbon balance of terrestrial ecosystems is the greatest unknown in the global C budget because the actual magnitud...

Stable isotopes are valuable tools for partitioning the components contributing to ecological processes of interest, such as animal diets and trophic interactions, plant resource use, ecosystem gas fluxes, streamflow, and many more. Stable isotope data are often analyzed with simple linear mixing (SLM) models to partition the contributions of diffe...

The concentration detection threshold (CDT) is the concentration of particles in solution beyond which a (serial dilution) assay detects particle presence. By our account, CDTs typically are not estimated but are fixed at some value. Setting a CDT to zero ( \(d=0\) ) implies perfect detection, a common assumption, and setting \(d>0\) gives results...

Plant functional traits are important determinants of survival and fitness, and wood density (WD) is a key trait linked to mechanical stability, growth rates and drought- and shade-tolerance strategies. Thus, rigorous WD estimates are necessary to identify factors affecting tree performance.We obtained 1766 records of WD from the literature for 141...

Quantifying the response of soil respiration to past environmental conditions is critical for predicting how future climate and vegetation change will impact ecosystem carbon balance. Increased shrub dominance in semiarid grasslands has potentially large effects on soil carbon cycling. The goal of this study was to characterize the effect of antece...

Scientists use deterministic models to study and forecast the behavior of complex environmental processes, with increasing emphasis on incorporating data to inform model input parameters and accounting for parameter uncertainty. We work with a deterministic, individual-based model (IBM) of tree growth and mortality, which is under development to ex...