Matching Items (26)
Learning Through Evaluation: A Tentative Evaluative Scheme for Sustainability Transition Experiments
Description
Transitions towards sustainability are urgently needed to address the interconnected challenges of economic development, ecological integrity, and social justice, from local to global scales. Around the world, collaborative science-society initiatives are forming to conduct experiments in support of sustainability transitions. Such experiments, if carefully designed, provide significant learning opportunities for making progress on transition efforts. Yet, there is no broadly applicable evaluative scheme available to capture this critical information across a large number of cases, and to guide the design of transition experiments. To address this gap, the article develops such a scheme, in a tentative form, drawing on evaluative research and sustainability transitions scholarship, alongside insights from empirical cases. We critically discuss the scheme's key features of being generic, comprehensive, operational, and formative. Furthermore, we invite scholars and practitioners to apply, reflect and further develop the proposed tentative scheme – making evaluation and experiments objects of learning.
ContributorsLuederitz, Christopher (Author) / Schäpke, Niko (Author) / Wiek, Arnim (Author) / Lang, Daniel J. (Author) / Bergmann, Matthias (Author) / Bos, Joannette J (Author) / Burch, Sarah (Author) / Davies, Anna (Author) / Evans, James (Author) / König, Ariane (Author) / Farrelly, Megan A. (Author) / Forrest, Nigel (Author) / Frantzeskaki, Niki (Author) / Gibson, Robert B. (Author) / Kay, Braden (Author) / Loorbach, Derk (Author) / McCormick, Kes (Author) / Parodi, Oliver (Author) / Rauschmayer, Felix (Author) / Schneidewind, Uwe (Author) / Stauffacher, Michael (Author) / Stelzer, Franziska (Author) / Trencher, Gregory (Author) / Venjakob, Johannes (Author) / Vergragt, Philip J. (Author) / von Wehrden, Henrik (Author) / Westley, Frances R. (Author)
Created2016-09-03
Description
Water is the main driver of net primary productivity (NPP) in arid ecosystems, followed by nitrogen and phosphorous. Precipitation is the primary factor in determining water availability to plants, but other factors such as surface rocks could also have an impact. Surface rocks may positively affect water availability by preventing evaporation from soil, but at higher densities, surface rocks may also have a negative impact on water availability by limiting water infiltration or light availability. However, the direct relationship between rock cover and aboveground net primary productivity (ANPP), a proxy for NPP, is not well understood. In this research we explore the relationship between rock cover, ANPP, and soil nutrient availability. We conducted a rock cover survey on long-term fertilized plots at fifteen sites in the Sonoran Desert and used 4 years of data from annual plant biomass surveys to determine the relationship between peak plant biomass and surface rock cover. We performed factorial ANCOVA to assess the relationship among annual plant biomass, surface rocks, precipitation, and fertilization treatment. Overall we found that precipitation, nutrients, and rock cover influence growth of Sonoran Desert annual plants. Rock cover had an overall negative relationship with annual plant biomass, but did not show a consistent pattern of significance over four years of study and with varying average winter precipitation.
ContributorsShaw, Julea Anne (Author) / Hall, Sharon (Thesis director) / Sala, Osvaldo (Committee member) / Cook, Elizabeth (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2015-05
Description
A large fraction of the world grasslands and savannas are undergoing a rapid shift from herbaceous to woody-plant dominance. This land-cover change is expected to lead to a loss in livestock production (LP), but the impacts of woody-plant encroachment on this crucial ecosystem service have not been assessed. We evaluate how tree cover (TC) has affected LP at large spatial scales in rangelands of contrasting social–economic characteristics in the United States and Argentina. Our models indicate that in areas of high productivity, a 1% increase in TC results in a reduction in LP ranging from 0.6 to 1.6 reproductive cows (Rc) per km[superscript 2]. Mean LP in the United States is 27 Rc per km[superscript 2], so a 1% increase in TC results in a 2.5% decrease in mean LP. This effect is large considering that woody-plant cover has been described as increasing at 0.5% to 2% per y. On the contrary, in areas of low productivity, increased TC had a positive effect on LP. Our results also show that ecological factors account for a larger fraction of LP variability in Argentinean than in US rangelands. Differences in the relative importance of ecological versus nonecological drivers of LP in Argentina and the United States suggest that the valuation of ecosystem services between these two rangelands might be different. Current management strategies in Argentina are likely designed to maximize LP for various reasons we are unable to explore in this effort, whereas land managers in the United States may be optimizing multiple ecosystem services, including conservation or recreation, alongside LP.
ContributorsAnadon, Jose Daniel (Author) / Sala, Osvaldo (Author) / Turner II, B. L. (Author) / Bennett, Elena M. (Author) / College of Liberal Arts and Sciences (Contributor) / School of Life Sciences (Contributor) / Julie Ann Wrigley Global Institute of Sustainability (Contributor) / School of Sustainability (Contributor) / School of Geographical Sciences and Urban Planning (Contributor)
Created2014-09-02
Description
The southwestern US will experience more frequent heat waves, prolonged droughts, and declining water supply. Riparian ecosystems are particularly at-risk under climate change predictions, but little is known about the thermal tolerance of plant species inhabiting these ecosystems. Populus fremontii, a pioneer and foundation tree species in riparian ecosystems throughout the southwest, is of concern given its importance in driving community structure and influencing ecosystem processes. This study compared leaf thermal tolerance across populations of P. fremontii to determine if local adaptation affects leaf thermal tolerance. I hypothesized that warm-adapted (low-elevation) populations would have larger leaf thermal tolerance thresholds, thermal safety margins, and thermal time constants than cool-adapted (high-elevation) populations. I expected warm-adapted populations to maintain lower maximum leaf temperatures due to local adaptation affecting leaf thermal regulation. Using a common garden at the warm edge of this species’ range, I measured leaf thermal tolerance metrics in eight populations spanning a 1,200 m elevational gradient. Data collection occurred in May, during mild air temperatures, and in August, during high air temperatures. The first two metrics were leaf thermal tolerance thresholds. The critical temperature (Tcrit) is the temperature at which the electron transport capacity of PSII is disrupted. T50 is the temperature at which the electron transport capacity decreases to 50%. The next metric was thermal safety margins (TSMs), which reflect a leaf’s vulnerability to reaching thermal tolerance thresholds. TSMs are the difference between either Tcrit or T50 and an experienced environmental variable such as leaf or air temperature. The last metric was the thermal time constant (?), which is a trait that represents how quickly leaf temperatures respond to changes in air temperatures. Tcrit, T50, and ? were not correlated with elevation regardless of season, suggesting that acclimation or phenotypic plasticity is affecting these metrics. Conversely, TSMs using maximum leaf temperature were negatively correlated with elevation in August because warm-adapted populations maintained lower maximum leaf temperatures. These findings suggest that warm-adapted populations are locally adapted to maintain cooler leaf temperatures, which is critical for their future survival since they do not maintain higher leaf thermal tolerance thresholds than cool-adapted populations.
ContributorsMoran, Madeline (Author) / Hultine, Kevin (Thesis advisor) / Throop, Heather (Thesis advisor) / Butterfield, Bradley (Committee member) / Arizona State University (Publisher)
Created2022
Description
Flowering phenology offers a sensitive and reliable biological indicator of climate change because plants use climatic and other environmental cues to initiate flower production. Drylands are the largest terrestrial biome, but with unpredictable precipitation patterns and infertile soils, they are particularly vulnerable to climate change. There is a need to increase our comprehension of how dryland plants might respond and adapt to environmental changes. I conducted a meta-analysis on the flowering phenology of dryland plants and showed that some species responded to climate change through accelerated flowering, while others delayed their flowering dates. Dryland plants advanced their mean flowering dates by 2.12 days decade-1, 2.83 days °C-1 and 2.91 days mm-1, respectively, responding to time series, temperature, and precipitation. Flowering phenology responses varied across taxonomic and functional groups, with the grass family Poaceae (-3.91 days decade1) and bulb forming Amaryllidaceae (-0.82 days decade1) showing the highest and lowest time series responses respectively, while Brassicaceae was not responsive. Analysis from herbarium specimens collected across Namibian drylands, spanning 26 species and six families, revealed that plants in hyper-arid to arid regions have lower phenological sensitivity to temperature (-9 days °C-1) and greater phenological responsiveness to precipitation (-0.56 days mm-1) than those in arid to semi-arid regions (-17 days °C-1, -0.35 days mm-1). The flowering phenology of serotinous plants showed greater sensitivity to both temperature and precipitation than that of non-serotinous plants. I used rainout shelters to reduce rainfall in a field experiment and showed that drought treatment advanced the vegetative and reproductive phenology of Cleome gynandra, a highly nutritional and medicinal semi-wild vegetable species. The peak leaf length date, peak number of leaves date, and peak flowering date of Cleome gynandra advanced by six, 10 and seven days, respectively. Lastly, I simulated drought and flood in a greenhouse experiment and found that flooding conditions resulted in higher germination percentage of C. gynandra than drought. My study found that the vegetative, and flowering phenology of dryland plants is responsive to climate change, with differential responses across taxonomic and functional groups, and aridity zones, which could alter the structure and function of these systems.
ContributorsKangombe, Fransiska Ndiiteela (Author) / Throop, Heather (Thesis advisor) / Sala, Osvaldo (Committee member) / Vivoni, Enrique (Committee member) / Pigg, Kathleen (Committee member) / Hultine, Kevin (Committee member) / Kwembeya, Ezekeil (Committee member) / Arizona State University (Publisher)
Created2023
Climate Sensitivity in Mature Versus Pre-Reproductive Saguaro Determined from Spine Isotopic Signals
Description
The saguaro cactus is vital to the unique biodiversity of the Sonoran Desert. Many animals rely on it for survival and shelter. Due to its thick waxy exterior, it is able to retain a massive amount of water in its succulent stems, making it an ideal habitat for many birds that are native to the region. It also holds a large cultural significance for many native tribes of this region. Thus, it is important to understand how these magnificent plants are affected by changing environmental conditions in order to protect them in the future. Measurements of carbon isotope (13C) signals in saguaros spine tissues have been shown to be a robust approach for evaluating plant responses to climate variation over multiple seasons and years. This study investigated growth and 13C signals in young saguaros (< 2.5 m tall) at a location north of Phoenix to compare with large saguaros (> 4 m tall) that actively flower in the spring. Adolescent saguaros were examined to determine how they responded to variation in moisture between the years 2012 through 2016. As with a previous study by Hultine et al. (2018), this research demonstrated a strong relationship between height growth and precipitation. Stem growth was also highly correlated with the number of areoles produced across both young and old plants. Winter and late summer moisture from the previous year had a significant effect on stem growth, and a legacy effect could be seen in the low growth rates in 2014 which may be a result of low precipitation during the previous fall and winter. This study also established that the adolescent saguaro may be less sensitive to seasonal changes than the mature saguaro. When comparing the large plants with the adolescent plants, spine 13C values were similar between mature and adolescent plants, indicating that perhaps flower does not impose a significant added cost to saguaro water budgets. However, identifying the cost of flowering requires more investigation than that from only spine carbon isotope measurements and coarse measurements of plant productivity.
ContributorsDe Leon, Isabella (Author) / Hultine, Kevin (Thesis advisor) / Pigg, Kathleen (Thesis advisor) / Maienschein, Jane (Committee member) / Arizona State University (Publisher)
Created2021
Description
As climate change continues, understanding the water use strategies and water relations of cacti becomes even more important in conservation. Cacti are not only one of the most threatened taxonomic groups but also ecologically important to desert ecosystems. Water conservation strategies vary among species of columnar cacti as a tradeoff between photosynthetic and water storage capacities, such as the different volume-to-surface-area ratios in Carnegiea gigantea and Stenocereus thurberi. These variations in water and growth relations could be associated with the basipetal xylem vessel widening pattern that has been observed in many woody plant species, and most recently in cacti as well. This phenomenon provides a buffer to the accumulation of hydrodynamic resistance in xylem vessels as the plant stem elongates, and in cacti, stem water storage tissues (cortex and pith) also provide a buffer. This thesis investigates the rate of basipetal xylem conduit widening in Carnegiea gigantea and Stenocereus thurberi, with the expectation that columnar cacti will show similar rates of widening as other plants. I found that while the xylem conduits in both species widened at significantly different rates, the rate of widening was much lower than expected. While there are a few possible explanations, such as buffering from the succulent cortex tissue, more research on cactus xylem anatomy and its reflection in plant water conduction strategies is needed.
ContributorsCaspeta, Ivanna (Author) / Hultine, Kevin (Thesis director) / Throop, Heather (Thesis director) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2021-05
Description
Drylands cover over 40% of the Earth’s surface, account for one third of global carbon cycling, and are hotspots for climate change, with more frequent and severe droughts coupled with deluges of novel magnitude and frequency. Because of their large terrestrial extent, elucidating dryland ecosystem responses to changes in water availability is critical for a comprehensive understanding of controls on global aboveground net primary productivity (ANPP), an important ecosystem service. The focus of this dissertation is to investigate cause-effect mechanisms between altered water availability and ecosystem processes in dryland ecosystems. Across a network of experimental rainfall manipulations within a semiarid Chihuahuan Desert grassland, I examined short- and long-term dynamics of multiple ecosystem processes—from plant phenology to nitrogen cycling—in response to directional precipitation extremes. Aboveground, I found herbaceous plant phenology to be more sensitive in greenup timing compared to deep-rooted, woody shrubs, implying that precipitation extremes will disproportionately affect grass-dominated compared to woody ecosystems. Surprisingly, after 14 years of experimentally adding water and N, I observed no effect on ANPP. Belowground, bulk soil N dynamics remained stable with differing precipitation amounts. However, mineral associated organic N (MAOM-N) significantly increased under chronic N inputs, indicating potential for dryland soil N sequestration. Conversely, the difference between low- and high-N soil N content may increase a drawdown of N from all soil N pools under low-N conditions whereas plants source N from fertilizer input under high-N conditions. Finally, I considered ecosystem-level acclimation to climate change. I found that N availability decreased with annual precipitation in space across continents, but it posed initially increasing trends in response to rainfall extremes at the Jornada that decreased after 14 years. Mechanisms for the acclimation process are thus likely associated with differential lags to changes in precipitation between plants and microorganisms. Overall, my dissertation demonstrates that examining linkages between multiple ecosystem processes, from aboveground phenological cycles to belowground N cycling dynamics, can provide a more integrative understanding of dryland response to climate change. Because dryland range is potentially expanding globally, water limited systems provide a unique and critical focus area for future research that revisit and revise current ecological paradigms.
ContributorsCurrier, Courtney (Author) / Sala, Osvaldo (Thesis advisor) / Collins, Scott (Committee member) / Reed, Sasha (Committee member) / Throop, Heather (Committee member) / Arizona State University (Publisher)
Created2023
Description
The study of organismal adaptations oftentimes focuses on specific, constant conditions, but environmental parameters are characterized by more or less marked levels of variability, rather than constancy. This is important in environments like soils where microbial activity follows pulses of water availability driven by precipitation. Nowhere are these pulses more variable and unpredictable than in arid soils. Pulses constitute stressful conditions for bacteria because they cause direct cellular damage that must be repaired and they force cells to toggle between dormancy and active physiological states, which is energetically taxing. I hypothesize that arid soil microorganisms are adapted to the variability in wet/dry cycles itself, as determined by the frequency and duration of hydration pulses. To test this, I subjected soil microbiomes from the Chihuahuan Desert to controlled incubations for a total common growth period of 60 hours, but separated into treatments in which the total active time was reached with hydration pulses of different length with intervening periods of desiccation, so as to isolate pulse length and frequency as the varying factors in the experiment. Using 16S rRNA amplicon data, I characterized changes in microbiome growth, diversity, and species composition, and tracked the individual responses to treatment intensity in the 447 most common bacterial species (phylotypes) in the soil. Considering knowledge of extremophile microbiology, I hypothesized that growth yield and diversity would decline with shorter pulses. I found that microbial diversity was indeed a direct function of pulse length, but surprisingly, total yield was an inverse function of it. Pulse regime treatments resulted in progressively more significant differences in community composition with increasing pulse length, as differently adapted phylotypes became more prominent. In fact, more than 30% of the most common bacterial phylotypes demonstrated statistically significant population growth responses to pulse length. Most responsive phylotypes were apparently best adapted to short pulse regimes (known in the literature as Nimble Responders or NIRs), while fewer did better under long pulse regimes (known as TORs or Torpid Responders). Examples of extreme NIRs and TORs could be found among bacteria from different phyla, indicating that these adaptations have occurred multiple times during evolution.
ContributorsKut, Patrick John (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Sala, Osvaldo (Committee member) / Zhu, Qiyun (Committee member) / Arizona State University (Publisher)
Created2023
Description
Xylem conduits, a primary feature of most terrestrial plant taxa, deliver water to photosynthetic tissues and play a critical role in plant water relations and drought tolerance. Non-succulent woody taxa generally follow a universal rate of tip-to-base conduit widening such that hydraulic resistance remains constant throughout the plant stem. Giant cacti inhabit arid regions throughout the Americas and thrive in water-limited environments by complimenting water-storing succulent tissues with resource-efficient Crassulacean Acid Metabolism. Considering these adaptations, the objectives of this study were threefold: 1) determine whether xylem conduits in columnar cacti follow universal scaling theory as observed in woody taxa; 2) evaluate whether xylem hydraulic diameter is inversely correlated with xylem vessel density; and 3) determine whether xylem double-wall thickness-to-span ratio and other hydraulic architectural traits are convergent among phylogenetically diverse cactus species. This thesis investigates the xylem anatomy of nine cactus species native to the Sonoran Desert of Arizona and Mexico, the tropical dry forests of southern Mexico, and the Alto Plano region of Argentina. Soft xylem tissues closest to the stem apex underwent a modified polyethylene glycol treatment to stabilize for sectioning with a sledge microtome. Across all species: hydraulic diameter followed a basipetal widening rate of 0.21 (p < 0.001), closely matching the universal rate of 0.20 for woody taxa; and xylem vessel density was inversely correlated with both length from stem apex (p < 0.001) and hydraulic diameter (p < 0.001). Double-wall thickness-to-span ratio had little to no significant correlation with either length from stem apex or hydraulic diameter. There was no significant difference in hydraulic architectural trait patterns between phylogenetically diverse species with various stem morphologies, nor was there a significant correlation between conduit widening rates and volume-to-surface-area ratios.
This study demonstrates that giant cacti follow similar internal anatomical constraints as non-succulent woody taxa, yet stem succulence and water storage behavior in cacti remain separate from internal hydraulic architecture, allowing cacti to thrive in arid environments. Understanding how cacti cope with severe water limitations provides new insights on evolutionary constraints of stem succulents as they functionally diverged from other life forms.
ContributorsCaspeta, Ivanna (Author) / Hultine, Kevin (Thesis advisor) / Throop, Heather (Thesis advisor) / Hernandez, Tania (Committee member) / Arizona State University (Publisher)
Created2023