Sensitivity of the Colorado plateau to change: climate, ecosystems, and society

Journal ArticleThe Colorado Plateau is located in the interior, dry end of two moisture trajectories coming from opposite directions, which have made this region a target for unusual climate fluctuations. A multidecadal drought event some 850 years ago may have eliminated maize cultivation by the first human settlers of the Colorado Plateau, the Fremont and Anasazi people, and contributed to the abandonment of their settlements. Even today, ranching and farming are vulnerable to drought and struggle to persist. The recent use of the Colorado Plateau primarily as rangeland has made this region less tolerant to drought due to unprecedented levels of surface disturbances that destroy biological crusts, reduce soil carbon and nitrogen stocks, and increase rates of soil erosion

Selbstwirksamkeitserwartungen und inklusiver Schreibunterricht : Entwurf eines schreibunterrichtsspezifischen Messinstruments

Die Bedeutung von Selbstwirksamkeit für professionelles Handeln im Unterricht ist gut dokumentiert (z. B. Klassen & Tze, 2014). Gerade im Kontext der Einführung inklusiver Lernumgebungen ist Selbstwirksamkeit als professionelle Ressource hoch relevant. Aus der Bildungsforschung liegen bereits diverse Skalen und Studien zum Einfluss und zur Entwicklung der Selbstwirksamkeit von Lehrpersonen vor. Dabei bleibt der Fokus auf Selbstwirksamkeit bisher generisch, obwohl Forschungen für andere Unterrichtsfächer zeigen können, dass durch einen fachdidaktischen Ansatz wertvolle Erkenntnisse erwartet werden können. Wir schlagen daher ein lernbereichsspezifisches Modell der Selbstwirksamkeitserwartungen für den Schreibunterricht in inklusiven Lernumgebungen vor, auf dessen Basis ein Online-Fragebogen entwickelt wurde. Der Fragebogen wurde im November 2020 in einer Pilotierungsstudie an der Bergischen Universität Wuppertal eingesetzt (N = 201, Analysestichprobe: N = 164). Die Ergebnisse weisen auf ein geeignetes Instrument zur Messung von Selbstwirksamkeit im inklusiven Schreibunterricht hin und bestätigen eine achtdimensionale Struktur mit spezifisch lernbereichsbezogenen latenten Konstrukten.The importance of self-efficacy for professional action in teaching is well documented (e.g. Klassen & Tze, 2014). Especially in the context of introducing inclusive learning environments, self-efficacy as a professional trait is highly relevant. Various scales and studies on the influence and development of teachers' self-efficacy are available to assess teachers' self-efficacy in education and training. Yet the focus on self-efficacy has so far remained generic, although subject-matter related research shows that valuable insights can be expected from a context-specific approach. We therefore propose a subject-matter related model and scale of self-efficacy expectations for writing instruction in diverse classrooms. The questionnaire was used in a pilot study in November 2020 (N = 201, analysis sample: N = 164) at the University of Wuppertal. The results indicate a suitable instrument for measuring self-efficacy expectations for writing instruction in diverse classrooms and confirm an expected eight-dimensional structure with specific subject-matter related latent constructs

Ecosystem thresholds, tipping points, and critical transitions

An organized session at the American Geophysical Union Fall Meeting in New Orleans, Louisiana, USA, December 201

Using hydrogeochemical and ecohydrologic responses to understand epikarst process in semi-arid systems, Edwards plateau, Texas, USA

The epikarst is a permeable boundary between surface and subsurface environments and can be conceptualized as the vadose critical zone of epigenic karst systems which have not developed under insoluble cover. From a hydrologic perspective, this boundary is often thought of as being permeable in one direction only (down), but connectivity between the flow paths of water through the epikarst and the root systems of woody plants means that water moves both up and down across the epikarst. However, the dynamics of these flows are complex and highly dependent on variability in the spatial structure of the epikarst, vegetation characteristics, as well as temporal variability in precipitation and evaporative demand. Here we summarize insights gained from working at several sites on the Edwards Plateau of Central Texas, combining isotopic, hydrogeochemical, and ecophysiological methodologies. 1) Dense woodland vegetation at sites with thin to absent soils (0-30 cm) is in part supported by water uptake from the epikarst. 2) However, tree transpiration typically becomes water-limited in dry summers, suggesting that the plant-available fraction of stored water in the epikarst depletes quickly, even when sustained cave drip rates indicate that water is still present in the epikarst. 3) Flow paths for water that feeds cave drips become rapidly disconnected from the evaporation zone of the epikarst and out of reach for plant roots. 4) Deep infiltration and recharge does not occur in these systems without heavy or continuous precipitation that exceeds some threshold value. Thresholds are strongly correlated with antecedent potential evapotranspiration and rainfall, suggesting control by the moisture status of the epikarst evapotranspiration zone. The epikarst and unsaturated zone in this region can be conceptualized as a variably saturated system with storage in fractures, matrix porosity, and in shallow perched aquifers, most of which is inaccessible to the root systems of trees, although woody vegetation may control recharge thresholds.Keywords: hydraulic disconnection, precipitation thresholds, root zone, plant water use, recharge, epikarst storage, barometric pressure.DOI: 10.3986/ac.v42i2-3.67

Plant dieback under exceptional drought driven by elevation, not by plant traits, in Big Bend National Park, Texas, USA

In 2011, Big Bend National Park, Texas, USA, experienced the most severe single year drought in its recorded history, resulting in significant plant mortality. We used this event to test how perennial plant response to drought varied across elevation, plant growth form and leaf traits. In October 2010 and October 2011, we measured plant cover by species at six evenly-spaced elevations ranging from Chihuahuan desert (666 m) to oak forest in the Chisos mountains (1,920 m). We asked the following questions: what was the relationship between elevation and stem dieback and did susceptibility to drought differ among functional groups or by leaf traits? In 2010, pre-drought, we measured leaf mass per area (LMA) on each species. In 2011, the percent of canopy dieback for each individual was visually estimated. Living canopy cover decreased significantly after the drought of 2011 and dieback decreased with elevation. There was no relationship between LMA and dieback within elevations. The negative relationship between proportional dieback and elevation was consistent in shrub and succulent species, which were the most common growth forms across elevations, indicating that dieback was largely driven by elevation and not by species traits. Growth form turnover did not influence canopy dieback; differences in canopy cover and proportional dieback among elevations were driven primarily by differences in drought severity. These results indicate that the 2011 drought in Big Bend National Park had a large effect on communities at all elevations with average dieback for all woody plants ranging from 8% dieback at the highest elevation to 83% dieback at lowest elevations

Spatiotemporal variation in the endangered Thymus decussatus in a hyper-arid environment

Aims: Arid environments are resource limited, with scarcity of water the key limiting factor, but hyper-arid environments are rarely studied. We test for spatial and temporal variation in ecologically important characteristics to deduce plant adaptations to the extreme climate. Methods: The endangered Sinai Thyme (Thymus decussatus) exists as a set of patches on mountaintops within the St Katherine Protectorate, South Sinai, a hyper-arid environment with rare events of good rains (every 10–15 years). Important Findings: From spatial and temporal patterns of plant mortality, size, condition and flowering among 10 patches on the Mt Sinai massif, we deduce that the incidence and amount of flowering responds relatively quickly (1–2 years) to rainfall fluctuations, but plant growth respond only very slowly. Small individuals are most at risk of death during drought, and a high proportion of plants were dead at the end of 8 years of very low or no rainfall. No recruitment of seedlings was observed even in years of good rainfall. Droughts are expected to become increasingly frequent due to climate change; this may have important consequences for Sinai Thyme and also its associated herbivores, such as the Critically Endangered Sinai Baton Blue (Pseudophilotes sinaicus) whose larval stage feeds exclusively upon the flowers of this plant

Evidence for an ecological cost of enhanced herbicide metabolism in Lolium rigidum

1. In some cases, evaluation of resource competitive interactions between herbicide resistant vs. susceptible weed ecotypes provides evidence for the expression of fitness costs associated with evolved herbicide-resistant gene traits. Such fitness costs impact in the ecology and evolutionary trajectory of resistant populations. 2. Neighbourhood experiments were performed to quantify competitive effects and responses between herbicide-susceptible (S) and resistant (R) Lolium rigidum individuals in which resistance is due to enhanced herbicide metabolism mediated by cytochrome P450. 3. In two-way competitive interactions between the S and R phenotypes, individuals of the S phenotype were the stronger effect competitors on both a per capita and per unit-size basis. The S phenotype also exhibited a stronger competitive response to wheat plants than did the R phenotype, displaying significantly greater (30%) above-ground biomass at the vegetative stage. When subjected to competition from wheat, R individuals produced significantly fewer reproductive tillers and allocated fewer resources to reproductive traits than individuals of the S phenotype. 4. The role of potential mechanisms underlying this resistance cost driven by traits such as plant size and tolerance to low resource availability, as well as the evolutionary implications of the results are discussed. 5. Synthesis. Evolved herbicide resistance due to enhanced-herbicide metabolism mediated by cytochrome-P450 in L. rigidum has been shown to be accompanied with an impaired ability to compete for resources. These results are consistent with the resource-based theory that predicts a negative trade-off between growth and plant defence

The role of climate and plant functional trade-offs in shaping global biome and biodiversity patterns

Aim: Two of the oldest observations in plant geography are the increase in plant diversity from the poles towards the tropics and the global geographic distribution of vegetation physiognomy (biomes). The objective of this paper is to use a process-based vegetation model to evaluate the relationship between modelled and observed global patterns of plant diversity and the geographic distribution of biomes.Location: The global terrestrial biosphere.Methods: We implemented and tested a novel vegetation model aimed at identifying strategies that enable plants to grow and reproduce within particular climatic conditions across the globe. Our model simulates plant survival according to the fundamental ecophysiological processes of water uptake, photosynthesis, reproduction and phenology. We evaluated the survival of an ensemble of 10,000 plant growth strategies across the range of global climatic conditions. For the simulated regional plant assemblages we quantified functional richness, functional diversity and functional identity.Results: A strong relationship was found (correlation coefficient of 0.75) between the modelled and the observed plant diversity. Our approach demonstrates that plant functional dissimilarity increases and then saturates with increasing plant diversity. Six of the major Earth biomes were reproduced by clustering grid cells according to their functional identity (mean functional traits of a regional plant assemblage). These biome clusters were in fair agreement with two other global vegetation schemes: a satellite image classification and a biogeography model (kappa statistics around 0.4).Main conclusions: Our model reproduces the observed global patterns of plant diversity and vegetation physiognomy from the number and identity of simulated plant growth strategies. These plant growth strategies emerge from the first principles of climatic constraints and plant functional trade-offs. Our study makes important contributions to furthering the understanding of how climate affects patterns of plant diversity and vegetation physiognomy from a process-based rather than a phenomenological perspective

The combined effects of a long-term experimental drought and an extreme drought on the use of plant-water sources in a Mediterranean forest

Vegetation in water-limited ecosystems relies strongly on access to deep water reserves to withstand dry periods. Most of these ecosystems have shallow soils over deep groundwater reserves. Understanding the functioning and functional plasticity of species-specific root systems and the patterns of or differences in the use of water sources under more frequent or intense droughts is therefore necessary to properly predict the responses of seasonally dry ecosystems to future climate. We used stable isotopes to investigate the seasonal patterns of water uptake by a sclerophyll forest on sloped terrain with shallow soils. We assessed the effect of a long-term experimental drought (12 years) and the added impact of an extreme natural drought that produced widespread tree mortality and crown defoliation. The dominant species, Quercus ilex, Arbutus unedo and Phillyrea latifolia, all have dimorphic root systems enabling them to access different water sources in space and time. The plants extracted water mainly from the soil in the cold and wet seasons but increased their use of groundwater during the summer drought. Interestingly, the plants subjected to the long-term experimental drought shifted water uptake toward deeper (10-35 cm) soil layers during the wet season and reduced groundwater uptake in summer, indicating plasticity in the functional distribution of fine roots that dampened the effect of our experimental drought over the long term. An extreme drought in 2011, however, further reduced the contribution of deep soil layers and groundwater to transpiration, which resulted in greater crown defoliation in the drought-affected plants. The present study suggests that extreme droughts aggravate moderate but persistent drier conditions (simulated by our manipulation) and may lead to the depletion of water from groundwater reservoirs and weathered bedrock, threatening the preservation of these Mediterranean ecosystems in their current structures and composition