1,720,985 research outputs found
Recommended from our members
A comparison of transpiration rates from three semi-arid tree species in response to partial stand clearing
Full text linkAs precipitation and temperature patterns continue to shift in response to climate change, total water availability including soil and surface waters are likewise altered. In central and west Texas, a common land management practice thought to increase surface water quantities and spring flow is the removal of Juniperus ashei commonly referred to as ashe juniper or cedar. Vegetative cover impacts the local water cycle through multiple feedback mechanisms including extraction of soil water by roots, and transpiration of water vapor back into the atmosphere. Through transpiration, plants exchange water for carbon from the atmosphere. This study aims to determine changes in transpiration rates pre- and post partial removal of ashe juniper (J. ashei) in a semi-arid forest located near Rocksprings, Texas using micrometeorological and sap flux data. We compared transpiration rates between three tree species - pinyon pine (Pinus remota), lacey oak (Quercus laceyi), and ashe juniper (J. ashei) under a variety of environmental conditions. Sap flow data revealed that ashe juniper used less water per day than the pines but more than the oaks. Transpiration rates increased after juniper removal with pines still transpiring the most water followed by juniper, and oaks using the least. Additionaly, it was found that pine trees located at lower elevations transpired more than individuals at higher elevations. By contrast, oak and juniper trees showed higher transpirations rates at higher elevations. An enhanced understanding of vegetation-climate interactions will provide key information for land management best practices to ensure resource resilience in the face of changing climate.Earth and Planetary Science
Recommended from our members
Evaluating abnormalities in daily transpiration patterns across tree species in a semi-arid climate
Full text linkClimate change causes shifts in precipitation, temperature, shifting climate zones and more, thus affecting the ecology and hydrologic feedbacks of many environments, specifically those existing in already warm, arid climates. Vegetation affects the local hydrologic cycle, as it promotes multiple feedback mechanisms, such as the extraction of soil water via roots, the re-wetting of the atmospheric boundary layer and lowering temperatures through transpiration. This study focuses on transpiration patters in a hot semi-arid environment, which is defined as having a total annual precipitation between one-fifth and one-half of potential evapotranspiration and an annual mean temperature above 18°C. Meteorological conditions, sap flow, leaf water potential, carbon assimilation, and stomatal conductance were all recorded during 2021 in order to observe the drivers of transpiration among ashe juniper, lacey oak and pinyon pines, along with abnormalities in their diurnal sap flow patterns, where the majority of sap flow occurs at dawn and dusk instead of midday. Sap flow was shown to increase in magnitude (up to 350% in pinyon pines’ case) when environmental conditions such as vapor pressure deficit (VPD), temperature and soil water potential (SWP) are favorable. Ashe juniper was found to have a weak relationship between leaf water potential (LWP) and VPD, along with a stronger relationship between LWP and SWP. Oaks were found to have a very strong relationship between LWP and VPD, while pines were found to have a weak relationship between LWP and VPD. Of the three species, only the oaks were found to have a relationship between carbon assimilation rates and VPD, carbon assimilation rates and SWP, and stomatal conductance and SWP. This makes oaks the most vulnerable of the three species to future climate change and shifting climate zones. Better understanding of plant responses to stressful climatic conditions and in arid environments will provide insight in plant durability and adaptations to a warming climate, all of which are important as our global and local climates continue to changeEarth and Planetary Science
Recommended from our members
Shorebird Habitat Nesting Preferences in Arctic National Wildlife Refuge
Full text linkOrnithological nest surveys done in Arctic National Wildlife Refuge in summer of
2019 determined the success or failure of over 200 nests to better understand how
environmental conditions implicate the fitness of four different shorebird species.
GIS and R Studio were used to find preferences within each of the four species for
different vegetation-based habitat types and different seasonal temperature
variations. This information will be useful to determine trends in their respective
population abundances and inform future oil and gas development.Jackson School of Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Recommended from our members
Assessing the effect of pollution on Rhizophora mangle in Jamaica : a comparative study
Full text linkThe motivation for this thesis is the fact that, coastal areas are being lost to urbanization and mangroves are not being spared; it is estimated that over one-third of the world’s mangrove forests have been lost. The loss of mangroves accelerates costal degradation because they provide important services such as habitat for many birds, crustacean, snakes, and mammal species. They also act as a barrier and protect coastlines from waves by lowering their intensity as well as attenuating sediment. Many studies have highlighted the role of mangrove forests as a valuable natural carbon sink. Furthermore, mangroves’ potential for remediating polluted waters has also been the focus of many studies. This thesis is a comparative study between a mangrove forest located at the outflow of a storm drain in Montego Bay (Bogue Lagoon), Jamaica and a protected mangrove forest in Port Antonio (Turtle Harbour Lagoon), Jamaica. This study aims to answer the following questions: (1) Are there differences in water chemistry and tree behavior between sites? (2) Are there changes along a land-to-sea transect at each site that can be attributed to the mangrove trees? (3) Does nutrient availability influence transpiration rates along the transects? In order to answer these questions, I collected water samples along a land to reef transect at both sites as well as soil samples at each tree location. Three trees at each site were instrumented to record air temperature, relative humidity, pressure, and sap flux. My result show two main findings. First, higher phosphate concentrations occur in Bogue Lagoon in both water and soil with the maximum value being 0.98 ppm in water and 1.32 ppm in soil. Second, soil in Turtle Harbour Lagoon is higher in calcium carbonate with values ranging between 15% and 28% whereas Montego Bay’s soil is higher in organic matter with values ranges from 19% to 39%. As countries put in place plans to decelerate the impact of climate change, protecting native coastal ecosystems that can mitigate climate change through natural processes is a crucial part of attaining sustainability.Earth and Planetary Science
Recommended from our members
Monitoring bedrock vadose zone water storage dynamics with time-lapse borehole nuclear magnetic resonance well logging
Full text linkBedrock vadose zone water storage dynamics are a critical component of the hydrologic cycle in many catchments, but direct observations of these dynamics are rare. Nuclear magnetic resonance (NMR) methods are sensitive to volumetric water content and to pore chemistry and structure, making NMR a candidate for directly observing bedrock vadose zone water storage dynamics and the material properties associated with them. However, applications of NMR to study water storage in bedrock vadose zones are rare. Here we present the first use of time-lapse borehole nuclear magnetic resonance well logging to monitor and characterize seasonal water content changes in the deeply weathered bedrock vadose zone at two sites in Northern California. The work is presented in two chapters, each of which focuses on one of the two aspects of the NMR measurement: water content and relaxation times. In the first chapter, we evaluate the ability of borehole NMR to quantify water content changes in weathered bedrock. We show strong agreement between estimates of dynamic water storage derived from NMR and independent estimates from neutron logging and mass balance calculations. The agreement between NMR and neutron estimates of dynamic storage suggests that all seasonally exchanged bedrock water is hosted in fractures, and not the matrix, at these sites. The depths of dynamic storage we observe are up to 9 m and likely reflect the depth extent of root-water uptake. In the second chapter, we document the relationship between bedrock weathering and NMR relaxation times. We find that the sum of echoes (SE) is a useful approach for characterizing NMR relaxation times in the vadose zone, and we use the functional dependence of SE on water content to show that enhanced bedrock weathering extent is associated with faster relaxation times. We find evidence that NMR relaxation times can be sensitive to changes in pore pressure associated with recharge events. The work presented here establishes borehole NMR well logging as a viable method for in situ vadose zone monitoring and characterization.Earth and Planetary Science
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
