112 research outputs found
Long-term ecological legacies in western Amazonia
M.B.B would like to acknowledge funding from the National Science Foundation (grant nos. EAR1338694 and BCS0926973), the Belmont Forum, and the National Aeronautics and Space Administration (grant no. NNX14AD31G). C.N.H.M would like to acknowledge funding from the European Research Council (ERC 2019 StG 853394). C.N.H.M and M.F.R would like to acknowledge funding from the Netherlands Organisation for Scientific Research (ALWOP.322). S.N.H, M.P, and Jo.V performed this research as a part of the BSc research program of the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam.1. Modifications of Amazonian forests by preâColumbian peoples are thought to have left ecological legacies that have persisted to the modern day. Most Amazonian palaeoecological records do not, however, provide the required temporal resolution to document the nuanced changes of preâColumbian disturbance or postâdisturbance succession and recovery, making it difficult to detect any direct, or indirect, ecological legacies on tree species. 2. Here, we investigate the fossil pollen, phytolith and charcoal history of Lake Kumpaka, Ecuador, during the last 2,415 years in c. 3â50 year time intervals to assess ecological legacies resulting from preâColumbian forest modification, disturbance, cultivation and fire usage. 3. Two cycles of preâColumbian cultivation (one including slashâandâburn cultivation, the other including slashâandâmulch cultivation) were documented in the record around 2150â1430 cal. year BP and 1250â680 cal. year BP, with following postâdisturbance succession dynamics. Modern disturbance was documented after c. 10 cal. year BP. The modern disturbance produced a plant composition unlike those of the two past disturbances, as fire frequencies reached their peak in the 2,415âyear record. The disturbance periods varied in intensity and duration, while the overturn of taxa following a disturbance lasted for hundreds of years. The recovery periods following preâColumbian disturbance shared some similar patterns of early succession, but the longerâterm recovery patterns differed. 4. Synthesis. The trajectories of change after a cessation of cultivation can be anticipated to differ depending on the intensity, scale, duration and manner of the past disturbance. In the Kumpaka record, no evidence of persistent enrichment or depletion of intentionally altered taxa (i.e. direct legacy effects) was found but indirect legacy effects, however, were documented and have persisted to the modern day. These findings highlight the strengths of using empirical data to reconstruct past change rather than relying solely on modern plant populations to infer past human management and ecological legacies, and challenge some of the current hypotheses involving the persistence of preâColumbian legacies on modern plant populations.Publisher PDFPeer reviewe
Bulk Scalar Stabilization of the Radion without Metric Back-Reaction in the Randall-Sundrum Model
Generalizations of the Randall-Sundrum model containing a bulk scalar field
interacting with the curvature through the general coupling are considered. We derive the general form of the effective 4D
potential for the spin-zero fields and show that in the mass matrix the radion
mixes with the Kaluza-Klein modes of the bulk scalar fluctuations. We
demonstrate that it is possible to choose a non-trivial background form
(where is the extra dimension coordinate) for the bulk scalar
field such that the exact Randall-Sundrum metric is preserved (i.e. such that
there is no back-reaction). We compute the mass matrix for the radion and the
KK modes of the excitations of the bulk scalar relative to the background
configuration and find that the resulting mass matrix implies a
non-zero value for the mass of the radion (identified as the state with the
lowest eigenvalue of the scalar mass matrix). We find that this mass is
suppressed relative to the Planck scale by the standard warp factor needed to
explain the hierarchy puzzle, implying that a mass \sim 1\tev is a natural
order of magnitude for the radion mass. The general considerations are
illustrated in the case of a model containing an interaction term.Comment: 22 pages, 3 figure
A Unified Conformal Model for Fundamental Interactions without Dynamical Higgs Field
A Higgsless model for strong, electro-weak and gravitational interactions is
proposed. This model is based on the local symmetry group SU(3)xSU(2)xU(1)xC
where C is the local conformal symmetry group. The natural minimal conformally
invariant form of total lagrangian is postulated. It contains all Standard
Model fields and gravitational interaction. Using the unitary gauge and the
conformal scale fixing conditions we can eliminate all four real components of
the Higgs doublet in this model. However the masses of vector mesons, leptons
and quarks are automatically generated and are given by the same formulas as in
the conventional Standard Model. The gravitational sector is analyzed and it is
shown that the model admits in the classical limit the Einsteinian form of
gravitational interactions. No figures.Comment: 25 pages, preprin
Experimental Constraints on the Neutrino Oscillations and a Simple Model of Three Flavour Mixing
A simple model of the neutrino mixing is considered, which contains only one
right-handed neutrino field, coupled via the mass term to the three usual
left-handed fields. This is a simplest model that allows for three-flavour
neutrino oscillations. The existing experimental limits on the neutrino
oscillations are used to obtain constraints on the two free mixing parameters
of the model. A specific sum rule relating the oscillation probabilities of
different flavours is derived.Comment: 10 pages, 3 figures in post script, Latex, IFT 2/9
On the role of power expansions in quantum field theory
Methods of summation of power series relevant to applications in quantum
theory are reviewed, with particular attention to expansions in powers of the
coupling constant and in inverse powers of an energy variable. Alternatives to
the Borel summation method are considered and their relevance to different
physical situations is discussed. Emphasis is placed on quantum chromodynamics.
Applications of the renormalon language to perturbation expansions (resummation
of bubble chains) in various QCD processes are reported and the importance of
observing the full renormalization-group invariance in predicting observables
is emphasized. News in applications of the Borel-plane formalism to
phenomenology are conveyed. The properties of the operator-product expansion
along different rays in the complex plane are examined and the problem is
studied how the remainder after subtraction of the first terms depends on
the distance from euclidean region. Estimates of the remainder are obtained and
their strong dependence on the nature of the discontinuity along the cut is
shown. Relevance of this subject to calculations of various QCD effects is
discussed.Comment: 50 pages, Latex, 1 Postscript figur
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Sporormiella as a tool for detecting the presence of large herbivores in the Neotropics
The reliability of using the abundance of Sporormiella spores as a proxy for the presence and abundance of megaherbivores was tested in southern Brazil. Mud-water interface samples from nine lakes, in which cattle-use was categorized as high, medium, or low, were assayed for Sporormiella representation. The sampling design allowed an analysis of both the influence of the number of animals using the shoreline and the distance of the sampling site from the nearest shoreline. Sporormiella was found to be a reliable proxy for the presence of large livestock. The concentration and abundance of spores declined from the edge of the lake toward the center, with the strongest response being in sites with high livestock use. Consistent with prior studies in temperate regions, we find that Sporormiella spores are a useful proxy to study the extinction of Pleistocene megafauna or the arrival of European livestock in Neotropical landscapes
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Amazonian pollen assemblages reflect biogeographic gradients and forest cover
Aim Pollen assemblages are commonly used to reconstruct past climates yet have not yet been used to reconstruct past human activities, including deforestation. We aim to assess (i) how pollen assemblages vary across biogeographic and environmental gradients, (ii) the source area of pollen assemblages from lake sediment samples and (iii) which pollen taxa can best be used to quantify deforested landscapes. Location Amazonia. Taxon Plantae. Methods Pollen assemblages (N = 65) from mudâwater interface samples (representing modern conditions) of lake sediment cores were compared with modern gradients of temperature, precipitation and elevation. Pollen assemblages were also compared with localâscale estimates of forest cover at 1, 2, 5, 10, 20 and 40 km buffers around each lake.ResultsOver 250 pollen types were identified in the samples, and pollen assemblages were able to accurately differentiate biogeographic regions across the basin, corresponding with gradients in temperature and precipitation. Poaceae percentages were the best predictor of deforestation, and had a significant negative relationship with forest cover estimates. These relationships were strongest for the 1 km buffer area, weakening as buffer sizes increased.Main conclusionsThe diverse Amazonian pollen assemblages strongly reflect environmental gradients, and percentages of Poaceae best reflect localâscale variability in forest cover. Our results of modern pollenâlandscape relationships can be used to provide a foundation for quantitative reconstructions of climate and deforestation in Amazonia
The Determination of alpha_s from Tau Decays Revisited
We revisit the determination of alpha_s(m_tau) using a fit to inclusive tau
hadronic spectral moments in light of (1) the recent calculation of the
fourth-order perturbative coefficient K_4 in the expansion of the Adler
function, (2) new precision measurements from BABAR of e+e- annihilation cross
sections, which decrease the uncertainty in the separation of vector and
axial-vector spectral functions, and (3) improved results from BABAR and Belle
on tau branching fractions involving kaons. We estimate that the fourth-order
perturbative prediction reduces the theoretical uncertainty, introduced by the
truncation of the series, by 20% with respect to earlier determinations. We
discuss to some detail the perturbative prediction and show that the effect of
the incomplete knowledge of the series is reduced by using the so-called
contour-improved calculation, as opposed to fixed-order perturbation theory
which manifests convergence problems. The corresponding theoretical
uncertainties are studied at the tau and Z mass scales. Nonperturbative
contributions extracted from the most inclusive fit are small, in agreement
with earlier determinations. Systematic effects from quark-hadron duality
violation are estimated with simple models and found to be within the quoted
systematic errors. The fit gives alpha_s(m_tau) = 0.344 +- 0.005 +- 0.007,
where the first error is experimental and the second theoretical. After
evolution to M_Z we obtain alpha_s(M_Z) = 0.1212 +- 0.0005 +- 0.0008 +- 0.0005,
where the errors are respectively experimental, theoretical and due to the
evolution. The result is in agreement with the corresponding NNNLO value
derived from essentially the Z width in the global electroweak fit. The
alpha_s(M_Z) determination from tau decays is the most precise one to date.Comment: 22 pages, 7 figure
Asymptotic Improvement of Resummation and Perturbative Predictions in Quantum Field Theory
The improvement of resummation algorithms for divergent perturbative
expansions in quantum field theory by asymptotic information about perturbative
coefficients is investigated. Various asymptotically optimized resummation
prescriptions are considered. The improvement of perturbative predictions
beyond the reexpansion of rational approximants is discussed.Comment: 21 pages, LaTeX, 3 tables; title shortened; typographical errors
corrected; minor changes of style; 2 references adde
Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements
Droughts in the western United States are expected to intensify with climate
change. Thus, an adequate representation of ecosystem response to water
stress in land models is critical for predicting carbon dynamics. The goal of
this study was to evaluate the performance of the Community Land Model (CLM)
version 4.5 against observations at an old-growth coniferous forest site in
the Pacific Northwest region of the United States (Wind River AmeriFlux
site), characterized by a Mediterranean climate that subjects trees to water
stress each summer. CLM was driven by site-observed meteorology and
calibrated primarily using parameter values observed at the site or at
similar stands in the region. Key model adjustments included parameters
controlling specific leaf area and stomatal conductance. Default values of
these parameters led to significant underestimation of gross primary
production, overestimation of evapotranspiration, and consequently
overestimation of photosynthetic 13C discrimination, reflected in
reduced 13CâŻ:âŻ12C ratios of carbon fluxes and pools. Adjustments
in soil hydraulic parameters within CLM were also critical, preventing
significant underestimation of soil water content and unrealistic soil
moisture stress during summer. After calibration, CLM was able to simulate
energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope
ratios of carbon fluxes and pools in reasonable agreement with site
observations. Overall, the calibrated CLM was able to simulate the observed
response of canopy conductance to atmospheric vapor pressure deficit (VPD)
and soil water content, reasonably capturing the impact of water stress on
ecosystem functioning. Both simulations and observations indicate that
stomatal response from water stress at Wind River was primarily driven by VPD
and not soil moisture. The calibration of the BallâBerry stomatal
conductance slope (mbb) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional
type (needleleaf evergreen temperate forest), despite significant differences
in stand composition and age and climatology, suggesting that CLM could
benefit from a revised mbb value of 6, rather than the default
value of 9, for this plant functional type. Conversely, Wind River required a
unique calibration of the hydrology submodel to simulate soil moisture,
suggesting that the default hydrology has a more limited applicability. This
study demonstrates that carbon isotope data can be used to constrain stomatal
conductance and intrinsic water use efficiency in CLM, as an alternative to
eddy covariance flux measurements. It also demonstrates that carbon isotopes
can expose structural weaknesses in the model and provide a key constraint
that may guide future model development
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