Sapling age structure and growth series reveal a shift in recruitment dynamics of sugar maple and American beech over the last 40 years

Northern hardwoods have undergone a marked change in their dynamics, with American beech (Fagus grandifolia Ehrh.) increasing in abundance relative to sugar maple (Acer saccharum Marsh.). This study aims to better understand this sudden shift in recruitment dynamics. We performed an extensive analysis of the age structure, radial growth pattern, and release history on >700 saplings from 34 mature maple–beech stands of southern Quebec. We found (i) that the sapling age structures showed a progressive decrease in the establishment of maple relative to beech starting about 40 years ago, (ii) a change in the species growth hierarchy that started in the 1980s due to increasing radial growth of beech, (iii) that this growth trend is negligible for both maple and beech when we account for size and suppression status, and finally (iv) that the growth trend appears to be independent of present soil conditions. These results contrast with previous studies conducted at the adult stage that reported a growth decline for maple. We conclude that this change in recruitment dynamics is not related to growth, and consequently, further studies investigating this phenomenon should concentrate on establishment and survival

Large-scale synchrony of gap dynamics and the distribution of understory tree species in maple-beech forests

Large-scale synchronous variations in community dynamics are well documented for a vast array of organisms, but are considerably less understood for forest trees. Because of temporal variations in canopy gap dynamics, forest communities—even old-growth ones—are never at equilibrium at the stand scale. This paucity of equilibrium may also be true at the regional scale. Our objectives were to determine (1) if nonequilibrium dynamics caused by temporal variations in the formation of canopy gaps are regionally synchronized, and (2) if spatiotemporal variations in canopy gap formation aVect the relative abundance of tree species in the understory. We examined these questions by analyzing variations in the suppression and release history of Acer saccharum Marsh. and Fagus grandifolia Ehrh. from 481 growth series of understory saplings taken from 34 mature stands. We observed that (1) the proportion of stems in release as a function of time exhibited a U-shaped pattern over the last 35 years, with the lowest levels occurring during 1975–1985, and that (2) the response to this in terms of species composition was that A. saccharum became more abundant at sites that had the highest proportion of stems in release during 1975–1985. We concluded that the understory dynamics, typically thought of as a stand-scale process, may be regionally synchronized

The inner craniodental anatomy of the Papio specimen U.W. 88-886 from the Early Pleistocene site of Malapa, Gauteng, South Africa

Cercopithecoids represent an essential component of the Plio-Pleistocene faunal assemblage. However, despite the abundance of the cercopithecoid fossil remains in African Plio-Pleistocene deposits, the chronological and geographic contexts from which the modern baboons (i.e. Papio hamadryas ssp.) emerged are still debated. The recently discovered Papio (hamadryas) angusticeps specimen (U.W. 88-886) from the Australopithecus sediba-bearing site of Malapa, Gauteng, South Africa, may represent the first modern baboon occurrence in the fossil record. Given the implication of U.W. 88-886 for the understanding of the papionin evolutionary history and the potential of internal craniodental structures for exploring evolutionary trends in fossil monkey taxa, we use X-ray microtomography to investigate the inner craniodental anatomy of this critical specimen. Our goal is to provide additional evidence to examine the origins of modern baboons. In particular,we explore (i) the tissue proportions and the dentine topographic distribution in dental roots and (ii) the endocranial organization. Consistent with the previous description and metrical analyses of its external cranial morphology, U.W. 88-886 shares internal craniodental anatomy similarities with Plio-Pleistocene and modern Papio, supporting its attribution to Papio (hamadryas) angusticeps. Interestingly, average dentine thickness and distribution in U.W. 88-886 fit more closely to the extinct Papio condition, while the sulcal pattern and relative dentine thickness are more like the extant Papio states. Besides providing additional evidence for characterizing South African fossil papionins, our study sheds new light on the polarity of inner craniodental features in the papionin lineage.Palaeontological Scientific Trust (PAST) Occitanie Region and the French Ministry of Higher Education and ResearchJNC201

Sequence and structure of the mouse gene coding for the largest neurofilament subunit.

We have determined the complete nucleotide sequence of the mouse gene encoding the neurofilament NF-H protein. The C-terminal domain of NF-H is very rich in charged amino acids (aa) and contains a 3-aa sequence, Lys-Ser-Pro, that is repeated 51 times within a stretch of 368 aa. The location of this serine-rich repeat in the phosphorylated domain of NF-H indicates that it represents the major protein kinase recognition site. The nfh gene shares two common intron positions with the nfl and nfm genes, but has an additional intron that occurs at a location equivalent to one of the introns in non-neuronal intermediate filament-coding genes. This additional nfh intron may have been acquired via duplication of a primordial intermediate filament gene

The Cold Big-Bang Cosmology as a Counter-example to Several Anthropic Arguments

A general Friedmann big-bang cosmology can be specified by fixing a half-dozen cosmological parameters such as the photon-to-baryon ratio Eta, the cosmological constant Lambda, the curvature scale R, and the amplitude Q of (assumed scale-invariant) primordial density fluctuations. There is currently no established theory as to why these parameters take the particular values we deduce from observations. This has led to proposed `anthropic' explanations for the observed value of each parameter, as the only value capable of generating a universe that can host intelligent life. In this paper, I explicitly show that the requirement that the universe generates sun-like stars with planets does not fix these parameters, by developing a class of cosmologies (based on the classical `cold big-bang' model) in which some or all of the cosmological parameters differ by orders of magnitude from the values they assume in the standard hot big-bang cosmology, without precluding in any obvious way the existence of intelligent life. I also give a careful discussion of the structure and context of anthropic arguments in cosmology, and point out some implications of the cold big-bang model's existence for anthropic arguments concerning specific parameters.Comment: 13 PRD-style pages, 2 postscript figures. Reference 26 corrected. Accepted to Phys. Rev.

Reversed anisotropies and thermal contraction of FCC (110) surfaces

The observed anisotropies of surface vibrations for unreconstructed FCC metal (110) surfaces are often reversed from the "common sense" expectation. The source of these reversals is investigated by performing ab initio density functional theory calculations to obtain the surface force constant tensors for Ag(110), Cu(110) and Al(110). The most striking result is a large enhancement in the coupling between the first and third layers of the relaxed surface, which strongly reduces the amplitude of out-of-plane vibrations of atoms in the first layer. This also provides a simple explanation for the thermal contraction of interlayer distances. Both the anisotropies and the thermal contraction arise primarily as a result of the bond topology, with all three (110) surfaces showing similar behavior.Comment: 13 pages, in revtex format, plus 1 postscript figur

Molecular hydrogen adsorbed on benzene: insights from a quantum Monte Carlo study

We present a quantum Monte Carlo study of the hydrogen-benzene system where binding is very weak. We demonstrate that the binding is well described at both variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC) levels by a Jastrow correlated single determinant geminal wave function with an optimized compact basis set that includes diffuse orbitals. Agreement between VMC and fixed-node DMC binding energies is found to be within 0.18 mHa, suggesting the calculations are well-converged with respect to the basis. Essentially the same binding is also found in independent DMC calculations using a different trial wave function of a more conventional Slater-Jastrow form, supporting our conclusion that the binding energy is accurate and includes all effects of correlation. We compare with empirical models and previous calculations, and we discuss the physical mechanisms of the interaction, the role of diffuse basis functions, and the charge redistribution in the bond.Comment: 12 pages, 4 figure

Big Bang Nucleosynthesis and Lepton Number Asymmetry in the Universe

Recently it is reported that there is the discrepancy between big bang nucleosynthesis theory and observations (BBN crisis). We show that BBN predictions agree with the primordial abundances of light elements, He4, D, He3 and Li7 inferred from the observational data if an electron neutrino has a net chemical potential xi_{nu_e} due to lepton asymmetry. We estimate that xi_{nu_e} = 0.043^{+0.040}_{-0.040} (95% C.L.) and Omega_bh^2 = 0.015^{+0.006}_{-0.003} (95% C.L.).Comment: 10 pages, using AAS LATEX and three postscript figure