Above- and below-ground competition effects of two heathland species: implications for growth and response to herbivory in birch saplings

We examined experimentally the effect of competition from two common heathland plant species (Calluna vulgaris or Molinia caerulea) on Betula pubescens saplings subjected to simulated mammalian browsing damage. We tested two hypotheses: that B. pubescens saplings alter their growth allocation in response to different patterns of competition from the two species in order to maximise resource acquisition; and that, when only B. pubescens saplings are damaged, herbivory reduces its ability to compete with both species. In an ex-situ experiment we grew B. pubescens saplings in the presence of below- or above- and below-ground interactions from C. vulgaris or M. caerulea. Saplings were also subjected to simulated browsing by clipping (50% of current year's growth), either pre-senescence or at bud-burst. We measured the morphology and dry mass allocation response of the saplings over a period of two years. We found that competition reduced sapling dry mass by approximately 50%, but C. vulgaris reduced dry mass to a greater extent than did M. caerulea. The total competition intensity of C. vulgaris was greater than that of M. caerulea, due to an apparent facilitative effect of M. caerulea shoots on birch growth. Saplings compensated for browsing damage, resulting in no difference in dry mass one year after damage. However, sapling morphological responses to browsing damage were dependent on the competing species. Despite the large competitive effect of below-ground interactions, saplings did not increase allocation to root growth as predicted. Additionally, in response to above-ground interactions from M. caeruela, saplings increased allocation to root growth. This study highlights the importance of patterns, as well as intensity, of competition in determining plant responses to inter-specific interactions. Sapling responses did not follow the pattern predicted by the balanced-growth hypothesis. We suggest that this is due to the multi-functionality of plant component parts and the balance between competitive and facilitative effects of interacting plants

How do different competing species influence the response of Betula pubescens Ehrh. to browsing?

When attempting to expand existing woodland through natural regeneration, herbivory and competition from the existing vegetation may impede the regenerating saplings. This work addresses how browsing and competition with other vegetation interact to drive sapling growth and morphology of the widespread tree species B. pubescens. We took above-ground morphological measurements of B. pubescens saplings within an intimate mosaic of Calluna vulgaris and Molinia caerulea, comparing saplings growing with each of the two plant species under three different red deer (Cervus elaphus) densities, allowing comparison of different levels of both past and present levels of browsing damage. Saplings growing in M. caerulea dominated vegetation responded to reduced browsing with faster growth than those growing in C. vulgaris dominated vegetation. However, we found that when natural browsing levels were high, browsing masked any differences in inter-specific interactions between plant species. We propose that, in regeneration schemes where deer densities are reduced, these differences should confer a competitive advantage to saplings growing with M. caerulea over those growing with C. vulgaris. Additionally, our results highlight the importance of browsing history, rather than just current browsing levels, in determining sapling growth responses under different herbivore management regimes. This study highlights the importance of multi-factor interactions in determining plant growth and morphology under different conditions. In particular we identify the prevalence of interactions between competition, herbivory and time, as determining the potential growth and morphology of B. pubescens saplings in regeneration areas. This has important implications for the management of sites where browsing impedes the natural regeneration of trees and shrubs, or where herbivore densities have been reduced to encourage woodland regeneration

Is cosmology consistent?

We perform a detailed analysis of the latest CMB measurements (including BOOMERaNG, DASI, Maxima and CBI), both alone and jointly with other cosmological data sets involving, e.g., galaxy clustering and the Lyman Alpha Forest. We first address the question of whether the CMB data are internally consistent once calibration and beam uncertainties are taken into account, performing a series of statistical tests. With a few minor caveats, our answer is yes, and we compress all data into a single set of 24 bandpowers with associated covariance matrix and window functions. We then compute joint constraints on the 11 parameters of the ``standard'' adiabatic inflationary cosmological model. Out best fit model passes a series of physical consistency checks and agrees with essentially all currently available cosmological data. In addition to sharp constraints on the cosmic matter budget in good agreement with those of the BOOMERaNG, DASI and Maxima teams, we obtain a heaviest neutrino mass range 0.04-4.2 eV and the sharpest constraints to date on gravity waves which (together with preference for a slight red-tilt) favors ``small-field'' inflation models.Comment: Replaced to match accepted PRD version. 14 pages, 12 figs. Tiny changes due to smaller DASI & Maxima calibration errors. Expanded neutrino and tensor discussion, added refs, typos fixed. Combined CMB data, window and covariance matrix at http://www.hep.upenn.edu/~max/consistent.html or from [email protected]

Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events

The $B^0$-$\bar B^0$ oscillation frequency has been measured with a sample of 23 million \B\bar B pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives $\Delta m_d = 0.493 \pm 0.012{(stat)}\pm 0.009{(syst)}$ ps$^{-1}$.Comment: 7 pages, 1 figure, submitted to Physical Review Letter

Weak Lensing and CMB: Parameter forecasts including a running spectral index

We use statistical inference theory to explore the constraints from future galaxy weak lensing (cosmic shear) surveys combined with the current CMB constraints on cosmological parameters, focusing particularly on the running of the spectral index of the primordial scalar power spectrum, $\alpha_s$. Recent papers have drawn attention to the possibility of measuring $\alpha_s$ by combining the CMB with galaxy clustering and/or the Lyman-$\alpha$ forest. Weak lensing combined with the CMB provides an alternative probe of the primordial power spectrum. We run a series of simulations with variable runnings and compare them to semi-analytic non-linear mappings to test their validity for our calculations. We find that a ``Reference'' cosmic shear survey with $f_{sky}=0.01$ and $6.6\times 10^8$ galaxies per steradian can reduce the uncertainty on $n_s$ and $\alpha_s$ by roughly a factor of 2 relative to the CMB alone. We investigate the effect of shear calibration biases on lensing by including the calibration factor as a parameter, and show that for our Reference Survey, the precision of cosmological parameter determination is only slightly degraded even if the amplitude calibration is uncertain by as much as 5%. We conclude that in the near future weak lensing surveys can supplement the CMB observations to constrain the primordial power spectrum.Comment: 12 pages, 10 figures, revtex4. Final form to appear in Phys Rev

Separating the Early Universe from the Late Universe: cosmological parameter estimation beyond the black box

We present a method for measuring the cosmic matter budget without assumptions about speculative Early Universe physics, and for measuring the primordial power spectrum P*(k) non-parametrically, either by combining CMB and LSS information or by using CMB polarization. Our method complements currently fashionable ``black box'' cosmological parameter analysis, constraining cosmological models in a more physically intuitive fashion by mapping measurements of CMB, weak lensing and cluster abundance into k-space, where they can be directly compared with each other and with galaxy and Lyman alpha forest clustering. Including the new CBI results, we find that CMB measurements of P(k) overlap with those from 2dF galaxy clustering by over an order of magnitude in scale, and even overlap with weak lensing measurements. We describe how our approach can be used to raise the ambition level beyond cosmological parameter fitting as data improves, testing rather than assuming the underlying physics.Comment: Replaced to match accepted PRD version. Refs added. Combined CMB data and window functions at http://www.hep.upenn.edu/~max/pwindows.html or from [email protected]. 18 figs, 19 journal page

Nitrate supply and the biophysics of leaf growth in salix viminalis

The influence of nitrogen on leaf area development and the biophysics of leaf growth was studied using clonal plants of the shrub willow, Salix viminalis grown with either optimal (High N) or sub-optimal (Low N) supplies of nitrate. Leaf growth rate and final leaf size were reduced in the sub-optimal treatment and the data suggest that in young rapidly growing leaves, this was primarily due to changes in cell wall properties, since cell wall extensibility (% plasticity) was reduced in the Low N plants.The biophysical regulation of leaf cell expansion also differed with nitrogen treatment as leaves aged. In the High N leaves, leaf cell turgor pressure (P) increased with age whilst in the Low N leaves P declined with age, again suggesting that for young leaves, cell wall plasticity limited expansion in the Low N plants. Measurements of cell wall properties showed that cell wall elasticity (%E) was not influenced by nitrogen treatment and remained constant regardless of leaf age

Do competition and herbivory alter the internal nitrogen dynamics of birch saplings?

• Deciduous trees recycle nitrogen (N) within their tissues. The aim of this study was to test the hypothesis that reductions in plant growth, due to competition and herbivory, reduce the sink strength for N during autumn nutrient withdrawal and reduce the storage capacity and hence the amount of N remobilised in the following spring. • We used 15N labelled fertiliser to quantify N uptake, leaf-N withdrawal and remobilisation. Betula pubescens saplings were grown with either Molinia caerulea or Calluna vulgaris, and subjected to simulated browsing damage. • Competition reduced B. pubescens leaf-N withdrawal and remobilisation, with C. vulgaris having a greater effect than M. caerulea. However, simulated browsing had no significant effect on sapling N dynamics. The patterns of leaf-N withdrawal and remobilisation closely followed sapling dry mass. • We conclude that the effect of competition on sapling mass reduces their N storage capacity. This reduces sink-strength for leaf-N withdrawal and the source-strength for remobilised N. The ability of saplings to compensate for browsing damage removed any potential effect of browsing on N dynamics