136 research outputs found
La rĂ©gĂ©nĂ©ration du bouleau jaune (Betula alleghaniensis) dans les forĂȘts feuillues amĂ©nagĂ©es de l'est de l'AmĂ©rique du Nord : importance du bois mort
L'abondance du bouleau jaune (Betula alleghaniensis) tend Ă diminuer dans plusieurs forĂȘts dĂ©cidues amĂ©nagĂ©es de l'est de l'AmĂ©rique du Nord. Le manque de lits de germination adĂ©quats, notamment une faible exposition du sol minĂ©ral, expliquerait en partie cette tendance. Bien que le bois mort soit Ă©galement reconnu comme Ă©tant un lit de germination pour l'espĂšce, son importance pour le maintien des processus de rĂ©gĂ©nĂ©ration demeure peu documentĂ©e. Par exemple, l'impact du l'identitĂ© spĂ©cifique du bois mort pour l'Ă©tablissement et la survie du bouleau jaune n'a que rarement Ă©tĂ© considĂ©rĂ©. De plus, la prĂ©sence occasionnelle d'une rĂ©gĂ©nĂ©ration prĂ©Ă©tablie de bouleau jaune sur bois mort et en sous-couvert amĂšne Ă penser que ces individus auraient une meilleure capacitĂ© de tolĂ©rance Ă l'ombre. Cela dit, les traits morphologiques et l'allocation de la biomasse d'individus juvĂ©niles de bouleau jaune occupant des lits de germination contrastĂ©s n'ont jamais Ă©tĂ© comparĂ©s. Le premier objectif de cette Ă©tude Ă©tait de caractĂ©riser et comparer les patrons d'Ă©tablissement du bouleau jaune, en lien avec les lits de germination connus comme Ă©tant importants pour cette espĂšce (bois mort avec ou sans mousse, sol minĂ©ral). Un Ă©chantillonnage alĂ©atoire a ainsi Ă©tĂ© rĂ©alisĂ© Ă l'intĂ©rieur de 4 Ă©rabliĂšres Ă bouleau jaune du sud-ouest du QuĂ©bec, amĂ©nagĂ©es par coupes de jardinage (6 et 15 ans). Le lit de germination, le microsite, l'espĂšce de bois mort et la hauteur de chaque individu rĂ©pertoriĂ© ont Ă©tĂ© identifiĂ©s. En second lieu, un Ă©chantillonnage destructif d'individus Ă©tablis sur bois mort (avec ou sans mousse) et sur sol minĂ©ral a Ă©tĂ© rĂ©alisĂ©. Un large gradient de taille (15 Ă 330 cm) et de lumiĂšre (3,5 et 50 % de lumiĂšre incidente) a Ă©tĂ© couvert. Les patrons de croissance, la rĂ©partition de biomasse dans les diffĂ©rents compartiments de l'arbre et divers traits morphologiques foliaires et racinaires ont ainsi Ă©tĂ© comparĂ©s en fonction du lit de germination. Nos rĂ©sultats ont montrĂ© que le bois mort soutient une plus grande proportion des individus rĂ©pertoriĂ©s comparativement au sol minĂ©ral. Le bois mort provenant des conifĂšres et du bouleau jaune lui-mĂȘme soutenait une plus grande proportion de ces individus. Les individus Ă©tablis sur le sol minĂ©ral Ă©taient majoritairement localisĂ©s sur les sentiers de dĂ©bardage rendant cette cohorte d'individus sujette Ă ĂȘtre nĂ©gativement affectĂ©e par la rĂ©utilisation de ces sentiers lors de coupes subsĂ©quentes. LiĂ© Ă notre second objectif, il ressort que la taille des individus influence fortement la majoritĂ© des paramĂštres estimĂ©s alors que le lit de germination n'avait que relativement peu d'effet direct. Par contre, les individus sur bois mort, en produisant significativement plus de racines fines par unitĂ© de biomasse et en conservant une taille plus petite sur une plus longue pĂ©riode de temps, sont plus aptes Ă survivre en sous couvert forestier. Ces variations intraspĂ©cifiques permettent d'amoindrir les effets ontogĂ©niques associĂ©s avec une augmentation de taille pour certains paramĂštres importants (LAR, FRMR). Les semis de bouleau jaune sur bois mort peuvent ainsi conserver une plus grande efficience dans la capture des ressources ce qui affecte positivement leur capacitĂ© de tolĂ©rance Ă l'ombre. En somme, nos rĂ©sultats dĂ©montrent que le bois mort du bouleau jaune et d'espĂšces conifĂ©riennes permet de maintenir une abondante rĂ©gĂ©nĂ©ration naturelle de bouleau jaune bien distribuĂ©e au sein des sites. De plus, la prĂ©sence d'une banque de candidats prĂ©Ă©tablis et prĂȘts Ă rĂ©agir Ă une ouverture de couvert forestier y est favorisĂ©e. Cet Ă©lĂ©ment structural, important pour les processus de rĂ©gĂ©nĂ©ration du bouleau jaune, devrait ĂȘtre davantage pris en compte dans une perspective d'amĂ©nagement Ă©cosystĂ©mique des forĂȘts feuillues du QuĂ©bec.\ud
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MOTS-CLĂS DE LâAUTEUR : Betula alleghaniensis, Lit de germination, IdentitĂ© spĂ©cifique du bois mort, RĂ©partition de la biomasse, Effet ontogĂ©nique, Coupe de jardinage
Birch and conifer deadwood favour early establishment and shade tolerance in yellow birch juveniles growing on sugar maple dominated stands
Small-seeded tree species such as yellow birch (YB, Betula alleghaniensis Britt.) require deadwood or mineral soil for their establishment. Although much research has been done comparing YB germination on leaf litter vs. exposed mineral soil, less is known about deadwood as a seedbed and how different seedbeds affect YB early growth along light availability and size gradients. We examine how three common seedbeds (deadwood, moss cover on deadwood, and mineral soil) affected establishment and growth, biomass partitioning, and morphological traits of YB juveniles growing in the understory of temperate mixed deciduous and coniferous forests in southern Quebec. A total of 274 YB were sampled in four sugar maple (Acer saccharum Marsh.) dominated northern hardwood stands where selective cuts had been applied 6 and 15 years prior to sampling. Over 75% of the YB found on deadwood were on material of birch and conifer origin, although these species made less than 40% of the basal area. YB juveniles growing on deadwood showed traits that improve survival in shade such as reduced height growth for tall plants, higher efficiency in resource capture, and multilayered crowns. Our results demonstrate the importance of deadwood of birch and conifer origin in maintaining an abundant, natural, spatially well-distributed, and multistoried regeneration of YB.The authors are particularly grateful to I. Pratte, D. Schönig,
A. Paquin, N. Bergeron, M. Messier, E. Messier, S. Carpentier,
Y. Gauthier, and E. Mauri for their valuable help with the field and
lab work. They also thank M. Mazerolle and S. Daigle for their
assistance with statistical models. This work was funded by a
MVRMF grant from the Ministry of Natural Resources of Quebec
(MRNQ). J.-B. Lambert was also awarded with a Fonds de recherche
du QuĂ©bec â Nature et technologies (FRQNT) scholarship
Measurement of the (eta c)(1S) production cross-section in proton-proton collisions via the decay (eta c)(1S) -> p(p)over-bar
The production of the state in proton-proton collisions is probed via its decay to the final state with the LHCb detector, in the rapidity range GeV/c. The cross-section for prompt production of mesons relative to the prompt cross-section is measured, for the first time, to be at a centre-of-mass energy TeV using data corresponding to an integrated luminosity of 0.7 fb, and at TeV using 2.0 fb. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the and decays to the final state. In addition, the inclusive branching fraction of -hadron decays into mesons is measured, for the first time, to be , where the third uncertainty includes also the uncertainty on the inclusive branching fraction from -hadron decays. The difference between the and meson masses is determined to be MeV/c.The production of the state in proton-proton collisions is probed via its decay to the final state with the LHCb detector, in the rapidity range . The cross-section for prompt production of mesons relative to the prompt cross-section is measured, for the first time, to be at a centre-of-mass energy using data corresponding to an integrated luminosity of 0.7Â fb , and at using 2.0Â fb . The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the and decays to the final state. In addition, the inclusive branching fraction of -hadron decays into mesons is measured, for the first time, to be , where the third uncertainty includes also the uncertainty on the inclusive branching fraction from -hadron decays. The difference between the and meson masses is determined to be .The production of the state in proton-proton collisions is probed via its decay to the final state with the LHCb detector, in the rapidity range GeV/c. The cross-section for prompt production of mesons relative to the prompt cross-section is measured, for the first time, to be at a centre-of-mass energy TeV using data corresponding to an integrated luminosity of 0.7 fb, and at TeV using 2.0 fb. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the and decays to the final state. In addition, the inclusive branching fraction of -hadron decays into mesons is measured, for the first time, to be , where the third uncertainty includes also the uncertainty on the inclusive branching fraction from -hadron decays. The difference between the and meson masses is determined to be MeV/c
Search for CP violation using T-odd correlations in D-0 -> K+K-pi(+)pi(-) decays
A search for violation using -odd correlations is performed using the four-body decay, selected from semileptonic decays. The data sample corresponds to integrated luminosities of and recorded at the centre-of-mass energies of 7 TeV and 8 TeV, respectively. The -violating asymmetry is measured to be . Searches for violation in different regions of phase space of the four-body decay, and as a function of the decay time, are also presented. No significant deviation from the conservation hypothesis is found
Measurement of CP asymmetry in B-s(0) -> D-s(-/+) K--/+ decays
We report on measurements of the time-dependent CP violating observables in decays using a dataset corresponding to 1.0 fb of pp collisions recorded with the LHCb detector. We find the CP violating observables , , , , , where the uncertainties are statistical and systematic, respectively. We use these observables to make the first measurement of the CKM angle in decays, finding = (115) modulo 180 at 68% CL, where the error contains both statistical and systematic uncertainties.We report on measurements of the time-dependent CP violating observables in B âââD K decays using a dataset corresponding to 1.0 fb of pp collisions recorded with the LHCb detector. We find the CP violating observables C = 0.53±0.25±0.04, A â=â0.37â±â0.42â±â0.20, , S = â1.09±0.33±0.08, , where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the B mixing phase â2ÎČ leads to the first extraction of the CKM angle Îł from B âââD K decays, finding Îłâ=â(115 )° modulo 180° at 68% CL, where the error contains both statistical and systematic uncertainties.We report on measurements of the time-dependent CP violating observables in decays using a dataset corresponding to 1.0 fb of pp collisions recorded with the LHCb detector. We find the CP violating observables , , , , , where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the mixing phase leads to the first extraction of the CKM angle from decays, finding = (115) modulo 180 at 68% CL, where the error contains both statistical and systematic uncertainties
Search for the lepton flavour violating decay tau(-) -> mu(-)mu(+)mu(-)
A search for the lepton flavour violating decay is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of 1.0 fb of proton-proton collisions at a centre-of-mass energy of 7 TeV and 2.0 fb at 8 TeV. No evidence is found for a signal, and a limit is set at 90% confidence level on the branching fraction, .A search for the lepton flavour violating decay Ï â ÎŒ ÎŒ ÎŒ is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of 1.0 fb of proton-proton collisions at a centre-of-mass energy of 7 TeV and 2.0 fb at 8 TeV. No evidence is found for a signal, and a limit is set at 90% confidence level on the branching fraction, .A search for the lepton flavour violating decay is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of of proton-proton collisions at a centre-of-mass energy of and at . No evidence is found for a signal, and a limit is set at confidence level on the branching fraction,
Observation of the B0 â Ï0Ï0 decay from an amplitude analysis of B0 â (Ï+Ïâ)(Ï+Ïâ) decays
Protonâproton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fbâ1 , are analysed to search for the charmless B0âÏ0Ï0 decay. More than 600 B0â(Ï+Ïâ)(Ï+Ïâ) signal decays are selected and used to perform an amplitude analysis, under the assumption of no CP violation in the decay, from which the B0âÏ0Ï0 decay is observed for the first time with 7.1 standard deviations significance. The fraction of B0âÏ0Ï0 decays yielding a longitudinally polarised final state is measured to be fL=0.745â0.058+0.048(stat)±0.034(syst) . The B0âÏ0Ï0 branching fraction, using the B0âÏKâ(892)0 decay as reference, is also reported as B(B0âÏ0Ï0)=(0.94±0.17(stat)±0.09(syst)±0.06(BF))Ă10â6
Angular analysis of the B-0 -> K*(0) e(+) e(-) decay in the low-q(2) region
An angular analysis of the decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 {\mbox{fb}^{-1}}, collected by the LHCb experiment in collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared () interval between 0.002 and 1.120. The angular observables and which are related to the polarisation and to the lepton forward-backward asymmetry, are measured to be and , where the first uncertainty is statistical and the second systematic. The angular observables and which are sensitive to the photon polarisation in this range, are found to be and . The results are consistent with Standard Model predictions.An angular analysis of the B â K^{*}^{0} e e decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 fb, collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared (q) interval between 0.002 and 1.120 GeV /c. The angular observables F and A which are related to the K^{*}^{0} polarisation and to the lepton forward-backward asymmetry, are measured to be F = 0.16 ± 0.06 ± 0.03 and A â=â0.10â±â0.18â±â0.05, where the first uncertainty is statistical and the second systematic. The angular observables A and A which are sensitive to the photon polarisation in this q range, are found to be A â=âââ0.23â±â0.23â±â0.05 and A â=â0.14â±â0.22â±â0.05. The results are consistent with Standard Model predictions.An angular analysis of the decay is performed using a data sample, corresponding to an integrated luminosity of 3.0 {\mbox{fb}^{-1}}, collected by the LHCb experiment in collisions at centre-of-mass energies of 7 and 8 TeV during 2011 and 2012. For the first time several observables are measured in the dielectron mass squared () interval between 0.002 and 1.120. The angular observables and which are related to the polarisation and to the lepton forward-backward asymmetry, are measured to be and , where the first uncertainty is statistical and the second systematic. The angular observables and which are sensitive to the photon polarisation in this range, are found to be and . The results are consistent with Standard Model predictions
A study of CP violation in B-+/- -> DK +/- and B-+/- -> D pi(+/-) decays with D -> (KSK +/-)-K-0 pi(-/+) final states
A first study of CP violation in the decay modes and , where labels a or meson and labels a or meson, is performed. The analysis uses the LHCb data set collected in collisions, corresponding to an integrated luminosity of 3 fb. The analysis is sensitive to the CP-violating CKM phase through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of using other decay modes
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