Response of Pinus sylvestris L. to recent climatic events in the French Mediterranean region

International audienceExceptional climatic events from 2003 to 2005 (scorching heat and drought) affected the whole of the vegetation in the French Mediterranean region and in particular Scott pines (Pinus sylvestris L.), one of the most important forest tree species in this area. To understand its response to these extreme conditions, we investigated its radial growth, branch length growth, architectural development and reproduction for the period 19952005, and linked these variables to climatic parameters. We used four plots situated in southeastern France and presenting different levels of site quality and potential forest productivity. The results show that: (1) the climatic episode 20032005 was highly detrimental to the growth (bole and branches), crown development, and cone production but favoured the production of male flowers; (2)these variables depend on climatic factors of both the current and previous years; (3) the 2003 scorching heat impact was strong but was mainly apparent from 2004; it was part of a 6-year-long unfavourable cycle beginning in 2000, characterized by high minimum and maximum temperatures and very dry springs;(4) in spite of a significant effect of site quality, the Scots pine's response to extreme climatic conditions was homogeneous in the French Mediterranean area; and (5) the stress induced by poor site conditions generally resulted in the same consequences for tree growth, architecture, and reproduction as in unfavourable climatic conditions.Des événements climatiques exceptionnels de 2003 à 2005 (canicule et sécheresse) ont affecté la végétation dans la région de la Méditerranée française et en particulier le pin sylvestre (Pinus sylvestris L.), une des principales essences forestières de cette région. Pour comprendre sa réponse à ces conditions extrêmes, nous avons examiné sa croissance radiale, la croissance en longueur des branches, le développement architectural et la reproduction pendant la période 1995-2005 et avons relié ces variables avec les paramètres climatiques. Nous avons utilisé quatre placettes situées dans le sud-est de la France et présentant des niveaux différents de qualité stationnelle et de productivité forestière potentielle. Les résultats montrent que : (1) l'épisode climatique 2003-2005 était fortement néfaste à la croissance (tronc et branches), au développement du houppier et à la production de cônes, mais a favorisé la production de fleurs mâles; (2) ces variables dépendent des facteurs climatiques des années en cours et précédente; (3) l'impact de canicule 2003 était fort, mais était principalement apparent de 2004; il faisait partie d'un cycle défavorable de 6 ans commençant en 2000, caractérisé par des hautes températures minimales et maximales et des printemps très secs; (4) malgré un effet significatif de la qualité stationnelle, la réponse du pin sylvestre aux conditions climatiques extrêmes était homogène dans la zone méditerranéenne française; Et (5) le stress provoqué par de mauvaises conditions stationnelles avait généralement les mêmes conséquences pour la croissance , l'architecture et la reproduction du pin sylvestre que des conditions climatiques défavorables

Le diagnostic architectural : un outil d’évaluation des sapinières dépérissantes

En région méditerranéenne, le sapin pectiné se trouve dans la limite sud de son aire de répartition et depuis 2003, des dépérissements sont observés dans le département de l’Aude et dans la région Provence-Alpes-Côte d’Azur. Ce constat préoccupe les forestiers et pose de façon cruciale la question du diagnostic de l’état de santé des arbres. Comment ne pas confondre vieillissement et dépérissement ? Quel est l’état normal, ou arbre de référence, d’un sapin ? Peut-on pronostiquer le caractère passager ou inéluctable d’un dépérissement ? La méthode d’analyse architecturale des arbres (ou méthode ARCHI) appliquée au sapin répond à ces interrogations. En reconstituant la dynamique de développement depuis la plantule jusqu’à la sénescence, elle nous renseigne sur l’ontogénèse du sapin. C’est en se référant à cette séquence que la méthode ARCHI peut prendre en compte les deux composantes d’un dépérissement, à savoir : les symptômes de dégradation des houppiers, c'est-à-dire les écarts à la normale, et les processus de résilience, c'est-à-dire les retours à la normale (ou à un état proche de la normale). Cinq états sont ainsi définis : l’état normal (arbre sain), les écarts à la normale (arbres stressés), les retours à la normale (arbres résilients et descentes de cimes) et les points de non-retour à la normale (arbres en dépérissement irréversible). Après simplification du protocole d’observation sur le terrain, une clef de détermination des types architecturaux est proposée aux gestionnaires forestiers. Les perspectives offertes par la méthode ARCHI sont passées en revue, de même que ses limites

Entanglement entropy of two disjoint intervals in c=1 theories

We study the scaling of the Renyi entanglement entropy of two disjoint blocks of critical lattice models described by conformal field theories with central charge c=1. We provide the analytic conformal field theory result for the second order Renyi entropy for a free boson compactified on an orbifold describing the scaling limit of the Ashkin-Teller (AT) model on the self-dual line. We have checked this prediction in cluster Monte Carlo simulations of the classical two dimensional AT model. We have also performed extensive numerical simulations of the anisotropic Heisenberg quantum spin-chain with tree-tensor network techniques that allowed to obtain the reduced density matrices of disjoint blocks of the spin-chain and to check the correctness of the predictions for Renyi and entanglement entropies from conformal field theory. In order to match these predictions, we have extrapolated the numerical results by properly taking into account the corrections induced by the finite length of the blocks to the leading scaling behavior.Comment: 37 pages, 23 figure

Entanglement entropy of two disjoint intervals and the recursion formula for conformal blocks

We reconsider the computation of the entanglement entropy of two disjoint intervals in a (1+1) dimensional conformal field theory by conformal block expansion of the 4-point correlation function of twist fields. We show that accurate results may be obtained by taking into account several terms in the operator product expansion of twist fields and by iterating the Zamolodchikov recursion formula for each conformal block. We perform a detailed analysis for the Ising conformal field theory and for the free compactified boson. Each term in the conformal block expansion can be easily analytically continued and so this approach also provides a good approximation for the von Neumann entropy

A contour for the entanglement entropies in harmonic lattices

We construct a contour function for the entanglement entropies in generic harmonic lattices. In one spatial dimension, numerical analysis are performed by considering harmonic chains with either periodic or Dirichlet boundary conditions. In the massless regime and for some configurations where the subsystem is a single interval, the numerical results for the contour function are compared to the inverse of the local weight function which multiplies the energy-momentum tensor in the corresponding entanglement hamiltonian, found through conformal field theory methods, and a good agreement is observed. A numerical analysis of the contour function for the entanglement entropy is performed also in a massless harmonic chain for a subsystem made by two disjoint intervals

On shape dependence of holographic mutual information in AdS4

We study the holographic mutual information in AdS(4) of disjoint spatial domains in the boundary which are delimited by smooth closed curves. A numerical method which approximates a local minimum of the area functional through triangulated surfaces is employed. After some checks of the method against existing analytic results for the holographic entanglement entropy, we compute the holographic mutual information of equal domains delimited by ellipses, superellipses or the boundaries of two dimensional spherocylinders, finding also the corresponding transition curves along which the holographic mutual information vanishes

Entanglement Hamiltonians in 1D free lattice models after a global quantum quench

We study the temporal evolution of the entanglement Hamiltonian of an interval after a global quantum quench in free lattice models in one spatial dimension. In a harmonic chain we explore a quench of the frequency parameter. In a chain of free fermions at half filling we consider the evolution of the ground state of a fully dimerised chain through the homogeneous Hamiltonian. We focus on critical evolution Hamiltonians. The temporal evolutions of the gaps in the entanglement spectrum are analysed. The entanglement Hamiltonians in these models are characterised by matrices that provide also contours for the entanglement entropies. The temporal evolution of these contours for the entanglement entropy is studied, also by employing existing conformal field theory results for the semi-infinite line and the quasi-particle picture for the global quench

On shape dependence of holographic entanglement entropy in AdS4/CFT3

We study the finite term of the holographic entanglement entropy of finite domains with smooth shapes and for four dimensional gravitational backgrounds. Analytic expressions depending on the unit vectors normal to the minimal area surface are obtained for both stationary and time dependent spacetimes. The special cases of AdS4, asymptotically AdS4 black holes, domain wall geometries and Vaidya-AdS backgrounds have been analysed explicitly. When the bulk spacetime is AdS4, the finite term is the Willmore energy of the minimal area surface viewed as a submanifold of the three dimensional flat Euclidean space. For the static spacetimes, some numerical checks involving spatial regions delimited by ellipses and non convex domains have been performed. In the case of AdS4, the infinite wedge has been also considered, recovering the known analytic formula for the coefficient of the logarithmic divergence