Dispersion active et passive de <i>Lymantria dispar</i> (L.) (Lép., Lymantriidae), cas de la subéraie marocaine atlantique

Fraval, Alain; Yousfi, Mounia El

doi:10.1111/j.1439-0418.1989.tb00466.x

Cited by 7 publications

(7 citation statements)

References 21 publications

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“…Parmi les facteurs naturels de ce phénomène figure le dépérissement occasionné par les attaques d'insectes phyllophages [6,15,24] et de champignons parasites ou saprophytes déclenchées par des cycles de sécheresse [6,22].…”

Section: Introductionunclassified

�valuation de la biomasse arbor�e et arbustive dans une s�quence de d�gradation de la suberaie � Cytise de Kroumirie (Tunisie)

Sebeï¹,

Albouchi

Rapp³

et al. 2001

Ann. For. Sci.

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(Reçu le 12 juillet 1999 ; accepté le 16 novembre 1999) Résumé -Les biomasses aérienne et souterraine des strates arborée et arbustive ont été étudiées dans une séquence de dégradation de la suberaie à cytise de Kroumirie. Des mesures de biomasse et de paramètres dendrométriques de douze arbres échantillons de chênes lièges ont été réalisées dans des parcelles bien venantes et d'autres appartenant à différents stades de dégradation. Les relations allométriques obtenues ont permis de déceler les meilleures variables explicatives des biomasses compartimentales au niveau de l'individu et de la parcelle. Au niveau individuel, la circonférence des branches à l'insertion sur le tronc en ce qui concerne la biomasse individuelle des branches et le diamètre à 1,30 m (DBH) en ce qui concerne les différents compartiments de l'arbre, sont des paramètres hautement explicatifs. Pour un arbre de taille moyenne (20 cm de DBH), la biomasse aérienne représente 81,5 % de la biomasse totale contre 18,5 % pour les racines. Le tronc renferme 57 % de la biomasse épigée avec 44 % dans le bois et 13 % dans le liège. Les 43 % contenus dans le houppier se répartissent entre le bois des branches (23 %), le liège des branches (12 %), les rameaux et les feuilles (4 % chacun). Par ailleurs, le pourcentage de liège dans la biomasse du tronc varie en sens inverse du DBH. Au niveau parcellaire, la surface terrière s'est avérée la meilleure variable de calcul de biomasses partielles des chênes lièges et un bon critère de l'état des peuplements. La dégradation s'est traduite par une diminution continue de la densité (723 à 223 tiges ha -1 ), du DBH moyen (20,21 à 2,97 cm), de la surface terrière (32,928 à 0,985 m 2 ha -1 ) et de la biomasse des chênes lièges (139 à 4 t ha -1 ). L'ouverture de la strate arborée, qui accompagne cette dégradation, entraîne une baisse quasi-linéaire de la biomasse des chênes lièges et constitue, de ce fait, un second critère quantitatif de l'état des peuplements. Cependant, jusqu'à un seuil de 70 %, cette ouverture a favorisé le développement du maquis (9 à 54 t ha -1 ). Au-delà, la biomasse du maquis a chuté en dépit d'un meilleur taux de recouvrement.biomasse / suberaie / dégradation / surface terrière / Kroumirie Abstract -Evaluation of the overstorey and understorey biomasses in a damaging sequence of cytisus cork oak forest in Kroumirie (Tunisia). The aerial and underground biomasses of the overstorey and understorey have been studied in a damaging sequence of cytisus cork oak stands in Kroumirie region. Measurements of biomass and dendrometric parameters on twelve sampled trees have been realized in different plots, with variable damage stages. The allometric relationships obtained allowed to detect the best predictive variables of partial biomasses at individual and stand levels. At individual level, branch girth at stem insertion and diameter at breast height (DBH) are highly predictive parameters. The aerial biomass of a tree cork oak of medium size (DBH = 20 cm) represents 81.5% of the total tree biomass aga...

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Section: Introductionunclassified

�valuation de la biomasse arbor�e et arbustive dans une s�quence de d�gradation de la suberaie � Cytise de Kroumirie (Tunisie)

Sebeï¹,

Albouchi

Rapp³

et al. 2001

Ann. For. Sci.

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“…A feature of the electric dipole-dipole interaction which will assist in scaling to a larger number of qubits, is that it can be effectively turned off by storing the quantum information in the dopants' optically * Electronic address: jevon.longdell@anu.edu.au addressable hyperfine states, this has been demonstrated experimentally [4]. Another benefit is that the hyperfine have long coherence times, tens of seconds have recently been measured for these hyperfine transitions [5].In a europium doped YSO crystal the europium ions substitute for the yttrium ions in the lattice and are distributed randomly throughout the available sites in the sample. In general, each of these ions has a unique optical transition frequency that is determined by the local crystal environment (i.e.…”

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confidence: 99%

mentioning

confidence: 99%

Demonstration of Conditional Quantum Phase Shift Between Ions in a Solid

2004

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Due to their potential for long coherence times, dopant ions have long been considered promising candidates for scalable solid state quantum computing. However, the demonstration of two qubit operation has proven to be problematic, largely due to the difficulty of addressing closely spaced ions. Here we use optically active ions and optical frequency addressing to demonstrate a conditional phase shift between two qubits.Solid state quantum computing is a field of active research spurred in part by the expectation that it will be easier to scale a solid state system to a large number of qubits. To date the only experimental demonstrations approaching that of a two qubit gate operation [1] have used qubits based on electron charge. While single electron charges are measurable, their strong interaction with the environment means that the coherence times are very short making necessary extreme experimental techniques.In this work we demonstrate a conditional quantum phase shift in a two-qubit system, based on local interactions between optically active centers in a solid. The qubits were based on optical transitions of the dopant ions. The gate operations are performed with sequences of precise optical pulses in a manner analogous to techniques used in nuclear magnetic resonance.The material chosen for the demonstration was Eu doped yttrium orthosilicate (YSO). This material was selected because of the narrow homogeneous linewidth of the 7 F 0 ↔ 5 D 0 transition of the Eu 3+ ions at 579 nm, which can be as narrow as 100 Hz [2]. The long coherence time associated with this narrow line width simplifies the implementation of the optical pulse sequences as it allows the use of microsecond time scale pulses to control the gate operations. These pulses can be generated by simple modulation of the output of a narrowband continuous wave laser.The dominant interaction between the europium ions is a non-resonant electric dipole-dipole interaction. The Eu 3+ dopant ion possesses a permanent electric dipole moment that depends on the electronic state of the ion, therefore exciting one ion induces linear Stark shift in the optical frequencies of surrounding ions. For europium ions in adjoining Y sites, separated by 0.5 nm, the interaction is expected to be of the order of 10 GHz [3]. The interaction falls off as the inverse of the cube of the separation between the ions and therefore is larger than the ions' homogeneous linewidth out to distances of approximately 500 nm. A feature of the electric dipole-dipole interaction which will assist in scaling to a larger number of qubits, is that it can be effectively turned off by storing the quantum information in the dopants' optically * Electronic address: jevon.longdell@anu.edu.au addressable hyperfine states, this has been demonstrated experimentally [4]. Another benefit is that the hyperfine have long coherence times, tens of seconds have recently been measured for these hyperfine transitions [5].In a europium doped YSO crystal the europium ions substitute for the yttrium ions in ...

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“…This experimental site was designed in 1978 for monitoring the evolution of the population density of L. dispar in a forest area of 20,000 ha (Fraval & Lahloui, 1980;Fraval, 1989). 240 plots of 1 ha were distributed about 1 km apart.…”

Section: Methodsmentioning

confidence: 99%

“…In July, larvae of Dasytes terminalis (Du Val) (Villemant, 1993(Villemant, , 1995ViUemant & Fraval, 1992). In the Mamora forest near Rabat moth outbreaks are cyclic and last about 10 years (Fraval, 1989). The latest outbreak ended in 1982 and a new one erupted in 1992.…”

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confidence: 99%

Predators ofLymantria dispar (Lep. lymantriidae) egg masses: Spatio-temporal variation of their impact during the 1988–89 pest generation in the mamora cork oak forest (Morocco)

Villemant

Ramzi²

1995

Entomophaga

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In the Mamora cork oak forest (Morocco), oophagous predators of the gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae) are one of the main mortality factors influencing pest population dynamics. The predators destroy egg masses more by disrupting their cohesiveness than by predation. From 1987 to 1990, the impact of oophagous enemies significantly contributed to the collapse of a localized gypsy moth outbreak. Variation of egg mass dislocation intensity was greater between trees than among the different strata of a tree. The number of gypsy moth egg masses and egg predator attacks increased when oaks were large and unhealthy. Forest degradation probably explains why egg mass destruction rates were so high (60 to 90 % of the eggs) in the infested forest. Oophagous predators find food and shelter under the dehiscent bark of unhealthy cork oaks.

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Dispersion active et passive de Lymantria dispar (L.) (Lép., Lymantriidae), cas de la subéraie marocaine atlantique

Cited by 7 publications

References 21 publications

�valuation de la biomasse arbor�e et arbustive dans une s�quence de d�gradation de la suberaie � Cytise de Kroumirie (Tunisie)

�valuation de la biomasse arbor�e et arbustive dans une s�quence de d�gradation de la suberaie � Cytise de Kroumirie (Tunisie)

Demonstration of Conditional Quantum Phase Shift Between Ions in a Solid

Predators ofLymantria dispar (Lep. lymantriidae) egg masses: Spatio-temporal variation of their impact during the 1988–89 pest generation in the mamora cork oak forest (Morocco)

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