Réflexions d'un écologue.

Réflexions d'un écologue qui pendant 30 ans a étudié et regardé la dynamique de la végétation après incendie dans la région méditerranéenne

Recuperación y regeneración de ecosistemas mediterráneos incendiados

Durante mucho tiempo el fuego ha sido considerado como un factor desencadenante de la degradación de la vegetación. En este artículo se analizan diversos estudios que versan sobre la dinámica de la vegetación después de un incendio. El efecto del fuego en las comunidades vegetales se estudia tomando como referencia trabajos realizados sobre formaciones forestales y de matorral típicamente mediterráneas.Forest fire has been considered for long as a mayor factor causing vegetation degradation. This paper review several research works about the vegetation dynamic after fire. Fire effect over vegetation communities is analysed using as a reference some researchs over tipical Mediterranean formations

Tentative d'analyse logique des recherches sur les feux de végétation entreprises au département d'écologie générale du C.E.P.E. Louis Emberger

Les recherches sur les feux ont trait aux conditions climatiques et végétales qui déterminent l'apparition des feux, au comportement du feu et à son impact sur les milieux. L'article donne quelques résultats concernant l'application

Recuperación y regeneración de ecosistemas mediterráneos incendiados

Durante mucho tiempo el fuego ha sido considerado como un factor desencadenante de la degradación de la vegetación. En este artículo se analizan diversos estudios que versan sobre la dinámica de la vegetación después de un incendio. El efecto del fuego en las comunidades vegetales se estudia tomando como referencia trabajos realizados sobre formaciones forestales y de matorral típicamente mediterráneas.Forest fire has been considered for long as a mayor factor causing vegetation degradation. This paper review several research works about the vegetation dynamic after fire. Fire effect over vegetation communities is analysed using as a reference some researchs over tipical Mediterranean formations

Réponses du chêne vert et du chêne blanc à l'action du feu

L'influence du feu a été étudié, dans le Bas Languedoc, de façon diachronique sur la dynamique de la composition floristique et de la structure des chênaies incendiées de Quercus ilex. De la même façon, la croissance post incendie a été suivie sur des individus de Quercus ilex et Quercus pubescens. Leur résistance aux incendies répétés a été mesurée expérimentalement

Réponses des végétaux ligneux méditerranéens à l'action du feu

The response of different Mediterranean wood species to fire action is studied in the neiglibourhood of Montpellier (France). Along 19 years (1969-1987), the author follows the evolution of 35 experimental plots undergoing artificial fires in the spring and fallow, and with different frequencies: 2,3 a 6 years. He controls moreover 52 areas burned from natural fires, for ten years after the burning. Concluding remarks show that woody species of Mediterranean region are, in general, rather fire-resistant. Some of them, however, such as Cistus monspeliensis, Juniperus oxycedrus and Rhamnus alaternus, con be eliminated if the fires are too frequent. Other, such as Quercus coccifera, Q. ilex or Q. pubescens, show, importance for the regeneration capability of the species, mainly for those being very sensitive to frequent fires.[fr] On étudie les réponses des végétaux ligneux méditerranéens l'action du feu dans une zone autour de Montpellier (France). L'auteur suit sur 19 ans (1969-1987) l'évolution de 35parcelles expérimentales, soumises au feu pendant le printemps ou l'automne et avec différentes fréquences: 2, 3 et 6 ans. Par ailleurs, étudie 52 zones d'observation brûlées par des feux sauvages pendant les dix premières années après l'incendie. L'auteur conclut en montrant que dans l'ensemble, les végétaux ligneux du bassin méditerranéen résistent au feu. Toutefois, certains (p. ex. Cistus monspeliensis, Juniperus oxycedrus, Rhamnus alaternus) peuvent être éliminés lorsque les feux sont trop fréquents. En revanche, d'autres (p. ex. Quercus coccifera, Q. ilex et Q. pubescens) montrent une résistance très forte. La saison des feux a une grande importance sur les capacités de régénération des espèces, et plus particulièrement celles qui sont extrêmement sensibles à la fréquence des incendies. [es] Se estudia la respuesta de diferentes especies leñosas mediterráneas a la acción del fuego en los alrededores de Montpellier (Francia). El autor sigue durante 19 años (1969-1987) la evolución de 35 parcelas experimentales sometidas a fuegos provocados en primavera o en otoño y con distintas frecuencias: 2, 3 y 6 años. Además controla 52 áreas quemadas con fuegos naturales durante los 10 años posteriores al incendio. Concluye señalando que en conjunto las especies leñosas de la cuenca mediterránea son bastante resistentes al fuego. Sin embargo, algunas como Cistus monspeliensis, Juniperus oxycedrus y Rhamnus alaternus llegan a ser eliminadas cuando los fuegos son muy frecuentes. Por el contrario, otras (Quercus coccifera, Q. ilex y Q. pubescens, por ejemplo) muestran una resistencia muy fuerte. La estación en que se quema tiene gran importancia en la capacidad de regeneración de las especies, especialmente en las extremadamente sensibles a los incendios repetidos

Towards a sounder fire ecology

This forum brings together fire ecologists from outside the current wildfire controversy in the US to give their views on three central topics related to ecosystems in which wildfires are an important process. First, how do fire behavior and ecological effects vary between ecosystems? Second, why does this variation require an understanding that goes beyond simple correlations between various fire and ecosystem variables to more careful causal models? Third, how can human values and goals be reconciled with fire disturbance processes in an ecologically sound manner

Stand, tree and crown variables affecting cone crop and seed yield of Aleppo pine forests in different bioclimatic regions in Tunisia

In Tunisia, the Aleppo pine seed has a great importance, since in the last decades human consumption has risen considerable. Thus its regeneration and seed production capacities are important factors to take into account to reach the necessities of the country. To study the production of cones and seeds of Aleppo pine, Tunisia’s native Aleppo pine forests were surveyed in summer 2006, using 79 plots (40 × 25 m: 1,000 m²) spread over four bioclimatic zones. Stand and tree characteristics, crown dimensions and cone/seed variables were measured from an average tree of each plot (i.e. a total of 79 trees). Recorded data were submitted to simple and multiple regression analyses for explaining the variability in crown volume and crown surface, cone number and seed yield per average tree. Results showed a negative correlation between the stand density, crown characteristics and number of cones and seeds harvested from the average tree. For crown volume and surface, age, stand density, tree height, diameter at breast height, crown diameter and crown height were important explanatory variables under multiple regression analyses. For cone number per tree, only the age, stand density and total height were the most determinant variables. Matures cone number per tree and cone mass per tree were the most informative parameters for the total seed yields per tree. Finally, forest managers should know that crown size affects cone and seed crop of the Aleppo pine individual tree grown in Tunisia, but has no effects on seed number per cone and seed mass per cone

Stable hepatitis C virus RNA detection by RT-PCR during four days storage

BACKGROUND: Suboptimal specimen processing and storage conditions of samples which contain hepatitis C virus (HCV) RNA may result in a decline of HCV RNA concentration or false-negative results in the detection of HCV RNA in serum. We evaluated the stability of HCV RNA in serum and clotted blood samples stored at room temperature or at 4°C for 4 days with the aim of optimizing the standard procedures of processing and storage of samples. METHODS: Blood from five HCV RNA positive patients was collected in tubes with and without separator gel, centrifuged 1 or 6 hours after collection. Samples were then left 6, 24, 48, 72 or 96 h at room temperature (21.5 – 25.4°C) or at 4°C before determining their HCV RNA level using the COBAS AMPLICOR HCV MONITOR Test, vs 2.0 (Roche Diagnostic Systems). RESULTS: The logarithm of the HCV RNA level measurements remained within a 0.3 value of the means for 4 days at both temperatures (room temperature or 4°C). CONCLUSIONS: We conclude that blood samples may be collected and aliquoted within 6 h of collection and can be stored at 4°C for 72 hours as proposed by the manufacturer without significant differences in measured HCV RNA level. Our results indicate that lapses in this scheme may still yield reliable results

Cross-resistance to elvitegravir and dolutegravir in 502 patients failing on raltegravir: a French national study of raltegravir-experienced HIV-1-infected patients

OBJECTIVES: The objectives of this study were to determine the prevalence and patterns of resistance to integrase strand transfer inhibitors (INSTIs) in patients experiencing virological failure on raltegravir-based ART and the impact on susceptibility to INSTIs (raltegravir, elvitegravir and dolutegravir). PATIENTS AND METHODS: Data were collected from 502 treatment-experienced patients failing a raltegravir-containing regimen in a multicentre study. Reverse transcriptase, protease and integrase were sequenced at failure for each patient. INSTI resistance-associated mutations investigated were those included in the last ANRS genotypic algorithm (v23). RESULTS: Among the 502 patients, at failure, median baseline HIV-1 RNA (viral load) was 2.9 log10 copies/mL. Patients had been previously exposed to a median of five NRTIs, one NNRTI and three PIs. Seventy-one percent harboured HIV-1 subtype B and the most frequent non-B subtype was CRF02_AG (13.3%). The most frequent mutations observed were N155H/S (19.1%), Q148G/H/K/R (15.4%) and Y143C/G/H/R/S (6.7%). At failure, viruses were considered as fully susceptible to all INSTIs in 61.0% of cases, whilst 38.6% were considered as resistant to raltegravir, 34.9% to elvitegravir and 13.9% to dolutegravir. In the case of resistance to raltegravir, viruses were considered as susceptible to elvitegravir in 11% and to dolutegravir in 64% of cases. High HIV-1 viral load at failure (P < 0.001) and low genotypic sensitivity score of the associated treatment with raltegravir (P < 0.001) were associated with the presence of raltegravir-associated mutations at failure. Q148 mutations were selected more frequently in B subtypes versus non-B subtypes (P = 0.004). CONCLUSIONS: This study shows that a high proportion of viruses remain susceptible to dolutegravir in the case of failure on a raltegravir-containing regimen