168 research outputs found
La forĂȘt : puits de carbone.
TrĂšs majoritairement jeune et en pleine expansion, la forĂȘt mĂ©diterranĂ©enne constitue un important puits potentiel de carbone, autant dans la biomasse aĂ©rienne que dans les sols actuellement dĂ©gradĂ©s et pauvres en matiĂšre organique. Cette fonction doit ĂȘtre prise en compte dans la conception et l'Ă©valuation des politiques publiques qui la concernent
Les changements globaux ont-ils dĂ©jĂ induits des changements de croissance en forĂȘt mĂ©diterranĂ©enne ? Le cas du pin d'Alep et du pin sylvestre de la Sainte-Baume (Var) ?
Un accroissement des tempĂ©ratures, mais Ă©galement celui des concentrations atmosphĂ©riques en CO2, peuvent ĂȘtre Ă l'origine d'une augmentation de la croissance et de la productivitĂ© de certaines espĂšces. La forĂȘt risque ainsi de produire davantage, tout irait donc bien serait-on tenter de penser ! Les auteurs nous montrent Ă travers l'Ă©tude du pin d'Alep et du pin sylvestre que les choses ne sont pas si simples que cela
Flore méditerranéenne et changement climatique : la course-poursuite est engagée -
Cet article dĂ©crit la « course-poursuite » engagĂ©e entre changement climatique et flore mĂ©diterranĂ©enne. En effet, on observe dĂ©jĂ de sĂ©rieuses modifications de composition de la flore mĂ©diterranĂ©enne. En outre, la compensation du dĂ©ficit hydrique d'origine climatique par des conditions stationnelles favorables, qui jusqu'Ă prĂ©sent permettait la survie d'espĂšces mĂ©sophiles, n'est plus suffisante. Les stratĂ©gies d'adaptation des plantes devraient permettre une rĂ©sistance temporaire et partielle, mais mĂȘme les scĂ©narios climatiques les plus optimistes ne laisseront guĂšre le temps Ă cette stratĂ©gie de se mettre en plac
Fire impact on forest soils evaluated using near-infrared spectroscopy and multivariate calibration
L'Ă©valuation des propriĂ©tĂ©s physicochimiques des sols forestiers affectĂ©s par des feux a Ă©tĂ© rĂ©alisĂ©e en utilisant la spectroscopie proche infra-rouge (SPIR) couplĂ©e avec des mĂ©thodes chimiomĂ©triques. Pour dĂ©crire les propriĂ©tĂ©s du sol, les mesures prises comprennent le carbone organique total sur phase solide, le contenu d'azote total, le carbone organique et l'absorbance spĂ©cifique Ă 254 et 280nm des substances humiques, le carbone organique dans des acides humiques et fulviques, des concentrations de NH4+, Ca2+, Mg2+, K+ et le phosphore en plus des spectres de PIR. Un indice de rĂ©pĂ©tition d'incendies a Ă©tĂ© dĂ©fini et calculĂ© selon les rĂ©gimes de feux affectant des sols. Ce calcul inclut l'occurrence des incendies et le temps Ă©coulĂ© depuis le dernier feu. Cette Ă©tude montre que la spectroscopie PIR pourrait ĂȘtre utilisĂ©e pour le contrĂŽle de qualitĂ© des sols, particuliĂšrement pour la prĂ©diction quantitative du carbone organique total, l'azote total, le carbone organique dans les substances humiques, les concentrations de phosphore, Mg2 +, Ca2 + et NH4 + et des substances humiques UVSA254. Une nouvelle validation dans ce domaine est nĂ©cessaire cependant pour une bonne prĂ©dictions de K+, du carbone organique dans des acides humiques et fulviques et les substances humiques UVSA280. De plus, la SPIR couplĂ©e avec la rĂ©gression PLS peut aussi ĂȘtre utile pour prĂ©voir l'indice de rĂ©pĂ©tition de feu et pour dĂ©terminer sa variabilitĂ© spatiale. Aussi cette mĂ©thode peut ĂȘtre utilisĂ©e pour dresser la carte de secteurs plus ou moins brĂ»lĂ©s et pour adapter les techniques de rĂ©habilitation, comme la reconstitution de l'humus avec des enrichissements organiques (composts) ou le reboisement. Finalement, on peut considĂ©rer que notre indice de rĂ©pĂ©tition est reprĂ©sentatif de l'Ă©tat des sols. / The assessment of physico-chemical properties in forest soils affected by fires was evaluated using near infrared reflectance (NIR) spectroscopy coupled with chemometric methods. In order to describe the soil properties, measurements were taken of the total organic carbon on solid phase, the total nitrogen content, the organic carbon and the specific absorbences at 254 and 280nm of humic substances, organic carbon in humic and fulvic acids, concentrations of NH4+, Ca2+,Mg2+, K+ and phosphorus in addition to NIR spectra. Then, a fire recurrence index was defined and calculated according to the different fires extents affecting soils. This calculation includes the occurrence of fires as well as the time elapsed since the last fire. This study shows that NIR spectroscopy could be considered as a tool for soil monitoring, particularly for the quantitative prediction of the total organic carbon, total nitrogen content, organic carbon in humic substances, concentrations of phosphorus, Mg2+, Ca2+ and NH4+ and humic substances UVSA254. Further validation in this field is necessary however, to try and make successful predictions of K+, organic carbon in humic and fulvic acids and the humic substances UVSA280. Moreover, NIR coupled with PLS can also be useful to predict the fire recurrence index in order to determine the spatial variability. Also this method can be used to map more or less burned areas and possibly to apply adequate rehabilitation techniques, like soil litter reconstitution with organic enrichments (industrial composts) or reforestation. Finally, the proposed recurrence index can be considered representative of the state of the soils
Characterization of woody roots located in dikes by near-infrared spectroscopy and chemometrics
International audienceThe decomposition of tree stump and roots is highly detrimental for the safety of dikes. Root decomposition in the fills generates significant risks, particularly a risk of internal erosion by piping. In order to characterize root decomposition and assess decomposition rate, root samples were buried in experimental site. The Near-Infrared spectroscopy (NIR) and analysis of the spectral data by chemometric tools, allowed distinguishing and predicting decomposition times, tree species and root diameters
Trends in recovery of mediterranean soil chemical properties and microbial activities after infrequent and frequent wildfires
Since the 1970s, increase in fire frequency has been observed in all European Mediterranean regions. The objectives of this study were (1) to determine the effects of wildfire frequency on the recovery at short- and long-term of soil chemical and microbial properties and (2) to identify the mechanisms underlying the recovery of these sites properties. Soils from 17 plots (Maures mountains range, Var, France) were classified into 5 wildfire regimes (i.e. not burned since at least 57 years ago, infrequently and frequently burned-with time since fire between 4 and 17 years). Soil samples from these plots were analysed for their nutrient content, chemical functions of soil organic matter (SOM) using FT-MIR spectroscopy and microbial mineralising activities. Our results showed that the frequent wildfire regime slowed down the recovery in the short term of SOM spectroscopic properties and nutrient availability. Both low quantity and low quality (i.e. high percentage of aromatic and phenolic organic forms) of soil organic matter were found to be related to soil microbial recovery at 4 years after frequent wildfires. The frequent wildfires improved the recovery in net nitrification and nitrate content, leading to an increase in catabolic evenness and a recovery in microbial C-substrate utilisation profiles between 4 and 17 years. However, frequent wildfires slowed down the recovery of hydrolytic enzyme pool (i.e. FDA hydrolases) and phenol oxidase activity, both involved in soil C cycling. Overall, our observations suggest that 4 fires in 50 years is a threshold beyond which soil quality may be endangered
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 Ă©vĂ©nements climatiques exceptionnels de 2003 Ă 2005 (canicule et sĂ©cheresse) ont affectĂ© la vĂ©gĂ©tation dans la rĂ©gion de la MĂ©diterranĂ©e française et en particulier le pin sylvestre (Pinus sylvestris L.), une des principales essences forestiĂšres de cette rĂ©gion. Pour comprendre sa rĂ©ponse Ă ces conditions extrĂȘmes, nous avons examinĂ© sa croissance radiale, la croissance en longueur des branches, le dĂ©veloppement architectural et la reproduction pendant la pĂ©riode 1995-2005 et avons reliĂ© ces variables avec les paramĂštres climatiques. Nous avons utilisĂ© quatre placettes situĂ©es dans le sud-est de la France et prĂ©sentant des niveaux diffĂ©rents de qualitĂ© stationnelle et de productivitĂ© forestiĂšre potentielle. Les rĂ©sultats montrent que : (1) l'Ă©pisode climatique 2003-2005 Ă©tait fortement nĂ©faste Ă la croissance (tronc et branches), au dĂ©veloppement du houppier et Ă la production de cĂŽnes, mais a favorisĂ© la production de fleurs mĂąles; (2) ces variables dĂ©pendent des facteurs climatiques des annĂ©es en cours et prĂ©cĂ©dente; (3) l'impact de canicule 2003 Ă©tait fort, mais Ă©tait principalement apparent de 2004; il faisait partie d'un cycle dĂ©favorable de 6 ans commençant en 2000, caractĂ©risĂ© par des hautes tempĂ©ratures minimales et maximales et des printemps trĂšs secs; (4) malgrĂ© un effet significatif de la qualitĂ© stationnelle, la rĂ©ponse du pin sylvestre aux conditions climatiques extrĂȘmes Ă©tait homogĂšne dans la zone mĂ©diterranĂ©enne française; Et (5) le stress provoquĂ© par de mauvaises conditions stationnelles avait gĂ©nĂ©ralement les mĂȘmes consĂ©quences pour la croissance , l'architecture et la reproduction du pin sylvestre que des conditions climatiques dĂ©favorables
Impact du changement climatique sur la forĂȘt mĂ©diterranĂ©enne
National audienceLe changement climatique a des effets Ă long terme en raison de la dĂ©rive de ses paramĂštres moyens : Ă©lĂ©vation de la tempĂ©rature, rĂ©duction des pluies de printemps ou d'Ă©tĂ©. Mais le climat a aussi un impact fort lorsque des conditions extrĂȘmes dĂ©passent les seuils supportables par certaines espĂšces : c'est le cas des canicules comme celle de l'annĂ©e 2003 ou, en Provence, de la rĂ©pĂ©tition exceptionnelle des sĂ©cheresses entre 2003 et 2008. On observe entre 1996 et 2008 une modification sensible de la composition floristique des forĂȘts. Les plantes les plus exigeantes en eau et en fraĂźcheur ont beaucoup perdu de terrain, tandis que les plus rĂ©sistantes Ă la sĂ©cheresse gagnaient en surface comme en abondance. La productivitĂ© et la croissance en hauteur des arbres mĂ©diterranĂ©ens comme le pin d'Alep ont progressĂ© de 40% durant le 20Ăšme siĂšcle, tandis que celle des espĂšces plus nordiques et montagnardes comme le pin sylvestre perdait au moins autant. En raison de la rĂ©pĂ©tition des annĂ©es trĂšs chaudes et sĂšches depuis 1998, et notamment entre 2001 et 2008, on observe une dĂ©gradation gĂ©nĂ©rale de l'Ă©tat de santĂ© des forĂȘts en Provence. La productivitĂ© du pin d'Alep se rĂ©duit fortement et le pin sylvestre meurt sur des milliers d'hectares. Les dimensions des feuilles et aiguilles des arbres se rĂ©duisent de 20 Ă 50%, tandis que leur durĂ©e de vie diminue tout autant. Les branches cessent de pousser en longueur, de nombreux fruits avortent ou donnent des graines non-viables. Dans le sous-bois, de nombreux vĂ©gĂ©taux meurent aussi partiellement ou totalement : la biomasse morte ainsi accumulĂ©e accroĂźt durablement le risque d'incendie. La sĂ©cheresse n'accroĂźt pas que le risque d'incendie: elle augmente aussi l'intensitĂ© des feux et les dĂ©gĂąts qu'ils causent sur l'environnement. Enfin, le changement climatique favorise le dĂ©veloppement Ă©pidĂ©mique de parasites (insectes, champignons) jusque lĂ considĂ©rĂ©s comme endĂ©miques et peu dangereux, et l'arrivĂ©e de nouveaux parasites en provenance de rĂ©gions plus chaudes. / The climate change has long-term effects because of the drift of its average parameters: rise of temperatures, reduction of spring or summer rains. But the climate also has a strong impact when extreme conditions exceed the thresholds for certain species: one example is the 2003 scorching heat in Provence, of the exceptional repeated droughts between 2003 and 2008. We observed between 1996 and 2008 a significant turn-over of forest flora composition. The most mesophilous and water-demanding plants lost ground, whereas drought-resistant species won in number and cover. The productivity and height growth of Mediterranean trees as Pinus halepensis (Aleppo pine) gained 40 % during 20th century, whereas that of more continental and mountain species as Pinus silvestris (Scotts pine) lost at least as much. Because of the repetition of very warm and dry years since 1998, particularly between 2001 and 2008, we observed a general degradation of forests health in Provence. The productivity of Aleppo pine was strongly reduced and thousands of hectares of Scotts pine were killed. The dimensions of tree leaves and needles were reduced from 20 to 50 %, whereas their life span decreases as much. Branches stopped growing in length and many fruits aborted or gave non-viable seeds. In the undergrowth, numerous plants withered partially or totally: the accumulated dead biomass increased durably fire risk. The drought does not only increase the fire risk: it also increases the intensity of fires and the damages to the environment. Finally, climate change favors the epidemic development of parasites (insects, fungus) considered up to now as endemic, and the settling of new parasites from warmer regions
Influence de la densité des peuplements sur la croissance en hauteur et radiale de Pinus sylvestris L. en région méditerranéenne française.
Un des principaux objectifs de cette étude est de mettre en évidence et de quantifier l'influence de la densité des peuplements sur la croissance en hauteur et radiale du pin sylvestre afin de pour pouvoir ensuite dissocier ce phénomÚne des autres causes de modification de la croissance (changements climatiques)
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