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Universidade de Coimbra (2008)

Age-dependent variations of radial growth, intra-annual density fluctuations and pointer years in Pinus pinaster under Mediterranean climate

Vieira, Joana

Titre : Age-dependent variations of radial growth, intra-annual density fluctuations and pointer years in Pinus pinaster under Mediterranean climate

Auteur : Vieira, Joana

Université de soutenance : Universidade de Coimbra

Grade : Mestre em Ecologia 2008

Résumé partiel
Dendrochronology generally assumes that climate-growth relationships are age independent once the biological growth trend has been removed. However, tree physiology changes with age, namely photosynthetic capacity and hydraulic conductivity. Additionally, in a scenario involving climate change it is important to verify if the relationship between tree growth and climate is also changing. We tested whether the radial growth response to climate and the frequency of intra-annual density fluctuations (IADFs) and pointer years (PY) of Pinus pinaster Ait. varied with age. It was also investigated whether the climatic factors triggering IADFs formation were stable over time. Trees were sampled in Pinhal de Leiria (Portugal), and were divided in two age-classes : young (<65 years-old) and old (>115 year-old). Earlywood and tree-ring width of young P. pinaster trees were more sensitive to climate influence while the response of latewood width to climate was stronger in old trees. Young trees start the growing season earlier, thus a time window delay occurs between young and old trees during which wood cells of young trees integrate environmental signals. Intra-annual density fluctuations (IADFs) in tree-rings are produced as a response to variations in climatic conditions during the growing season, particularly water availability. Young trees usually have a longer growing season and respond faster to climate conditions, thus young P. pinaster trees presented a higher frequency of IADFs compared with old trees. Most of the IADFs were located in latewood and were positively correlated to autumn precipitation. The radial-growth response of P. pinaster to climate and the IADFs frequency were age dependent. The use of trees with different age to create a tree ring chronology for climate studies can increase the resolution of climatic signals. Age-dependent responses to climate can also give important clues to predict how young and old trees react to climate change. If IADFs frequency was higher in young P. pinaster, how was the frequency of IADFs when old trees were young ?

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