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Accueil du site → Doctorat → États-Unis → 2000 → The ecology and dynamics of Mediterranean evergreen pine-oak forests

Princeton University (2000)

The ecology and dynamics of Mediterranean evergreen pine-oak forests

Zavala, Miguel Angel

Titre : The ecology and dynamics of Mediterranean evergreen pine-oak forests

Auteur : Zavala, Miguel Angel

Université de soutenance : Princeton University

Grade : Doctor of Philosophy (PhD) 2000

Understanding the mechanisms governing stand dynamics and composition in forest communities is a central goal in plant ecology and a critical issue for the formulation of sustainable forest management practices in the Mediterranean region. Here I derive a theory of spatio-temporal dynamics to explain the observed evolutionary convergence of community assembly mechanisms in Mediterranean holm oak ( Quercus ilex L.)-Aleppo pine ( Pinus halepensis Mill.) forests with other Mediterranean plant communities. The theory explains the regional coexistence of the two dominant functional types of Mediterranean vegetation—seeders and resprouters—based on allocational tradeoffs related to light competition and tolerance to drought, and recurrent disturbances. A top-down probabilistic model calibrated with forest inventory data indicates that the distribution of holm oak and Aleppo pine can be ascribed largely to aridity gradients resulting from both geographical and physiographical factors. I formulate a mechanistic bottom-up model parameterized with experimental data to explain patterns of pine-oak segregation or coexistence along an aridity gradient. According to the model, Aleppo pine predominance at the arid end of the gradient is explained by the pine seedlings’ greater tolerance to water stress relative to holm oaks. At the mesic end, however, holm oak establishment is facilitated by pines, which provide optimal radiation levels for oak seedlings’ survival. In turn, pines are outcompeted by oaks, due to Aleppo pines’ intolerance of shade at the sapling stage. Changes in water balance or disturbance intensity produce shifts in pine-oak interactions that trigger transitions from historically-dependent vegetation dynamics to secondary forest succession. A physiologically-based model of water use by Mediterranean evergreens is presented to explain how leaf-level tradeoffs in carbon gain versus water loss scale up to the whole plant. The model reconciles leaf-level physiological processes with whole-plant strategies and explains how Mediterranean plants integrate stomatal control with below-ground responses in order to optimize water use. Together these three models address the scaling of physiological and demographic plant responses to the stand-level, which are essential to the understanding of mechanisms of community assembly in these forests and to the formulation of biologically-based models of forest dynamics in Mediterranean regions.

Mots clés : Ecology, Mediterranean, Evergreen, Pinus halepensis, Biological sciences, Pine-oak forests Quercus ilex, Botany, Forestry

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Page publiée le 12 mars 2015, mise à jour le 9 décembre 2018