Climate change impacts on the mediterranean forest and shrubland, their ecophysiology, demography and community composition

• Autores: Daijun Liu
• Directores de la Tesis: José Peñuela (dir. tes.), Romá Ogaya Inurrigarro (codir. tes.)
• Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2017
• Idioma: español
• Tribunal Calificador de la Tesis: Carlos García Soto (presid.), Josep Maria Espelta Morral (secret.), Santiago Sabaté Jorba (voc.)
• Programa de doctorado: Programa de Doctorado en Ecología Terrestre por la Universidad Autónoma de Barcelona
• Materias:
  • Ciencias de la vida
    • Biología vegetal (botánica)
      • Ecología vegetal
• Enlaces
  • Tesis en acceso abierto en:  TESEO  TDX 
• Resumen

  • Abstract Anthropogenic disturbances induce rapid global warming and precipitation changes with a great impact on Mediterranean ecosystems, leading to changes in plant physiological processes (e.g. photosynthesis), demography (e.g. stem growth, mortality and seedling recruitment) and community structure and composition (e.g. species loss, dominance shifts). Moreover, great changes for future climate scenarios are expected to be unabated by most climatic models, and the potential threats of these climatic changes are still dramatic even in the context of under 2 °C global warming target. However, to date, the effective method to accurately assess species growth, community structure and composition shifts in response to future climate change are not well-established. Here, we conducted long-term (≥15 years) climate manipulation experiments in a Mediterranean holm-oak forest and in a Mediterranean shrubland to study the changes in plant ecophysiology, demography and community structure.

    In the Mediterranean forest, long-term experimental drought decreased photosynthetic rates of the dominant species of Q. ilex and P. latifolia, but the latter was more resistant to drought, which could lead it to gain a competitive advantage relative to Q. ilex in the future. Moreover, the long-term experimental drought significantly decreased the biomass increment and increased stem mortality, branch and leaf litterfall, and these responses were also strongly correlated with natural droughts. However, these responses were associated with natural droughts, but were also species-specific because Q. ilex resulted more vulnerable to drought than P. latifolia. Moreover, there was a dampening effect of these changes in aboveground net primary productivity (ANPP) during the long-term experimental drought. The long-term experimental drought also increased annual rates of stem mortality and decreased stem growth at the community level in plots dominated by tall trees (high canopy plots (H-)) and low trees (low canopy plots (L-)) over the study period. The changes in mean stem mortality, recruitment, stem density and growth indicated that Q. ilex was more sensitive to drought than P. latifolia. The long-term experimental drought combined with natural droughts accelerated the decreases in percentage of abundance and basal area of Q. ilex, but promoted the increases for P. latifolia in low canopy plots (L-), indicating a vegetation shift with drier conditions.

    In the Mediterranean shrubland, long-term experimental warming moderately influenced photosynthetic rates, shoot water potential and stomatal conductance in E. multiflora, whereas drought treatment strongly influenced these variables, especially during summer. However, E. multiflora also improved the acclimation to drier and hotter conditions by the adjustments of stomatal conductance and water-use efficiency. And yet, we found that warming and drought imposed the decrease in species abundance associated with the species distributions. Long-term experimental warming caused a progressive decrease in the abundance of those species distributed in cooler regions. Correspondingly, reduced precipitation resulted in abrupt decreases in wet-distributed species, followed by a delayed increase in dry-distributed species. Moreover, we observed that the decreases in species richness in both warming and drought treatments, and the strongest decreases in community diversity and evenness were found under the drought treatment. The responses in community structure and compositional shifts were also strongly correlated with natural droughts. Thus, our results suggest that rapid warming and drought have imposed profound influences on plant physiological processes, population demography and community composition. More attention should also be paid on these changes at regional- and global-scales.