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Universidade de Coimbra (2016)

The decline of cork oak woodlands : biotic and abiotic interactions in Portuguese montados

Arosa González, Maria Luisa

Titre : The decline of cork oak woodlands : biotic and abiotic interactions in Portuguese montados

Auteur : Arosa González, Maria Luisa

Université de soutenance : Universidade de Coimbra

Grade : Doutoramento em Biociências, na especialidade de Ecologia 2016

Cork oak (Quercus suber L.) is an evergreen tree species restricted to the western Mediterranean basin. The largest cork oak woodlands are found in southern Portugal where they are known as montados. This Mediterranean ecosystem has a distinctive patchy appearance, which is the result of long-term ecological and land use dynamics that have shaped the landscape. In some cases, overexploitation of the land has led to soil degradation and lack of cork oak natural regeneration which is putting at risk the conservation of this ecosystem. This thesis studied the factors implicated in the decline of the montado, most particularly those which can have an effect on cork oak regeneration paying special attention to management. The initial evaluation of cork oak nutritional dynamics showed that the amount of leaf fall was identical in different land uses, there was a delayed decomposition rate in exposed soils (shrubs absent), and litter quality varied according to land use, which probably had an effect in soil microbial dynamics and in resultant nutrient release. Soil nematode communities were thus studied in order to test for differences among land uses. Nematode composition was a good predictor of changes in decomposition in the soil food web and plant succession in the montado, however temporal variations had a greater influence on results rather than land uses. Additionally, plant-parasitic nematodes were highly abundant in the soil but were not found in roots of cork oak seedlings, and therefore are not likely a limitation to cork oak regeneration. The lack of regeneration in cork oak populations severely affects the future of the montado, and on the third chapter of this thesis the most important limitations to cork oak during the early stages of regeneration (seedling emergence and survival to the first summer) were identified and related to management practices. Temperature and relative humidity regulated seedlings emergence and survival, and early-emerging seedlings showed higher drought tolerance and resprouting ability. Bigger acorns and higher plant cover significantly assisted emergence, survival and resprouting of seedlings, putting forward the preservation of the shrub layer and the reforestation by direct sowing as important strategies to overcome the lack of cork oak regeneration in montados in the short-term. To better support these conclusions, a System Dynamics Model was developed to recreate the management practices associated with cork oak montado and the main environmental factors influencing this ecosystem, i.e. acorn germination, competition, fire, drought, livestock damage, shrub clearing, and cork oak death. Model predictions confirmed that the long-term sustainability of this ecosystem seems to be guaranteed if we limit the quantity and quality of livestock and if we extend the shrub clearing period. This thesis presents evidence that the future of the cork oak montado is severely threatened while inadequate management practices are common.

Mots clés  : Regeneração Sobreiro Litter decomposition Natural regeneration Quercus suber


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