The Montado is a Mediterranean semi-natural agroecosystem dominated by cork oak, Quercus suber, and often with crops or pasture as understory. Its sustainability is largely dependent on human land use and on abiotic factors, namely drought, which may influence cork oak regeneration, development, performance, and susceptibility to antagonistic organisms.
Our overarching objective was to assess the factors involved in the ecological sustainability of cork oak and the Montado. We conducted integrative studies that combine the collection of data from field observations under different land use or contrasting tree health with experiments in controlled conditions. Data was collected on: the spatial distribution of cork oak regeneration; the influence of increasing tree density on water use efficiency; the role of fallows in maintaining soil fertility and biodiversity; the nematode communities, biological indicators of soil processes; and the mutualistic ectomycorrhizal (ECM) fungal communities, that affect nutrient cycling and plant community structure.
Results/Conclusions
Our results suggest the existence of an optimum density with respect to annual rainfall, and specific leaf area was strongly and positively correlated with this parameter. The significant increase in carbon isotope discrimination towards the wetter end of the gradient suggests an adjustment to water availability. Such leaf changes associated with precipitation seem to influence water economy, improving water use efficiency of cork oak.
Extensive silvo-pastoral exploitation regimes and low mortality of cork oak support the ECM fungi richness, while the maintenance of shrubs, natural pastures and agricultural fields contribute to the turnover of ECM species. Extensive silvo-pastoral exploitation with shrub cutting without soil tillage allowed ECM fruiting to recover more rapidly from disturbance.
Cork oaks seem to be the preferred host of three of 12 genera of plant parasitic nematodes found in Montado areas, but their susceptibility to these nematodes is still being assessed. Soils under wheat crops harbour a large number of parasites that drops after a 2-year fallow and/or after rotation with a leguminous crop. The Nematode Channel Ratio was significantly higher in areas of healthier cork oaks and also under legumes, indicating a potentially higher decomposition rate of N-rich compounds, and correspondingly a more fertile soil.
The integration of our results will clarify the role of biotic and abiotic factors on the ecology of cork oak. This will be key in designing future management practices that improve the sustainability of cork oak and Montado ecosystems.