Vânia Proença, Helena Martins, Tiago Domingos. MARETEC – Marine, Environment and Technology Centre, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
Montado is a High Natural Value wood-pasture system characteristic of the SW region of the Iberian Peninsula. High levels of biodiversity are maintained by the structural diversity at different spatial scales and by the large spatial extent and overall continuity of the system. Cork and holm oaks are the dominant species and key structural and functional elements. Tree mortality and insufficient tree recruitment are causing a gradual decline in tree density which threatens the whole system and its survival.
Excessive stocking rates, motivated by the Common Agricultural Policy, and soil destructive shrub control practices are causing soil degradation and preventing tree recruitment. Moreover, interacting effects between soil degradation and changing rainfall patterns are affecting trees’ vigour and increasing their vulnerability to pests and diseases. In areas of declining tree density, increased fire frequency due to shrub encroachment and drought events also causes tree mortality, prevents recruitment, and leads to further soil degradation.
The decline of tree density will have an effect on ecosystem regulating functions, in the habitat structure for wild species, and on the production of important tree products. It may also affect ecological processes at different spatial levels, including (i) the local level, where changes in canopy structure may affect vertical ecosystem structure, tree recruitment, primary productivity, and local biodiversity levels, (ii) the watershed level, with impacts in hydrological processes, and ultimately (iii) the landscape level, through habitat fragmentation.
The sustainability of these wood-pasture systems lies in the balance of management practices. That is, the same activities that enable the multifunctional use also create habitat diversity for species, but can become a threat if inadequately managed. For instance, grazing is needed to keep an open understory and contributes to the cycling of nutrients, but high stocking rates may hamper tree recruitment, reduce habitat heterogeneity, and cause soil compaction and trampling. Similarly, habitat diversity is promoted by intermediate levels of shrub cover, requiring a careful management of this ecosystem component. Therefore, responses to threats will mostly rely on best practices of ecosystem management, namely the management of soil, grazing and ecosystem structure.
The main research questions regarding the degradation of the Montado are intended to lead to a better understanding of its severity and its effect on the delivery of the multiple environmental services provided by this system. The combined use of in-situ data and remote sensing data will be used to assess the effects of structural changes, both of horizontal structure (e.g., tree cover patterns, patch metrics) and vertical structure (e.g., relative cover of vegetation layers), on ecosystem functions and biodiversity and different scales.
Tree cover patterns and condition are prone to be monitored using time series of EO data, which also allow testing the association between observed changes and management practices. The development of EO based methods to assess and guide management practices (e.g., shrub control methods, sowing of improved pastures) may enable faster response times and better adjustment to local contexts. Nevertheless, the savannah structure of Montado poses a challenge to the development of EO based methods, which will have to account for the horizontal and vertical structural components of the system and their interactions. Process-based models, namely the MOHID Land, will be used to combine in-situ and EO data and to simulate the effects of vegetation structure on soil and hydrological processes. This will enable assessing the implications of management practices on tree mortality and recruitment in current conditions and in future scenarios of environmental change.