Spatiotemporal analysis of montado land cover dynamics in southern Portugal: the influence of anthropogenic and natural disturbances

Abstract

The montado is a traditional agroforestry system in Portugal that combines cork or holm oak trees with pastures and crops. It provides multiple ecosystems services and supports rural livelihoods. However, in recent decades, the montado has faced several threats that have caused its decline and degradation. Here, we analyse the recent changes in montado cover—between 2006 and 2018—and assess the main drivers and processes of change. We used a 2006 montado cover map as a baseline and overlayed it with aerial photographs of 2018, examining the montado areas for land use shifts by installation of intensive crops, wildfire occurrences or tree plantations. Our results show that the montado covered 1,189,390 hectares (ha) in 2018, and that there was a decrease of the montado area from 2006 by 31,312 ha (95% CI 29,706–32,943 ha), declining at an annual loss of 2609 ha (0.21% year−1; 95% CI 0.201–0.223% year−1). Although this is a slower rate compared to an early analysis, the impact of large-scale events (record burned areas) and infrastructure (large dam) likely explains it. The montado area shifts were mainly caused by wildfires (70%), the opening or broadening of clearings due to tree mortality (18%) and the new installations of intensive crops (olive or almond groves and irrigated cereals—8.4%). Most of the analysed quadrats (60%) exhibited one category of loss in montado patches: perforation, loss of area, fragmentation or decrease in the number of patches; but fragmentation was the type of dynamic with higher value of area loss. The perforation specific analysis revealed that this phenomenon of the early phase of decline is prevalent throughout the montado land cover. The main process identified was tree mortality linked to pathogens, pests, and inadequate management, while wildfires and the establishment of intensive agricultural practices were ranked second and third, respectively. Despite the efforts to slow the decline of the montado, we have observed its continuing transformation into smaller, more fragmented and less connected montado patches. These resulting patches are considerably less resilient to the pressures they are facing. In a scenario of the continuation of the decline and loss pressures, the evolving transformation will continue and may even accelerate.