This research investigates the ways in which remote sensing can contribute to habitat restoration in a typical Portuguese mosaic of rare habitats and intensive agriculture and forest ecosystems, the Eastern Guadiana, Alentejo. This is part of a broader project to promote biodiversity conservation, provision of ecosystem services, resilience to climate change and a sustainable socioeconomic development in the region.
Land use intensification, land abandonment and climate change have degraded the quality and reduced the area of the biodiversity-rich habitats characteristic of the area. In places, abandonment of former arable and grazing land has resulted in expansion of Cistus ladanifer-dominated shrubs, adapted to degraded soils. C. ladanifer is tolerant of summer drought, the intensity of which is increasing, and recover quickly after autumn rains; acts as fuel for wildfires, which are also increasing in extent and frequency; has become dominant or co-dominant in the understorey of natural and semi-natural woodlands. While these shrublands (known as esteva) provide protection from soil erosion they are less diverse in terms of associated species richness of birds, butterflies and other vascular flora compared with mixed-species shrublands (known as matagal). Targeted clearance of esteva to create fire-breaks and to allow for recovery of other vegetation and habitats is integral to the broader project. In contrast, areas of matagal usually have higher conservation importance; protecting and restoring these especially in areas of oak woodland, near streams and in sloping areas is a key objective. One of the challenges is to be able to plan where action is needed across the large study region and to avoid wrongly targeting matagal instead of esteva.
Remote sensing can contribute detail to the differentiation of these two shrub communities. This research aims to establish which remotely-sensed platforms are best used for this in terms of spatial resolution, band combinations, indices and possible fusion of active (radar) and passive (optical) sensors. The focus is use of Landsat versus the Sentinel series of satellites. The former has the advantage of nearly 40 years of imagery while the latter has higher resolution and provides both radar (Sentinel-1) and optical (Sentinel-2) data, but only extends back for about 5 years.
A second contribution of this research to the broader project is monitoring and mapping agricultural intensification following the completion of the Alqueva irrigation project in 2002, Europe’s largest water reserve. The Landsat archive allows areas of irrigated land to be identified and quantified; the shape of these areas also provides an indication of crop type. This is important for conservation as some areas irrigated in summer are important for migrating birds which over-winter in the Alentejo.
The outputs from these two foci of research contribute to landscape modelling across the study region. An aim of the broader project is restoring habitat patches to be large enough to maintain healthy population numbers of targeted species, mammals and birds, as well as connecting patches via corridors. Maps based on the remotely-sensed land cover classifications, such as differentiated areas of shrubland, irrigated areas and forest cover, will be key to working with local stakeholders and conservation organisations in identifying priority areas for targeted intervention and restoration. This will help towards the goal of re-establishing a wilder, more functional and climate-resilient landscape, maintaining ecological, social and cultural values.
This project is funded by The Endangered Landscapes Programme and the research is in collaboration with colleagues at the Liga para a Potetcção da Natureza, WCMC and Fauna and Flora International.
Cistus ladanifer shrubland encroaching onto grassland.
Irrigation changes 1984-2020 in areas of a) vineyard and tree crops (olives and orchards) shown in pale yellow) and b) arable shown in pale purple. Green represents change between 1984 and 2009, blue between 2009 and 2013, red between 2013 and 2015, black between 2015 and 2017, and dark purple between 2017 and 2020. The region shown is around the town of Serpa.