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Remote Sensing and the landscape ecology of Mediterranean shrubland ecosystems

Remote Sensing and the landscape ecology of Mediterranean shrubland ecosystems

This project investigates whether it is possible to use a fusion of data from Sentinel-1 (radar) with Sentinel-2 (optical) to map different Mediterranean shrubland communities based on their structure (canopy height, closure, local variability) and surface reflectance (biomass, plant functional type, species-specific response).

In particular we seek to differentiate mixed species from more mono-specific, Cistus ladanifer-dominated, shrublands. Sentinel-2 provides us with a new range of vegetation indices and red-edge positions that should enable better mapping of the extent and connectivity of these two habitats. However the approach should be more widely applicable to other shrubland ecosystems. The project builds upon the successful outcome of our recent work on Mediterranean wood pastures for biodiversity.

Background

Across the Mediterranean, shrubland areas are increasing, for example by encroachment into former arable and grazing lands, olive groves and, in the western Mediterranean, oak  pasture woodlands.

Our recent work in the Moura-Mourão-Barrancos area of the Alentejo, Portugal  has shown an increase of 29% in shrubland area between 1984 and 2009, based on analysis of Landsat imagery (Allen et al., 2018). However, it was not possible using Landsat spectral information to differentiate between mixed species shrublands and those dominated by Cistus ladanifer.

The ability to map these individually is important as the species composition of the shrub matrix is strongly associated with the diversity of mammals, birds, insects and other plant species (Simonson et al., 2018): mixed species shrublands (matagal in Portugal) have a higher diversity of associated wintering and breeding birds and butterfly species than cistus-dominated shrublands (esteval).

Moreover, the cistus shrublands represent a stage of arrested succession, perpetuated as part of a positive feedback with recurrent fires: cistus shrubs are the fuel for fire, the germination of its seeds from the soil seedbank is promoted by fire and they have an allelopathic action producing phytotoxic compounds inhibiting the growth of other plants. These shrublands are generally regarded as a degraded landscape, prone to soil erosion, but one which is becoming more widespread.

A main driver of shrub increase is land abandonment partly in response to demographic changes, as populations become more urban and the rural population ages, and partly in response to EU agricultural polices favouring more economically productive systems, such as irrigated arable farming and intensive olive production.

Mapping the changing extent and connectivity of mixed and mono-specific shrublands is therefore of potential use in developing policies and land management practices for these areas.


Cistus shrubs encroaching into oak wood pasture, Alentejo, Portugal Shrubs invading dryland agriculture, Alentejo, Portugal
Cistus shrubs encroaching into oak wood pasture, Alentejo, Portugal Shrubs invading dryland agriculture, Alentejo, Portugal

References

  • Allen, H.D., Simonson, W.D., Parham, E., Santos, E. and Hotham, P. 2018. Satellite remote sensing of land cover change in a mixed agro-silvo-pastoral landscape in the Alentejo, Portugal. International Journal of Remote Sensing, doi: 10.1080/01431161.2018.1440095
  • Simonson, W.D., Allen, H.D., Parham, E., Santos, E. and Hotham, P. 2018. Modelling biodiversity trends in the montado (wood pasture) landscapes of the Alentejo, Portugal. Landscape Ecology, doi: 10.1007/s10980-018-0627-y