The impact of fire on the habitats of the Serra de Monchique

Monchique heathland before the fire, June 2003

Fire is a natural part of many ecosystems in the northern hemisphere but their number, frequency and extent have increased in recent years. Most fires now have a human origin and climate change is thought to be contributing to their spread and severity. Portugal has experienced an increasing amount of forest fire (as measured, for example, by the average area burned each year in the 1980s, 1990s and 2000s) but their impact on montane vegetation has been little studied.

The Serra de Monchique is the highest range of hills in the Algarve, the peaks of Foia (902 m) and Picota (774 m) rising above the surrounding lower hills. This upland area is a Special Area of Conservation within the European Natura 2000 network and A Rocha Portugal has been monitoring its birds, butterflies and plants for over 20 years. The general landscape and vegetation has been heavily modified by farming and forestry practices that include terraced cultivation, coppicing of Sweet Chestnut Castanea sativa, harvesting from Cork Oak Quercus suber and the commercial plantation of eucalyptus, pine and acacia. The native flora contains a unique mix of Mediterranean and Atlantic species.

Monchique heathland after the fire, December 2003

Forest fires swept through the Foia study site in 2003 just after a vegetation survey had been completed, and there was another fire in 2004. Plots (10 m by 10 m) had been established on a range of semi-natural vegetation cover (heathland, rhododendron thicket, remnants of low native woodland, rocky outcrops), and pine and eucalyptus plantations, and these were surveyed again in 2005. Multivariate statistical tools were applied to the cover/abundance plant data, showing that two years after the fire heathland, the most common habitat, was more resilient to fire than the rarer native woodland, rocky and rhododendron habitats. This was not unexpected as many of the dwarf shrubs of heathland are fire-adapted species. There was no evidence that fire was altering the relative area of different habitats. Instead, fire was altering the plant community composition, increasing species richness by enabling post-fire colonists to become established but these were mostly common and widespread annual and herbaceous species that were of less conservation importance.

Monchique heathland recovering, March 2005

With the aid of fire occurrence maps for the area since 1990, a further study was made of the impact of fire on heathland, comparing species composition in heathland areas with different fire histories. The five most common species had responded differently to fire frequency and the time since the last fire. There was no change in the area covered by Bramble Rubus ulmifolius, Dwarf Gorse Ulex minor and Bracken Pteridium aquilinum but with more fires Sage-leaved Cistus Cistus salvifolius increased at the expense of Spanish Heath Erica australis. These preliminary results suggest that higher fire frequencies may be changing the heathland to a less specific and therefore less valuable type. New data were collected from all plots in 2007, and will be used to test this hypothesis further, and contribute to our understanding of post-fire vegetation recovery in the context of climate change.

Project leaders: Will Simonson and Ruth Mitchell

Partners: Bioparque Monchique, British Ecological Society