Characterisation of a basin mire in the Azores archipelago

The Azores archipelago in the North Atlantic is an extremely important area for biodiversity because it is rich in rare species and habitats, and almost undisturbed. The Lagoa do Madruga is a small basin mire located at 956 m a.s.l. on Santa Bárbara Mountain, Terceira Island. It is an extremely good example of a peatland type that was first discovered in 1998, and has not previously been described in the international literature. This paper provides baseline information on its flora, vegetation communities, structure and hydrology. Thirty-one plant species including eight Sphagnum species and nine endemic vascular plants have been recorded, and four plant communities are distinguished. The maximum peat depth is three metres.
The mire receives flowing water from its margins and from a small stream entering at its eastern end, in addition to intercepted precipitation and fog. The accumulated water forms pools and soakways which feed other wetlands downstream. The conservation status of the mire is good, but it is subject to increasing pressure from garbage generated during maintenance operations at a nearby antenna array.
The Lagoa do Madruga (Madruga’s Mire) is a typical example of the basin mires on Terceira Island in that it has a marginal community which is dominated by Juniperus brevifolia (Seub.) Antoine. Three additional plant communities have been identified, two dominated by Sphagnum (pools and lawn) and one by Eleocharis multicaulis (Sm.) Desv (lawn).
This is an extremely important Azorean Natura 2000 site because it is the largest (32,760 m2) basin mire on Santa Bárbara Mountain, it is rich in rare species (biodiversity) and habitats, and it
is almost undisturbed. The flora includes nine endemic species, two of which are regarded as rare; and the full list of 31 species contains no exotic species for the island, underlining the natural condition of the mire. The only threat to the site arises from rubbish disposal, and this should be addressed.
The mire is also an important landform for water retention due to the surface relief, the properties of Sphagnum and the depth of peat. This function is especially important on islands with limited water resources. The water supply to the mire consists predominantly of direct precipitation and intercepted fog with low concentrations of plant nutrients; but the shrub-dominated marginal community also receives drainage from the surrounding hillsides, which is richer in nutrients.

Given the importance of peatlands, even if viewed no more widely than at regional scale, this first detailed description of an Azorean Sphagnum mire is long overdue. It provides a starting-point for building an understanding of these complex habitats, but also reveals an urgent need for the acquisition of further knowledge to support measures for their conservation. However, the fact that most of the Terceira Island mires lie within Natura 2000 areas is likely to favour their conservation and study.

(In E. Dias and C. MendesMires and Peat, Volume 2 (2007), Article 08)