Boundaries

This ecoregion encompasses the Atlantic coastal rivers of Portugal and Spain, including the drainages of the Duero (Douro) and Tagus (Tajo) rivers, which are separated from the Ebro basin by the NW-SE trending Sistema Iberico to the east. The southeastern edge is bordered by the lower Guadiana River. It is also bounded by the Montes de Toledo, which divide the Tagus and the Guadiana rivers. The northwestern border is the drainage of the Miño (Minho) River. It encompasses all of Portugal and western Spain.

Topography

This ecoregion includes rolling plains, plateaus, deep valleys, and steep mountains. The Tagus and Duero drain two large Cenozoic basins, which include high flat plateaus, also known as the Meseta Central. Dividing these basins is the Sistema Central, which is a granitic mountain range that comprises the Sierra de Gredos and Sierra de Guadarrama.   Elevations range from sea level to more than 2000 m asl in the Sistema Central, and exceed 2400 m asl at Pico Almanzor (Hijmans et al. 2004). More than half of the ecoregion lies above 700 m asl on the Meseta Central. Other ranges include the Cantabrian Mountains in the north and Montes de Toledo in the south. Many mountain peaks are snow-capped throughout much of the year. The ecoregion is dominated by Paleozoic metamorphic and granitic basements formed during the Alpine orogeny (Gibbons & Moreno 2003).

Freshwater habitats

The Tagus, which stretches more than 1000 km, is the longest river on the Iberian Peninsula. It originates in the Sierra de Albarracín (1590 m asl) and drains the southern Meseta Central, emptying into the Atlantic Ocean near Lisbon with a discharge averaging 318 m³/s. The Tagus’ flow regime has high interannual variability and seasonality, with maximum discharge occurring in February-March and minimum discharge in August. Its tributaries include the Jarama, Alberche, Tiétar, Alagón, Guadelia, Almonte, and Salor rivers in Spain and the Erges, Ponsul, Zêzere, and Sorraia rivers in Portugal. The upper river cuts through the plateau through deep gorges and is punctuated by waterfalls. It then flows through hills and plains before reaching the Atlantic (Sabater et al. 2009).

The Duero (927 km) is the third largest river after the Tagus and Ebro. It originates at Picos de Urbión (2140 m asl) in the Iberian Range and drains the northern Meseta and Cantabrian, Iberian, and Carpetovetonic mountains, emptying into the Atlantic Ocean near Oporto, Portugal with a discharge averaging 903 m³/s at its mouth. Its course flows through steep valleys of the Iberian Range, and then meanders through an open valley with soft sediments. For the last 200 km it flows through narrow valleys at a low gradient. Its tributaries include the Côa, Tua, Sabor, Corgo, Tabora, Paiva, Tâmega, Balsemão, Esla, Pisuerga, Tormes, and Sousa rivers, most of which are small and fast-flowing (Sabater et al. 2009).

The Mondego (237 km) drains the Serra da Estrela, the highest mountain range in Portugal. It flows through steep and narrow valleys and a wide alluvial plain before emptying into the Atlantic with a mean annual discharge of 88 m³/s (Sabater et al. 2009). 

There are also many important freshwater and brackish lagoons, marshes, and estuaries, as well as the largest representation of saline steppe wetlands in Europe (Wetlands Internationl 2002). These saline lagoons, such as Lagunas de Villafáfila, include halophytic species such as Suaeda fruticosa, Microcnemum coralloides, Aizoon hispanicus, Arthrocnemum glaucum, and Limonium ovalifolium (WWF 2001).

Terrestrial habitats

This ecoregion spans five terrestrial ecoregions, including (from north to south) the Cantabrian mixed forests, Northwest Iberian montane forests, Iberian sclerophyllous and semi-deciduous forests, Iberian conifer forests, and Southwest Iberian Mediterranean sclerophyllous and mixed forests. Evergreen broadleaf and conifer species occur throughout the Meseta Central. Holm oak (Quercus ilex), cork oak (Q. suber), Pyrenean oak (Q. pyrenaica), and holly oak (Q. coccifera) are common, although much of the land has been transformed. Wild olive (Olea europaea) and carob (Ceratonia siliqua) woodlands and maquis occur in the valleys of the Duero and Tagus basins. The Duero is also home to sclerophyllous species like the olive (Olea europaea), and turpentine tree (Pistacia terebinthus) (WWF 2001).

Description of endemic fishes

Endemism is particularly high in the Iberian Peninsula due to isolation and likely Pleistocene refugia (Weiss & Ferrand 2007). Within it, endemism is higher in Western and Southern [413] Iberia than in Eastern Iberia [414]. Approximately one-third of the species are strictly endemic to Western Iberia. These occur in the genera Achondrostoma, Iberochondrostoma, and Pseudochondrostoma (split from Chondrostoma), as well as Cobitis, Barbus, and Squalius (Kottelat & Freyhof 2007).  More than 50% are restricted to the Iberian Peninsula. Some noteworthy endemics include Achondrostoma salmantinum, western ruivaco (A. occidentale), ruivaco (A. oligolepis), Iberochondrostoma lusitanicum, and Cobitis vettonica.

Ecological phenomena

The ecoregion supports species such as the catadromous European eel (Anguilla anguilla) and anadromous sea lamprey (Petromyzom marinus), European river lamprey (Lampetra fluviatilis), allis shad (Alosa alosa), and twaite shad (A. fallax) (Kottelat & Freyhof 2007).

Justification for delineation

Southern European ecoregions were delineated based on a bottom-up approach employing both published and unpublished field data and expert assessment (Abell et al. 2008). Within the Iberian Peninsula the northern and southern regions were geographically well-differentiated during all of the Cenozoic period. In the north three main endorreic lakes were present during the Miocene period. At the end of Pliocene the uplifting of the Iberian Peninsula resulted in two of them draining the Atlantic slope and one draining the Mediterranean slope (Lopéz-Martínez 1989; De la Peña 1995). This resulted in very different freshwater fish fauna between the Atlantic and Mediterranean sides of the Iberian Peninsula (Doadrio and Carmona 2003). There are also important ecological differences between these two regions. The Ibero-Mediterranean ecoregion (Eastern Iberia [413]) is composed of limestone formations from sea deposits. The rivers are temporary and characterized by water scarcity during the summer and flooding events during autumn. The Ibero-Atlantic [Western Iberia] occurs in the old craton of Europe and is composed of rocks that are silica-rich. Here, the rivers are more plentiful and more permanent because of Atlantic winds.

Level of taxonomic exploration

Fair