Location and General Description
The Iberian sclerophyllous and semi-deciduous forests cover the central plateaus, valleys, and low plains of the interior portion of the Iberian Peninsula. The ecoregion is composed of a variety of substrates. Mesozoic and Quaternary sedimentary rocks, such as sand, sandstone, conglomerate, and limestone, predominate in the central plateaus. Salt and gypsum substrates characterize small, closed basins related to the Ebro and Duero Rivers. Old crystalline substrates, including granite, schist, and quartzite characterize the western part of the central plateaus, between Spain and Portugal.
Climatically, the ecoregion experiences very hot and dry summers and relatively mild and subhumid winters. The northern plateau has a more continental climate, which tends to decrease winter temperatures considerably. Annual average temperatures range from 8-15ºC, and the minimum average temperature of the coldest month ranges from 1-5ºC. Annual rainfall averages range from 300-850 mm.
The forest ecosystems of the region are primarily evergreen broadleaf and conifer canopy species. Holm oak (Quercus ilex) forest was once widely spread along the deep fertile soils of the warmer, dry coastal and inland plains; this has since been intensively transformed into agricultural land. Only a few remnants maintain the natural structure of this forest type. Human impact, mainly from grazing, fires, and firewood collection, has transformed the majority of the existing holm oak forest into secondary, dense shrubland, known as "maquis", or into agro-forestry landscapes constituted by scattered trees on grasslands or crops. Mixed cork oak (Quercus suber) and holm oak sylvopastoral woodlands frequently appear in the western part of the ecoregion.
Wild olive (Olea europaea) and carob (Ceratonia siliqua) woodlands and maquis are mainly distributed in the southern part of the ecoregion and in river canyons of the Duero and Tajo basins. These native plants have been widely domesticated in order to produce olive oil and food crops. A large number of high shrubs or small trees characterize these woodlands and maquis such as the small palm tree Chamaerops humilis, Pistacia lentiscus, Phillyrea latifolia, P. angustifolia, and Myrtus communis. Lianas are also present, including Clematis cirrhosa, C. flammula, Smilax aspera, Tamus communis, Rubia peregrina, and Bryonia dioica. Herbaceous species, such as Arisarum vulgare, Vinca difformis, Allium triquetrum, and Ballota hispanica, frequently appear within the dense and shady tree layer.
The endemic shrub Securineia tinctorea has a distributional range almost completely restricted to the Guadiana and Tajo River basins. Together with several other shrub and tree species (Tamarix canariensis, T. africana, Salix alba, Alnus glutinosa, Populus alba, P. Nigra, Fraxinus angustifolia, Ulmus minor), this assemblage typifies small riparian woodlands and is well adapted to periodical flooding.
The stone pine (Pinus pinea) and maritime pine (Pinus pinaster), both well adapted to sand and siliceous rocky substrates, are dominant on sandy soils such as the North Castile inland sand dunes of the Iberian plateaus, mainly in the northern part of the ecoregion. These pine forest ecosystems are very valuable from both a socio-economic (sustainable management of stone pine-nuts and maritime pine resin collection is an important income-generating activity for rural economies) and a conservation point of view (soil stabilization and biodiversity preservation).
Aleppo pine (Pinus halepensis) and holly oak (Quercus coccifera) mixed forests, and juniper (Juniperus thurifera, J. phoenicea) woodlands are well adapted to the limestone, marl and gypsum substrates that characterize the southeastern part of the ecoregion and the Ebro valley. These forests and woodlands alternate with extensive steppe grasslands (Stipa tenacissima, Lygeum spartium) and shrub communities (Artemisia herba-alba, Thymelaea hirsuta, Ononistridentata, Helianthemum squamatum, Thymus mastigophorus) resulting a complex mosaic-like landscape.
The central Iberian plateaus and Ebro basin host significant inland drainage systems with fluctuating, shallow, saline swamps, characterized by numerous halophyte species such as Suaeda fruticosa, Microcnemum coralloides, Aizoon hispanicus, Arthrocnemum glaucum, and Limonium ovalifolium.
Thus far, there is no quantifiable data regarding the endemic vascular plant species of the ecoregion. Generally speaking, the endemism rate (strict endemic species) is below 10% of the total ecoregional flora. The ecoregional steppe flora has a significant rate of endemism (126 endemic plants from the 302 strict steppe species), mainly reflecting halophyte taxa (Vella pseudocytisus, Boleum asperum, Gypsophila struthium, G. hispanica, Sideritis linearifolia).
Evergreen oak woodlands (Quercus ilex, Q. suber), extensive and highly diverse shrublands with a large number of endemic species (i.e. species from the genera Cistus, Lavandula, Genista, Thymus, Erica, etc), and varied semi-natural grasslands form a complex landscape pattern. This vegetation is very valuable in terms of biodiversity conservation, soil protection, and hydrological stability.
Rivers in the region harbor a unique relict fauna, including the endemic fish Anaecypris hispanica and Barbus microcephalus, both included in IUCN’s Red List of threatened species. They also represent an important refuge for certain mammals, such as otter (Lutra lutra), an important number of reptiles (i.e. Emys orbicularis, Mauremis caspica), and wintering (i.e. Anas strepera, Netta rufina) and nesting (Ardea purpurea, Nycticorax nycticorax, Circus aeruginosus) bird species.
The largest wolf (Canis lupus) population in the Iberian Peninsula is located in the Northern Castile plateau, spread widely on extensive wheat-cultivated land. The region’s steppes host a very diverse bird fauna, well adapted to semi-arid conditions, such as Dupont’s lark (Chersophilus duponti), shore lark (Eremophila alpestris), roller (Coracias garrulus), and black wheatear (Oenanthe leucura).
Altogether, the ecoregion boasts more than 220 breeding vertebrates, about twenty percent of which are raptors (i.e. Elanus caeruleus, Circaetus gallicus, Aegypius monachus, and Gyps fulvus). The woodlands constitute important wintering enclaves for thousands of cranes (Grus grus), and also breeding areas for hundreds of white storks (Ciconia ciconia) and the endangered black stork (Ciconia nigra). The south-western Iberian sylvopastoral landscapes are also fundamental for the preservation of some of the most endangered species in Europe, the Iberian lynx (Lynx pardinus), the Spanish imperial eagle (Aquila heliaca), and the great bustard (Otis tarda).
Most of the ecoregion has been intensively transformed into agricultural land of extensive wheat crops, vineyards, almond and olive groves, fruit tree orchards, and other irrigated crops. A small number of degraded oak coppice and conifer woodlands, thickets, and isolated trees occupy the less fertile soils on rocky hills and outcrops, saline and gypsum substrates, and sand soils. The southwestern part of the ecoregion is characterized by a manmade, semi-natural landscape, formed of extensive semi-natural sylvopastoral woodlands -known as "montados" in Portugal and "dehesas" in Spain. These have historically represented very efficient and rational multipurpose management systems and are well adapted to adverse environmental conditions imposed by low quality soils and harsh climate.
Major land-use changes induced by governmental policies are responsible for the past and on-going land degradation and habitat fragmentation in the ecoregion. The socio-political instability of the first half of the 20th century provoked clearance of vast woodlands, which were transformed into marginal lands unable to sustain agriculture, and supported by governmental subsidiary policies, known as the "Wheat Campaign" in Portugal. By 1950 it was officially recognized in Portugal and Spain that soil degradation had reached serious proportions in the south. The subsequent agricultural decline, followed by a human desertification process (rural abandonment and emigration to urban areas), led the governmental subsidies to promote productive reforestation programs, mainly based upon non-native conifer and eucalyptus species. Large-scale production of timber and pulpwood transformed large semi-natural areas of marginal lands and woodlands into artificial plantations, and new irrigation and marshland drainage plans destroyed significant marshlands and woodlands in the main river basin. The short-term high productivity of the eucalyptus plantations (Portugal has the second largest world plantation, with more than 300,000 hectares) is obtained at the expense of a severe environmental degradation that threatens the long-term preservation and potential productivity of natural resources.
Although the surface area covered by eucalyptus has almost reached its peak and is not currently expanding (it is even decreasing in Southern Spain), the environmental incentives put in place by the European Union under the CAP reform, to convert marginal agricultural land into more or less natural forests, do not favor the survival and restoration of the original forest ecosystems. Ironically, after a total EU investment of 1.27 billion ECU between 1993-97 for environmental forestry measures, of which one third went to Spain, important natural habitats of forest, scrub, and grassland are still being cleared or destroyed. Soil erosion is increasing, biodiversity is decreasing, and the viability of the small and fragmented populations of highly threatened species like the Iberian lynx is becoming uncertain. Inadequate reforestation in terms of methods and species, under CAP subsidies in the Guadiana Valley Natural Park, cover more than 16,000 hectares -about 13% of the territory- provoking high erosion rates. According to Vale Formoso Experimental Erosion Centre, the oldest European research center on desertification located within the Park boundaries, erosion is estimated at 40 tons of soil loss per hectare/year, while under natural scrubs and pasture lands it becomes almost insignificant.
Types and Severity of Threats
Human impact remains high in this ecoregion. Degradation is mainly a result of agricultural intensification and large irrigation plans including extensive greenhouse crops on coastal land, inadequate forestry programs promoted by European Union subsidies, dam construction, road building, and inadequate and overly intense hunting practices.
Justification of Ecoregion Delineation
This ecoregion is equivalent to the DMEER (2000) unit of the same name. It is primarily a product of the DMEER development process, with the exception of two montane Mediterranean ecoregions which were pulled out as a result of discussions with Drs. P. Regato and U. Bohn. It comprises the bulk of the Iberian peninsula and includes a number of units from Bohn et al. 2000. The two primary vegetation types are meso- and supra-Mediterranean Quercus ilex (subsp. rotifundifolia) forests. The units of Kermes oak forests and scrub, wild olive-locust tree forests, and small inclusions of cork oak forests on the Iberian peninsula are also included.
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Prepared by: Pedro Regato
Reviewed by: In process