The woodlands of the Iberian Peninsula are distinct ecosystems on the Iberian Peninsula (which includes Spain, Portugal, Andorra, Gibraltar and Southern France). Although the various regions are each characterized by distinct vegetation, the borders between these regions are not clearly defined, and there are some similarities across the peninsula.
Origin and characteristics It has been established that the Mediterranean Sea has gone through great changes in sea level and the relative positions of the continental plates of Europe and Africa. These brought changes in climate and vegetation.
The Iberian Peninsula is in the south west of Europe and is located near North Africa and, as a result, saw the arrival of many types of plant species from both regions, including wetland thermophilic plant species (those that require a great deal of heat), xerophilic plants (those that require a dry climate), orophiles (sub-alpine plants) and boreo-alpine plants, many of which managed to remain thanks to the diversity of environments that exist in the peninsula's mountain ranges, which allowed plant species to rise in elevation if the climate became too warm, or descend if it became too cold. The geological complexity of the majority of Iberian mountains, especially of the Cordillera Bética, Sistema Ibérico, and Pyrenees, also greatly increased the number of environments in which it was possible for plant species to adapt, resulting in today's wide variety of flora.
The Eurosiberian region
The "Eurosiberian" Atlantic zone extends through northern Portugal, the Galician Massif, Cantabrian Mountains and the western and central Pyrenees. It is characterized by a humid climate which is moderated by the influence of the ocean, with somewhat cold winters and the lack of a distinct dry season. The mainland extends to the north of Portugal, the greater part of Galicia, Asturias, Cantabria, the Basque Country, northwest of Navarre, and western Pyrenees. However, its influence in the form of communities or defined species extends inwards, especially in the north and west.
The vegetation is deciduous oak forest: both sessile oaks (Quercus petraea)CSIC List of Iberian flora Quercus sp. and pedunculate oaks (Quercus robur), with European ash (Fraxinus excelsior) and hazels in the coolest and deepest soil at the bottom of the valley. The mountain layer is characterised by the presence of beeches and, at times in the Pyrenees, silver firs (Abies alba); these beeches and silver firs occupy the cool slopes with shallow soil. The Mediterranean influence is felt in the presence of Holm oaks (Quercus rotundifolia) and bay laurel, which are situated on the warmest crests and slopes, especially above chalky soil, where the dryness becomes more pronounced.
Improvement by humans has transformed much of this woodland into meadows, which conserve at their edges remnant hedgerows () made up of the species of the primitive forest. Clumps of thorny shrubs, such as the wild rose, blackberry bushes, blackthorn, hawthorn and other more or less thorny shrubs, also grow in glades and clearings; this role can also be filled by smaller thorny plants, , and clumps of broom.
The major forests in this area are beech, oak, birch, and fir.
Beech forests
Beech forests (Fagus sylvatica) are found in the mountain layer of the Iberian Eurosiberian region from 800 to 1500 metres up. The soil is cool, as often chalky as siliceous (rich in silica), and nearly always acidified by rain. The layer is characterised by the beech tree. These project a deep shadow, and so their dense foliage usually excludes other woodland species. The forest, therefore, has little undergrowth.
In spite of their Atlantic character, these forests reach Moncayo, in the centre of the peninsula. The southernmost borders are at the Hayedo de Montejo (in the autonomous community of Madrid) and the northernmost borders of the province of Guadalajara, in the Parque Natural del Hayedo de Tejera Negra (Cantalojas), and Somosierra-Ayllón. The forests seek watercourses and shade and so their reforestation is very difficult, and they are being displaced by the Pyrenean Oak (Quercus pyrenaica). The Irati "rainforest", comprising 170 square kilometres in the Navarran Pyrenees, is one of the most important beech and fir forests in Europe.
Oak forests
Oak forests, above all pedunculate oak (Quercus robur), are the most common in the Atlantic zone. They represent the typical forest floor formation of basal trees, extending to an elevation of some 600 metres. In higher regions, as the elevation rises, they yield to beech forests; at the bottom of the valleys, they are replaced by ash trees and hazel tree groves. There are two main types of oak: the pedunculate oak and the sessile oak (Quercus petraea). The latter extends furthest into the interior and highest in elevation, but plays a secondary role; in general, when the climate begins to become continental, these oak forests are replaced by Pyrenean oak.
The land on which these oaks stand is the most altered, as it is well suited to meadows and crops. Oaks are often accompanied by chestnut trees and birches. When these forests degrade, they are taken over by thorny plants, , and finally heather and gorse. The pedunculate oak is indigenous to a large part of the area currently occupied by pine forests and eucalyptus.
Birch forests Along the Atlantic coast, birches (Betula species) form small enclaves or copses at the foot of rocky cliff edges or in the clearings of beech forests, on poor or acidic soils, accompanied by aspen (Populus tremula) and mountain ash (Sorbus aucuparia). Birch may also grow in pure stands near the beech forests, in the mountainous areas on siliceous bedrock; these areas are typically small and generally quite patchy, with sessile oak (Quercus petraea) and trees of the genus Sorbus.
Fir forests
The silver fir (Abies alba) is found on the cool, deep-soiled slopes of the flanks of the Pyrenees, from Navarre to Montseny, forming pure fir woods or, more often, growing alongside beech trees. The most important areas are in Lleida (Lérida), covering 170 square kilometres. The fir forest extends from 700 to 1700 meters elevation, but its main areas are localized in more humid and dark valleys; these forests are dark, with acidic soil, due to the decomposition of the needles of evergreens. At higher elevations, they are often replaced by black pine (Pinus uncinata). These fir forests sometimes contain maples (Acer pseudoplatanus)Flora digital de Portugal Acer pseudoplatanus and their undergrowth is very similar to that of the beech forest. Like beeches, firs are distinctly Euro-Iberian.
The Mediterranean region The large Mediterranean region occupies the rest of the peninsula, as well as the Balearic Islands. The principal characteristic of the region is the existence of a lengthy period of summer drought, which may last anywhere from 2 to 4 months, but which, regardless of length, is always quite distinct. Rainfall can range from 1500 mm to less than 350 mm. Temperatures range from regions that have no frost for many years to those that reach -20 °C, or even lower, every winter.
If one ignores the influence of the mountains, the typical Mediterranean peninsular forest is made up of evergreen trees: oak forests, cork oaks, wild olives, juniper, and so on. These are accompanied, replaced (in warmer regions) and eroded by Aleppo pine (Pinus halepensis), and by juniper and stone pine forests in areas of sandy ground and fixed sand dunes. Exceptions to the rule are the more arid region in the southeast, the lower regions of the provinces of Murcia and Almeria, where the only vegetation is the European fan palm (Chamaerops humilis), and thorny thickets of blackthorn and, at higher elevations, Kermes oak groves and mastic (Pistacia lentiscus). The same can be said of the salty or endorheic zones, with great differences in temperature, such as the depression of the Ebro, Hoya de Baza and the chalky marls further inland.
Pyrenean Oaks Of all the oaks, the Pyrenean oak (Quercus pyrenaica) is the most resistant to drought and the continental-style climate. These forests, of a sub-Atlantic character, often represent the shift from Mediterranean vegetation to Atlantic vegetation. They cover a wide area of the peninsula and are of great importance, mainly on the mountain ranges in the centre of the peninsula; from the interior of Galicia and extending south of the Cordillera Cantábrica they extend throughout the Sistema Central, reaching, to the south, (though scarce by the time they reach this region) the Sierra Nevada and Cádiz. They usually extend from 700 to 800 metres to 1500 to 1600 m elevation. They prefer siliceous soil and, as elevation increases, they replace the damp oak forests and cork oak; on the high ground they give way to Scots pine (Pinus sylvestris) forests or to with creeping juniper. In areas where the influence of the Atlantic is more evident, they are taken over by heather and Erica australis; in the remainder, in clearings and in more degraded phases, rock rose (Cistaceae) mixed with laurel leaf and Spanish lavender (Lavandula stoechas) is more frequent. Their natural range is usually covered by forests of Scots pine or maritime pine.
Groves, riparian forests, and valley floors In the groves, riparian forests, and valley floors, there are enclaves of deciduous forests that favor the moist ground, which is constant almost all year; this allows them to avoid the consequences of the summer drought so characteristic of a Mediterranean climate.
A characteristic pattern appears moving outward from the edge of the riverbed, in that the woodlands that are most dependent on the aquifer (alders and willow groves) are on the riverbank, and those less dependent on water (such as ash, elm, and poplar groves) are located further away.
These woodlands are formed by willows, poplars, alder, ash, elm and sometimes by Pyrenean oak (Quercus pyrenaica), lime trees, birches and hazel trees. When the humidity starts to diminish in barren areas of the Ebro valley, the Levante and the southern half of the peninsula, the dryness is often accompanied by an increase of salts in the ground; under such conditions, one can find formations of tamarisk shrubs, oleanders and giant reeds (Saccharum ravennae), sometimes accompanied by heather. In soils rich in silica but not in salts, such as those of the Sierra Morena and the Montes de Toledo, spurge appears, accompanied, in the warmest places, by oleanders and tamarisks.
In the lowlands further inland, mainly in the marls and clay soils, field elms (Ulmus minor) and poplar groves are more common, with occasional ashes and willows. At the bottom of granite valleys and on siliceous riverbanks, there are very typical formations of ash with Pyrenean oak, especially at the foot of thin interior mountain ranges. The sheltered gorges of the Serranía de Cuenca have mixed riparian forests of lime and hazel trees, ashes, willows and Wych elm (Ulmus glabra).
Because these woods occupied some of the most fertile lands, where people have planted orchards since ancient times, they have not been well preserved.
Spanish firs The Spanish fir (Abies pinsapo) is a true relic which has remained preserved in some mountain ranges around Málaga and Cádiz. Spanish firs are related to the North African spruce forests of the Jbala region in the western Rif of Morocco. They come into contact with Algerian oak (Quercus canariensis) and other oak trees, and sometimes even form mixed communities with them. Among the woody species also found in these forests are the hawthorn, barberry, butcher's broom (Ruscus aculeatus), Viburnum tinus, ivy, and Daphne laureola.