Forests of the Iberian Peninsula

Thewoodlands of the Iberian Peninsulaare distinctecosystemson theIberian Peninsula(which includesSpain,Portugal,Andorra,GibraltarandSouthern 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.
It is now known that theMediterranean Seawent through great changes in sea level and variations in the relative positions of thecontinental platesof Europe and Africa. These broughtchanges in climateand vegetation.
The Iberian Peninsula is in the south west ofEuropeand located nearNorth Africa, and as a result, saw the arrival from both regions of many types of plant species, including wetlandthermophilicplant species (those that require a great deal of heat),xerophilicplants (those that require a dry climate), orophilic (sub-alpine) plants, boreo-alpine plants, and so on, many of which managed to remain, thanks to the diversity of environments that exist in the peninsula's mountain ranges, and 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 theCordillera Bética,Sistema Ibérico, andPyrenees, 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" Atlantic zone extends through northernPortugal, theGalician Massif,Cantabrian Mountainsand the western and centralPyrenees. It is characterized by a humidclimatewhich 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 ofGalicia,Asturias,Cantabria, theBasque Country, northwest ofNavarre, and western Pyrenees. However, its influence in the form of communities or defined species extends inwards, especially in the north and west.
The vegetation isdeciduousoakforest: both sessile oaks (Quercus petraea)and pedunculate oaks (Quercus robur), with European ash (Fraxinus excelsior) andhazelsin the coolest and deepest soil at the bottom of the valley. The mountain layer is characterised by the presence ofbeechesand at times, in the Pyrenees, by 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) withbay 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, "setos", of the species of the primitive forest. Clumps of thorny shrubs grow also in glades and clearings, such as thewild rose,blackberry bushes,blackthorn,hawthornand other more or less thornyshrubs; this role can also be filled by smaller thorny plants,los piornales, and clumps ofbroom.
The major forests in this area are beech, oak, birch, and fir.
Beechforests (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 insilica), and nearly alwaysacidifiedby rain. The layer is characterised by the beech tree. The beech tree projects a deepshadow, and so its dense foliage usually excludes other woodland species. It therefore has littleundergrowth.
In spite of their Atlantic character, these forests reach Moncayo, in the centre of the peninsula.  The southernmost are at the Hayedo de Montejo (in theautonomous communityofMadrid) and in the northernmost area of the province ofGuadalajara, in the Parque Natural del Hayedo de Tejera Negra (Cantalojas), and Somosierra-Ayllón. The forests seekwatercoursesand shade, and so their reforestation is very difficult and they are being displaced by thePyrenean Oak(Quercus pyrenaica). The Irati "rainforest", of some 170 square kilometres in theNavarranPyrenees, is one of the most important beech and fir forests in Europe.
Oak forests, above all of pedunculate oak (Quercus robur), are the most common in the Atlantic zone. They represent the typicalforest floorformation of basal trees, extending to an elevation of some 600 metres. In higher regions, as one ascends the mountains, they yield to beech forests; at the bottom of the valleys they are replaced byash treesandhazeltree 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 part; in general, when the climate begins to show its continental character, these oak forests are replaced by Pyrenean oak.
The land on which these oaks stood is the most altered, as it is well suited to meadows and crops. Oaks are often accompanied bychestnuttrees andbirches. When these forests degrade, they are taken over by thorny plants,piornales,and in the final extremeheatherand gorse. The pedunculate oak would have been indigenous to a large part of the area currently occupied by pine forests andeucalyptus.
Along the Atlantic coast, birches (Betulaspecies) 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 of only small extent and generally quite patchy with sessile oak (Quercus petraea) and trees of the genusSorbus.
The silver fir (Abies alba) is found on the cool, deep-soiled slopes of the flanks of thePyrenees, fromNavarretoMontseny, forming pure fir woods or, more often, mixed forests with beech trees. The most important areas are inLleida(Lérida), with 170 square kilometres. It 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 byblack pine(Pinus uncinata). These fir forests sometimes contain maples (Acer pseudoplatanus)and their undergrowth is very similar to that of the beech forest. Like these, they are distinctly Euro-Iberian.
The Mediterranean region occupies the rest of the peninsula (the greater part of it), as well as theBalearic Islands. The principal characteristic of the region is the existence of a quite 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, for the moment, the influence of the mountains, the typical Mediterranean peninsular forest is made up ofevergreentrees:oakforests, cork oaks, wild olives, juniper, and so on. These are accompanied or replaced in the warmer regions and eroded by forests of Aleppo pine (Pinus halepensis) and in areas of sandy ground and fixed sanddunesbyjuniperandstone pineforests. Exceptions to the rule are the more arid region in the southeast, the lower regions of the provinces ofMurciaandAlmeria, where the only vegetation is the European fan palm (Chamaerops humilis), and thorny thickets ofblackthornand at higher elevations,Kermes oakgroves and mastic (Pistacia lentiscus). The same can be said of the salty orendorheiczones, with great differences in temperature, such as the depression of theEbro, Hoya de Baza and the chalky marls further inland.
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, above all on the mountain ranges in the centre of the peninsula; from the interior ofGaliciaand extending south of theCordillera Cantábricathey extend throughout theSistema Central, reaching, to the south, (though scarce by the time they reach this region) theSierra NevadaandCádiz. 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 andcork oak; on the high ground they give way to Scots pine (Pinus sylvestris) forests or tolos piornales serranoswith creeping juniper. In areas where the influence of the Atlantic is more evident, they are taken over byheatherandErica 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 ormaritime pine.
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.
There we see a characteristic pattern, as we move outward from the edge of the riverbed, so that the woodlands that are most dependent on the aquifer are on the riverbank, that is, (aldersandwillowgroves) and those less dependent on water are located further away, such as the (ash,elm, andpoplargroves).
These woodlands are formed by willows, poplars, alder, ash,elmand sometimes by Pyrenean oak (Quercus pyrenaica),lime trees, birches andhazeltrees. When the humidity starts to diminish in barren areas of the Ebro valley, theLevanteand 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 theSierra Morenaand the Montes de Toledo,spurgeappears, accompanied, in the warmest places, by oleanders and tamarisks.
In the lowlands further inland, above all 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 granitevalleysand on the 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, with 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.
The Spanish fir (Abies pinsapo) is a true relic which has remained preserved in some mountain ranges aroundMálagaandCádiz. Spanish firs are related to the North African spruce forests of the Jbala region in the westernRifofMorocco. They come into contact with Algerian oak (Quercus canariensis) and other oak trees and sometimes even form mixed communities with these. Among the woody species also found in these forests are thehawthorn,barberry, butcher's broom (Ruscus aculeatus),Viburnum tinus, ivy, andDaphne laureola.
It forms dense and dark forests in very distinct enclaves, in areas with high rainfall (from 2,000 to 3,000 mm, due to the sudden cooling, with elevation, of humid winds), at elevations of over 1,000 metres. The forest has abundant moss and lichens, but very few shrubs and herbaceous plants. In all cases, Spanish fir occupies high mountain zones (such as theSierra de las Nieves, Sierra Bermeja, andSierra de Grazalema).
Forests of Holm oak (Quercus rotundifolia) form natural forests in most of the Mediterranean region as well as penetrating into the warmer sun-exposed areas and hillsides of the Atlantic region; they extend from sea level, with the subspeciesilex, to an elevation of 1400 metres, in some mountains and high plains of the interior; in the continental zone, the oak found is the subspeciesrotundifolia, more resistant to such a climate. The holm oak can also be found at higher elevations, but as isolated trees, not forming forests. Coastal oak forests and those of sublittoralmountainsare extraordinarily rich and varied, with a variety of shrubs andlianas; often accompanied bybramble,honeysuckle,ivy,Viburnum tinus,butcher's broomand, in the southwest of the peninsula, wildolivetrees. The oak forests of theBalearic Islandsare also rich, and incorporate characteristic species of the islands, such as the Balearic cyclamen (Cyclamen balearicumWillk.).
Towards the interior of the peninsula, these forests become progressively more scarce: as the continental characteristics of the climate become stronger, the species most sensitive to cold become steadily more scarce. The continental groves, on soils lacking lime (calcium oxide), tend to be rich in junipers (Juniperus oxycedrus) and are superseded at higher elevations and on cooler slopes by Pyrenean Oaks. This phenomenon is apparent in theSierra de Guadarrama: when the oak forests have been destroyed, the soil is so poor and the environmental conditions so unfavourable, that it leads to ragged thickets dominated by common rock rose, Spanish lavender androsemary. On limy soils something similar takes place, above all at elevations of over 900 metres, oaks are accompanied by Spanish juniper (Juniperus thurifera) and the scarcity of shrubs is such that the same Holm oak (Q. ilexsubsp.rotundifoliaorballota) dominates almost entirely on its own the first phases of deterioration of the forest. The degradation caused by burning or felling leads to thickets of Scorpion's thorn (Genista scorpius),thymeand common lavender (Lavandula angustifolia).
Cork oak forests occupy around 10,000 square kilometres on the peninsula, more than half of the world's extension of this kind of forest.
Thecork oakforest needs siliceous soils of a sandy texture, and a mild, slightly damp climate. Under such conditions it totally or partially displaces the Holm oak; Holm oak may be found in stands of Cork Oak with a certain frequency, as well as Portuguese oaks (Quercus fagineasubspbroteroi). The area occupied by oak forests corresponds above all to the southwest quadrant of the peninsula, but also toCatalonia,Menorcaand even the non-coastal valleys ofGalicia. They often alternate with the oaks, which occupy the drier slopes and with thequejigaresofAlgerian oak(Quercus canariensis), that occupy the ravines and cool, shady northward slopes.
The cork oak forests often contain wild olives, and like some of the cool groves, are often accompanied by strawberry trees (Arbutus unedo) with mock privet (Phillyrea angustifolia) which grow in the clearings of these forests and dominate their regressive phases. In western Andalusia, other common components of theecosystemare the areas of common broom, genusCytisus.
The termquejigarrefers to forests of many different characteristics. 
Forests of Algerian oaks (Quercus canariensis) are well represented in westernAndalusiaand very patchily by hybridizations inCataloniaand the Cordillera Mariánica. They are the most demanding as to temperature and humidity, and therefore do not usually stray too far from areas with a maritime climate; they prefer the cooler, shady northward slopes, damp meadows and the banks ofstreamsof the lower ground. In general, they alternate with the Cork Oaks, which they displace in the coolest zones; both prefer siliceous soils. In the clearings and degraded stages of these forestslos piornos(Teline sp.,Cytisus baeticus), heather (Erica arborea,Erica scoparia), and  rock rose (Halimium lasianthum) are common.
Los quejigaresof Portuguese oaks (Quercus fagineasubspfaginea) are the most typical and common of the peninsula, since they are found from theSerranía de RondainAndalusiato the lower slopes of the Pyrenees.  They are much more resistant to the cold and damp thanQ. canariensis; on the other hand, they need cooler and deeper soils than the Holm oaks with which they come into contact. Although they can grow in any type ofsoil, in siliceous soils the usually play a secondary part with respect to Holm oaks, cork oaks, and Pyrenean oaks; it is only on chalky soils that it formsforestsof any consideration, especially in the northeast quadrant and centre of the Peninsula. The natural area corresponding to thequejigois frequently the black pine (Pinus nigrasubspsalzmannii), which often has been extended at its expense.
Los quejigarescan often includemaples, serbales,European serviceberry or snowy mespilus (Amelanchier ovalis), common privet (Ligustrum vulgareL.) and common dogwood (Cornus sanguinea); their degradation can lead to extensive thickets ofbox.
The lastquejigo,Quercus fagineasubspbroterirequires the most moisture and is least resistant to cold. It is found principally in the southwest quadrant and prefers siliceous soils, somewhat cool. More frequently than in pure concentrations, it is found mixed with cork oaks and Holm oaks.
The most characteristic natural pine forests are those ofpino negro(Pinus uncinata) and Scots pine (Pinus sylvestris). The former is often associated withRhododendron ferrugineum, blueberries,Salix pyrenaicaand other shrubby species on the subalpine slopes of thePyrenees. Over less washedlimestonesoils it is usually accompanied by Savin juniper (Juniperus sabinaL.), common juniper (Juniperus communissubsp.hemisphaerica), and common bearberry ([Arctostaphylos uva-ursi]). Such forests make up thetree linein most of the Pyrenees, reaching 2400 metres.
TheScots pineplays the same part in the other peninsular mountains, both siliceous and limy. It is accompanied and superseded at high elevation bypiornales,dwarf junipers, and hummocky high mountain thickets. Their lower altitudinal limit remains patchy, having been extended at the expense of deciduous forests.
The maritime pine (Pinus pinaster) is found at an intermediate elevation and on generally siliceous soil, which inGaliciagoes down to sea level and inland alternates with Pyrenean oak. Over limestone, the black pine (Pinus nigrasubspsalzmannii)plays an important role in many of the mountain ranges in the centre, east and south of the Peninsula; in limy soil, and at the same elevation, it usually displaces the former. Both are displaced at higher elevations by the Scots pine.
The warmest of all the pine forests are those of Aleppo pine (Pinus halepensis), which are situated on rocky crests and sunny hillsides. Aleppo pine is the typical pine of the Mediterranean coast, from sea level to an elevation of 800–1000 metres in the interior; these prefer limy soils.
The stone pine (Pinus pinea), possibly the most characteristic of all, occupies sandy soils. It grows extensively both in the sandy areas of the lowlands in the provinces ofCádizandHuelva, as well as points further inland (Valladolid,Cuenca, andMadrid). Finally, especial mention is necessary of the Monterey pine (Pinus radiata), because of its importance in reforestation and managed forests.
The juniper groves of Spanish juniper (Juniperus thurifera) constitute a curious formation that occupies the highheathsandmesetasof the interior, nearly always above 900 metres elevation. The principal woodlands of this type are in the Serranía de Cuenca, Sistema Ibérico,Alcarria, Maestrazgo and other mountains of the interior. They do not usually form dense forests, but rather parkland or small woods in meadows. They prefer soils developed overlimestone, especially those of an ochre or reddish color and rich inclay,de carácter relicto (Terra rosa, Terra fusca);on occasions, as in the region ofTamajón(Guadalajara), they also colonize siliceous terrain.
They are adapted to an exceptionally harsh continental climate, where practically no other species of tree is a rival; except for the Holm oak, which occupies some of the old,deforestedjuniper groves, and the European black pine (Pinus nigra) which can accompany it with a certain frequency. The common juniper (Juniperus communissubsp.hemisphaerica) is habitually a secondary species of these groves. At high elevations they come in contact with forests of Scots pine and with theSavin juniper; the latter sometimes forming part of the shrubby stratum.
The fact that these are to be found mainly in areas which have been exposed for a large part of theTertiaryand over soils consideredrelictos, supposes a great antiquity for such groves. The harsh climatological conditions, with the surface of the ground undergoing processes of alternate freezing and thawing (cryoturbation), makes difficult the development of elevated brush. In their regressive stages, they tend toward hummocky thickets ofcambrones(Genista pumila) ortomillaresy prados de diente dominados pordwarf shrubs anddog's tooth grass. At lower elevations these groves can also alternate withespliegoyaliaga.
The Phoenicean juniper (Juniperus phoenicea) habitually plays a secondary part and does not often form dense woods. Only on some rocky shelves or in special environments such as fixed dunes and sandy areas near the coast do they manage to form woodlands of any importance.
The high Mediterranean mountains above 1700 metres present some special characteristics. Winters are very harsh and long; the thickness of the snow and strong frosts prevent almost any type of biological activity. Once the snow has disappeared, the soil dries quickly due to the strong sun and hightemperaturesreached in summer. The period suitable for the growth of vegetation is therefore very short and for the above-mentioned reasons, the land is dry most of the time. Under such conditions, the forest enters a state of crisis, being replaced bypiornales(ciste and broom formations) and thicketspluvinularesaccompanied at lower levels byScots pine, often isolated individuals twisted and deformed by the snow.
Siliceous mountains such as theSistema Central,Serra da Estrela, theSistema Ibéricoof the region ofSoria, and parts of theCantabrianmountains, are covered by thickets ofCytisus purgans(variously known as "Andorra broom", "Provence broom", or "Spanish gold hardy broom") or Alpine juniper (Juniperus communissubsp.alpina). In theSierra Nevada, on the other hand, under similar conditions, theGenista baetica,is more dominant, sometimes accompanied byCytisus purgansand another species of juniper (J. communissubsp.hemisphaerica).
In the limestone mountains such as the Maestrazgo and Serranía de Cuenca,  a shrubby formation of Savin juniper (Juniperus sabina) accompanied by Scots pine is characteristic. In the limestone mountains  ofAndalusiaa detectable role is played by thicketspluvilunaresand  hummocks of common buckthorn (Rhamnus cathartica).
From an ecological point of view, shrubby borders are fundamental in forest ecosystems to guarantee the natural regeneration of the woods, as well as to provide food and refuge for the associated fauna.
They are made up of spiny shrubs, depending on the forest and climate, such asgorse,box, thyme, and so on.
It is possible to identify successive stages in the process of degradation of these various forest formations, from an optimum state to the final phase of desertification.
These regressive states, in the case of leafy forests, are the following: