Forests of the Iberian Peninsula
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 mainland extends to the north of Portugal, the greater part of Galicia, Asturias, Cantabria, the Basque Country, northwest of Navarre, and western Pyrenees.
The Mediterranean influence is felt in the presence of Holm oaks (Quercus rotundifolia) with bay laurel, which are situated on the warmest crests and slopes, especially above chalky soil, where the dryness becomes more pronounced.
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).
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.
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.
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, 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 granite valleys and 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).
Among the woody species also found in these forests are the hawthorn, barberry, butcher's broom (Ruscus aculeatus), Viburnum tinus, ivy, and Daphne laureola.
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 subspecies ilex, to an elevation of 1400 metres, in some mountains and high plains of the interior; in the continental zone, the oak found is the subspecies rotundifolia, more resistant to such a climate.
Coastal oak forests and those of sublittoral mountains are extraordinarily rich and varied, with a variety of shrubs and lianas; often accompanied by bramble, honeysuckle, ivy, Viburnum tinus, butcher's broom and, in the southwest of the peninsula, wild olive trees.
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 the Sierra 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 and rosemary.
The degradation caused by burning or felling leads to thickets of Scorpion's thorn (Genista scorpius), thyme and common lavender (Lavandula angustifolia).
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 of streams of the lower ground.
The maritime pine (Pinus pinaster) is found at an intermediate elevation and on generally siliceous soil, which in Galicia goes down to sea level and inland alternates with Pyrenean oak.
Over limestone, the black pine (Pinus nigra subsp salzmannii)[3] 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.
It grows extensively both in the sandy areas of the lowlands in the provinces of Cádiz and Huelva, as well as points further inland (Valladolid, Cuenca, and Madrid).
The fact that these are to be found mainly in areas which have been exposed for a large part of the Tertiary and over soils considered relictos, 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 of cambrones (Genista pumila) or tomillares y prados de diente dominados por dwarf shrubs and dog's tooth grass.
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.
Under such conditions, the forest enters a state of crisis, being replaced by piornales (ciste and broom formations) and thickets pluvinulares accompanied at lower levels by Scots pine, often isolated individuals twisted and deformed by the snow.
In the Sierra Nevada, on the other hand, under similar conditions, the Genista baetica,[4] is more dominant, sometimes accompanied by Cytisus purgans and another species of juniper (J. communis subsp.
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.
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.
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.
