The Iberian Ranges and Highlands

Chapter 11 The Iberian Ranges and Highlands Manuel Peinado, Juan Luis Aguirre, and Alejandro Aparicio Abstract One of Spain’s main mountain ranges, the Iberian System, separates the Ebro basin and Meseta Central (Inner Plateau) and runs northwest-southeast from the La Bureba corridor in Burgos to the Mediterranean coastal ranges in Castelloń and Valencia. The barren, rugged slopes of this range cover an area close to 61,140 km2. Each mountain chain has different geological characteristics depending on the outcropping materials of the Alpine orogeny, either those of the Hercynian basement or Mesozoic materials. The former give rise to the acid soils of the Sierras of Demanda or Moncayo and Peaks of Urbioń, and the latter to the basic substrates of the Sierras of Gu´dar, Javalambre, the Iberian High Plateau (“parameras” or “pa´ramos”) and the serranıás of Cuenca and Albarracıń. Vegetation varies according to both geological/edaphic factors and a complex orogeny. The prevailing ombroclimate is subhumid, reaching humid to hyperhumid, and the predominant thermoclimate is supramediterranean. Potential vegetation mainly comprises forests. Rocky areas, steep slopes or southern exposures of lower mountain zones sustain large patches of supramediterranean Quercus rotundifolia forests. Marcescent oak forests, both of Quercus pyrenaica and Quercus faginea subsp. faginea (Q. faginea hereafter), dominate large areas of the gentle relief of the sierras’ foothills though, in many zones, they have been repopulated with pines or given over to grazing. In more moist areas, generally of northern or eastern exposures, we find beech forests dominated by Fagus silvatica. In the north-west zone of the Iberian System, these occupy extensive areas. Large expanses of conifers from plantations of the twentieth century exist, though in some zones we find natural pine forests dominated by Pinus sylvestris var. iberica, P. nigra subsp. salzmannii and P. nigra subsp. latisquama (P. iberica, P. salzmannii and P. latisquama, respectively, hereafter). Also appearing are some relict groves dominated by P. uncinata. The dominance of coniferous formations is magnified by the large expanses of Juniperus thurifera woodlands of the Iberian parameras and of creeping Juniperus sabina in some summit areas. The online version of this chapter (doi:10.1007/978-3-319-54784-8_11) contains supplementary material, which is available to authorized users. M. Peinado (*) • J.L. Aguirre • A. Aparicio Department of Life Sciences (Plant Biology), University of Alcala´, 28871-Alcala´ de Henares, Madrid, Spain e-mail: [email protected] © Springer International Publishing AG 2017 439 J. Loidi (ed.), The Vegetation of the Iberian Peninsula, Plant and Vegetation 12, DOI 10.1007/978-3-319-54784-8_11 440 M. Peinado et al. Scrublands range from heaths dominated by Cytisus and Erica species in the rainiest zones, to scrub of the laurel-leaf rock rose Cistus laurifolius (“jarales”) and Genista scorpius (“ahulagares”) in drier or more exposed areas. In some shady zones appear formations of Buxus sempervirens or Berberis hispanica and in windier zones spiny formations of Genista rigidissima or Erinacea anthyllis.In the northern region occur mixed Ilex aquifolium woodland formations comprising several deciduous trees (Acer monspeliensis, A. campestre, Corylus avellana, etc.). Riverbank formations include those typical of the interior peninsula with a dominance of series of forest, woodlands and thickets dominated by willows (Salix purpurea, S. alba, S. atrocinerea, etc.), poplars (Populus alba, P. nigra) and elms (Ulmus minor). The sierras comprise large rocky habitats that sustain the growth of an interesting rupicolous flora with several significant endemisms. Habitats of basic substrate on rocky, steep slopes are dominated by open thickets of Juniperus phoenicea (“sabina negral”). The Iberian System is one of the most under-populated regions of Spain with large expanses of Teruel, Soria, Burgos, Cuenca and Guadalajara being home to fewer than 10 inhabitants/km2. Its setting is therefore one of immense, well- preserved zones. The area comprises mountains and sierras that are largely protected, sometimes because they form part of the Red Natura 2000 or because they harbour a protected feature such as the Natural Parks of the Alto Tajo, Moncayo, Sierra de Cebollera, Laguna Negra and Circos Glaciares de Urbioń. 11.1 Introduction Limits Running for over 500 km NW-SE between the Ebro basin and Meseta Central, the Iberian System is one of Spain’s principal mountain ranges and the main forest region of Mediterranean Spain. The system’s haphazard and motley series of mountain chains (“sierras” or “serranıás”), massifs, high plateaus and interior depressions extends southeastwards from the Corredor de La Bureba in Burgos, close to the Cantabrian Ranges, to the Mediterranean coastal ranges in Castelloń and Valencia, covering an area approaching 61,140 km2 (see Figs. 11.1, and S.11.1, S.11.2 as electronic supplementary material). Geological and Orographical Features (Figs. S.11.3, S.11.4, S.11.5, S.11.6, S.11.7 and S.11.8) After the Variscan or Hercynian orogeny, a gigantic mountain range formed and crossed in a NW-SE direction all the current land occupied by the Spanish Meseta Central. This huge Palaeozoic massif was so intensely and persis- tently eroded that, before the start of the Mesozoic era, a large portion had developed into a peneplain sloped towards its eastern flank. This flank was to be shaped by several Mesozoic marine transgressions and regressions such that from the Triassic (which saw the origin of the spectacular red sandstones known as “rodenos”), to the Cretaceous, deposits were left by invading marine waters and by continental sediments arising from erosion of the old Palaeozoic massif (Pe´rez- Estauń et al. 2004). This was followed in the Late Mesozoic by fracturing due to 11 The Iberian Ranges and Highlands 441 Fig. 11.1 Study area Alpine orogeny pressures of the hardened Palaeozoic basement and folding of Mesozoic deposits to induce anticlines (horsts) and synclines. The latter comprised depressions of varying size that filled with continental sediments throughout the Tertiary and Quaternary (Fig. 11.2). Besides folded Mesozoic rocks, the Alpine orogeny gave rise to different Iberian System relief features: on one hand to the Palaeozoic outcrops (quartzite, schist, Cambrian limestone and dolomite) of La Demanda, and on the other hand to the Tertiary materials that filled interior depressions. The Palaeozoic basement of La Demanda forms the series of mountains of the North Oroiberian Sierran biogeo- graphical sector, divided into two well-differentiated parts by the narrow depression of the river Najerilla, a tributary of the Ebro. To the north of the Najerilla appear the sierras of San Millań (2131 m) and San Lorenzo (2262), formed mainly by Silurian quartzite. To the south of this river, that basement, more reduced, sinks below the Mesozoic mantle, which forms an impressive mass of Jurassic and Cretaceous limestones comprising the sierras Urbioń (2228) and Cebollera (2147). The landscape of these mountains is abrupt, especially in the narrow valleys of the northern slope, and summits show a glacier erosion model. Most of the rocks are siliceous (except for the Cambrian dolomites of Mansilla) and belong to the Palaeozoic core as well as to the Mesozoic mantle: quartzite, slate, sandstone or conglomerate. Large islands of base-rich materials, limestone and marl of the Jurassic and Cretaceous, are also present. Some of these materials, such as the siliceous conglomerates of the Lower Cretaceous, are highly resistant to erosion and form marked shelves and ridges, among which the most outstanding peaks are those of the Urbioń (Urbioń, Castillo de Vinuesa, etc.). 442 M. Peinado et al. Fig. 11.2 Evergreen oak forest (Teucrio scorodoniae-Quercetum rotundifoliae) in the Moncayo foothills (Soria) The sierras making up the massif are arranged as three differentiated complexes (see orographical profiles as electronic supplementary material S.11.4, S.11.5, S.11.6, S.11.7 and S.11.8): the more north-western complex occurs around the sierra La Demanda; to the south of which and separated by the Canales depression appears the Neila-Urbioń-Cebollera complex, the longest and largest of the three, which with the Alba sierra, forms the source of the Duero. From here, now in a southeast direction, continue the small sierras of Almuerzo and Madero in Soria, which connect with the Sierra del Moncayo, where the peak summit of the Iberian System is found at 2316 m. From Moncayo southeastwards arise a series of modest alignments that extend to the headwaters of the river Huerva, where they join with the Sierra de Gu´dar. The Moncayo is a half raised fault block (semihorst), with a Palaeozoic core and Triassic cover reworked by glacial and periglacial erosion. Except in the Moncayo and its south-eastern irradiations, whose waters all flow into the Ebro both directly or via its tributaries Jaloń, Jiloca and Huerva, the northern massifs of the Iberian system constitute the divide between the waters of the Ebro and Duero. The northern slope drains towards the Ebro via a series of rivers (Tiroń, Oja, Najerilla, Iregua, Leza and Cidacos) that carve narrow valleys ending in the Rioja plains of the Ebro depression (Fig. 11.3). The northern slope continues southeastwards through the valleys of the river Alhama and Tierra de A´ greda until the foot of the Moncayo. The southern slope of the Neila-Urbioń- Cebollera alignment rests on the Meseta Central, which in this region of Soria 11 The Iberian Ranges and Highlands 443 Fig. 11.3 Cliffs and bluffs of conglomerates usually mark the transition between the Iberian System and the Ebro valley. Iregua river gorge at Islallana, La Rioja reaches heights close to 1000 m. A glacis of sandy substrates fed by the river Duero confers a gentle landscape rising towards the summit of the Picos de Urbioń.

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