La Vegetación de la comarca burgalesa de Espinosa de los Monteros

Abstract

The Cantabrian Fringe, in northern Spain, is a narrow strip of mountainous territory stretching along approximately 600 km from the Pyrenees in Navarre to the northwestern corner of the Iberian Peninsula (Galicia). It has a temperate climate (with summer rainfall) and biogeographically it is related to the Atlantic and Central Europe (Eurosiberian Region). This is due to the strong influence of the Atlantic Ocean and the repeated invasions of frontal systems associated to low pressures originating in the North Atlantic area. Nevertheless, the long Iberian border with the neighbouring Mediterranean Region influences the flora and ecosystems of this unique territory. This monograph focuses on the vascular plant communities of the area around Espinosa de los Monteros, located in the northernmost sector of the Burgos province, bordering with the Autonomous Community of Cantabria. It comprises an area of ca. 300 km2 in which the main human settlement is the town of Espinosa de los Monteros. Like the rest of the Cantabrian Area, it is an abrupt territory, with two main mountain ranges crossing it in an east-west direction, leaving a wide valley in between. The northern range is the highest (summit Castro Valnera 1,710 m a.s. l.) and it is almost entirely siliceous (sandstone), while the southern range is calcareous and reaches lower elevations (summit Mt. Bedón 1,088 m a.s. l.). The latter is also the frontier with the Mediterranean Region and many Mediterranean plants and communities move northwards favoured by the limestone substrates. Between these two ranges, the wide valley of Espinosa allows a prosperous agriculture and husbandry and concentrates the majority of the human settlements. Two main subunits can be recognized according to the topography and lithology: 1. The northern one, siliceous, with higher summits where some remnants of subalpine flora can be found, and very moist due to abundant orographic precipitation collected from the North and Northwest. This allows the presence of Nardus meadows and mires for example. 2. The southern one is calcareous, less humid (rain shadow) and lower in altitude, which favours the existence of a rich sub-Mediterranean flora and ecosystems practically absent in the northern sector. The field survey was carried out along several summer campaigns during which a number of releves were collected, 299 of which are shown in the 36 tables presented in the text. Upon these we have recognised 45 community types at association level, grouped into 20 phytosociological classes. Looking at the structure of plant communities, there are three main types of vegetation which are particularly relevant in this area: forests, heathlands and meadows. The majority of the forests are summergreen, deciduous, typical of the temperate Europe, and they encompass a high variability. The dominating tree species are: Alnus glutinosa (riverine), Fagus sylvatica, Quercus faginea, Quercus pyrenaica and Quercus petraea. The forests dominated by the latter species represent an original and remarkable feature of this area in the context of the Cantabrian territories, as they are not a common type of forest. The heathlands are mostly found in the siliceous part and cover large areas. Due to the high rainfall values in the mountains, these heathlands are rich in hygrophilic elements, such as Erica tetralix, and are sustained largely on peat substrates. Meadows also cover large surfaces and are maintained by human management. There are two basic types of management. One is through harvesting and collecting grass for hay. These meadows are seldom grazed and belong to the Malvo-Arrhenatheretum association (Arrhenatherion). They are concentrated in the lower altitudes, surrounding the permanent human dwellings, and they are used to provide winter forage for cattle. The second type are the grazing meadows of Merendero-Cynosuretum (Cynosurion) and are dedicated to cattle grazing during summer. They cover large areas in the slopes of the northern mountains along a wide altitude range. This determines that, throughout the growing season, a typical local transhumance is practised by the local cattle owners (Pasiego people), which starts grazing the lower altitude meadows, continues with the intermediate ones, and ends in the highest ones at the end of the growing season.