Biological Characteristics

Vegetation Cover

The territory is located primarily in the transition between two distinct biogeographical sectors (MARTINEZ RIVAS, 1987) (Galician- Asturian industry and Galician-Portuguese industry) further comprising a gradient of bioclimatic horizons from the thermocline to the upper montane. To the variety of biogeographic conditions (figure below) particular mesoclimatic and edaphic situations, with an azonal character, are added. In addition, the variability in the intensity of land use has shaped over more than 3000 years of land use a diverse cultural landscape, where natural, seminatural and anthropogenic environments coexist.

Chronological division of biogeographic subsectors and bioclimatic horizons.

The potential domain of vegetation correspongs, according to the biogeographical territory and bioclimatic floors of the area, to different types of tree formations dominated by planedeciduous species: Quercus robur, Quercus petraea, Betula alba, and marcescent: Quercus pyrenaica.

Besides these types of climatophilous vegetation, other azonal vegetation formations appear in response to particular ecological conditions, linked to hydromorphic situations (azonal hygrophytic vegetation) or to limiting lithologies (azonal edaphophilic vegetation). Thus, within the proposed area there are important areas occupied by azonal vegetation with varying degrees of hygrophilia, particularly in the most northern part and associated to peat systems, as well as in the central zone, in sedimentary depressions and alluvial valley bottoms where wetlands appear linked to watercourses and seasonal phenomena of flooding. The azonal edaphophilic vegetation is much less represented than the hygrophytic. Confined to different types of rock outcrops, linked to forms of exhumation in areas of granitic lithology, the presence of quartzite side shoots arising from differential erosion phenomena, or the existence of colluvium deposits and other periglacial genesis deposits, all substrates incapable of supporting the climatophilous vegetation of the territory itself.

Climatophilous zonal potential vegetation
Galician-Asturian hill-mountain oak groves
Galician-Portuguese hill oak groves
Galician-Portuguese mountain oak groves
Orocantabrian hill-mountain Pyrenean oak woods
Orocantabrian mountain birches
Hygrophytic azonal potential vegetation
Blanket bogs
raised bogs
Hygrophytic and peatland-related heather
Floodplain forests
Riparian alder grove
Edaphophilic azonal potential vegetation
Silica-rich rocks
Limestone rocks

Synthesis of potential vegetation present in the territory.

Current plant cover is largely due to the effect of anthropogenic uses and activity recorded in the area, so in a large part of the territory, tree formations that constitute the potential plant cover have been displaced by grass, scrubs, agricultural and forest crops, as well as infrastructure, buildings and facilities. Out of those locations where special mesoclimatic or substrate conditions favour the predominance of azonal ecosystems, the presence of bushy formations corresponds to roughly advanced stages of forest degradation.

There is also a significant proportion of herbaceous formations that can be grouped under the generic heading of grassland. In many cases, due to their status as serial vegetation that requires a high degree of human intervention for its persistence, and a gradation in the intensity of management and exploitation by humans (irrigation, fertilization, tillage, grazing load...), makes it difficult to differentiate their semi-natural or anthropogenic condition. Moreover, many of the meadows are installed on at least temporarily waterlogged soils, which have strong affinities with hygrophytic azonal vegetation. Other herbaceous formations that are installed on poorly developed soils or directly on rocky outcrops or deposits unsuitable for maintaining zonal potential vegetation of the territory, are considered azonal edaphophilic vegetation.

Consequently, the presence of a semi-herbaceous formations character (serial) and not hygrophytic is limited to certain formations that have resulted from the degradation of heather and gorse, due to the repeated incidence of fires, the strong livestock load or the intense weedings. In such formations, grasses such as Agrostis duriei, Aira praecox, Agrostis curtisii, Pseudarrenatherum longifolium, Avenula sulcata, Anthoxantum odoratum predominate, along with other pioneering herbaceous species such as Tuberaria guttata, Vulpia myurus, Asphodelus albus, Prunella vulgaris, etc.

In cases in which areas of natural vegetation have been preserved, the structure and original composition thereof may have been modified to varying degrees, depending on the uses and activities that traditionally, and to the present day, they have endured. The different intensity of use has led to the current state of the plant communities presenting a gradation in the level of disturbance or intervention, so that the difference between natural and semi-natural vegetation is not always clear as a criterion of naturalness.