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Environmental Zones
Author: Jan Jansen
Serra da Estrela Natural Park
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Overall geographical setting
Serra Estrela. Photo: Jan Jansen

The Serra da Estrela is situated in central-east Portugal and a large part of the mountain lies within the limits of the Parque Natural da Serra da Estrela. The Park covers around 100,000 ha and is administered by six municipalities: Seia, Gouveia, Celorico da Beira, Guarda, Manteigas and Covilhã. These are included in two districts: in the north the Guarda district and in the south the Castelo Branco district.

The Serra da Estrela holds by far the highest summit (1,993 m) of continental Portugal. Together with the Serra do Açor (1,349 m) and Lousã (1,202 m) the massif constitutes the western part of the Central Range (Portuguese: Cordilheira Central). This range stretches some 500 km over the Iberian Peninsula in an east-west direction, dividing the major Atlantic drainage system in the northern Meseta (Douro basin) and the southern Meseta (Tagus basin).

The Serra da Estrela towers over the lowland plains of the Mondego and the Zêzere (tributary of the Tagus). In the north-eastern part of the massif the drainage divide of three major catchment basins coincide: of the Douro, the biggest river of the Iberian Peninsula, of the Tagus, the longest river of the Iberian Peninsula, and of the Mondego, the biggest river that has its offspring in Portugal.

Geology - soil

The mountain consists mainly of granite rock in its central part and schists in its periphery. Due to erosion, soils are often shallow or even absent, especially on slopes. Depletion of materials takes place in convex areas and accumulation takes place in all kinds of depressions. Without entering into detail, major soil-types include lithosols, rankers, cambisols and fluvisols. The first type has no horizons, being little more than a deposit of coarse mineral fragments on hard rock; the second includes soils with an organic horizon often having a clear boundary with the mineral material; the third type includes temperate brown soils; and the fourth type includes both alluvial soils mostly found along rivers and colluvial soils mostly found below slopes. Derived from granites the rankers occur in the higher parts; the cambisols, derived from schists, occur in the lower parts of the mountain.

Geomorphology

The Central Range is part of the Hesperian Shield, an old core of mostly Palaeozoic materials. Some 300 million years ago the Central Range underwent a mountain-forming process generally known as the Hercynian orogeny. After a long period of erosion it was more or less levelled to a plain and from it a major part of the Meseta evolved. Some 70-90 million years ago, the Eurasian and African plate got close, starting a compressive general regime period for the whole Iberian micro-plate. As a result, on the borders of the plates important mountain ranges (Alps, Pyrenees, etc.) were uplifted during the Tertiary (65-2,5 million years ago) in a general tectonic event called the Alpine orogeny. The Alpine compressions induced also the reactivation of the Serra da Estrela resulting in a huge vertical dislocation up to some 1,500 m. Glacial and periglacial processes during the Quaternary (period of the last 2,5 million years) made a strong contribution to the present day morphology of the higher parts of the mountain. The highest plateau area of the Estrela, the Planalto Superior, was covered by an ice cap and from it seven major glacier lobes diverged towards the lower parts. Roughly 25,000 years ago the Zêzere lobe outreached the present village of Manteigas. With some 13 km it was the longest glacier lobe, more or less equalling ‘ La Mer de Glace’, the longest glacier of the present-day Mont-Blanc massif.

Through millions of years denudation processes flattened off parts of the mountain resulting in several high plains. Granites are more resistant against erosion than schists. Therefore the granite areas are marked both by a better conservation of the planation surfaces and scarps, and by a rich variety of weathering forms.


Climate

Temperature and precipitation are generally used to quantify major meteorological phenomena. Distribution of both temperature and precipitation in the Estrela is very complex. Both are mainly controlled by global latitudinal position (mainly north-south directed influences from the Temperate and southeast-northwest directed influences from the Mediterranean macroclimate) and longitudinal position in respect of the Atlantic and the Iberian interior (mainly west-east directed maritime, east-west directed continental influences). The resulting actions are intensified or weakened by the relief (mainly by means of altitude, orientation and ‘barrier effect’: the massif functions as a barrier for the Atlantic air masses). Usually both wind velocity and precipitation increase while temperature drops (ca. 0,6 ° each 100 m) with increasing altitude. In general the Atlantic influence predominates the western piedmont areas and the higher zones, whereas the Mediterranean influence increases in the eastern and southern parts of the massif (especially in deep valleys) that are situated in the lee side of the prevailing westerly winds. Within horizontal distances of a few km one may pass from the cryogenic grasslands on the Planalto Superior to the evergreen Portugal laurel galleries in the Loriga valley; or from the meso-Temperate Pyrenean oak remnants of the Planalto de Videmonte to the meso-Mediterranean Holm-oak groves in the deeply incised Mondego valley near Quinta do Fragusta.

Some of the plateaus and valleys may have meso-climates, often ruled by local winds (so-called mountain, valley and drainage winds). Mountain and valley winds follow a daily alternation of direction in a manner similar to land and sea breezes. The air moves from valleys, upward over rising mountain slopes, toward the summits during the day, when slopes are intensely heated by the sun. The air then moves valley-ward, down the ground slopes, when the same slopes have been cooled at night by radiation of heat from ground to air. Drainage winds include the flows of cold air under the influence of gravity. Such cold air may accumulate in valleys. Fog banks in the valleys may persist when at the same time the higher plains have sunshine throughout the day. In table 1 and 2 temperatures, precipitation and wind characteristics of several sites are presentated.

Climate tables
Vegetation
Vegetation in the Estrela with affinities to the Euro-Siberian region includes heathlands

Bioclimatology tries to find relations between climate (temperature and precipitation in particular) and the distribution of plants, vegetation types, and vegetation series. Global bioclimatic classification includes five macrobioclimates: Tropical, Mediterranean, Temperate, Boreal and Polar. Within each of the macrobioclimates various subtypes can be recognized depending on temperature, precipitation and vegetation patterns.

In the Serra da Estrela two macroclimates meet, the Temperate generally ruling at the western and northern slopes and the highest elevations, the Mediterranean at the (lower) eastern slopes and in some valleys. Both macroclimates are represented by rather similar subtypes because their end ranges meet in the Estrelean territory.

The Temperate macrobioclimate is represented by the ‘oceanic  sub-Mediterranean’ subtype and the Mediterranean by the ‘pluviseasonal-oceanic’ subtype. Both these subtypes have close affinities; as for instance the oceanic sub-Mediterranean subtype may have a dry period in at least one summer month. A dry period is often expressed by the aridity index of P < 2T, in which P is monthly precipitation in mm and T monthly mean temperature.

Altitudinal vegetation belts

Vertical zonation in mountains can also be attributed to altitudinal variants within each macrobioclimate. The vegetation of the Serra da Estrela reveals the presence of 5 or 6 altitudinal variants. The Temperate macrobioclimate is assumed to cover a larger part of the massif including the meso-, supra-, oro- (and perhaps) cryoro-Temperate belt; the Mediterranean includes the meso- and supra-Mediterranean belt. Each belt has its own climax formations and the degraded stages of one series frequently differ from those of other series, and so does land use. As our knowledge of the Estrelean vegetation is not sufficiently enough to distinguish and attribute all stages of the climax series, it is decided to use the more general terms for the 5 or 6 belts including them in one lower, one middle and one upper belt. The lower includes both meso-belts stretching from the foot of the mountain to ca. 800 m a.s.l.; the middle belt includes both supra-belts from ca. 800 to ca. 1,600 m; and the upper one includes the oro-Temperate from ca. 1,600 m to the top and locally perhaps fragments of the cryoro-Temperate at strongly exposed sites with the highest elevations. In the following a concise survey of these belts is given.

Lower belt

Under rather humid conditions, the potential natural vegetation of the meso-Mediterranean belt would mainly be formed by evergreen or mixed evergreen deciduous oak forests predominated by Quercus suber; under less humid conditions by Quercus rotundifolia. The potential natural vegetation of the meso-Temperate belt would be mainly formed by deciduous oak forests with evergreen elements mostly predominated by Quercus robur. More humid soils would have supported Fraxinus angustifolia forests and along the rivers in the valleys Alnus glutinosa and Prunus lusitanica galleries.

In both meso-belts, human settlement is most dense and disturbance consequently the strongest. All climax forests disappeared and have been replaced by various degraded formations due to human activities like burning, cutting, grazing, ploughing, afforestation, and cultivation. Today there are only very small and incomplete fragments of semi-natural forests left. Degraded phases include small areas covering thickets and large areas covering dwarf-shrub formations, especially those in which Cistus species and Lavandula species thrive. Further degradation may lead to relatively open grasslands rich in annuals. Locally, on relatively nutrient-rich soils, semi-natural grasslands originated by man’s activities (pasturing, hay-making, irrigation). Weed communities originated from arable farming.

Middle belt

The potential natural vegetation of the supra-Mediterranean belt would be formed by deciduous or mixed deciduous evergreen oak forests with Quercus pyrenaica and Quercus rotundifolia. The potential natural vegetation of the supra-Temperate belt would be mainly formed by forests predominated by Quercus pyrenaica. In addition under special climatic and edaphic conditions both Betula celtiberica and Taxus baccata woods, sometimes mixed with Ilex aquifolium would be the final stage in spontaneous forest development. More humid soils would have supported Fraxinus angustifolia (2.2.4) forests and along the rivers in the valleys Alnus glutinosa galleries. Of all these forests only small and incomplete examples remained, mainly as a result of wildfires, and agricultural and sylvo-pastoral activities.

Degradation of the original woodlands mainly led to heathlands, broom fields, or hedgehog-heaths and further degradation to pioneer grasslands or in humid situations to bracken fields (Pteridium aquilinum). Through irrigation and hay-making man has produced interesting semi-natural grasslands; Rye cultivation created rich weed communities mounting up to the upper belt.

Upper belt

The potential natural vegetation of the highest belt would be mainly formed by Dwarf juniper formations and thorn-cushion scrub of Echinospartum ibericum subsp. pulviniformis. Edaphoclimatic vegetation includes rock, scree and bog communities, formations of small ponds, rivulets and lakes and perhaps some chionophilous (thriving under prolonged snow-cover) or frost-tolerating grasslands. Some of these communities, especially those related to cryogenic forces, show tendencies known from cryoro-Temperate vegetation belts in the Sierra de Gredos and Montes de Leon in Spain. Burning and summer grazing still produce degraded phases including heathlands, Cytisus oromediterraneus broom fields, semi-natural grasslands and pioneer grasslands.

In all belts a number of micro habitats occur in which mosses and lichens play a major role, but nowhere so conspicuous like in the oro-Temperate belt.

The detailed study of the geographic distribution of plants (phytogeography) provides a highly useful and objective criterion for the evaluation of areas for subsequent land use planning. Species may be distributed all over the world (cosmopolitan), restricted to a particular area (endemic) or occur in two or more separated areas (discontinuous). A certain area or territory can be characterized by the assemblage of species or in other words by its flora. The territories can be placed as units in a hierarchical model, going from the highest rank to lower: from kingdom via region, provinces, sub-provinces, sectors, sub-sectors, districts to even sub-districts.

Being part of the Holarctic kingdom, the Iberian Peninsula encloses three regions, namely the Euro-Siberian, the Mediterranean and the Macaronesian region. The position of the Serra da Estrela territory is complicated, since in or near its territory two regions, two provinces and three sub-provinces coincide. In a way the area may be seen as an important cross-road of the Portuguese interior ecological network. A more detailed description will be given in order to understand the position of the Estrelean flora and vegetation.

Most of the Serra da Estrela or perhaps all its territory may be considered a proper phytogeographic sector. This Estrelean sector is part of the Carpetano-Leonesean sub-province; in the west and in the south it intergrades into the Luso- Extremadurean sub-province (all Mediterranean region, Ibero-Atlantic province) and in the north at some distance there is the Cantabro-Atlantic sub-province (Euro-Siberian region, Euro-Atlantic province).

The Euro-Atlantic province stretches as a fringe along the Atlantic including North-west Portugal, North-Spain, large parts of France, Ireland and the British Isles (The Benelux, Denmark and the coastal areas of southern Sweden and Norway are often included in the same province). The Cantabro-Atlantic sub-province forms the southernmost part of the Euro-Atlantic province and is limited in the south by the Galicio-Portuguese sector (including most of Galicia and North-west Portugal). Vegetation in the Estrela with affinities to the Atlantic province includes heathlands, broom fields, Matt-grass swards, hay-meadows, bogs and poor remnants of summergreen broadleaved forests of Quercus robur and of Betula celtiberica.

The Ibero-Atlantic province embraces a major part of the western Iberian Peninsula. Vegetation in the Estrela with affinities to the Ibero-Atlantic province includes remnants of evergreen forests with Quercus suber, Quercus rotundifolia, and summergreen forests with Quercus pyrenaica. Other characteristic vegetation includes broom fields, Cistus scrub, Halimium scrub, Lavender scrub and some heathlands.

The Ibero-Atlantic province is divided into three sub-provinces of which two are present in the Estrela: Carpetano-Leonesean and Luso-Extremadurean. The former includes most of the Serra da Estrela, Central-east and North-east Portugal and large parts of the western Spanish Meseta; the latter includes the southern and western parts of the Estrela, a major part of South-Portugal (except the coastal fringe area from the Algarve to the Troia Peninsula: the Gaditano-Onubian-Algarvian province) and South-west Spain. Knowledge about the Iberian biogeography is still in a state of flux and according to the latest information the Beiranean Litoral subsector would now be part of the Coastal-Lusitano-Andalusean (=Gaditan-Onubian-Algarvian) province.

The Estrelean sector is more or less defined by its particular flora and its vegetation series.
Flora
The flora of the Serra da Estrela comprises more than 900 vascular plant taxa. For a quasi-complete list see:
Jansen, J. (2002). Geobotanical guide of the Serra da Estrela. Instituto da Conservação da Natureza. Ministério das Cidades, Ordenamento do Território e Ambiente. Lisboa. 276 pp. Endemics The flora includes a handful of endemic species and dozens of species within Portugal restricted to the Estrela.

Most of the species within Portugal restricted to the Serra da Estrela are Iberian endemics belonging to the Mediterranean flora, in particular the mountain flora of the Ibero-Atlantic province. Some are relicts of populations that came from North- or Central-Europe invading the area during the cold periods of the Quaternary. Within Portugal some 70 taxa are more or less restricted to the Serra da Estrela.

Mediterranean floristic elements

The Mediterranean flora evolved during the late Tertiary when the climate was getting drier. Some so-called palaeo-Mediterranean species originally belonging to the palaeo-Tropical or sub-Tropical flora adapted to the new conditions. These include genera like Ilex, Laurus, Olea, Osyris, Phillyrea, and Quercus. In general neo-Mediterranean species evolved from the Holarctic extra-Tropical element. These are mostly found in the mountains and northern parts of the Iberian Peninsula, including genera mostly representing scrub species like Cistus, Cytisus, Erica, Genista, Halimium, Helianthemum, Lavandula, and Ulex. Moreover, the Alpine orogeny resulted in the additional formation of a rich Mediterranean mountain flora. In the Serra da Estrela the latter and the group of neo-Mediterranean species are well-developed.

Many of them occur in the north-western quadrant of the Iberian Peninsula. Nine are restricted to the Carpetano-Leonesean sub-province. Another twenty or more have a wider range but are optimally developed in the same sub-province. Ibero-Atlantic endemics in Estrela include 8 taxa.

Northern floristic elements

The Boreo-Alpine and Arctic-Alpine elements include at least 6 species.

European Temperate floristic elements

The European Temperate flora in the Estrela generally occupies habitats with sufficient water supply in summer. This element is represented by some 20 taxa. In Portugal most of these species are more or less restricted to mountains of the Cantabro- and Ibero-Atlantic sub-provinces. In addition there are Lusitanian and Iberian endemics with a rather similar distribution in Portugal, bridging the limits of the Mediterranean and Euro-Siberian region.

Fauna

The diversity of vegetation and terrain provides habitats for a wide range of fauna, both native and introduced.

Approximately 40 mammal species and around 100 bird ones, circa 30 species of reptiles and amphibians, 8 kinds of fish and numerous invertebrate species live in the Serra da Estrela. A nearly complete list of all species (except arthropods and molluscs) can be found in Jansen (2002).

Mammals

Most of the mammals in the area are active at night and hide during the day. Therefore the visitor will not see many of them, all the more so because a major part of the species does not occur in large numbers.

The insect-eating mammals include six species, including Pyrenean Desman, a Tertiary relict with a distribution restricted to the northern half of the Iberian Peninsula. More than half of the Estrelean mammal species are represented by bats. There are 19 species, which is some 75% of the total number in Continental Portugal. The weasel family is represented by five species, including the Otter. The Wolf is now probably extinct in the territory.

Birds

The avifauna of the Serra da Estrela includes some 100 nesting species. The total number of observed bird species is much higher, but winter visitors and birds passing by are not included in this guide. The area is especially important for mountain birds. In the lower belt a number of typical Mediterranean species can be found. Within Portugal one species is restricted to the upper belt of the Estrela, namely the White spotted bluethroat. It is part of a specific Iberian mountain population mostly distributed in mountains in Spain, a pattern that is quite similar to that of the mountain lizard.

Fishes

At least 9 species of freshwater fish are reported from the Serra da Estrela. This is about one fifth of the total number occurring in Portugal. They include one strictly Portuguese endemic and 5 Iberian endemics.

Reptiles frogs and salamanders

The Serra da Estrela is largely covered with rocks and mosaics of scrub, open grasslands and water bodies providing ideal habitats for herpetofauna. Eight of the 10 Portuguese snake species have been reported. In general lizards are much more observed than snakes. One of them is a strictly endemic taxon: Lacerta monticola subsp. monticola. The waters in the uplands are, with a few exceptions, more or less free from pollution and provide an ideal habitat for frogs and salamanders. In the Serra da Estrela 12 species occur, which is no less than 70% of all amphibians of Continental Portugal.

Biodiversity & trends

The heathland-based agro-pastoral land-use system in Estrela mountains is one of the best last living examples of traditional open landscape management systems in Western Europe. As a result soils stayed poor in nutrients and biodiversity remained of high quality biodiversity. However, in the past decades the Estrelean farming system suffered from socio-economic marginalisation. The major threats for the open landscape, and its associated biodiversity include abandonment, industrial afforestation, and eutrophication from intensive husbandry.

Abandonment will lead to encroachment and the disappearance of the traditional open landscape, including landscape type categories B, D and E: Managed scrublands and heathlands, Cultural grasslands and Arable lands. Risk of wildfires will increase.

The spectre emerges that from industrial afforestation the area will be covered with same age-class tree plantations and monotonous “improved” grasslands with non-indigenous breeds or genetically manipulated mutants. (both crops and livestock). However, these threats may already decrease as intensification is not regarded as an appropriate future option for mountain areas such as Estrela, especially while there is a surplus of agricultural land. In addition forestry is no economic alternative, although some space is available for the development of climax woodland. The question remains as to how much, should be answered from balancing nature conservation and fire protection (Diemont & Jansen 2003).

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