Sierra de Guadarrama National Park

Above an altitude of 1,900 metres, the weather conditions are particularly harsh. The weather can be very changeable, sometimes within a few hours; a day of intense sunshine can be followed by a night of hard frosts. During the coldest months, snow is abundant, preventing the growth of trees. The vegetation that thrives in these places is made up of high mountain meadows and pastures, which alternate with rocky outcrops and rocky outcrops.

Peak meadows
These meadows are referred to in the scientific literature as “psicroxerophilous meadows”, due to two features that characterise these environments: cold and dryness. Although rainfall is high on the summits, the water here is frozen for a large part of the year and, in addition, the winds blow strongly, which increases the dryness. Despite being at very high altitudes, they are not usually covered by snow for very long periods of time, as they are very exposed places where the snow is blown away by the wind.

The summit meadows are one of the most interesting habitats, as here we find a group of very unique species, adapted to the harsh conditions of the high mountain range. The species that dominates the vegetation landscape is the reed-breaker (Festuca indigesta), a grass with short, curly, rigid leaves barely a hand’s breadth high, which is often arranged to form edges or terraces, due to periglacial phenomena. The typical species in these environments are almost always of very small size. Among the most common are Jurinea humilis, a small thistle with purple flowers, Jasione crispa subsp. Centralis with its cushiony appearance and attractive pale blue flowers, and the mountain hedgehog (Armeria caespitosa) with striking pink flowers. Adaptations to water scarcity are evident in all these species.

High mountain crags
These enclaves, like the previous ones, have very harsh environmental conditions, especially aridity and very low temperatures. The lichen communities are particularly noteworthy here, with a high diversity of species. For example, in the Peñalara Natural Park 141 species of lichen have been found living on rocks. The most characteristic and abundant of these lichens is Rhizocarpon geograficum, which looks like a yellowish green crust and owes its name to its resemblance to a map.

In the high mountain crags we find an interesting group of plants, which settle in crevices and ledges. Of particular note are the comfrey (Saxifraga pentadactylis), the alchemilla (Alchemila saxatilis) and the murbequiela (Murbeckiella boryi).

Pyornales
These are dense thickets dominated by the mountain piorno (Cytisus oromediterraneus), a shrub with green, flexible branches, thanks to which it can remain buried by snow without suffering damage for a good part of the winter. Another common shrub in these formations is the creeping juniper (Juniperus communis subsp. hemisphaerica). The pyralnales extend from the upper limit of the pine forest up to an altitude of approximately 2000 to 2200 metres.

At the end of June, with the flowering of the broom myrtle, the high slopes of Guadarrama are tinged with yellow, clearly marking the distribution of the broom myrtle groves in the area. The flowering of the piorno is a real spectacle that attracted the attention of travellers crossing the mountain passes in the 19th century. Thus, Charles Dembowski, recounting a journey from Madrid to Segovia, refers to the Navacerrada pass, whose surroundings ‘are covered in a beautiful yellow colour with broom’ (1838-1840).

Among the most characteristic plant species of this environment are the wolf asparagus (Orobanche rapum-genistae), a species that lives at the expense of the piorno, and the hierbaluco (Linaria nivea).

Wet meadows, fawn grasslands
In areas with very wet but well-drained soils, there are very compact grasses dominated by the fawn (Nardus stricta). They are frequent on the floor of the pyramidal forest due to the high rainfall and the regular supply of water provided by snowmelt. They are located in depressions or landings, where water has a greater tendency to accumulate. They are highly nutritious pastures for livestock, which is why they have traditionally been used in the summer season.

Among the plant species that can be found in the cervunales are the snow daffodil (Narcissus bulbocodium), the Serrano saffron (Crocus carpetanus), the gallarito (Pedicularis sylvatica) and a showy purple-flowered bellflower (Campanula herminii).

Canchales
These are accumulations of loose stones that appear on summits and high headlands, almost always associated with important rocky outcrops. They are composed of angular stones of various sizes, generally larger, but also with more diverse sizes, near the rocky outcrops, and of lesser size, and with more homogeneous dimensions, in the lower parts. The rock fragments that make up the rocky cliffs or boulders have originated from the action of ice, which has been crumbling the rocks.

The scree is an unstable mobile environment, also subject to strong thermal contrasts. At first glance, they look like deserts of life, although detailed observation reveals a wide range of species. Among the plants that take root in these difficult environments are the alder cherry (Prunus padus) and the foxglove (Digitalis purpurea). But perhaps the most characteristic species on the area’s pebbles is a fern, Cryptogramma crispa, whose bright green fronds begin to emerge among the stones with the arrival of good weather.

Peat bogs and hygro-turbated grasslands
These enclaves, which are small in size, occur in waterlogged and fairly flat areas where water accumulates continuously. In the area they are known as ‘trampales’ (when you step on them the ground sinks), ‘tremedales’ or ‘paulares’. In these places, dead vegetation is deposited at a faster rate than it decomposes, and peat accumulates.

These environments are very poor in oxygen (the water hardly moves and therefore contains little oxygen), very acidic and noticeably cold. Most of the micro-organisms capable of degrading organic matter are aerobic (they cannot live in the absence of oxygen). Therefore, plant matter accumulates without decomposing. Nitrates are also very scarce in these environments, as nitrifying bacteria, which are aerobic, are scarce, while denitrifying bacteria, which live in the absence of oxygen (anaerobic), thrive.

The group of plant species adapted to these environments is, as can be expected, very unique. Mosses (mainly the genus Sphagnum) and hornworts dominate. We also find here the flycatcher (Drosera rotundifolia). Other species typical of these enclaves are the peat heather (Erica tetralix) and the marsh violet (Viola palustris), a delicate violet with white flowers.

Lagoons
The lakes in the Sierra de Guadarrama are of glacial origin and are located at an altitude of over 2,000 metres. Of particular interest are the Laguna Grande de Peñalara, the Laguna de Los Pájaros, the Cinco Lagunas complex and the Laguna de El Nevero.

Pine forests
The Scots pine forests (Pinus sylvestris) are the most emblematic tree formation in the Sierra de Guadarrama. They have a high biogeographical and also genetic value, as the Scots pine of the Sierra de Guadarrama has different characteristics to those that grow in other mountains on the Iberian Peninsula, such as the Pyrenees or the Sierra Nevada. The tree layer of the pine forest is made up only of Scots pine. It is a fairly open forest, which allows abundant light to penetrate the undergrowth. Some shrubs grow under the trees, the most common of which are the broom (Genista florida), the jabino (Juniperus communis) and the piorno serrano (Cytisus oromediterraneus), although the latter is only abundant in the higher areas.

From a floristic point of view, the higher areas contain a group of species typical of humid forests in the north of the peninsula, such as the blueberry (Vaccinium myrtilus) or the much rarer fox grape (Paris quadrifolia), which takes refuge in some streams.

Oak woods
Oak forests (Quercus pyrenaica) thrive in the Sierra de Guadarrama at an altitude of between 1000 and 1600 metres. It is possible, however, to find small stands of oak groves in the pine forest clearings at higher altitudes. Until recently, the oak groves – locally called “matas” – were intensively exploited for firewood and charcoal, but the cessation or attenuation of this exploitation has led to their recovery in recent decades.

The melojo begins to lose its leaves in September, but in many cases the dry leaves remain on the branches for a good part of the winter. The new leaves sprout very late (mid-May), which is an adaptation to late snowfalls, which are frequent in this area.

Where the oak grove is dense and has good-sized specimens, few shrubs grow in the undergrowth. However, when the woodland is not very dense, the oak is accompanied by a varied group of shrubs and woody bushes such as rockrose (Cistus laurifolius), blackthorn (Prunus spinosa), buckthorn (Rhamnus catharticus), privet (Ligustrum vulgare) and hawthorn (Crataegus monogyna). In the undergrowth of the undergrowth of the melojar there are many herbaceous species, such as gamones (Asphodelus albus), peonies (Paeonia broteroi), lemon balm (Melittis melissophyllum), aristolochia (Aristolochia paucinervis), geos (Geum sylvaticum). In the clearings of the oak grove, the meadowsweet (Filipendula vulgaris) and orchids (Orchis morio) bloom.

Holly trees
Holly is a species that can be found all over the Sierra de Guadarrama, dotting the pine forests. It is rarer to find stands and groves of holly of a certain size. One of the best examples is in the Pinar de la Acebeda pine forest (Montes de Valsaín), where it is a frequent species in the undergrowth and near watercourses.

Holm oak groves
The Carpetan holm oak groves, formations of Quercus ilex subsp. Ballota with juniper (Juniperus oxycedrus), are located in the lower areas of the Sierra, reaching up to 1000 m in altitude. In a large part of their natural distribution area they have been replaced by pastureland. Associated with the holm oak grove are various aromatic shrubs such as lavender (Lavandula stoechas), marjoram (Thymus mastichina) and yellow evergreen (Helychrysum stoechas).

Ash groves
Ash groves occur in hollows, valleys and areas where the soil is deep and humidity is abundant. The dominant species is the ash tree (Fraxinus angustifolia), although the honey oak and other deciduous trees may also appear. Ash groves have traditionally been felled and thinned to encourage the development of perennial grasslands, which are very productive. Thus, we usually find these formations cleared.

The Sierra de Guadarrama contains other forest formations of interest, such as birch groves, yew groves and juniper groves.

Rivers and riverbanks
The rivers and streams of the Sierra de Guadarrama are clean, fast-flowing and well oxygenated, fed by rainfall and snow melt. Only in the lower areas of the valleys do the rivers and streams have developed riverside vegetation. The most common species are ash willows (Salix atrocinerea) and arraclanes (Frangula alnus). In some enclaves we can also find ash trees (Fraxinus angustifolia) and aspens (Populus tremula).

Steppes
These are fairly dense thickets, with dark green tones, dominated by the steppe rockrose (Cistus laurifolius), a robust shrub, no more than a metre and a half high, with twisted stems, from which strips of honey-coloured bark peel off. The evergreen steppe has a fairly uniform appearance throughout the year. It is only during the flowering of the steppe rockrose that the appearance of the scrub changes strikingly; for a few days its large flowers splash the steppes with white.

Broom and scrubland.
The leguminous thickets appear as shrub thickets or replacement stages of the mountain oak groves. The main species that characterise these formations are Genita florida, Adenocarpus complicatus and Cytisus scoparius. Often these formations are exclusive to Genista (broom groves) or Adenocarpus (cohoak groves).

Forest meadows.
These are open clearings in pine or oak woods for livestock grazing. Some of the most characteristic species of these enclaves are: Festuca indigesta, F. iberica, Hieracium castellanum, Agrostis castellana, A. trucatula, Deschampsia flexuosa and Poa bulbosa.

Thermophilic crags
The rocky environment has original features, among which the following stand out:

• Large thermal oscillations due to the low specific heat of the rock.
• Very low availability of water at different times of the year.High diversification of environments due to the different orientations, presence of crevices…

Some of the most characteristic plant species of these environments are the navel of venus (Umbilicus rupestris), the rock narcissus (Narcissus rupicola) and the carnation (Dianthus lusitanus).