Where wild habitat remains in the mountains, it is dominated by oak groves growing alongside ash, beech, birch, hazel, pine, and holly trees. 

Muniel.los Forest is the best-preserved English oak forest in Europe. The climate is influenced by the ecoregion’s proximity to the Atlantic Ocean, which creates many diverse habitats.

Oakwood is the predominant vegetation in the zone. In addition to this there are also important spots of beechwood.

In this is well preserved forest, little evidence of human presence is visible. At the bottom of bigger valleys, according to legend, there are as many of these as days in a year. Hazelnut trees, maples, ash trees, willows or alders, spread all over the place.

Although trees dominate the landscape, over 400 species of vascular plants are present in the Reserve, some included in the Catalogue of Threatened Species from the Flora of Asturies.

Fungi, mosses and mainly lichens show great diversity. The endemism Ranunculus parnassifolius ssp. muniellensis and algae from Batrachospermun genus are exclusively found at Muniellos.    

Muniellos displays almost every vertebrate described in Asturies, a total of 160 species. 

The presence of brown bear (Ursus arctos) and of the last remaining Capercaillies (Tetrao urogallus) outstands above any other species, and both species are protected, finding here one of their last redoubts. 

Wolves (Canis lupus), roe deers (Capreolus capreolus), wild boar (Sus scrofa), chamonix (Rupicapra rupicapra parva), otters, to a hundred of species of fowls and over 15,000 invertebrates. 

The great variety of bats deserves a mention. Over 15 species catalogued so far, among them some Greater horseshoe bats (Rhinolophus ferrumequinum), one of the threatened rarest species of Europe.

Bears find its better adaptation to the oak and beech woods of Sumiedu and Muniellos (Asturies). A lot of years ago it was was very common at Asturian mountains, but uncontrolled hunting has put this animal in danger of extinction. Nowadays only about 50 brown bear specimens remain all over Asturies.

The Foundation "Oso Pardo" is an organization, presided by the Asturies crown prince, which is dedicated to the protection of this endangered species: they plant holly trees on extensive areas of the Cantabrian Mountains and have located all the specimens that still live in Asturies.

The owneship of the Muniellos Forest is rather obscure, only historical research starts to shed some light on this matter. It probably belonged to the Mual village council, although the House of Torenu (Queipo family) would have held its ownership by usurpation until the end of the modern age.

Until the middle of the 18th century and as timber prices were increasing further to high demand for naval construction in Ferrol, the inhabitants of Mual agreed to a judicial transaction in favour of the earl of Torenu. However there are records proving that this forest provided timber in the 16th century to fix some of the ships that returned from the Spanish Armada. 

During the 19th century timber uses diversified as were required for industrial use (railway sleepers, mining buttresses, construction beans...) Nevertheless the underwood remained property of the Queipo family until 1901, when they sold it in instalments, together with their share in the woodland of other forest in the area. In 1964 ownership of the woodland went into Spanish Foresty Heritage for an intended period of 40 years, after which the partnership would disappear and both wood and underwood would be owned by Muniellos Inc. however, this only lasted for a decade, since, at the beginning of 1973 the ICONA bought the forest from the company. 

A similar historical evolution was followed by the ownership of the Valdebóis and La Viliella Forests, subsequently bought by ICONA in 1983 and 1980.

The integrity as a woodland full of leafy native trees was not protected for a long time while it was threatened by industrial exploitation. During the 1960s, the International Biological Programme and the WWF showed some interest in buying the forest for its preservation for scientific purposes. At the same time, some biological studies were undertaken. 

In 1964, the government put forth the 9 July 2395/1964 Decree, declaring the "wonderful virgin Muniellos forest" as a picturesque spot, "with a surface of fifty square kilometres", little is know about the effectiveness of that tutelage. On 17 February 1973 was purchased by ICONA, and ten days later declared to be a public utility (MUP 339) and a royal decree of 15 October (RD 3128/1982) created the Muniellos Biological Reserve. Years later, by means of a decree of February (21/1988), Valdebóis Forest and A Valía d'Abraedo (MUP 345) and the La Viliella Forest (MUO 349) were included in the Reserve. In 11994 it became the Muniellos Integral Natural Reserve and in 2000 was designated Biosphere Reserve by UNESCO within Man and Biosphere Programme (MAB).

The main road access from Uvieo to the Biologic Reserve of Muniellos is the N-630 to Curniana, then take the AS-15 via Cangas, up to Ventanueva (near Rañadoiro) by El Couniu to San Antolín d'Ibias. 2 kms from Ventanueva take a right hand road (AS-211) to Mual, starting point of a long trail to Tablizas, where the Admission Centre can be found next to the ranger's hut. 

The access to Valdebóis is from the AS-211 ascending to El Couniu surrounding the Reserve, leaving to the North the Mount of Valdebóis and to the South Mount Muniellos, further to El Couniu , descending 4 miles to Valdebóis.

1. Las Llagunas.

It is the most recommendable itinerary. Starting from the ranger's cabin in Tablizas, after 8 miles, reaches the beautiful glacier lagoons through Fonculubrera, skirting round the La Candanosa valley.  

From this route the best view of the mountains can be enjoyed. The ascent is comfortable. 50 yds from the spring of Fonculubrera, the Old Oak of Fonculubrera can be found, a marvelous specimen with 7 meters diameter and over 30 metres high, (there are many other impressive specimens with over 10 metres diameter throughout the forest).

The return can be by the river (only 5 miles). One kilometre from the crossing of both routes the three lagoons can be found: First La Llaguna la Isla, and later La Llaguna Fonda and La Llaguna Grande. There is a smaller lagoon (La Llaguna la Piña) but during the Summer has little water.

2. The Three Valleys (Las Llagunas).

Longer route, only recommendable to take during the Summer. Starting from Tablizas, after crossing the bridge to the left. This route goes through the three main valleys.

Just after starting, an Old Beech Tree, known as "La Osa" (The Bear) due to its splintered shape resembling the head of a bear.

This route crosses the impressive quartzitic sediments popularly know as " l.leirones". Once by the lagoons, the return can be by the river as in itinerary 1.