Before this landscape started to be changed by human action, the oak groves covered almost the entire North-East of the Iberian Peninsula. Presently natural woods (not planted) are still more abundant in the PNPG. However now they are only a small fraction of what they were in the past.
These woods are mainly constituted by pedunculate oak (Quercus robur) and/or by Pyrenean oak (Quercus pyrenaica) (habitat 9230). Where we now stand, due to its height (above 1000 metres), only the latter kind of oak can be found. The pedunculate oak is predominant in woods occurring up to 700-800 metres high, being gradually substituted by Pyrenean oak above this height.
Some of the flora species that can be seen here are holly trees (Ilex aquifolium), bilberry (Vaccinium myrtillus), ivy (Hedera helix), dogtooth violet (Erythronium dens-canis) and the wood anemone (Anemone trifolia subsp. albida). In this particular case one can also notice the very significant presence of broom (Genista florida), this being because the oak grove does not have a sufficient density of trees to reduce the entrance of light. The broom, as well as other heliolatrous shrubs, is not adapted to conditions of low levels of light.
One can also notice the strong presence of lichen covering the trunks of oak trees, which indicates reduced air pollution. One can also notice the dense covering of moss, resulting from the great humidity of the oak grove.
One can see several animal species, such as the European pine marten (Martes martes), goshawk (Accipiter gentilis), great spotted woodpecker (Dendrocopos major), coal-tit (Parus ater) or the Eurasian jay (Garrulus glandarius).