sentences:  In altitude, it extends from 700 to 1700 meters, but its main areas are localized in more humid and dark valleys; these forests are dark, with acidic soil, due to the decomposition of the needles of evergreens.At higher altitudes, they are often replaced by black pine ("Pinus uncinata").These fir forests sometimes contain maples ("Acer pseudoplatanus") and their undergrowth is very similar to that of the beech forest.