It is one of the most important atlantic forests in the Galicia Autonomous Community and a clear example of a "fraga", a humid space covered by plants. At Pontedeume, where is the most interesting area of the Park, next to the ruins of the Monastery of Caaveiro, can be found the most characteristic plant species.

There is an enormous variety of microclimates in the area. The phenomena of thermical inversion in the depth of the valleys, the different orientation of the hillsides and the abruptness of the fluvial canyons bring about the proliferation of varied climatic conditions.

The vegetation at As Fragas do Eume depends on the proximity to the river. The most humid areas, by the rivers and brooks, are home to Tertiary relict ferns, such as the Woodwardia radicans, Culcita macrocarpa, Hymenophyllum tunbrigense and the Vandenboschia speciosa. The park is also covered by oaks, ash trees, chestnuts, birches, willows, maples, hazel trees, laurels and strawberry trees.

The most significant animal species in the area include invertebrates that can only be found in Galicia and Europe, such as the Elona quimperiana, Geomalacus maculosus, Margaritifera margaritifera, Coenagrion mercuriale, Euphydryas aurinea and the Lucanus cervus.