The Dune of Circeo National Park consists of three main areas, featuring diverse morphology and vegetation.
The water edge is the dune portion immediately facing the sea. Waves break on the beach until a sort of terrace called berm.
The dune front is the portion of dune which waves normally do not reach, but which is however directly exposed to salty wind.
High temperatures, long droughts, scarcely fertile land, and strong winds make it hard for plants to survive, and have forced them to develop specific ways of adapting themselves to this environment.
Mostly halophyte plants grow on the dune front, such as sand couch, sea camomile, sea holly, coastal medick, the wonderful sea daffodil, and marram grass. These colonising plants settle on the dune's most unstable and windswept end. Thanks to their strong, long roots, fastening them to the ground, they mitigate the effect of the Lebeche wind, thus opposing erosion and allowing the Mediterranean scrub to progressively settle.
The dune back is the portion of dune that is protected from sea winds, where a luxuriant Mediterranean scrub grows and is replaced by a sclerophyll forest down by the lakes. The first shrub we find is the large-fruited juniper (Juniperus oxycedrus macrocarpa), whose huge bushes, shaped by the wind, net the sand. Going on towards the inland, we meet mastic, myrtle, Italian buckthorn, Erica multiflora, and climbing shrubs such as old man's beard (Clematis vitalba) and the thorny Smilax aspera, locally known as "breeches ripper". The scrub is largest on the dune slope overlooking the lakes, where evergreen oaks, Phoenicean junipers, honeysuckles and strawberry trees also grow.
In the early morning, countless traces and footprints are visible on the beach of Circeo National Park, revealing the presence of the dune's true inhabitants, that prefer to keep out of the way during daytime, when the dune - especially in the summer - is crowded with people, and come out at night to look for food.
Beside seagulls, the dune is inhabited by ruin lizards and several types of beetles, such as pimelia, dung beetles and tiger beetles.
By the lakes we can find European green toads and, among the reptiles, Hermann's tortoises, green lizards, wall lizards, green whip snakes and the dreaded asps.
Mammals include numerous wild rabbits as well as their enemy, foxes. Badgers and crested porcupines live in the thickest wood areas.
As far as birds are concerned, the dune is particularly important for the breeding of Kentish plovers (Charadrius alexandrinus) and little ringed plovers (Charadrius dubius).