Within the Forest of Circeo National Park we can find several types of vegetation, according to micro-environmental conditions.
Turkey oaks (Quercus cerris), mixed with Italian oaks (Quercus frainetto) and pedunculate oaks (Quercus robur), characterise vegetation in dry areas. Downy oaks (Quercus pubescens), cork oaks (Quercus suber), and evergreen oaks (Quercus ilex) are instead rarer.
The undergrowth is thick and tangled, and mainly consists of butcher's-broom (Ruscus aculeatus), bracken (Pteridium aquilinum), and wild asparagus (Asparagus acutifolius).
Trees growing around the "Piscine" are pedunculate oaks (Quercus robur), mixed with narrow-leafed ash (Fraxinus oxycarpa), black alder (Alnus glutinosa), and some aspens (Populus tremula). Hygrophilous grasses include common rush (Juncus effusus), purple loosestrife (Lythrum salicaria), water dropworts (Oenanthe aquatica), greater pond sedge (Carex riparia), water mint (Mentha aquatica), yellow flag (Iris pseudacorus), and many more.
As regards fauna, the wild boar is undoubtedly the forest's king, although many more species live there.
Among mammals: badgers, foxes, hares, hedgehogs, hazel dormice and fallow deers (allochthonous).
Among reptiles: Hermann's tortoises, green lizards, four-lined snakes, green whip snakes, Aesculapian snakes and asps.
Amphibians living on drier ground include tree frogs, green toads and common toads.
Water-dwelling reptiles and amphibians live instead by the Piscine: water frogs, agile frogs, grass snakes and pond turtles. In the spring, smooth and crested newts also live in the ponds.
The forest is also home to several species of woodpeckers (lesser and greater spotted woodpecker, green woodpecker and Eurasian wryneck), birds of prey both diurnal (black kites, honey buzzards, hobbies) and nocturnal (little owls, tawny owls), Columbidae and passerines such as tits, wrens, treecreepers and chaffinches.