The altimetric differences, which from 2005 m of Monte Papa degrade up to 300 m of the base of the Murgia of S. Oronzo and ecological heterogeneity, have shaped over the centuries an extraordinarily rich nature of plant biodiversity. The areas with the highest naturalistic value, fall mainly in the phytoclimatic mountain range which is approximately from 1,000 to 1,800 m. s.l.m: the area pertaining to the Beech (Fagus sylvatica).
The beech-woods of the Maruggio Mountains, Arioso and Pierfaone, are ascribable to the type Aceri Lobelii-Fagetum thanks to the presence of majestic beech trees in association with noble broad-leaved trees such as the Maple of Lobel (Acer lobelii), the Acer Opalus, the Country Maple (Acer campestris), the Carpinella (Carpinus orientalis). In the northern area of the park, there is a powerful forest complex that extends over the slopes of Monte Serranetta and includes the Bosco di Rifreddo, where the splendid beech forests as the altitude falls are enriched by different species, in particular the Turkey oak (Quercus cerris).
In support are found many species typical of heliophilous woods such as eastern hornbeam (Carpinus orientalis), black hornbeam (Ostrya carpinifolia), hazel (Corilus avellana), maple of Hungary (Acer obtusatum), Acer lobelii, Pyrus spp. Among the herbaceous plants there are Veronica officinalis, Anemone apennina, Scilla bifolia, Atropa belladonna, Allium ursinum formante, in the freshest and most fertile valleys, extensive vegetable coulters together with Sambucus nigra and Galantus nivalis.
In the rupicolous areas of Serra di Monteforte there is the Lucanian yarrow (Achillea lucana). In the south-east direction rises the mountainous cordon formed by the Serra Mountains of Calvello, Monte Volturino, Monte Madonna di Viggiano, Monte S. Enoc, M. Caldarosa which host the most imposing forest of the Region. Numerous endemisms give value to the flora of the grasslands of altitude: we remember Hippocrepis glauca exclusive of the Volturino, Schlerantus perennis, Geranium cinereum, Veronica austriaca. A site already designated as a SIC area is the Abetina di Laurenzana, a high forest with subjects as high as 40 m, predominantly of silver fir (Abies alba). The typical association Spruce-Beech leaves the phytosociological patterns of the Apennine areas of central-northern Italy as it represents a more thermophilic and heliophilous variant with the presence of species such as holly, hawthorn, dog rose and, among the herbaceous ones, the Seal of Solomon, the Myosotis, the cyclamen, the odorous little star.
To the west, south-west, on the border with Campania, we find a spectacular example of thermophilic beech-wood: the Faggeto di Moliterno framed by the association Aquifolio - Fagetum. The herbaceous cover is of great value and includes in addition to the species mentioned above: Lathirus venetus, Euphorbia amygdaloides, Lilium bulbiferum and, in the Sterraturo prairies, numerous orchids such as, among others, Orchis simia, Ophiris apifera, Ophiris lucana, Ophiris sphegodes. Lake Laudemio is framed by the limestone massif of Mount Sirino - Pope extensive beech forests combining with the Neapolitan alders (Alnus cordata) of the lake shores. The area includes rare floristic endemisms such as Vicia sirinica and Astragalus sirinicus.
In the hills up to 500 m dominates the Mediterranean vegetation that encloses the horizon of the heliophilous broadleaf trees, dominated by the Leccio. In relation to altitude and exposure, the Lecceta gives way to mixed stands of Turkey oak and downy oak, often accompanied by other deciduous species such as Quercus fraineto, Acer obtusatum, Fraxinus ornus, Alnus cordata, Ostrya carpinifolia and Castanea sativa, the ciavardello (Sorbus torminalis) and rowan of the birdies (Sorbus aucuparia).
Among the common shrubs is Butcher's Broom, wild asparagus, hawthorn, privet, cotognastro, and cornel. Where the morphology softens, the holm oak rises forming small woods rich in junipers; widespread nuclei of lentisks (Pistacia lentiscus), terebinths (Pistacia terebinthus) and filliree (Phyllirea latifoglia) enrich the picture of the Mediterranean flora which, in the most arid areas, gives way to cysts (Cistus salvifolia and C. monspeliensis) and to the scented broom (Spartium jungeum). Interesting is the cerreta of the regional state forest Fieghi-Cerreto located in Piano dei Campi at the foot of Monte Raparo. Lago del Pertusillo is surrounded by thermophilic Roverella woods, rich in mushrooms and truffles. Oaks, holm oaks, lentisk cores, junipers, phillyrea, up to the cysts and the broom, enrich the edges of the valley forming a dense green carpet. Below, the Agri river flows in its twisted bed, the waters of which bathe the woods of poplars, willows and viburnum that in spring offer a spectacular white bloom.