Owned by the Duke D'Alessandro of Pescolanciano and extending over about 500 hectares, the wood of Collemeluccio was brought as a dowry to him by the noblewoman Desiderata Mellucci, from whom the name seems to derive and who purchased it in 1628 from the University of Pietrabbondante. It remained the property of the D'Alessandro family until 1895, when the Banco di Napoli sold it to local families.

Today the Nature Reserve of Collemelluccio is a protected natural area in the Molise region, in the province of Isernia. It falls entirely within the municipal territory of Pescolanciano and covers an area of 347 hectares. It was established in 1971 and is a UNESCO Biosphere Reserve, awarded of the international qualification by UNESCO for conservation and protection of the environment, within the program on Man and Biosphere - MAB.

The forest is characterized for more than 80% by silver fir, present in Collemeluccio with spontaneous formations as a relict of the ancient abetine that in millennia covered the Apennine ridge and that today, in addition to Molise, are found with small nuclei in Abruzzo, Tuscany and Calabria. In this particular reality, in fact, past management, based on a moderation of cuts and their distribution over the entire surface of the forest, have led to an excellent preservation of the silver fir.

The other dominant species is the turkey oak (Quercus cerris), which characterizes the areas on the edge. Beech is associated with fir in cooler exposures. To these are added the hornbeam, the field maple, the field elm, the ciavardello and the greater ash.

In the lush undergrowth grow hawthorn, holly, blackthorn and hazelnut.

In the clearings and along the edges are frequent apple trees, wild pear trees, rowan trees and among the bushes the dog rose and the wild plum tree.