A green cloak in spring, which burst into colour in autumn
The Park's woods are concentrated in the mountain belt and can be schematically subdivided into:
Valley bottom woods
Woods of noble broadleaf trees
These are well represented in the Pesio Valley, the most widespread are chestnut woods, the mixed woods of broad-leaved trees and oak trees, which, as a whole, are the crown of the Charterhouse of Pesio. The chestnut groves of the Park are part of the Italian area that has the largest chestnut woods in Europe. Within the protected area the pure chestnut groves are very small and the other woods are recovering the lost ecological spaces. This is due, above all, to the progressive abandonment of the mountain and some chestnut tree diseases spread throughout Europe such as bark cancer and ink disease. The most suggestive chestnut tree and, perhaps, also the oldest in the Park is located at the Cascina San Michele and is in the typical shape of the old specimens, with a strongly hollowed trunk. The plant undoubtedly faster in resettlement is the birch, Betula pendula, heliophilous tree (lover of light) easily recognizable by the white bark.
The querceti of the Park survive on the warmer slopes of small rocky areas with little fertile soil which, for these reasons, have not been converted over time into chestnut groves; the most significant examples can be found near Madonna d'Ardua, the "Bagni" of Vallone Cavallo, Testa and Serra del Pari. If men had not introduced chestnut trees, the oak groves at Quercus petraea, the oak, would have been much more widespread on acidified soils, which are, for the most part, those that surround the Charterhouse.
They are rather fragmented thickets, but with lush vegetation, which in Valle Pesio, thanks to the particular climatic conditions, are very luxuriant: in a few square meters you can count over 50 different species of grasses, shrubs and trees. These are the mixed deciduous woods also called gorge woods, because they are located in the shady and cooler areas surrounding the Pesio river and its tributaries. The trees that make up these woods (maples, elms, limes, wild cherry trees, ash trees), are always found mixed, never in purity, and in the forest are defined "of noble broadleaf trees". This term has been attributed to underline their uncommon presence, the demand for a soil with good fertility, and the quality of the wood.
Other trees we find in these woods, with less valuable or smaller timber, but always of great ecological importance, are the Acer campestre, the Carpinus betulus, with a calorific value even higher than beech, the willow, Salix caprea, the Alnus glutinosa, and towards the bottom of the valley, other willows: Salix alba and eleagnos, with the less common Salix aurita and daphnoides; besides poplars, Populus nigra, tremula and the rare canescens, with characters intermediate between the last two.
The beech is the most important broadleaf tree in the Park, at least in terms of quantity. In Piedmont the beech is the most widespread tree species after the chestnut tree, but only in the south-western Alps beech forests are represented in purity. They provide a wood of excellent calorific quality.
In the Park beech forests occupy about 600 hectares, twice as much if you also count the surface area of the wooded formations where beech trees are not predominant (abetine, mixed forests, etc.). The location of the beech woods is above 900 metres but, in reality, it is artificial. Especially in Valle Pesio, the cultivation of the chestnut tree has not in fact allowed beech woods to flank the oak woods at lower altitudes. The beech woods in the Park are almost all coppice, with the exception of a few hectares of woodland, which are difficult to access, so cultivation has been abandoned because it is uneconomic. The coppice has ancient origins: already Carthusian monks and valley dwellers used these woods not only for domestic use but also to supply kilns, potteries and steam hammers.
In the Park there are no monumental beeches. Close to Villaggio Ardua, near Pian Gambin, an almost centenarian specimen of considerable girth survives stoically, despite the cowardly engravings of rude tourists.
As the altitude increases, conifers can be found: in the Pesio Valley the silver fir (Abies alba) dominates, in the Carnino Valley the stone pine and in the Upega Valley the larch. The abetine of Prel and Buscaiè and the lariceta of Bosco delle Navette are among the first Italian woods to be registered in the National Book of Seed Woods.
The white spruce, Abies alba, is a large tree with a crown of "combed" needles. When the tree is over a century old, the top of the tree forms a so-called 'stork's nest' due to the stunted growth of the apex. This aspect, in the silver firs of the Pesio Valley, is scarcely present because, until the Park was established, deforestation led to an excessive cutting of trees, including almost all the oldest firs. Fortunately, this has not compromised the structure of these marvellous fir woods, which are among the most interesting in the entire Alpine arc. The exuberant luxuriance of the fir forests is due to two essential factors. The first is ecological: while the pedoclimatic conditions in the Pesio Valley are excellent for beech trees, they are exceptional for silver fir. Suffice it to say that the speed of growth in height and diameter of these fir woods is unequalled in Piedmont. The second factor is... religious; the presence of the Carthusians, with their particular monastic philosophy, has brought notable innovations in the organisation and techniques of agriculture and silviculture, and has ensured that the silver fir has been preserved and increased. The Park's fir forests cover more than 700 hectares.
In the Park, the spruce, Picea abies, is present in an almost relict form, mixed with the dominant silver fir; one of the few, very small, pure stands can be seen near the Pis del Pesio. This valley is thus the southern limit of the alpine range of this species. The Pesio Valley is also home to the Swiss pine, Pinus cembra. Although there are no Swiss pine groves; some groups of trees can be found on the peaks of Sestrera and Biecai. This latter locality was once called Piecal, which in the ancient Occitan language means 'rocky area surrounded by pine forests'. This would suggest that there was a deliberate reduction, not so long ago, in the presence of pine trees, in favour of pastures.
The pine forest of Larzelle di Carnino, in the upper Tanaro Valley, is a rare example in Piedmont of a forest of dwarf mountain pine, Pinus mugo subsp. uncinata, in the arboreal form. In the Park, the dwarf mountain pine is more widespread in the shrub form, now almost invasive in the subalpine pastures, not to be confused, however, with the rare mountain pine, Pinus mugo subsp. mugo, a shrub of considerable phytogeographic value, which takes refuge in the Conca delle Carsene and Colla Carbone.
The larch forest of the Bosco delle Navette extends over 2770 hectares above the village of Upega, in the upper Tanaro Valley and is one of the most valuable, beautiful and extensive larch forests in the Western Alps. The name derives from the fact that in ancient times the wood from it was used for building boats and ships on the nearby Ligurian coast. Since 2016, the Bosco delle Navette has been under the protection of the Park.