The northern slopes of Monte Somma, wetter and cooler than Vesuvius, are covered by large chestnut groves at altitudes between 250 and 900-950 meters. The high spread of the species is certainly due to the intervention of man who has preferred the chestnut tree to other species for its usefulness. Often, however, the chestnut groves no longer used are affected by processes of recolonization by other indigenous tree entities, and especially by phenomena of invasion by Robinia (Robinia pseudoacacia) a fabacea introduced for the first time in Europe in 1601, and used on Vesuvius for its high capacity to emit root suckers and thus stabilize the slopes; pioneer species and highly invasive, Robinia has colonized large areas competing with native species and forming in some cases almost monospecific formations.
The mixed deciduous woods, rich in undergrowth, are present throughout the Vesuvian area, especially on the northern side, also with very extensive formations, and consist, in addition to the chestnut (Castanea sativa), also of downy oak (Quercus pubescens), black hornbeam (Ostrya carpinifolia), manna ash (Fraxinus ornus), Neapolitan alder (Alnus cordata), various species of maple (Acer spp.), and made even more interesting by the presence of some scattered nuclei of birch (Betula pendula).
Among the deciduous oaks, the downy oak (Quercus pubescens) is one of the most common forest species in this area as it is part of the composition of many mixed forest coenosis. Relatively not very demanding in relation to the characteristics of the soil, this entity forms consortia even on rather superficial substrates and little evolved.
