In the ravines of the Oder Valley's slopes there are humid forests, dominated by ash trees (Fraxinus exelsior). This humid ash forest is particularly remarkable, since it is relatively rare in Germany.
Beautiful wooded slopes can be found in the Hölzchen woods near Lunow, in the Gellmersdorf Forest, in the southern part of the Peter Mountains and in the North between Gartz and Mescherin.
Beech naturally dominates these wooded slopes, as can be seen today in the Gellmersdorf Forest. On superficially silted soils there are luzula-beech-forests which regularly feature acidity indicators such as wavy hair grass (Deschampsia flexuosa), spinulose wood fern (Dryopteris carthusiana), or pill sedge (Carex pilulifera). On soils rich in lime, for instance on boulder clay, sometimes a sedge-beech-forest, marked by mountain sedge (Carex montana) and a number of orchids (such as Cephalanthera damasonium), can be found.
However, most common in the Lower Oder Valley are woodruff- (Galium odoratum) and wood-barley- (Hordelymus europaeus) beech-forests. Species on the ground layer of such forests are the yellow archangel (Lamium galeobdolon), spiked rampion (Phyteuma spicatum), woodruff (Galium odoratum), wood melick (Melica uniflora), baneberry (Actaea spicata), liverleaf (Hepatica nobilis), or, more rarely, turk's cap lily (Lilium martagon).
Many of these locations are now populated by hornbeams (Carpinus), sessile oak (Quercus petraea), English oak (Quercus robur), or small leafed linden (Tilia cordata) and also have a pristine appearance. Such hornbeam forest communities are, however, most likely an anthropogenic, artificial product, that is a result of continued coppicing by the forest industry. According to the latest findings the oak-hornbeam-forests of the Oder Valley's slopes and hills are man made. The location factors correspond to those of beech forests. However, where the vigorous and shade-tolerant beech can prevail, it suppresses inferior species of trees. In some typical hornbeam-forests, for instance in the Lunow Hölzchen woods, young beech-forests are beginning to come up, initiating the natural development. Until now, experts had been convinced that the beech could not prosper in most of these locations, and that instead they would be left to oak and hornbeam.
A particular rarity within the National Park's forest ecosystem are the elm forests on the steepest of slopes of the Oder Valley. All three species of elm can be found there: the fluttering elm (Ulmus laevis), the field elm (Ulmus minor), and the Scots elm (Ulmus glabra). On the ground level the rich flora features such species as Corydalis pumila and Myosotis sparsiflora.