The old oaks and crops of common hazel create the characteristic atmosphere of Tammisto. Most of the oaks grow in the southern and western parts of the area, whereas the forest in the northern and eastern parts is dominated by spruces. Higher up the hill, the grove gradually becomes a boreal forest where visitors can spot old pine trees with a thick layer of bark. The forest floor's vegetation is dominated by bilberry. The tops of the rocky hills are exposed to the elements. They are treeless fi…eld areas covered by plants such as sticky catchfly, sweet vernal grass, orpine and wild pansies.
The groves growing on the hillsides feature multi-layered and lush vegetation. Sunlight enters the bottom layer only occasionally, and the shadowy forest remains pleasantly cool also during heatwaves. The large leaves of the common hazel bushes catch the light in the middle layer, and bottom layer plants only get plenty of sunlight during spring and early summer. Due to this, the bottom layer mostly has plants that bloom early, such as liverworts and lily-of-the-valleys, and other vegetation typical to groves, such as different species of ferns. The berries of mountain currants and fly honeysuckles turn bright red in late summer.
More than 30 species of birds nest in the oak forest, including hawfinches, European goldfinches, common linnets, song thrushes, common blackbirds, stock doves, icterine warblers and Eurasian blackcaps, which are very common in the area. Long-eared owls and tawny owls have also sometimes nested in the area. In winter, visitors can sometimes spot migrating white-backed woodpeckers, Eurasian three-toed woodpeckers and Eurasian nuthatches among the oak trees. The decaying trees in the area feed both insects and the lesser spotted woodpecker and black woodpeckers eating the insects. Northern goshawk can also sometimes be spotted in the forest. Visitors should remember to also keep an eye out for merveille du jour, a moth that only feeds on leaves and flowers of oak, and purple hairstreak, a butterfly feeding on oak with beautiful bluish wings.