Plant life in Tyresta’s evergreen forest has characteristically limited species diversity. But the variety of mosses, lichens and fungi is great.
Of the 800-plus species of mosses and lichens that cover the ground and trees, perhaps the most prominent are the beard lichen and other lichens that hang from the tree branches. They benefit from the clear air and the slow growth of the trees.
On the ground can be seen beautiful shades of green, shifting between reindeer lichen, knight's plume moss and haircap moss.
On the wetlands grow several species of sphagnum moss in various shades of green, brown and red. Thanks to the area’s many wetlands, including bogs and marshes, sweet-smelling plants such as bog myrtle and marsh Labrador tea grow here, and during the summer months their sweet scents spread through the forest. Also blooming then are the forest’s orchids, including the heath spotted orchid. Species that thrive in ancient forests grow here as well, including creeping lady's-tresses, lesser twayblade and northern ground cedar.
In addition to edible mushrooms such as the chanterelle, penny bun and other Boletales fungi, the long unbroken history of dead wood has made it possible for polypore fungi such as Phlebia centrifuga, Fomitopsis rosea and Phellinus ferrugineofuscus to thrive on tree stumps and fallen rotting logs. On pine trees over 150 years old, the fungus Phellinus pini is often seen extending its brown-coloured slab, and the older spruces are often covered with red-banded bracket fungus, appearing like beautiful orange-brown hooves on the trunk.
Ancient forest and biological diversity
In Tyresta the forest has retained its ancient character. Here, there are trees of varying age and species — primarily spruce and pine, with elements of broad-leaved trees such as aspen and alder.
First and foremost, the forest is characterised by a steady large supply of dead wood. Many of the forest’s threatened species of fungi, mosses, lichens and insects are linked to dead wood in various stages of decay. Death is clearly linked to life in the Tyresta forest. In a logged forest, dead wood does not accumulate since trees are harvested before they become old and die.
Here and there old trees have fallen, leaving a light opening in the tree cover where new life can thrive. On rocky ground fire may have raged and left nature to start over, with broad-leaved trees dominating for up to 100 years before evergreen forest takes over again. This can be seen most clearly in the area of the 1999 forest fire, which covers 20% of the national park’s area.
There is great biological diversity in Tyresta National Park, due to the fact that the forest has been allowed to be forest for very long time — since 10,000 years ago, when the ice sheet retreated and the trees made their entrance.