Almost one-third of Søhøjlandet is covered by forest. Deciduous forest grows in terrains that was difficult to cultivate. Coniferous forest grows in sandy areas and former moorland. In the western part of the area there is a moor where junipers grow, amongst others.
There are several springs full of ochre in the steep slopes leading down towards the melt-water valley of Julsø. This is owing to the soil of these hills being full of sand, clay and lignite. The 20-million-year-old layers contain pyrite which causes the springs to become full of ochre. The combination of the green moss, the fiery-red ochre and the clear water makes a beautiful colour scheme.
The soil is very diverse with washed-out sand in valleys and on slopes, while the soil is loamier in the hinterland. It provides good conditions for the beech and spruce in Sønderskov and for oak around Himmelbjerget, which is also characterised by heather. The woods around Slåensø are forested by selective felling of trees. The forest first and foremost renews itself by seeds from old trees sowing themselves. The objective of selective felling is to achieve as naturally varied a forest as possible – i.e. a forest with trees of all ages, species and sizes. At the same time, the ambition is to produce quality trees. Today, silver fir has grown up between the beech trees and the anticipation is that beech trees will sprout under the silver firs in a couple of hundred years.
In Sønderskov you may spot roe deer, red deer and fallow deer. The forest is also rich in birds and the common varieties of woodpecker – black woodpecker, green woodpecker and spotted woodpecker - may be seen here. Common buzzards, European honey buzzards and ravens may often be seen and heard over the meadows. Common buzzards may be observed above the more open areas around Høgdal and around Skovfogedstedet (the dwelling of the Forest Supervisor) in Sønderskov. Kingfishers and grey wagtails breed at Slåensø (in which perches, roaches, burbots and pikes are abundant), and during the winter you may see dippers at Millingbæk and at several of the brooks that run through the hills from the highlands and into the valleys.
Slåensø is one of the prime spots in Denmark for experiencing grass snakes. For most of the summer, they snooze in the sun on the north-western side of the lake and are not bothered by people. At Himmelbjerget, there are also adders. However, the most spectacular inhabitant of the area is probably Denmark's largest spider – Dolomedes (or raft spider). The female is larger than the male and may be up to 2.5 cm long and has a stride of 5-6 cm. This brown spider with yellow stripes is usually found at the edges of puddles and ponds.
The snakes and spiders may sound formidable; however, the most dangerous potential encounters during a visit to the forest are still those with the wood tick and the wasp.