Thy National Park is Denmark's largest wilderness area. Here waves from the North Sea wash up on the beaches, and the wind blows the sand up in the high dunes. Behind the dunes is a landscape with dune heaths and crystal clear lakes. Further inland are the large, coherent forest areas which can be dark and impassable.

This is a relatively deserted area, and it creates the framework for some of the most unique habitat types in Denmark, some of which are also rare in an international context.

The dunes

Thy National Park comprises a large part of Denmark's total dune area. The dune landscape is dynamic and can hold great variation, even within small distances. The dune vegetation is influenced by physical conditions, such as the drifting of sand, lime content, nutrients, dune slope orientation and distance to the groundwater table.

Different types of dunes are represented in Thy National Park. The national park includes sea shores with incipient dune formation and the white dunes characterised by continued sand drift, as well as the more stable dune shapes such as the calcareous and vigorous green dune and the grey dune with its permanent cover of lichen and dwarf shrubs.

The dune heath

The dune heath is characterised by coherent vegetation of dwarf shrubs. The dune heath is a mosaic of plains and massive dune formations dominated by crowberry and heather as well as sand plains with temporary lakes and wet sand hollows where bell heather, bog myrtle and bog bilberry dominate the landscape. Sand hollows also create a living space for some of the more rare species such as marsh gentian and alcon blue.

The largest dune heaths in the national park are Hanstholm Nature Reserve, Vangså Klithede and Ålvand Klithede as well as the dune heaths between Stenbjerg and Lodbjerg. These dune heaths hold large populations of red deer, otter and adder, and they are breeding grounds for many rare birds such as cranes and wood sandpipers.

Lakes in the national park

There are more than 200 large and small lakes in Thy National Park. Many of them are among the cleanest lakes in Denmark and are habitats for many rare plants. Many of the dune lakes are lobelia lakes. These are nutrient-poor, clear-water lakes with sandy bottoms. The characteristic lobelia dortmanna plant, and often other underwater plants such as quillwort, plantain shoreweed and pillwort, grow here.

Thy National Park also has the large karst lakes Vandet Lake and Nors Lake. These are the only places in Denmark where the slender naiad grows.

In the southern part of the national park are Ørum Lake and the brackish Flade Lake. Both lakes used to be part of Krik Vig inlet. They are very shallow and relatively rich in nutrients.

Limestone slopes

The elevated layer of chalk in the subsurface is visible in many places in the old sea cliffs from the Stone Age. They have a distinctive flora, very different from the dune heaths and plantations.

The plant species growing here include hoary whitlowgrass, gentian species, spathulate fleawort and not least Euphrasia dunensis, which only grows in northern Jutland.

Dune plantations

The first attempts to plant trees in west Thy were in 1816-20. The attempts were unsuccessful, but by the middle of the century the planters had discovered methods and foreign tree species such as mountain pine that could grow in the sandy, salty and windy climate.

Since then many other species of conifer from distant regions have been planted between the mountain pines. One of the objectives of the national park is now to create more species-rich forests with indigenous, deciduous trees and a more natural water level.

Nature preservation

The nature in Danish dune heaths is vulnerable. The largest threats are overgrowing by invasive species of conifers and dog rose in particular. Previous drainage and high nitrogen levels in the air have a negative impact on the dune heath.

In order to bolster the original heath vegetation, some parts of the heath are being grazed. Occasionally the vegetation is cleared or burned. Grazing is usually carried out with livestock, but a growing population of red deer also help ensure survival of the dune heaths in Thy National Park.

The natural water level in the open dune landscapes will be restored by gradual removal of drainage and ditches. The objective is for more close-to-nature forestry which, in the long term, will ensure stable, species-rich and recreationally valuable forests.