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.
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.
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.