The Aarnescht has multiple biotopes :
- Hornbeam — Oak wood
- Common beech wood
- Thermophile oak wood
- Pine wood
- Black Pine wood
- Thermophile forest edge
- Semi-arid grasslands with erosion cracks
- Molinia wetland
The present biotopes are the result of the specific geological properties as well as the different human interventions. The importance of the semi arid grasslands with their high lime component soil has to be pointed out. They are to be found in the centre and Southside of the Aarnescht and show about the major part of the 23 different orchids of the site (corresponding to 64% of all the present orchids in Luxembourg) and many other rare flora species (for example 2 kinds of gentian or the melampyrum).
Large orchards are covering the south-west part of the Aarnescht and its fruit trees on the lower slopes stand for the charming beauty of the protected site.
On the plateau are extending the hornbeam woods, beech, black pine and pine forestland.
On the west border you can find a common beech wood with a thermophile forest edge just in front of the hornbeam wood. Molinia wetland developed itself over the years especially on the wet grounds in the erosion cracks and trenches.