While down in the valley the diversity of nature already significantly changed from early in the Neolithic (first agriculture), the rocks make for a safe haven as here nature remains untouched for a long time. Eventually in the 20th century also the rock ecology is disturbed and pushed back to a minimum as the rock is 'cleaned' for climbing.
The impact of climbing is summarized as follows:
The opening of these routes and their maintenance led to the destruction of the vegetation that was deemed annoying. Moreover, earth (that over centuries had slowly formed) was extracted from ledges, cracks and other cavities. The repeated passage of climbers on the limestone walls planes the vegetation and disturbs the birds which nest in the cavities. Finally, the trampling of the top of the rocks leads to destruction of specific vegetation making banal and ruderal species overtake the places." (usually nettles and thorny blackberries)
Paradoxically, the fauna of the Freyr rocks has been little studied so far and the available data are sparse. Only a few species of vertebrates and insects are cited by BUNGART and SAINTENOY-SIMON (2008).
On obsirocbel.com Guy Bungard approaches the impact of climbing carefully, gathering numerous studies:
(Ecological) importance of the cliffs (English translation from French)
The reality is complex. The government lists a series of measures taken by the Club Alpin Belge. Elephant paths need to be discouraged, thorns and ivy pulled (recently done on Fromage) and bird nests need to be signaled. Guy's personal account of the authorities' and exploiter's protection is sceptical:
Whilst in some countries appropriate signage seems to offer sufficient protection, we must note that this is not the case in our country, where since 1997, as active observers, we conduct an Information Policy towards the authorities without any significant results. In fact every year we observe that protected species are deliberately uprooted or trampled. - Guy Bungart 6 December 2015
From my own perspective I have been quite disappointed from the few times I reported a nest on Jeunesse. Only seldom an indication is made with a lint, hardly bothering the series of student clubs that booked Freyr. It is also said abseiling and the use of the top rope should be regulated (and if not for ecological reasons then at least for safety), but it remains a common practice of groups, even of the military government. It is time to communicate with the military, time to demand visible contributions from said student clubs, like cleaning the trash and clearly educating their groups.