The well-known botanist Josias Braun-Blanquet is considered as the founder of plant sociology, wherein the relationships amongst plants and towards their environment are studied. He was able to gather much of his knowledge in this field in the National Park.
Braun-Blanquet recognised that vegetation develops slowly according to certain rules. In 1917 he assumed that the absence of human intervention would lead to the spread of forestation in the National Park; to investigate this he defined several long-term test areas in the Park, which he visited regularly. Further areas were later added by other researchers and continue to be the object of long-term studies.
Since reforestation was only minimal, fences were erected around small areas. These enclosed areas provide the possibility to compare vegetation development with and without ungulate grazing. Over the last years no clear increase in forest rejuvenation has been observed.