The future bison release in freedom in the VNNP’s area, estimated for 2011, represented the reason and the main object for this scientifical research. It is well-known that the damages produced by free European bison to forest ecosystems, especially for the forest tree species, represent one of the main ‘threats’ for the reintroduction program. For this research, in two consecutive years (2009 - 2010), we performed a complete assessment of the damaged trees for a surface of 45 ha inside the acclimatisation enclosure.