The Kostrzyca Forest Gene Bank application concerns actions for the ex situ conservation of common ash, wych elm, field elm and European white elm in Poland which were done within the framework of a wider project on preserving the biological diversity of habitats in Natura 2000 areas (FraxUmLBG). The actions focused on the active protection of riparian habitats (mainly) by preserving the genetic variability of their important woody components, which act as “ecosystem scaffolding”. The mentioned species have become quite rare in forests across Europe, due to the fragmentation and progressive degradation of their respective habitats and because of fungal diseases which are decimating these species. The habitats of our special concern were: 91E0 - Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae), 9170 - Galio-Carpinetum oak-hornbeam forests and 91F0 - Riparian mixed forests of Quercus robur, Ulmus laevis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia, along the great rivers (Ulmenion minoris). 71 Natura 2000 sites (in which at least one of the three habitat types mentioned above was present) were monitored all over Poland. 46 were selected for collection of seeds and ash winter buds (overall no. of batches was 121). In the Kostrzyca FGB the plant material was cleaned, dried and tested for its quality and viability. Afterwards these batches (i.e. genetic resources) were put into our cryogenic bank. When the time comes they can be used to strengthen or restore endangered habitat populations, but until then they are securely stored in liquid nitrogen vapours which can last for hundreds of years. For the main Natura 2000 site targeted by the application (PLH280005 Puszcza Romincka) 38 genetic resources were created.