Introduction of exotic tree species in french elimination arboreta: lessons of the past and identification of valuable forest reproductive materials for the future.
Résumé
Their initial goal was to identify species, able to resist to pollution or to be an alternative to species endangered by pathogen problems. These arbore-ta are located in three different climates: oceanic, mountainous and Medi-terranean. Numerous species are present at least in two different arboreta enabling comparison of their behavior under contrasted climates. In this project, we have measured survival and diameter on 254 taxa (17835 individ-uals). Moreover, total height of the three biggest trees per plots has also been measured. Thus, we can compare oldest results obtained in these arboreta in terms of growth and survival with those after several climatic accidents (drought, heat). We also have recorded the temperature and precipitations in order to identify years which are the most different from the average. We lastly began a study of chronodendrometry in view to determine the reac-tions (in terms of radial growth) of different species under climate stresses. The ultimate goal of the project is to identify species offering the best com-promise between overall growth and growth to stress during extreme years. These studies have showed that species which were the best thirty years ago are not the best nowadays. For example, in 1989, in the Mediterranean arboreta, the best choice for broadleaves was, species of genus Fraxinus, Alnus or Arbutus. Presently, the best species belong to the genus Eucalyptus spp. in spite of 1985’s intensive frost. Arboreta also provide information on the invasive character of non-native species such as Hakea spp. Moreover, native species are not always better adapted in terms of growth and climate adapta-tion. It is for example the case in the arboreta under oceanic climate for Pinus sylvestris L., worse than Sequoia sempervirens (D. Don) Endl. or Abies grandis (Douglas ex D. Don) Lindl.. We have also shown that arboreta could be very interesting places to educate forest managers on the interest of new species under climatic changes. Indeed, in managed forest the number of species is low, and generally forest manager badly know or ignore non-native spe-cies’ autecology. Arboreta are suitable places where they could increase their knowledge and thus discover the potentiality for forest purposes of more than hundred species in real forest conditions like Alnus rubra or Nothofagus or still Chamaecyparis and Thuya spp.