Noyer aile du Caucase

The main threats to Pterocarya fraxinifolia include the destruction of its habitat, as well as logging and cutting by local people. Riparian forests in low altitude have already been severely cut in the past or converted into grassland or monospecific forests stands. In Iran, during the second half of the twentieth century, it is estimated that about 50% of the Hyrcanian forest area has disappeared. The most severe damages impact the plain and lower elevation forests, which represent the most suitable habitat for P. fraxinifolia and more generally riparian communities. The same analysis can be made in Georgia where 90% of the original lowland forests have been completely destroyed in the last century (Kozlowski and Gratzfeld 2013). Even in protected areas, logging and cutting by local people still represent a problem. In Iran, it is forbidden since 2017 for local people to cut trees in the forests located in Northern Iran, but the trees located in riparian environment and corridors along rivers are still impacted and sometimes destroyed because of their proximity with agricultural lands, especially for the culture of rice. The future of the species is also tributary of the possible transformation of low-altitude watercourses and river banks for hydroelectric power stations. Even if the distribution of the species seems important, the fragmentation and vulnerability of the different subpopulations is very high. Future changes toward drier climates might further endanger the species (Maharramova et al. 2017). Low genetic diversity may restrict the adaptation of the species to a changing environment.

Field surveys are needed to review old indications and the implementation of a long term monitoring for the species and the quality of its habitat is required. A global management plan and a strict conservation policy of the riparian environment should be developed in the different countries where the species grows. The species is currently under protection in national parks and state reserves in Azerbaijan, Georgia and Iran. However, populations from Iran which possess a larger diversity of plastid haplotypes and private alleles were sampled outside the protected areas. To counter possible losses of genetic diversity due to global warming or other human impacts, we propose that Hyrcanian populations of Pterocarya fraxinifolia deserve both ex situ and in situ conservation, as they contain higher amounts of genetic diversity than other populations of the genus (Maharramova et al. 2017). The main seed dispersal vector among P. fraxinifolia populations is rivers, thus it would be important to collect specimens for ex situ culture at watershed level (Yousefzadeh et al. 2019). Globally, the species is well represented in botanic gardens and recorded in 112 collections from across the globe (BGCI 2019). However, special attention should be put to ensure better conservation of the genetic diversity of the species in ex situ collections.