The Conservation Status of Fraxinus Species
The Red List of Fraxinus (January 2018) reveals 79% of ash species are not threatened with extinction in the wild.
Fraxinus ornus (Least Concern). Photo Credit - Ian Harvey-Brown
Ash species make up significant parts of temperate forests and woodlands where they perform important ecosystem functions, creating habitats with many other hardwood species and providing fodder for native wildlife. They are also common street trees and found in many botanic gardens across the northern hemisphere.
A total of 53 species of Fraxinus were assessed for The Red List of Fraxinus, which includes all of the world’s ash species. Encouragingly, only 21% of the group are considered to be threatened with extinction, which is much lower than other botanical groups that have been assessed such as the magnolias (48% threatened).
However, with 11 species threatened with extinction, there is still work to be done and it is necessary to conserve these species due to the scale of the global threats facing them. These threats are a great risk to even the largest populations of these valuables trees.
This is no better highlighted than in North America where an invasive pest, the emerald ash borer, originally from Asia, has devastated previously abundant and dominant ash tree populations.The population decline in eastern North American ash is so great that one species is Endangered and five species Critically Endangered on the IUCN Red List.
Fraxinus americana (Critically Endangered). Photo Credit - The Morton Arboretum
The report identified pests and diseases as the greatest threat to Fraxinus species. The five remaining threatened species of Fraxinus are at risk due to small and fragmented geographic ranges, where they are also exposed to risk from human-led habitat conversion or logging for timber.
Eighty-fiver percent of Fraxinus species occur in ex situ collections (botanic gardens and arboreta) worldwide, with only one threatened species not yet covered by this extinction safeguard. In fact, the majority of threatened Fraxinus occur in a large number of ex situ collections.
The report highlights the important work of The International Plant Sentinel Network, The UK Forestry Commission and The Morton Arboretum who are using ash ex situ collections to fight back against problematic pests and diseases. The occurrence and use of Fraxinus in botanic gardens offers a unique opportunity to study resistance to pathogens such the emerald ash borer.