The status of arboreta in South Africa and the taxa they contain

Collections of living trees (hereafter arboreta) are important for conservation, research on species selection for forestry, and as sentinel sites for monitoring pests and diseases. Arboreta can also be the source of propagules for biological invasions. Between 2012 and 2022 a survey was undertaken to assess the status of arboreta in South Africa and the taxa present in such sites, the first such assessment since 1986. At least 172 arboreta have existed in South Africa, but 51 of these are no longer present, with the total number of arboreta peaking around 1980 and declining thereafter. Arboreta have been lost mostly because of conversion of sites to other land-uses, but in some cases because the specimens were felled or burnt down and not replaced. Most of the remaining 121 arboreta are on municipal or forestry land. The biggest challenge facing the extant arboreta is the financial burden of maintaining the collections. The extant arboreta house 2 309 taxa from 158 plant families; of these, 128 taxa (occurring variously in 88 arboreta) are listed as Vulnerable, Endangered, Critically Endangered or Extinct in the Wild under the 2020 IUCN Red List, and 400 taxa (occurring variously in 113 arboreta) have been listed as invasive somewhere in the world. Biogeographic regions that are relatively well represented include the East African Steppe, Sino-Japanese Region, West African Rainforest, North-Eastern Australia, and the Caribbean, making the arboreta valuable sources of germplasm for taxa from these regions. Arboreta are an important resource for South Africa, but a resource that appears to be shrinking. If the value of current arboreta for conservation, education, and research is to be fulfilled, they need to be formally catalogued, their species lists regularly updated, and measures put in place to ensure their sustainability.