A living inventory of planted trees in South Africa derived from iNaturalist

Abstract

• South Africa has a long history of introduction of trees from other parts of the world, starting with introductions in the mid-17th century. • Planted trees (both native and non-native) now dominate treescapes in many part of the country, especially in urban ecosystems. • Although planted trees are a key component of South Africa's green infrastructure and provide diverse ecosystem services, no up-date list of planted tree species exists. • This study used the citizen science platform iNaturalist to compile a spatially-explicit “living inventory” of planted tree species for South Africa. • The planted tree flora of South Africa comprises over 35,000 records of 805 taxa, 79 % of which are non-native. Over a third these taxa belong to three families: Fabaceae, Myrtaceae and Arecaceae. • Examples are provided of uses of the inventory for managing diverse aspects of South Africa's treescapes, including for monitoring the emergence of new invasions. Trees have a multifaceted influence on ecosystems globally. Treescapes have been manipulated by humans over millennia for ecological, economic, and cultural reasons that have changed over time and continue to change. In South Africa tree planting over three centuries has radically affected the composition of treescapes, contributing important ecosystem services, but also disservices. Rapid global change calls for diverse interventions to create more resilient ecosystems. Many nature-based solutions involve manipulating tree cover in rural and urban landscapes. There is a need for a spatially-explicit database of planted trees in South Africa to serve as the foundation for policy and management decisions. We used the community science platform iNaturalist to create a comprehensive database of planted trees in South Africa. Records were carefully checked to verify the accuracy of taxon identifications, locality data, and categorization as planted rather than wild-growing trees. The cleaned database contained 35,303 records of 805 planted tree taxa; over 90 % of records were identified to species level. Almost a third of taxa (32.2 %) belong to three families: Fabaceae (97 taxa), Myrtaceae (80 taxa) and Arecaceae (78 taxa). Rarefaction and extrapolation curves suggest fairly comprehensive sampling, but several regions are under-sampled. Non-native taxa dominate, with Melaleuca viminalis having the most records. The Western Cape has the highest number of records and taxa, particularly in urban areas. Both native and non-native trees provide key ecosystem services, but non-natives dominate. The database provides the first spatially-explicit open-access resource for guiding decisions on tree planting and the management of planted trees in South Africa. It offers a snapshot of tree planting trends, predominantly from recent years, leading to some underrepresentation of historically planted species. The database has numerous potential uses, including guiding management of trees pests and diseases, urban greening initiatives, monitoring for new invasions, and planning nature-based solutions.

Topics & Concepts