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New Findings Reveal The Number of Tree Species That Exist Worldwide

Logos for The Morton Arboretum and Botanic Gardens Conservation International
April 5, 2017


London-based Botanic Gardens Conservation International (BGCI), the organization that represents the world’s botanic gardens and partner of The Morton Arboretum, has an answer to the question ‘how many tree species exist in the world?’ Based on more than two years of research, working with its partner botanic institutions across the world, and consulting more than 500 published references, the answer is 60,065.

A scientific paper published in The Journal of Sustainable Forestry, the global tree list highlights the fact that more than half of all tree species only occur in a single country, and many rare species are under threat of extinction. Brazil has the most tree species, with 8,715 species, followed by Colombia (5,776) and then Indonesia (5,142). Apart from the Arctic and the Antarctic (which have no trees), the region with the fewest tree species is the Nearctic region of North America, with fewer than 1,400 species.

BGCI’s main reason for publishing the list is to provide a tool and baseline for people trying to conserve rare and threatened tree species. Currently, around 10,000 tree species are known to be threatened, largely by deforestation and over-exploitation. This number includes more than 300 species that are critically endangered with fewer than 50 individual trees remaining in the wild. By compiling this information, BGCI has enabled the conservation community to put into context the scale of the task at hand—protecting the world’s tree diversity from extinction. We now know that at least 17 percent of all tree species are threatened with extinction, compared to 13 percent of birds, for example. The list provides the essential starting point for knowing how rich our tree flora is and where the global diversity hotspots are, enabling researchers, land managers, and policymakers to prioritize conservation action.

Working in collaboration since 1992, The Morton Arboretum and BGCI are key partners in catalyzing tree conservation, with the Arboretum acting as one of two United States hubs for the botanic garden network. In addition to contributing to this monumental effort to ascertain the number of tree species worldwide, a team of five from the Arboretum’s Global Tree Conservation Program, including Murphy Westwood, Ph.D., Director of the Arboretum’s conservation program, run several collaborative tree conservation projects with BGCI and other strategic partners around the world. One endangered tree species the program is targeting for protection is Quercus brandegeei, an evergreen oak native to the tip of southern Baja California in Mexico. Q. brandegeei trees may live up to 800 years, but experts suspect the species is struggling with a lack of seedling establishment, since no trees younger than around 100 years old have been found in the wild. Threats to the species include overgrazing by livestock and climate change. Arboretum scientists and their collaborators are conducting field studies and greenhouse experiments to understand what is preventing regeneration. Seedlings will be propagated in partner gardens in Mexico for eventual reintroduction to suitable habitats in the wild.

“The global tree list is a major achievement and represents the culmination of hundreds of years of botanical effort to catalog and understand the diversity of trees in the world,” said Gerard T. Donnelly, Ph.D., President and CEO of The Morton Arboretum and a member of the BGCI Board of Directors. “Forests provide much of the framework of the natural world. With this information, we are better able to set clear and realistic goals and prioritize conservation action.”

The total number of known tree species in the world is unlikely to remain static, as around 2,000 new plants are discovered and described each year. For this reason, BGCI has published the list on a database called Global Tree Search that will be regularly updated as new tree species are identified.

“Although it seems extraordinary that it has taken us until 2017 to publish the first global, authoritative list of tree species, it is worth remembering that Global Tree Search represents a huge scientific effort encompassing the discovery, collection and describing of tens of thousands of plant species,” said Paul Smith, BGCI’s Secretary General and one of the paper’s authors. “This is ‘big science’ involving the work of thousands of botanists over a period of centuries.”

The Global Tree Specialist Group of the International Union for Conservation of Nature (IUCN) will use Global Tree Search as the baseline to assess the conservation status of all known tree species by 2020 under an initiative called the Global Tree Assessment. The Morton Arboretum is leading the effort to assess all of the world’s oak species as part of this initiative, but there are still thousands of other tree species that need evaluation.

“We have the expertise assembled to carry out the survey and inventory work, but not all the funding we need,” said Sara Oldfield, Chair of the Global Tree Specialist Group of IUCN and co-author of the global tree list. “We estimate that it will cost in the region of $5 million to do this work, and we will be approaching governments and other funders to support us in this endeavor. Our aim is to ensure that no tree species becomes extinct, but first we need to know which species need urgent conservation action. The Global Tree Assessment will tell us this.”

About Botanic Gardens Conservation International
There are an estimated 2,500 botanic gardens and arboreta in the world attracting 500 million visitors each year. Collectively, it is estimated that botanic gardens conserve at least one third of the world’s plant species in their living collections. Botanic Gardens Conservation International (BGCI) is at the center of this network. Its members include the largest, most renowned gardens in the world – Kew, New York, Missouri, Singapore, Sydney, and Shanghai – and they also include many smaller gardens situated in the world’s plant diversity hotspots. All of these gardens share a commitment to making sure that no plant species becomes extinct, and a combined workforce of many thousands of horticulturists and scientists is working toward that end. BGCI works as an advocate for botanic gardens, coordinates plant conservation action and serves as a knowledge hub for plant conservation policy, practice, and education. BGCI’s membership comprises the largest plant conservation network in the world.

About The Morton Arboretum and BGCI
The Morton Arboretum is an internationally recognized outdoor tree museum and tree research center located near Chicago in Lisle, Illinois. As the champion of trees, the Arboretum is committed to scientifically-informed action, both locally and globally, and encourages the planting and conservation of trees for a greener, healthier, and more beautiful world. Having common goals with Botanic Garden Conservation International, The Morton Arboretum is one of two United States hubs for the organization, coordinating and activating the U.S. botanic garden network as it works toward systematic conservation of threatened and endangered trees. Arboretum President and CEO Gerard T. Donnelly, Ph.D. is on the BGCI Board of Directors and chairs its International Advisory Committee. The Arboretum’s Director of Global Tree Conservation Murphy Westwood, Ph.D. serves as a Global Tree Conservation Officer with BGCI. In this role, she is the U.S.-based representative for the Global Trees Campaign, a joint initiative between BGCI and Fauna & Flora International to study and protect threatened trees.

About The Journal of Sustainable Forestry
The Journal of Sustainable Forestry provides an international forum for dialogue between research scientists, forest managers, economists, and policy and decision makers who share the common vision of sustainable use of natural resources. JSF publishes peer-reviewed, original research on forest science. While the emphasis is on sustainable use of forest products and services, the journal covers a wide range of topics from the underlying biology and ecology of forests to the social, economic, and policy aspects of forestry. Short communications and review papers that provide a clear theoretical, conceptual, or methodological contribution to the existing literature are also included in the journal. Common topics covered in JSF include: Ecology, management, recreation, restoration, and silvicultural systems of all forest types, including urban forests; all aspects of forest biology, including ecophysiology, entomology, pathology, genetics, tree breeding, and biotechnology; wood properties, forest biomass, bioenergy, and carbon sequestration; simulation modeling, inventory, quantitative methods, and remote sensing; environmental pollution, fire and climate change impacts, and adaptation and mitigation in forests; forest engineering, economics, human dimensions, and natural resource policy and planning.