The question of how many different tree species exist does not have a single, fixed answer, reflecting the dynamic nature of biology and the continuous process of scientific discovery. Scientists are constantly cataloging, defining, and revising the status of species globally. The number of species is a measure of biodiversity, contrasting with the total count of individual trees, which number in the trillions, and the current estimate is the result of massive international collaboration.
The Current Global Estimate of Tree Species
The most recent and comprehensive scientific estimate places the total number of tree species on Earth at approximately 73,300 species. This figure, published in 2022, is derived from a vast global dataset that includes information on over 38 million individual trees across 90 countries and 100 territories. The methodology combines ground-sourced data with advanced statistical modeling to account for both known and undiscovered species.
The estimate suggests that around 9,000 tree species have yet to be formally discovered and documented by science. This number is about 14% higher than the previously accepted count of documented species, which was approximately 60,065 species as of 2017.
This global inventory highlights that a significant portion of the undiscovered species are likely rare, with very small populations and a limited geographic distribution. Nearly one-third of all species are thought to be rare, making them vulnerable to environmental changes. The focus of the methodology is on identifying where the gaps in knowledge exist to better inform conservation strategies.
Defining What Qualifies as a Tree
Counting the world’s tree species is complicated because the definition of a “tree” is not always strictly defined in botany. A tree is generally understood to be a perennial, woody plant, but the precise distinction from a shrub or bush can be ambiguous. Most working definitions, such as the one used by the IUCN’s Global Tree Specialist Group, require a woody plant to typically have a single, self-supporting stem or trunk.
An important criterion is size, with trees generally growing to a height of at least two meters, or about 6.6 feet. Shrubs, in contrast, are typically shorter and characterized by multiple stems branching from or near the ground line. Some definitions also require a single vertical stem to reach a minimum diameter of five centimeters at breast height to qualify as a tree.
This taxonomic ambiguity means that certain multi-stemmed plants, or those that rarely reach the minimum height due to harsh environmental conditions, can be classified differently by various experts. Furthermore, some species exhibit variable life forms, growing as a shrub in one location but as a tree in another. For the purpose of global censuses, any species that naturally grows as a tree anywhere in its native range is typically included in the count.
Geographic Hotspots of Tree Diversity
Tree species are not distributed evenly across the planet; instead, species richness is heavily concentrated in specific geographic regions. The Neotropics, which encompasses Central and South America, stands out as the most species-rich biome, containing over 23,000 known tree species. South America alone is estimated to harbor about 43% of all tree species on Earth, making it the primary center of global tree diversity.
Within South America, the Amazon basin exhibits the highest local diversity, with some areas having more than 200 tree species per hectare. This immense richness is thought to be driven by a combination of a large geographic area, long-term evolutionary stability, and favorable climatic conditions that allow for species accumulation and coexistence. Other high-diversity regions include the Indo-Malay biome and specific island ecosystems like Madagascar, which harbor high numbers of endemic species due to geographic isolation.
The distribution pattern follows a general trend where diversity is highest near the equator and declines toward the middle and higher latitudes. After South America, the next most diverse continents are Eurasia, Africa, North America, and Oceania, in descending order of species count. This concentration of species in tropical and subtropical regions means that conservation efforts must be highly focused on these specific hotspots to protect the majority of the world’s arboreal biodiversity.
Factors Driving the Fluctuations in Species Count
The global number of tree species is dynamic, constantly subject to change from two opposing forces: discovery and loss. Ongoing botanical field research in remote areas, particularly in tropical lowlands and mountains, leads to the formal description of new species. For instance, a significant portion of the estimated undiscovered species, roughly 40%, is expected to be found in South America, where access is often difficult.
The second major factor is the loss or reclassification of known species. Extinction, driven primarily by human-caused habitat destruction and climate change, removes species from the global count. Compounding this, taxonomic revision, which uses new genetic analysis techniques, can either “lump” previously separate species into one, or “split” a single species into multiple distinct ones.
These taxonomic revisions are a natural part of the scientific process, but they directly affect the numerical count by changing what qualifies as a unique species. The combination of discovery and revision means the total number will never be completely static. The accelerating rate of extinction poses a serious threat to the rare and undiscovered species that make up the majority of the world’s tree diversity.