The number of tree species on Earth

Cazzolla Gatti R, Reich, PB, Gamarra, JGP, Crowther T, Hui C, Morera A, Bastin JF, de-Miguel S, Nabuurs GJ, Svenning JC, Serra-Diaz JM, Merow C, Enquist B, Kamenetsky M, Lee J, Zhu J, Fang J, Jacobs DF, Pijanowski B, Banerjee A, Giaquinto RA, Alberti G, Almeyda Zambrano AM, Alvarez-Davila E, Araujo-Murakami A, Avitabile V, Aymard GA, Balazy R, Baraloto C, Barroso JG, Bastian ML, Birnbaum P, Bitariho R, Bogaert J, Bongers F, Bouriaud O, Brancalion PHS, Brearley FQ, Broadbent EN, Bussotti F, Castro da Silva W, César RG, Češljar G, Chama Moscoso V, Chen HYH, Cienciala E, Clark CJ, Coomes DA, Dayanandan S, Decuyper M, Dee LE, Del Aguila Pasquel J, Derroire G, Djuikouo MNK, Van Do T, Dolezal J, Đorđević IĐ, Engel J, Fayle TM, Feldpausch TR, Fridman JK, Harris DJ, Hemp A, Hengeveld G, Herault B, Herold M, Ibanez T, Jagodzinski AM, Jaroszewicz B, Jeffery KJ, Johannsen VK, Jucker T, Kangur A, Karminov VN, Kartawinata K, Kennard DK, Kepfer-Rojas S, Keppel G, Khan ML, Khare PK, Kileen TJ, Kim HS, Korjus H, Kumar A, Kumar A, Laarmann D, Labrière N, Lang M, Lewis SL, Lukina N, Maitner BS, Malhi Y, Marshall AR, Martynenko OV, Monteagudo Mendoza AL, Ontikov PV, Ortiz-Malavasi E, Pallqui Camacho NC, Paquette A, Park M, Parthasarathy N, Peri PL, Petronelli P, Pfautsch S, Phillips OL, Picard N, Piotto D, Poorter L, Poulsen JR, Pretzsch H, Ramírez-Angulo H, Restrepo Correa Z, Rodeghiero M, Rojas Gonzáles RDP, Rolim SG, Rovero F, Rutishauser E, Saikia P, Salas-Eljatib C, Schepaschenko D, Scherer-Lorenzen M, Šebeň V, Silveira M, Slik F, Sonké B, Souza AF, Stereńczak KJ, Svoboda M, Taedoumg H, Tchebakova N, Terborgh J, Tikhonova E, Torres-Lezama A, van der Plas F, Vásquez R, Viana H, Vibrans AC, Vilanova E, Vos VA, Wang HF, Westerlund B, White LJT, Wiser SK, Zawiła-Niedźwiecki T, Zemagho L, Zhu ZX, Zo-Bi IC, Liang J. (2022) The number of tree species on Earth. Proceedings of the National Academy of Sciences (USA) 119(6): e2115329119. 11 p. ISSN: 0027-8424

One of the most fundamental questions in ecology is how many species inhabit the Earth. However, due to massive logistical and financial challenges and taxonomic difficulties connected to the species concept definition, the global numbers of species, including those of important and well-studied life forms such as trees, still remain largely unknown. Here, based on global ground-sourced data, we estimate the total tree species richness at global, continental, and biome levels. Our results indicate that there are ∼73,000 tree species globally, among which ∼9,000 tree species are yet to be discovered. Roughly 40% of undiscovered tree species are in South America. Moreover, almost one-third of all tree species to be discovered may be rare, with very low populations and limited spatial distribution (likely in remote tropical lowlands and mountains). These findings highlight the vulnerability of global forest biodiversity to anthropogenic changes in land use and climate, which disproportionately threaten rare species and thus, global tree richness.