Basin-wide variation in tree hydraulic safety margins predicts the carbon balance of Amazon forests
Julia Valentim Tavares, Rafael S. Oliveira, Maurizio Mencuccini, Caroline Signori‐Müller, Luciano Pereira, Francisco Carvalho Diniz, Martin Gilpin, Manuel J. Marca Zevallos, Carlos A. Salas Yupayccana, Martin Acosta Oliveira, Flor M. Pérez Mullisaca, Fernanda Barros, Paulo Bittencourt, Halina Soares Jancoski, Marina Corrêa Scalon, Beatriz Schwantes Marimon, Imma Oliveras Menor, Ben Hur Marimon, Max Fancourt, Alexander Chambers-Ostler, Adriane Esquivel‐Muelbert, Lucy Rowland, Patrick Meir, Antônio C. L. da Costa, Alex Nina, Jesús M. Bañon Sanchez, José Sanchez Tintaya, Rudi Cruz, Jean Baca, Leticia Fernandes, Edwin R. M. Cumapa, João Antônio R. Santos, Renata Teixeira, Ligia Tello, Maira Tatiana Martinez Ugarteche, Gina A. Cuellar, Franklin Martinez, Alejandro Araujo‐Murakami, Everton Cristo de Almeida, Wesley Jonatar Alves da Cruz, Jhon del Águila Pasquel, Luis E. O. C. Aragão, Timothy R. Baker, Plínio Barbosa de Camargo, Roel Brienen, Wendeson Castro, Sabina Cerruto Ribeiro, Fernanda Coelho de Souza, Eric G. Cosio, Nallaret Davila Cardozo, Richarlly da Costa Silva, Mathias Disney, Javier Silva Espejo, Ted R. Feldpausch, Leandro Valle Ferreira, Leandro Lacerda Giacomin, Níro Higuchi, Marina Hirota, Eurídice N. Honorio Coronado, Walter Huaraca Huasco, Simon L. Lewis, Gerardo Flores Llampazo, Yadvinder Malhi, Abel Monteagudo Mendoza, Paulo S. Morandi, Víctor Chama Moscoso, Robert Muscarella, Deliane Penha, Mayda Rocha, Gleicy Rodrigues, Ademir Roberto Ruschel, Norma Salinas, Monique Bohora Schlickmann, Marcos Silveira, Joey Talbot, Rodolfo Vásquez, Laura B. Vedovato, Simone Aparecida Vieira, Oliver L. Phillips, Emanuel Gloor, David Galbraith
Abstract
Abstract Tropical forests face increasing climate risk 1,2 , yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, $$\varPsi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Ψ</mml:mi> </mml:math> 50 ) and hydraulic safety margins (for example, HSM 50 ) are important predictors of drought-induced mortality risk 3–5 , little is known about how these vary across Earth’s largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters $$\varPsi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Ψ</mml:mi> </mml:math> 50 and HSM 50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both $$\varPsi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Ψ</mml:mi> </mml:math> 50 and HSM 50 influence the biogeographical distribution of Amazon tree species. However, HSM 50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM 50 are gaining more biomass than are low HSM 50 forests. We propose that this may be associated with a growth–mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM 50 in the Amazon 6,7 , with strong implications for the Amazon carbon sink.