Rate of Tree Carbon Accumulation Increases Continuously with Tree Size

STEVENSON NL; DAS AJ; CONDIT R; RUSSO S; BAKER P; BECKAM N; COOMES A; LINES ER; MORRIS W; RUGGER N; ALVAREZ E; BLUNDO C; BUNYAVEJCHEWIN S; CHUYONG G; DAVIES SJ; DUQUE A; EWANGO CN; FLORES O; FRANKLIN J; GRAU, HR; HAO Z; HARMON M; HUBBELL SP; KENFRAK D; LIN Y; MARKANA J; MALIZIA, A; MALIZIA L; PABST RJ; PONGPATTANANURAK N; SU SH; SUN T; TAN S; THOMAS D; VAN MANTGEM PJ; WANG X; WISER S; ZABALA M

NATURE

NATURE PUBLISHING GROUP

Lugar: Londres; Año: 2014 vol. 507 p. 90 - 93

0028-0836

Forests are major components of the global carbon cycle, providing substantial feedbacks to atmospheric greenhouse gas concentrations1. Our ability to understand and predict changes in the forest carbon cycle ? particularly net primary productivity and carbon storage ? increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands2,3. Yet despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree: as trees increase in size and age do their rates of absolute mass growth ? and thus carbon accumulation ? decrease, remain constant, or increase4?7? Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, rather than large, old trees primarily acting as senescent carbon reservoirs, they actively fix tremendous amounts of carbon, with a single big tree adding the carbon equivalent of an entirely new mid76 sized tree to the forest each year. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-8?10 and stand-level10 productivity can be explained, respectively, by increases in whole-tree leaf area that outpace declines in per-unit-leaf-area productivity and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to understand and model forest carbon dynamics, and have additional implications for theories of resource allocation11 and plant senescence12.