Stephenson, N. L.; Das, A. J.; Condit, R.; Russo, S. E.; Baker, P. J.; Beckman, N. G.; Coomes, D. A.; Lines, E. R.; Morris, W. K.; Ruger, N.; Alvarez, E.; Blundo, C.; Bunyavejchewin, S.; Chuyong, G.; Davies, S. J.; Duque, A.; Ewango, C. N.; Flores, O.; Franklin, J. F.; Grau, H. R.; Hao, Z.; Harmon, M. E.; Hubbell, S. P.; Kenfack, D.; Lin, Y.; Makana, J.-R.; Malizia, A.; Malizia, L. R.; Pabst, R. J.; Pongpattananurak, N.; Su, S.-H.; Sun, I-F.; Tan, S.; Thomas, D.; van Mantgem, P. J.; Wang, X.; Wiser, S. K.; Zavala, M. A. 2014. Rate of tree carbon accumulation increases continuously with tree size. Nature. 2014/01/15/online:1476-4687. doi:https://doi.org/10.1038/nature12914.
Forests are major components of the global carbon cycle, providing
substantial feedback to atmospheric greenhouse gas concentrations.
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 stands. 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, in
part because we lack a broad empirical assessment of whether rates
of absolute treemass growth (and thus carbon accumulation)decrease,
remain constant, or increase as trees increase in size and age. 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, large, old trees do not act simply as senescent
carbon reservoirs but actively fix large amounts of carbon
compared to smaller trees; at the extreme, a single big tree can add
the same amount of carbon to the forest within a year as is contained
in an entire mid-sized tree. The apparent paradoxes of individual
tree growth increasing with tree size despite declining leaf-level
and stand-level productivity can be explained, respectively, by
increases in a tree’s total leaf area that outpace declines in productivity
per unit of leaf area and, among other factors, age-related
reductions in population density. Our results resolve conflicting
assumptions about the natureof tree growth, informefforts to undertand
and model forest carbon dynamics, and have additional implications
for theories of resource allocation and plant senescence.