Large seasonal swings in leaf area of Amazon rainforests

^aDepartment of Geography and Environment, Boston University, 675 Commonwealth Avenue, Boston, MA 02215;
^cEcosystem Science and Technology Branch, National Aeronautics and Space Administration (NASA) Ames Research Center, Mail Stop 242-4, Moffett Field, CA 94035;
^dDepartment of Soil, Water, and Environmental Science, University of Arizona, Tucson, AZ 85721;
^eSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332;
^gJet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109;
^hCalifornia State University at Monterey Bay and Ecosystem Science and Technology Branch, NASA Ames Research Center, Mail Stop 242-4, Moffett Field, CA 94035;
ⁱSan Jose State University and Ecosystem Science and Technology Branch, NASA Ames Research Center, Mail Stop 242-4, Moffett Field, CA 94035;
^kBiospheric Sciences Branch, NASA Goddard Space Flight Center, 8600 Greenbelt Road, Mail Code 614.4, Greenbelt, MD 20771;
^mTerrestrial Information Systems Branch, NASA Goddard Space Flight Center, 8600 Greenbelt Road, Mail Code 614.5, Greenbelt, MD 20771;
ⁿDepartment of Geography, University of Maryland, College Park, MD 20742;
^oGeographic Information Science Center of Excellence, South Dakota State University, Wecota Hall, Box 506B, Brookings, SD 57007;
^pRaytheon Technology Services Corporation at NASA Goddard Space Flight Center, 8600 Greenbelt Road, Mail Code 614.5, Greenbelt, MD 20771;
^qSchool of Forestry, University of Montana, Missoula, MT 59812;
^rScience Systems and Applications, Inc., at NASA Goddard Space Flight Center, 8600 Greenbelt Road, Mail Code 614.5, Greenbelt, MD 20771; and
^sDepartment of Geography and Meteorology, University of Utah, Salt Lake City, UT 84112-0110

Contributed by Robert E. Dickinson, December 22, 2006 (received for review June 5, 2006)

Abstract

Despite early speculation to the contrary, all tropical forests studied to date display seasonal variations in the presence of new leaves, flowers, and fruits. Past studies were focused on the timing of phenological events and their cues but not on the accompanying changes in leaf area that regulate vegetation–atmosphere exchanges of energy, momentum, and mass. Here we report, from analysis of 5 years of recent satellite data, seasonal swings in green leaf area of ≈25% in a majority of the Amazon rainforests. This seasonal cycle is timed to the seasonality of solar radiation in a manner that is suggestive of anticipatory and opportunistic patterns of net leaf flushing during the early to mid part of the light-rich dry season and net leaf abscission during the cloudy wet season. These seasonal swings in leaf area may be critical to initiation of the transition from dry to wet season, seasonal carbon balance between photosynthetic gains and respiratory losses, and litterfall nutrient cycling in moist tropical forests.

Footnotes

^fTo whom correspondence should be addressed. E-mail: robted{at}eas.gatech.edu
Author contributions: R.B.M. and A.R.H. designed research; Y.K., R.I.N.J., H.H., K.I., N.V.S., B.T., P.R., and M.A.F. performed research; R.R.N., R.F., R.I.N.J., S.S.S., H.H., K.I., J.L.P., J.T.M., E.F.V., D.P.R., R.E.W., M.A.F., S.W.R., P.V., N.E.-S., S.D., and V.V.S. contributed new reagents/analytic tools; W.Y., K.D., and Y.S. analyzed data; and R.B.M., A.R.H., R.E.D., R.F., J.L.P., J.T.M., E.F.V., D.P.R., and S.W.R. wrote the paper.
↵ ^bPresent address: Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109.
↵ ^jPresent address: Earth Resources Technology, Inc., 10810 Guilford Road, Suite 105, Annapolis Junction, MD 20701.
↵ ^lPresent address: Remote Sensing and Applications Division, National Oceanic and Atmospheric Administration, National Climatic Data Center, 151 Patton Avenue, Asheville, NC 28801.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0611338104/DC1.
Abbreviations:

LAI,

leaf area index;

MODIS,

Moderate Resolution Imaging Spectroradiometer.
Freely available online through the PNAS open access option.