Large Seasonal Swings in Leaf Area of Amazon Rainforests

• Published in: Proceedings of the National Academy of Sciences - PNAS 2007-03, Vol.104 (12), p.4820-4823
• Main Authors: Myneni, Ranga B., Yang, Wenze, Nemani, Ramakrishna R., Huete, Alfredo R., Dickinson, Robert E., Knyazikhin, Yuri, Didan, Kamel, Fu, Rong, Juárez, Robinson I. Negrón, Saatchi, Sasan S., Hashimoto, Hirofumi, Ichii, Kazuhito, Shabanov, Nikolay V., Tan, Bin, Ratana, Piyachat, Privette, Jeffrey L., Morisette, Jeffrey T., Vermote, Eric F., Roy, David P., Wolfe, Robert E., Friedl, Mark A., Running, Steven W., Votava, Petr, El-Saleous, Nazmi, Devadiga, Sadashiva, Su, Yin, Salomonson, Vincent V.
• Format: Article
• Language: English
• Subjects: Brazil; Datasets; Dry seasons; Ecosystem studies; Ecosystems; Geography; Greenbelts; Leaf area; Organ Size; Phenology; Physical Sciences; Pixels; Plant Leaves - anatomy & histology; Plant Leaves - growth & development; Plant Leaves - radiation effects; Precipitation; Rain; Rainforests; Rainy seasons; Satellite Communications - instrumentation; Seasons; Solar radiation; Sunlight; Time Factors; Trees - anatomy & histology; Trees - growth & development; Trees - radiation effects; Tropical rain forests; Vegetation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0611338104

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.