Field‐quantified responses of tropical rainforest aboveground productivity to increasing CO2 and climatic stress, 1997–2009. Issue 2 (30th May 2013)

• Record Type: Journal Article
• Authors: Clark, Deborah A.; Clark, David B.; Oberbauer, Steven F.
• Is Part Of: Journal of geophysical research. Volume 118:Issue 2(2013:Jun.)
• Page Start: 783
• Page End: 794
• Publication Date: 2013-05-30
• Subjects: net primary productivity -- climate change -- CO2 fertilization -- global carbon cycle -- La Selva -- tropical rainforest; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/jgrg.20067
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: [1] A directional change in tropical‐forest productivity, a large component in the global carbon budget, would affect the rate of increase in atmospheric carbon dioxide ([CO2 ]). One current hypothesis is that "CO2 fertilization" has been increasing tropical forest productivity. Some lines of evidence instead suggest climate‐driven productivity declines. Relevant direct field observations remain extremely limited for this biome. Using a unique long‐term record of annual field measurements, we assessed annual aboveground net primary productivity (ANPP) and its relation to climatic factors and [CO2 ] in a neotropical rainforest through 1997–2009. Over this 12 year period, annual productivity did not increase, as would be expected with a dominant CO2 fertilization effect. Instead, the negative responses of ANPP components to climatic stress far exceeded the small positive responses associated with increasing [CO2 ]. Annual aboveground biomass production was well explained (73%) by the independent negative effects of increasing minimum temperatures and greater dry‐season water stress. The long‐term records enable a first field‐based estimate of the [CO2 ] response of tropical forest ANPP: 5.24 g m −2 yr −1 yr −1 (the summed [CO2 ]‐associated increases in two of the four production components; the largest component, leaf litterfall, showed no [CO2 ] association). If confirmed by longer data series, such a small response from a fertile tropical rainforest would indicate that current global models overestimate the benefits from CO2 fertilization for this biome, where most forests' poorer nutrient status more strongly constrains productivity responses to increasing [CO2 ]. Given the rapidly intensifying warming across tropical regions, tropical forest productivity could sharply decline through coming decades. Key Points: Tropical forest aboveground productivity shows no directional change over 12 yr Climatic stress dominates interannual changes in production components The possible positive carbon‐dioxide response is smaller than expected