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Understanding Tropical Forest Productivity
Principal Investigator
Chris Doughty
Collaborators
Yadvinder Malhi (University of Oxford)
Overview
Our project team currently measures bottom-up productivity in >50, one ha plots spread throughout South America, Africa and Asia where each component of net primary production (NPP), autotrophic (Ra) and heterotrophic respiration (Rh) is measured separately. We also have extensive leaf trait and spectral data at >30 of these plots. My research suggests that remote sensing can predict leaf traits such as leaf thickness and that such traits are strongly correlated with forest productivity. Therefore, I am in the unique position to create and test a remote sensing algorithm to more accurately predict tropical forest productivity than is currently being used.
I am also interest in understanding the role that reserves of sugars (NSCs) may play in determining a forests resilience to extreme events. In tropical forests, NSCs may play a particularly important role in drought response. Recent data from a network of lowland tropical forest plots where we are conducting intensive carbon budget monitoring indicate a seasonal and inter-annual discrepancy between total photosynthesis and total carbon used, which we hypothesize is due to seasonal accumulation and depletion of NSC pools. I propose to quantify, the role of NSCs in the full carbon budget of tropical forests at multiple locations. In addition, I seek to understand NSCs following a tree girdling experiment in Malaysia. I also will measure leaf spectroscopy on the same leaves which are measured for NSCs and then to develop an empirical model predicting total tree NSC with spectroscopy. The combination of observational and experimental approaches proposed will significantly advance our understanding of the role that NSCs play in tropical forest function in the present, as well as how they may contribute to their resilience in the future.
Every year tropical forests uptake about 18% of human CO2 emissions, likely due to CO2 fertilization effects and increased forest productivity, but this uptake may be decreasing. At some point, such fertilization effects will decrease as tropical forest growth is limited by climate change induced droughts and those human caused CO2 emissions will remain in the atmosphere further increasing global warming. In 2005 and 2010, the Amazon basin experienced two strong droughts, driven by shifts in the tropical hydrological regime possibly associated with global climate change. My research uses field, remote sensing, and computational techniques to closely monitor tropical forest productivity to better understand when tropical forests may reduce their CO2 uptake because this will have large climate implications for all humanity.
Funding
- Google Earth Engine Research Awards Program, 2016-2017
- John Fell Fund, 2013-2016
Representative Publications
- Doughty, C.E., D.B. Metcalfe, C. A. J. Girardin, et al., Impact of the 2010 drought on Amazonian carbon dynamics and fluxes. Nature, 2015
- Doughty, C.E., D.B. Metcalfe, C. A. J. Girardin, F.F. Amezquita, L. Durand, W. Huaraca Huasco, J. E. Silva-Espejo, A. Araujo-Murakami, M. C. da Costa , A. C. L. da Costa, W. Rocha , Y. Malhi. Source and sink carbon dynamics and carbon allocation in the Amazon basin. Global Biogeochemical Cycles, 2015
- Rowland, L. da Costa, A. C. L., Mencuccini, M., Galbraith, D. R., Oliveira. R. S., Binks, O. J., Oliveira, A. A. R., Pullen, A. M., Doughty, C.E. et al. Death from drought in tropical forests is triggered by hydraulics not carbon starvation. Nature, 2015
- Doughty, C.E., Y. Malhi, D.B. Metcalfe, A. Araujo-Murakami, et al. Allocation trade-offs dominate the response of tropical forest growth to seasonal and interannual drought. Ecology, 2014
- Gatti, L. V. J. Miller, E. Gloor, Doughty, C.E., et al. Drought sensitivity of Amazonian carbon balance revealed by atmospheric measurements. Nature, 2014