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BACKGROUND
The expansion of rubber (Hevea brasiliensis) cultivation to higher latitudes and higher elevations in southeast Asia is part of a dramatic shift in the direction of rural land cover change in the region toward more tree-covered landscapes. While recent drops in rubber prices may have slowed the pace of expansion in some areas, cultivation of rubber is often supported by government subsidies and remains economically advantageous as compared to other land uses, and entire regions are being progressively blanketed by rubber trees. Questions remain about the sustainability of the industry regarding environmental issues such as water use of the plantations and its ability to sequester carbon from the atmosphere in biomass and the soil. To address this gap in knowledge about the fundamental processes occurring within this widely distributed and economically viable species, we set out in the field to gain a deep understanding of the ecosystem processes in rubber plantations and the impacts of rapid expansion on hydrology and carbon cycling in the region. To investigate the possible effects of increasing rubber cultivation in the region on these ecosystem services, eddy covariance towers were established to measure ecosystem fluxes within two rubber plantations, one each in Bueng Kan, northeastern Thailand, and Kampong Cham, central Cambodia.
RESEARCH QUESTIONS?
How much water do rubber plantations use?
How strong of a carbon sink is rubber?
What are the functional characteristics of rubber plantation ecosystems with respect to carbon, water, and energy exchanges?
What are the seasonal and interannual patterns of water use and carbon exchange with respect to the long (~6 month) dry season in the region?
How do survey based biometric methods relate to CO2 flux measurements from the tower?
Can we successfully model rubber plantation productivity as related to climate variation and change?
FIELD MEASUREMENTS
Above canopy measurement of CO2 and H2O fluxes
30-minute resolution meteorological observations including radiation, temperature, wind, rain, and soil temperature, soil heat flux, and soil water.
Biomass temperature, air temperature, and leaf wetness measurements are made within the canopy
Short term observations of CO2 storage within the plant canopy enable more accurate estimation of plant/atmosphere CO2 exchange
Canopy access tower at CRRI for measurements of photosynthetic characteristics in the rubber canopy.
Observations of Soil CO2 fluxes at both sites over a range of stand ages and clones.
Regular measurements of Leaf Area Index (LAI) were taken throughout the annual cycle to better understand seasonal ecosystem responses to environmental change.
Soil samples taken for analysis of soil water holding characteristics and soil carbon content.
Sequential tree measurements, soil respiration, litterfall traps, and soil carbon storage were monitored to validate ecosystem fluxes at the tower.
Evapotranspiration and related observations
Biomass temperature, air temperature, and leaf wetness measurements are made within the canopy
PEOPLE
Thomas Giambelluca - PI, UH Manoa, Department of Geography
Tomo'omi Kumagai - PI, Nagoya University, Hydrospheric Atmospheric Research Center
Ryan Mudd - Field technician, PhD student, UH Manoa
Nakako Kobayashi - Sapflow at CRRI site. Nagoya University
Yoshiyuki Miyazawa - Leaf level photosynthetis, Kyushu University / UH Manoa
Wen Liu - Ecosystem dynamics modelling, data processing. UH Manoa
Maoyi Huang - data processing, PNNL
Mak Sophea Veasna - Director at CRRI
Yin Song - Former director of CRRI
Lim Khan Tiva - Crop Research Manager at CRRI
Nobuaki Tanaka - Throughfall and stemflow at CRRI site, Nagoya University
Michael Nullet - Data and field support specialist, UH Manoa
Alan D. Ziegler - Field and logistical support. National University of Singapore
RESEARCH SITES
SRRS (Smallholder Rubber Research Site), northeastern Thailand
Mature rubber trees at the SRRS site from above and below the rubber tree canopy. Rubber cultivation in northeastern Thailand, a nontraditional rubber growing area, has replaced upland field crops, fallow land, and more recently lowland rice paddy. An eddy covariance station was established in a mature smallholder plantation in Feburary, 2009 when the plantation was 16 years old. The site was decommissioned in January, 2015.
CRRI (Cambodia Rubber Research Institute), Cambodia
A second flux observation tower was constructed in September, 2009 in a 6 year old rubber stand at the CRRI field research station in Kampong Cham Province, central Cambodia. Observations are currently ongoing in collaboration with Nagoya University, Japan, and the Cambodia Rubber Research Institute. The two study sites have different climate and soil, and represent plantations under different life-cycle stages, and thus are spatially and temporally positioned to capture the variability of ecosystem fluxes in rubber plantations in the seasonal tropics.
Masts were used to secure meteorological instruments above each rubber canopy
Funding
This study was conducted as cooperative project between the University of Hawai‘i (USA), Kyushu and Nagoya Universities (Japan), and the Cambodian Rubber Research Institute (CRRI), with support from NASA grants NNG04GH59G and NNX08AL90G, a grant from the Ministry of Agriculture, Forestry and Fisheries, Japan for the project “Estimation and simulation of carbon stock change of tropical forest in Asia (2011–2014)”. ADZ was supported by National University of Singapore (NUS) grant R-109-000-092-133 and Asia-Pacific Net-work for Global Change Research (APN) grant #ARCP2008-01CMY. MH was supported by the US Department of Energy (DOE) Biological and Environmental Research (BER) through the Terrestrial Ecosystem Science program.
PUBLICATIONS
Giambelluca, T.W., Mudd, R.G., Liu, W., Ziegler, A.D., Kobayashi, N., Kumagai, T., Miyazawa, Y., Lim, T.K., Huang, M., Fox, J., Yin, S., Mak, S.V., and Kasemsap, P. 2016. Evapotranspiration of rubber (Hevea brasiliensis) cultivated at two sites in southeast Asia. Water Resources Research, doi: 10.1002/2015WR017755. [data]
Kumagai, T., Mudd, R.G., Giambelluca, T.W., Kobayashi, N., Miyazawa, Y., Lim, T.K., Liu, W., Huang, M., Fox, J.M., Ziegler, A.D., Yin, S., Sopheaveasna, M., and Kasemsap, P. 2015. How do rubber (Hevea brasiliensis) plantations cope with seasonal drought in northern Thailand and central Cambodia? Agricultural and Forest Meteorology 213: 10-22, doi:10.1016/j.agrformet.2015.06.011.
Kobayashi, N., Kumagai, T., Miyazawa, Y., Matsumoto, K., Tateishi, M., Lim, T. K., Mudd, R. G., Ziegler, A., Giambelluca, T. W. and Yin, S. (2014) Transpiration characteristics of a rubber plantation in central Cambodia. Tree Physiology, 34(3), P285-301
Kumagai, T., Mudd, R. G., Miyazawa, Y., Liu, W., Giambelluca, T. W., Kobayashi, N., Lim, T. K., Jomura, M., Matsumoto, K., Huang, M., Chen, Q., Ziegler, A. and Yin, S. (2013) Simulation of canopy CO2/H2O fluxes for a rubber (Hevea brasiliensis) plantation in central Cambodia: the effect of the regular spacing of planted trees. Ecological Modelling, 265, P124-135.
Kumagai, T., Sato, H., Fujii, S., Khun, Kakada, Miyazawa, Y., Mizoue, N., Kobayashi, N., Mudd, R.G., Giambelluca, T.W., Igarashi, Y., Saito, T., Lim, T.K., Yin, S., Sopheaveasna, M. In review, Forest Ecology and Management. Simulation of a rubber plantation productivity in central Cambodia using the modified individual-based dynamic vegetation model SEIB-DGVM: R-SEIB.
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