Ecosystem Fluxes in SE Asia Rubber Plantations

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