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Title: How do rubber (Hevea brasiliensis) plantations behave under seasonal water stress in northeastern Thailand and central Cambodia?

Plantation rubber (Hevea brasiliensis Müll. Arg.) is a viable economic resource for Southeast Asian countries. Consequently, rubber plantations are rapidly expanding into both climatically optimal and sub-optimal environments throughout mainland Southeast Asia, potentially changing the partitioning of water, energy, and carbon at multiple scales, compared with the traditional land covers they are replacing. Delineating the characteristics of biosphere-atmosphere exchange in rubber plantations is therefore important to understanding the impacts of such land use change on environmental processes. We have conducted eddy flux measurements in two rubber plantation sites: (1) Som Sanuk (SS), located northern Thailand; and (2) Cambodian Rubber Research Institute (CRRI), central Cambodia. Both sites have a distinct dry season. Measurements were made over a 3-year period. We used combination of actual evapotranspiration (ET) flux measurements and an inversed version of a simple 2-layer ET model for estimating the mean canopy stomatal conductances (gs), which is among the most effective measures for describing water and energy exchanges and tree water use characteristics. A main novelty in this analysis is that the rubber canopy conductance can be extracted from total surface conductance (including the canopy and the vegetation floor effects) and hence environmental and biological controls on rubber tree gsmore » are explicitly compared at each site in different seasons and years. It is demonstrated how each studied rubber plantation copes with each strong seasonal drought via tree water use strategies. Potential tree water use deficit (precipitation (P) – potential evaporation (ET_POT)) for each season (i.e., December-February: DJF, March-May: MAM, June-August: JJA, and September-November: SON) revealed in which season and how the water use should be controlled. We found that in seasons when actual tree water use deficit (P – ET) was negative (i.e., DJF and MAM), the deficit was compensated by soil water from the previous season stored within the soil layer at depths of 0-2 m at the Thailand site, and at depths of 0-3 m at CRRI. Two ecophysiological parameters, the reference value of gs (gsref) and the sensitivity of gs to atmospheric demand (m), as well as their proportionality (m/gsref), were derived from the logarithmic response curve of gs to vapor pressure deficit (D) for each season and each site. At both sites, gsref and m appeared to be smaller in DJF and MAM than those in the other seasons (i.e., JJA and SON). On average in a whole year, m/gsref was less than 0.6 at SS and almost 0.6 at the CRRI site, suggesting that there was less sufficient stomatal regulation at SS, where the risk of water stress-induced hydraulic failure is low because of its high annual rainfall amount. In comparison, at CRRI where annual P – ET_POT was negative, there was stricter stomatal regulation that prevents excessive xylem cavitation. These tendencies imply that in the drier season, i.e., DJF and MAM, the rubber trees in SS and CRRI adopt the stomatal control strategy of changing gsref with reluctance and positive to change m, respectively.« less
 [1] ;  [2] ;  [2] ;  [1] ;  [3] ;  [4] ;  [2] ;  [5] ;  [6] ;  [7] ;  [4] ;  [4] ;  [8]
  1. Nagoya Univ., Nagoya (Japan)
  2. Univ. of Hawaii, Honolulu, HI (United States)
  3. Kyushu Univ. Fukuoka (Japan)
  4. Cambodian Rubber Research Institute, Phnom Penh (Cambodia)
  5. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  6. East-West Center, Honolulu, HI (United States)
  7. National Univ. of Singapore (Singapore)
  8. Kasetsart Univ., Bangkok (Thailand)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0168-1923; KP1703020
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Agricultural and Forest Meteorology (Print); Journal Volume: 213; Journal Issue: C
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Org:
Country of Publication:
United States
tropical deciduous forest; stomatal control; transpiration; water vapor flux; eddy covariance; soil moisture