Large-scale altitudinal gradient of natural rubber production in Vietnam

Investigation of elevation dependence of latex productivity of natural rubber (NR, Hevea brasiliensis Mull. Arg.) plantations and determination of elevation thresholds for landuse management are an urgent need of study. The current study was, therefore, conducted, aiming to investigate attitudinal gradient of NR production in Vietnam. The study was based on 146,000 ha of harvested NR plantations located from the southeast region to highland. There were 45 NR clones planted in the areas studied and GT1, the clone planted with a largest portion, was examined separately from the other 44 clones, combined in processing (the Rest). Three main variables, latex productivity, individual yield and tapping density were calculated for two tapping periods, from year 1 to 10(1-10) and from year 11 to 20(11-20). Over the investigated elevation range, 15-738m, the latex productivity declined at different rates, 109 for GT1 (1-10), 127 for GT1 (11-20), 110 for the Rest (1-10) and 117 kg ha(-1) year(-1) for the Rest (11-20) for every 100-m increase in elevation. An S-like curve, obtained by fitting latex productivity along the altitudinal gradient using 3-order polynomial could be separated into three stages, of which the first and the last stages were characterized with a rapid drop of, and the middle was with a stability of, latex productivity. With a rise in elevation, tapping density (tapped tree ha(-1)) and individual yield (kg tree(-1) year-1) significantly declined. As tapping density increased, individual yield declined whereas latex productivity rose. The results indicated that not all lands are suitable for a good NR production and that only areas with elevation under a certain magnitude depending on individual NR clones should be considered for NR cultivation. The altitudinal gradient of NR production could involve a number of soil and climatic variables, which need to be further investigated. (C) 2012 Elsevier B.V. All rights reserved.