This study investigates the differences in light intensity between pararubber rows and the root distribution of pararubber (Hevea brasiliensis (Kunth) Müll. Arg.) (RRIM600), in order to select suitable trees to plant between the rows of pararubber. The study was carried out in a monoculture pararubber plantation in Chiang Rai Province, with tree age ranging 1-10 years and a spacing of 3 m × 7 m Light intensity varying from 60 – 85%, was found in pararubber aged 1-3 years old, and continuously decreasing to 10 – 20% after the age of 6 years. Root distribution also varied with age and was affected by the direction from the stem and was the highest in East – West side of the tree at age 5 years old. Root dry biomass was the highest in the age of 5-6 years old. Root dry biomass showed a positive correlation with the canopy area (r = 0.70). There was no difference in root distribution along the 3 m distance away from the base indicating of uniformly distributed root over the distance. Selection of inter-row species should be based on the variation in light intensity and root distribution of pararubber. We suggest planting any species between rows when the pararubber trees are 1-3 years old because at this stage, pararubber roots are not fully developed and also with a high light intensity. Caution should be taken when pararubber trees are between 4-7 years old, due to the highest growth along with a more developed canopy area and root system of the pararubber. After age 7, shade tolerant species are recommended due to very low light intensity in the inter-rows and that the growth and root system of pararubber are fully developed.
Keywords: Pararubber, light intensity, dry root biomass, shade tolerant species, inter-row species