Timber production in high density planting of Hevea brasiliensis (Rubber)
Kelum Silva, Upul Subasinghe and Lakshman Rodrigo
Paper presented for the 14th International Forestry and Environmental Symposium 2009
The demand of natural rubber has increased continuously with the increase of population and living standards of the human being. Rubber plantations are also a major source of timber and fuels wood. In order to meet the continuous increase in demand for latex, timber and fuelwood, the productivity of rubber plantations should be increased. Whilst producing high yielding clones for improved latex and timber yield per tree which is a long-term process in perennial crops, planting density could be adjusted to obtain high productivity in rubber plantations. The present level of planting density of rubber in Sri Lanka has been decided on the experiments conducted with the genotypes which are not in common use at the moment. Therefore the present study was aimed to identify the suitable planting density for the recently developed and commonly used genotypes of rubber. This paper is focused to assess the timber production of rubber with respect to high density planting.
The experiment was set up in Rathnapura District of Sri Lanka in 1992. Rubber was planted in three high densities, i.e., 600, 700 and 800 trees per hectare. Also three genotypes (clones), i.e., RRIC 100, RRIC 110 and RRIC 121 were incorporated with the statistical design of split plot where the planting densities were laid as the main plot whilst clones were in the sub-plots. Five trees in each sub-plot were randomly selected and used for the measurements of total tree height (TH), crown height (CH), thickness of the untapped bark (BT) and tree diameter at breast height. Thereafter, stem volumes were determined using the Newton’s formula.
Both TH and CH did not vary significantly among the planting densities tested. Although not statistically significant, there was a marginal decrease in tree diameter with the increase in planting density. Irrespective of the clone used, BT and mean merchantable timber volume per tree decreased significantly with increase in planting density. Nevertheless, this decrease was compensated by the increased number of trees in high densities resulting in comparable level of merchantable volume per hectare among different densities. Total stem volume per tree remained same among four densities tested with that total stem per hectare increased significantly with the increase of planting density. Therefore, higher densities are more useful in the industries of fuelwood, pulp, MDF boards etc. Among the clones tested, the clone RRIC 212outperformed in growth and timber production. The clone RRIC 110 was infected with the Corynespora disease hence showed poor performance in all densities. Despite the increase in total timber production with the increase in planting density, overall financial viability of different densities is to be assessed considering all cost components and valuing both timber and latex produced before making any firm recommendation.