Complete yield table for Eucalyptus torelliana

Construction of a complete yield table for Eucalyptus torelliana using the height-age relationship
by
Menaka Thirunadarajah and Upul Subasinghe

Yield table is a useful way of predicting yield and growth of forest plantations. It shows the expected volume and other important parameters per unit area according to a combination of measurable characteristics of the forest plantation and age. Although the yield and growth of trees can be predicted using advanced techniques in forestry, the information contained in traditional yield tables is still considered as valuable.

Eucalyptus torelliana is one of the eucalypt species planted in Sri Lanka especially in the low country wet zone. Due to unavailabiity of growth prediction methods for this species in Sri Lanka, a complete yield table and a two parameter volume table were constructed in this study using height-age relationship.

Data were collected from five plantations selected in Matara and Rathnapura districts. These even-aged plantations were 10 to 14 years old and varied in extent from 1.2 to 20.0 ha. In order to represent the whole area of each plantation, stratified random sampling was used and 5-10 circular plots (0.02 ha) were used for data collection. Total height and dbh were measured primarily from the trees located in the sample plots. For the volume estimations, each tree stem was divided into sections and for each section, log length, end, mid and top diameters were measured without felling the trees. Then the stem volume was calculated by adding the section volumes estimated using the Newton's formlula.

Due to the unavailability of re-measured data for the selected species, it was decided to develop a relationship between height and tree age. In order to build this relationship, it was assumed that a tree produced one node per year. That was statistically proven to be correct later in the same study.

For the construction of the yeild table, three relationships were mathematically constructed, i.e., height-age, dbh-height and height, dbh-volume. 10 trees were selected from each plantation and nodes were counted to build the height-age relationship. Moreover the distance between nodes were also measured.

By using the above constructed models, a complete yield table and a two parameter volume table (volume = f dbh, height) were constructed. As it was found that there were no significant differnces among the selected plantations in growth, the yield table was recommeded for the use of E. torelliana plantations growing in the low country wet zone of Sri Lanka.