Prediction of individual tree volume of Alstonia macrophylla

Construction of a precise growth model to predict the individual stem volume of Alstonia macrophylla
by
Rangika Bandara and Upul Subasinghe

In order to reduce the pressure on existing natural forests of Sri Lanka, Forest Department promoted growing timber species as plantations and in homegardens. Among the suggested species, Alstonia macrophylla (Hawari nuga) has recently become popular due to its faster growth rate, ease of estabishment and timber value.

However, at present, there is no method for estimating the stem volume of this species. Therefore mathematical models were built in this study to predict the individual stem volume of the selected species grown as plantations and in homegardens.

Hawari nuga is sidely found in wet zone of Sri Lanka and therefore the study sites were selected from Kalutara and Galle Districts. For the non-forest areas, sampling was carried out in individual basis and ten 0.02 ha circular plots with slope correction were randomly laid out for each plantation in order to measure the necessary parameters.

Dbh, total height and height to the crown base of the trees were measured. Necessary measurements were also taken to calculate the stem volume using Newton's formula.

A theoritical model structure was developed using the relationship between form factor, volume, basal area and total height. Regression analysis was used to fit the data into the model. Untransformed as well as transformed combinations of the model structures were tested in order to select the best models. After examining the statistical performances of the resultant models, two models were finally selected for plantation grown trees and open grown trees. Those models had very high modelling efficiencies and negligible bias. When validated with the reserved data at the beginning of the modelling procedure, the selected models proved the capability of predicting stem volumes of Alstonia macrophylla grown in plantations and homegardens.

Variation of teak stem taper with age

Variation of stem taper with age for Tectona grandis (teak)
by
Mohomed Nafees and Upul Subasinghe

Taper is the rate of change of diameter over a specific length along the tree stem. Taper varies not only by species, but also by dbh, tree height and other tree parameters. Taper is important for the foresters to predict the upper stem diameters especially in volume calculations.

The main objective of the present study to find out the variation of stem taper with different ages of teak. Three plantations (22, 27 and 35 years old) were selected in Block 01 of Kotagoda teak plantation in Ampara Forest Division for the data collection. Since the plantations were selected from the same Block, it was assumed that the site variation is not significant. Data were collected from 12 sample plots (0.05 ha circular). Dbh, total height, sectional diameters at 5 m and 10 m intervals along the main stem were measured for all the trees in the sample plots.

The the taper for all the trees were separately estimated using the collected data by applying the equation developed by Kozak et al in 1969. For this reason, the 1969 equation was re-parameterized for three ages of the selected plantations separately. Then those three models were statistically tested to identify whether they were significantly different from each other. The results revealed that, the equations were not different from each other proving that the taper does not vary in significant manner for teak with the age. Therefore, a common model was finally developed to estimate the taper for teak irrespective of age. For this reason, the pooled data of all three plantations were re-fitted to 1969 model estimate a completely new set of paramters.

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.

Evaluation of Teak Growth in Farmer Woodlots in Sri Lanka

Evaluation of growth of teak (Tectona grandis) managed as farmer woodlots in dry and intermediate zones of Sri Lanka with reference to selected soil physical and chemical properties
by
Thilina Jayarathne and Upul Subasinghe

The replanting activities using new species were started in Sri Lanka as early as 1680s with the introduction of teak. Since then teak has become widely planted in dry and intermediate zones of the Island. One of the main methods of establishing teak plantations was by the farmer woodlots with a participatory approach.

However, the growth studies of those woodlots have not widely been conducted in Sri Lanka to identify the social issues and the management problems. Therefore this study was conducted to identify the growth of teak under diffferent soil parameters of farmer woodlots and to identify the possible relationships among growth parameters and soil properties. For this purpose, 17 teak plantations were selected for the data collection with age varying from 8 to 13 years. Those plantations were seleced from Anuradhapura and Polonnaruwa Forest Divisions to represent the dry zone and from Kurunegala Forest Division to represent the intermediate zone. Three farmer woodlots from each plantation were randomly selected and three sample plots were laid in each woodlot. Dbh and total height were measured for all trees in each sample plot. Bulk density, pH, mechanical properties, colour, soil nitrate, phosphorus, potassium, magnesium and calcium were measured using standard methods at the laboratory for the collected soil samples.

After statistical and graphical analysis of those variables, it was observed that both height and dbh indicated exponential relationship with plantation age. The sand% of the selected plantations varied from 68.6 to 96.4%. The clay% varied from 0.3 to 7.5%. Silt% changed from 3.2 to 27.2%. The observed soil types were belonged to sand, sandy loam and loamy sand. The heighest bulk density was 2.313 gcm-3 while the lowest was 0.896 gcm-3. The observed nitrate values varied from 2.133 to 7.466 ppm. The highest and lowest values of phosphorus concentration were 254 and 56 ppm respectively. Potassium varied from 4.126 to 8.326 ppm. However, calcium was not detected for most of the soil samples. It was important to note that the pH values were below 7.0 for all plantations.

When the sand% of soil increased, the growth of teak showed a decreasing trend and higher growth rates were observed with increasing clay%. Moreover, both height and a growth index developed for this study showed an increase with high amounts of nitrogen. Moreover, it was observed that soil nitrogen and phosphorus tend to increase with increasing clay% of soil. Growth of teak in most farmer woodlots are in between height classes II and III according to the yield tables published by Sri Lanka Forest Department.

Determination of Biomass and Carbon for Pinus caribaea in Sri Lanka

Determination of Biomass and Carbon for Pinus caribaea in Sri Lanka
by
Upul Subasinghe and Gayani Muinasinghe

Forests in Sri Lanka contribute to the mitigation of global climate change through sequestrating a net amount of CO2 and also maintaining C stocks as forest biomass. Therefore a research was carried out to study the biomass and C storage by the forest plantations in Sri Lanka. 27 year old Pinus caribaea plantation from Low Country Wet Zone of Sri Lanka was selected for this study and the required measurements were taken using 0.05 ha sample plots. Core samples were obtained to calculate the stem biomass and C withoug felling the trees. In order to determine the branch and leaf mass and C values, those were representatively sampled. C was analysed using Walkley-Black method.

It was found that the above ground tree mass of a 27 year old Pinus caribaea tree was 368.9 kg and the C amount was 215.9 (58.5%) respectively. The C% of the canopy was 64.5% from the dry mass. The C% of the primary, secondary and tertiary branches and leaves were 61.7%, 59.1%, 79.6% respectively.

Studies on Forest Management

The following studies have been conducted by Upul Subasinghe for different forest species.

1. Prediction of individual tree volumes of Pinus nigra in Great Britain, Tectona grandis in Sri Lanka and Eucalyptus grandis in Sri Lanka

2. Modelling dbh and height gorwth of Eucalyptus grandis

3. Modelling crown parameters of Eucalyptus grandis

The abstracts of those studies will be published soon.

Forest Management in Sri Lanka

1. Forest plantations in Sri Lanka

The area of natural forests has declined drastically during the last 100 years. With the decline of the natural forest, the main alternatives for meeting the present and future needs for wood are trees grown on non-forest land, and forest plantations. With the expanding population and economy, the demand for industrial forest products, logs, and fuelwood will continue to grow. At present, Sri Lanka is almost self-sufficient in most wood-based forest products, but imports appear to be increasing. Also, some of the wood supplies are being met from illicit fellings. Also the gap between demand and sustainable supply of roundwood will continue, which means that action needs to be taken now to meet future needs. If the supply of wood from home gardens and other non-forest lands will decline in the future, there is an even greater need for intensively managed forest plantations.

Forest plantations were established for the first time in the 1870s, although most of the planting has taken place since the 1950s. Within that period, about 89,000 ha of forest plantations of varying quality have been established. This area comprises some 5000 ha of mainly fuelwood plantations, which are under the control of tea estates and a tobacco company.

Forest plantations in Sri Lanka were mainly established using exotic species due to their faster growth rates over the indigenous species. Although the history of introducing exotic timber species goes back to 1870s, most of the planting has taken place since the 1950s. The idea of this exercise was to have an alternative timber resource to protect the existing natural forest and to rehabilitate the environmentally damaged areas within a short period of time.