CONSTRUCTION OF A PRECISE GROWTH MODEL TO PREDICT THE NDIVIDUAL STEM VOLUME OF Alstonia macrophylla WALL. EX G. DON

W A R T W Bandara, S M C U P Subasinghe
Department of Forestry & Environmental Science, University of Sri Jayewardenepura

In order to reduce the pressure on existing Natural Forests in Sri Lanka, Forest Department promoted growing timber species as plantations and in home gardens. Among the suggested species Alstonia macrophylla (Hawarinuga) has recently become popular due to its fast growth rate, ease of establishment and timber value. There are about 1913 ha extent of Alstonia macrophylla plantations at the end of the year 1998 maintained by the Forest Department of Sri Lanka. However, this figure must be higher than that because many other private organizations are establishing Alstonia macrophylla plantations in the wet zone in large scale. This species is also grown in home gardens, alleys and borders as non-blocks (non-plantations).

However, at present there is no method at present for estimating the stem volume of this species, which is considered as the most important variable in commercial forestry. Therefore a mathematical model was constructed in this study to predict the individual stem volume of Alstonia macrophylla trees grown in plantations.

Since Alstonia macrophylla is widely found in wet zone of Sri Lanka, study sites were selected from Galle (two even-aged plantations from Pituwala and Wattehena Beats) districts. The ages of these plantations were 19 and 16 respectively. Ten 0.02 ha circular plots with slope correction were randomly laid out for each plantation, in order to measure the necessary parameters from the individual trees. Diameter at breast height (dbh), total height and height to the crown base of all the trees inside the plots were measured. Newton’s formula was used in this research because it is the most accurate method. In order to calculate the volume using the Newton’s formula, the stem of each tree was hypothetically divided into 4 -5 sections. Then the bottom, mid and top diameters and section lengths were measured using Speigal Relascope and Blume Leiss Altimeter respectively. The final section of the tree was assumed as a cone and only the bottom diameter and height were used in that particular section. The total volume of each section was estimated by adding the section volumes calculated using Newton’s formula to the volume of the final section.

First a theoretical model structure was developed using the relationship of form factor with volume, height and area at the base. Regression analysis was used to fit the data into the model. Untransformed as well as transformed combinations of all variables were tested. In this procedure the combined variable (basal area * tree height) was always kept as the first explanatory variable. After trying with many combinations of selected variables with volume, final model was selected using its compatibility with the real world, R2 values, and residual distributions, model bias value and modeling efficiency. The selected models at the preliminary stage indicated very high performance and insignificant bias. In order to select a final one, the above models were validated with a new set of data. The final selected model in this study to predict the individual stem volume with insignificant bias of Alstonia macrophylla is; √v = 0.659 log BA*Ht + 0.00404 √Cr ht

EFFECT OF DIAMETER ON VOLUME MEASUREMENTS OF Pinus caribaea (MORELET).

S Hewage & S M C U P Subasinghe
Department of Forestry & Environmental Science, University of Sri Jayewardenepura

Foresters use different methods to estimate the individual tree volume since it is the most important parameter in commercial forestry especially at the mature stage. Among those methods, the most common way is to use Smalian’s, Huber’s and Newton’s formulae. In order to use these three formulae the stem should be divided into sections and volume of each section should be determined separately. Huber’s formula is the easiest one to use because it needs only one diameter measurement of the log. Smalian’s formula needs two diameter measurements while Newton’s formula needs three. Log length is required for all three formulae. Due to the low number of measurements Huber’s formula is more popular among the foresters. However, Smalian’s and Huber’s formulae can introduce errors because they use fewer measurements compared to the Newton’s formula. Therefore the present study was conducted to identify the variation of the error with increasing diameter of trees when Huber’s and Smalian’s formulae are used. Newton’s formula was considered as the one that provides precise values in volume estimation.

Present study was conducted in the 26 year old Pinus caribaea plantation in Yagirala Forest Reserve situated in the low country wet zone of Sri Lanka. In order to represent the whole area of the forest, stratified random sampling method was used and one 0.05ha sample plot was laid in each stratum (i.e., valley, slope and ridge).

Each tree of the plot was divided into twelve 1m long sections using a ranging staff. Bottom, mid and top diameter of the each section was measured using the Spiegal relascope. Other than above measurements, diameter at the breast height and height of the tree were measured using the diameter tape and the Blume Leiss Altimeter respectively.

In order to find out whether the diameter at breast height affected on volume calculations using above formulae, trees were grouped into two centimeter diameter classes. At each diameter class, volumes estimated using Huber’s formula were tested separately for different section lengths using one way ANOVA. Results indicated that at 95% probability level diameter does not have a significant influence in volume measurements for Huber’s formula up to twelve meter stem length.

First part of this study was conducted to identify the effect of Huber’s and Smalian’s formula in volume calculations without considering the diameter differences of trees in the forest and results proved that Huber’s formula produced least errors when compared with Smalian’s formula. However, in this instance the maximum stem length that can be measured using Huber’s formula became 6m. According to both tests, it can be concluded that Huber’s formula can be use effectively up to 6m stem length in volume calculations with out considering the diameter range of trees.

PREFACE

Sustainable Development is development which takes account of Social, Economic, Environmental and Technological dimensions. Development which came with industrial revolution and associated innovations in Science and Technology without heeding for environmental repercussions have resulted in many environmental problems which are evident daily. At an unprecedented rate natural resources are depleting, global climate is changing, most lands are becoming unproductive, natural disasters are reported from all over the world and health and safety problems faced by the human population are daily getting more complex irrespective of the advances in the field of medical science. Lack of development also result in many environmental complexities like over exploitation of natural resources, malnutrition etc. Hence it is incontestable that for the betterment of the society and natural environment development must continue but in a sustainable manner.

The theme of the 10th Annual Forestry and Environment is “Forestry and Environment for Sustainable Development”. The symposium organized by the Department of Forestry and Environmental Science, University of Sri Jayewardenepura is held for the 10th time this year. The objective of this symposium is to provide a neutral forum for research scientists and practitioners in the field of Forestry and Environmental Science to present and deliberate their findings in front of peers and policy makers. This document contains 59 abstracts of papers under Forest Resource Management and Utilisation, Natural Resource Management and Utilisation, Ecosystems and Ecosystem Management, Plant Propagation and Tree Improvement, Pollution Control and Waste Management, Biodiversity, and Sustainable Agricultural Practices. The key points and recommendations emerging from these presentations will be very useful in formulating strategies for Sustainable Development in Sri Lanka. Each session will be preceded by a theme talk by an eminent scientist in that field.

We wish to acknowledge the financial support granted to us by the University Grants Commission, the Forest Resource Management Project and the National Ozone Unit. The publication of this abstract was sponsored by the Forest Resource Management Project.

We also wish to thank all invited guests, authors, participants, theme speakers and chairpersons of sessions and supporting staff who made this event a reality. We wish all participants a thought provoking and rewarding symposium.

Symposium Organising Committee
Department of Forestry & Environmental Science
University of Sri Jayewardenepura
2nd December 2005

Forestry and Environment Symposium organized by University of Sri jayewardenepura

Abstracts of the papers published at Thenth Forestry and Environment Symposium 2005organized by University of Sri jayewardenepura can be found here.