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

Abstract

is the most important parameter in commercial forestry especially at themature stage. Among those methods, the most common way is to useSmalian's, Huber's and Newton's formulae. In order to use these threeformulae the stem should be divided into sections and volume of each sectionshould be determined separately. Huber's formula is the easiest one to usebecause it needs only one diameter measurement of the log. Smalian'sformula needs two diameter measurements while Newton's formula needsthree. Log length is required for all three formulae. Due to the low number ofmeasurements Huber's formula is more popular among the foresters.However, Smalian's and Huber's formulae can introduce errors because theyuse fewer measurements compared to the Newton's formula. Therefore thepresent study was conducted to identify the variation of the error withincreasing diameter of trees when Huber's and Smalian' s formulae are used.Newton's formula was considered as the one that provides precise values involume estimation.

Present study was conducted in the 26 year old Pinus caribaea plantation inYagirala Forest Reserve situated in the low country wet zone of Sri Lanka. Inorder to represent the whole area of the forest, stratified random samplingmethod was used and one O.OSha 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 aranging staff. Bottom, mid and top diameter of the each section wasmeasured using the Spiegal relascope. Other than above measurements,diameter at the breast height and height of the tree were measured using thediameter tape and the Blume Leiss Altimeter respectively.

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

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