JAS log volume estimates of New Zealand radiata pine and Douglas ...

JAS log volume estimates of New Zealand 

radiata pine and Douglas-fir logs 

J.C. Ellis, D.H. Sanders and D. Pont* 

Abstract 

Sectionally measured radiata pine and Douglas$r sawlog data 

has been analysed to study the relationship between true volume 

and that derived using the Japanese Agricultural Standard (JAS). 

Although JAS volume estimates on logs of average dimensions 

are close to true cubic, large errors are introduced with increase 

in log taper and decrease in small-end diameter. 

Introduction 

Softwood logs exported from New Zealand are almost all sold 

on volume based on the Japanese Agricultural Standard (JAS). 

This scale, now in metric, has been in use since 1945 (Zumwalt, 

1946). Within New Zealand, logs have historically been sold on 

underbark volume, although some local board rules were used 

to a limited extent (Duff, 1954). The NZ forest industry is used 

to being paid on true cubic content. There is no F i relationship 

between JAS and cubic metres and this has caused distrust 

amongst those being paid on the basis of JAS cubic metres. In 

1993 the Canterbury Sawmillers Association published a notice 

in the local paper (The Christchurch Press, February 13,1993) 

warning those intending to sell logs on the basis of JAS cubic 

metres. 

This study was undertaken to provide average conversion values 

between JAS and cubic metres for logs covering a range of 

small-end diameters, length and taper. 

It is normal practice for individual forestry companies to compile 

and use their own conversion values to relate volume in JAS 

to NZ cubic metres and vice versa. The conversion values are 

used to relate JAS to true cubic metres for stand reconciliation, 

contract payment and log purchasing and selling. 

Scaling for JAS 

Volume in JAS is derived from two formulae, one for logs of less 

aan 6.0 metres in length and the other for logs of 6.0 metres and 

longer, (Ellis 1994). For short logs with little eccentricity, volume 

is that of a rectangular solid based on the shortest diameter 

through the sawn small-end of the log of the same length as 

shown in Figure 2. 

Mgure 1 The JAS volume of this load of logs is about 30% less than 

true cubic 

Figure 3 

The portion of the rectangle at the smalland falling outside 

the log is considered to be equal to the taper portion of the log 

outside h rectangle, further along @ log. 

For long logs, tb JAS formula has a taper allowance and it 

is possible for the rectangular solid (represknted by the JAS 

formula) to be outside the round of the log for its whole length 

- 

* NZFRI, Rotorua. 

(Fgm 3), although it is more usual to include part of the larger 

end of the log. 

Diameters at the small-end are rounded down to the nearest 

even centimetre (single centimetres for diameters below 14 cm) 

and based on the &st axis unless there is a difference of at 

least 6 cm between s M and long axis. If the shortest axis is 40 

cm or larger, two centimetm am added for e v e r 

between shortest and longest diameter. Lengths of 3.0 m and 

above m rounded down to the nearest 0.2 m except for the 

lengths 3.3 m, 3.65 m and 4.3 m which fit in between the normal 

classes (Kuchimura, 1989). 

Basic data 

In the 25 years prior to 1983 the New Zealand Forest Service used 

32 N.Z. FORESTRY MAY 19%

volume tables based on small-end diameter (underbark) and 

length to estimate the volume of logs removed from state exotic 

forests. Each speciedlocality had a separate table once logging 

commenced. The total number of tables produced was about 400 

with up to 100 in use at any one time. Tables were tested and 

more often than not updated within five years of issue. 

The basic data for each "approved" log volume table comprised 

at least 200 logs. Each of them was sectionally measured 

for volume. This was based on diameters measured with girthtape 

at butt, 1.5 metres (5 feet), 3.0 metres (10 feet), 6.0 metres 

(20 feet) and so on from the butt, and at the small end so that no 

section exceeded 3 metres (10 feet) in length. Smalian's formula 

was then applied to each section. 

Many thousands of sectionally measured logs were accumulated 

but for this study only the data of radiata pine and Douglas- 

Table 1 

Logs 

sed 

(em) 

length 

(m) 

taper 

(cmlm) 

Table 1 Radiata pine 

Table 2 

Logs 

sed 

(em) 

length 

(m ) 

taper 

(cmlm) 

Table 2 Douglas -fir 

min 

4.8 

2.4 

0.0 

mi11 

5.8 

38574 

mean 

25.5 

7.9 

1.09 

5733 

mean 

20.0 

max 

88.4 

18.0 

9.5 

--- 

2.4 

0.1 

8.4 

1.10 

inax 

66.5 

15.4 

5.2 

length class (m) 

small-end diameter class (cm) 

I 

10-20 20-30 30-40 ALL 

Table 4 Number of Douglas-lir logs by diameter and length 

fir are used. The full range of data is shown by small-end diameter 

(sed), length and taper in Table 1 and Table 2. 

From the above range of data only those data which represented 

the normal extremes in log dimensions were used. Tables 

3 and 4 show the number of logs by length and small-end diameter 

for radiata pine and Douglas-fir that are used in this study. 

Basic data used to calculate the conversions were principally 

collected from domestic sawlogs rather than export logs. The 

large amount of data adequately covers the lengths and small-end 

diameters common in current sawlogs. Many of the log measurements 

were from "old crop", not young-crop stands. It is thought 

that the use of taper classes should adequately represent logs from 

youngcrop stands. The present log distribution of sed, length and 

taper frts into the 0.8-1.19 cmlm taper class for the varying smallend 

diameter and length classes required for export grades. 

The study 

A computer program was written to process the basic data and 

calculate sectional volumes and volumes by a variety of methods 

including JAS. The small-end diameters and lengths were also 

calculated by rounding or truncating according to the particular 

scaling conventions. 

It should be noted that the basic data (diameter and bark thicknesses 

along the length of each log) were in imperial units until 

1978. Such data were converted to metric using the values of 1 

inch = 2.54 centimetres and 1 foot - 0.3048 metres. For further 

calculations the exact figures for diameter, bark thickness and 

length were used with no rounding. 

For each log the computer program calculated small-end 

diameter (u.b.), actual volume, JAS volume, length and taper. 

These data were then written to two summary files (radiata pine 

and Douglas-fir) and analysed by a statistical program which calculated 

the bias in JAS volume for small-end diameter, length 

and taper classes. Bias is defined as 100* (JAS volume - cubic 

metres)/JAS volume. 

Results 

It was found that over half of the bias in JAS volume (56% radi- 

Table 3 

'igure 4a 

3.0-5.9 metre radiata pine 

"8'1b.79 0.8.; .I 9 1 .2-; 59 1.6-; .99 2-;.A9 

Taper classes cmlm 

Tabk 3 Number of radiata pine logs by diameter and length 

Figure 4a Bias in JAS volume on sed and taper 

N.Z. FORESTRY MAY 1996 33

Figure 4b 


Figure 4f 

9.0-11.9 metre Douglas fir 

SED class 

10-20cm 

20-30cm 

30-40cm 

(~glLb.79 0.8.; .I 9 1.2-; ,59 1.6-\ 99 2-d.k 


Figure 4b Bii in JAS volume on sed and taper 

Figure 4c 


@8!/b79 0.8-; 19 1.2- 5 1.6-) ,90 21:!J9 

Taper classes crnlm 

Figure 4c Bii in JAS volume on sed and taper 

Figure 4d 


(88!Lb.79 0.8.; .I 9 1.2.; .59 1.6-; .99 2-d.A9 


ata pine, 62% Douglas-fir) could be accounted for by changes in 

sed, taper and length. Figures 4a to 4f show the bias in percent 

between JAS volume and true volume plotted on taper and sed 

for each length class. 

The greatest change in bias is due to changes in taper, followed 

by sed and then length. The figures show that the bias 

increases from +lo% (for 0.4 - 0.79 cdrn taper) to -77% (2.0 - 

2.39 cmlm taper) in radiata pine of 9.0 - 11.9 m length and 10 - 

20 cm sed. For any taper class the change in bias on sed class is 

at a maximum in the 2.0 - 2.39 cdm taper where the bias 

changes from -77% (10 - 20 cm) to - 1 1 % (30 - 40 cm) for radiata 

pine in the 9.0 - 1 1.9 m length class. In the maximum taper 

class (2.0 - 2.39 cdm) and minimum sed class (10-20 cm) bias 

changes from -54% for 3.0 - 5.9 m length to -77% for 9.0 - 11.9 

m length in radiata pine. The bias in Douglas-fir logs is less than 

that 6 radiata pine. 

Conversion factors between cubic metres and JAS units 

Conversion values were calculated from the respective JAS vol- 

Table 5a 

Taper (cmlm) 


10-20 

20-30 

30-40 

0.4 - 0.79 

0.887 

0.925 

0.970 

0.8 - 1.19 

0.809 

0.880 

0.937 

1.2 - 1.59 

0.753 

0.837 

0.901 

1.6 - 1.99 

0.690 

0.815 

0.879 

'88!Lb.79 0.8-; .I 9 1 .2-'I .59 1 .6-; .99 2-d.L 


Figure 4d Bii in JAS volume on sed and taper 


2.0 - 2.39 0.651 

0.782 0.854 

Table 5a Conversion Prom JAS to cubic metres mdiata pine 3.0 - 5.9 

m 

Table 5b 

I 

Taper (cm/m) 


~8!Lb.79 0.8-;1 9 1 .z-\,a 1 .s-; 2-A9 


Figure 4e Bias in JAS volume on sed and taper 

Table 5b Conversion from JAS to cubic metres radiata pine 6.0 - 

8.9 m 

34 N.Z. FORESTRY MAY 1996

Table 5c 

Taper (cmlm) 

0.4 - 0.79 

0.8 - 1.19 

1.2 - 1.59 

1.6 - 1.99 

small-end diamel 

20-30 

1.119 

1.033 

0.942 

0.867 

r class (cm) 

30-40 

1.127 

1 .O68 

1.022 

0.959 

2.0 - 2.39 0.566 0.799 0.901 

Table 5c Conversion from JAS to cubic metres radfata pine 9.0 - 

11.9 m 

Table 5d Conversion from JAS to cubic metres Douglas-& 3.0 - 

5.9 m 

Table 5e 

10-20 

1.115 

0.942 

0.795 

0.662 

umes and actual volumes for each small-end diameter, length and 

taper class. Each conversion factor is the JAS volume divided by 

the actual volume. Tables 5a to f give conversions from cubic 

metres to JAS, which is the amount of JAS per cubic metre. To 

convert from JAS units to m3, the JAS volume is divided by the 

table value. 

The precision of each table value (Table 5a to f) was calculated. 

The probable limit of error for each value was generally 

within 0.5% for radiata pine and within 1.3% for Douglas-fir. 

However, where there are relatively few observations such as the 

10-20 cm sed in the 2.0-2.39 cmlm taper class the PLE averaged 

9% and 16% for radiata pine and Douglas-fir respectively. The 

probable limit of error (PLE) is the confidence interval (approximately 

2* standard error) of each conversion expressed as a percentage 

of the respective average conversion value. 

Discussion 

Bias in JAS volume (Figs 4a to f) and implied in the conversion 

values (Tables 5a to f) are from sed which is based on girth measurement 

Any overestimate in diameter due to the use of the girth 

tape is common to sed and volume and therefore has no effect on 

the result. However, the JAS conventions of sed always being 

rounded down, and sed being based on the shortest axis, do have 

a direct bearing on volume. 

For most of the diameter range (14 cm upwards) the JAS sed 

is the diameter in even centimetres. For example, a diameter 25.9 

cm is recorded as 24 cm in JAS. In theory this rounded-down 

JAS should be 1.0 cm lower than the actual sed In practice, sample 

data show the rounded-down JAS about 0.9 cm lower than 

the actual sed. This is because where the diameter is close to the 

even centimetre, the scaler identifies a 2 mm division more easily 

than a single millimetre. 

In this study the effective JAS diameter is based on the girth 

tape and therefore approximates an average of shortest and 

longest axis of the small-end section. The difference between 

using JAS based on average sed and "shortest" sed was examined 

on an external data set of 2253 export logs measured 

throughout New Zealand. 

Table 6 below shows the diameter and volume differences due 

to using a short axis instead of an average diameter. 

Species 

I 

small-end dia meter class in centinetres 

20.0 - 29.9 30.0 - 39.9 

I 

0.69 

(2.7%) 

0.49 

(1.9%) 

0.028 

(5.2%) 

0.026 

0.99 

(2.9%) 

0.65 

(1.9%) 

0.OM) 

(6.3%) 

0.046 

Table 5e Conversion from JAS to cubic metres Douglas-& 6.0 - 

8.9 m 

Vol reduction (m3) 

Table Sf 

Table Sf Conversion from JAS to cubic metres Douglas-& 9.0 - 

11.9 m 

l4.h%) 

(4.8%) 

Table 6 Diameter and volume reductions due to use of short ads on 

end section 

Values in brackets give volume reduction as a percentage of 

average volume. 

The above reductions are independent of taper and for practical 

purposes do not affect length. Small-end diameter and 

species do have an effect on the magnitude of the reduction. Volumes 

used in compiling the graphs (Fig. 4) and conversion values 

(Tab. 5) have been altered by the reductions in Table 6. 

Douglas-fir is more cylindrical and less tapered (for same sed and 

length) than radiata pine. Thus Douglas-fir has higher JAS to 

cubic metre conversions than radiata pine. 

N.Z. FORESTRY MAY 1996 35

Acknowledgements 

This work would not have been possible without the foresight 

of the late G. Duff who, with G.A.V. Bary, pioneered log volume 

tables in New Zealand for exotic conifers. The basic data 

were painstakingly collated and corrected by J. Penman but many 

New Zealand Forest Service and Forest Research Institute staff 

have unknowingly contributed to this work. The authors would 

like to thank Messrs M.O. Kimberley and A.D. Gordon for their 

help in setting up the statistical programs. 

References 

Anon., 1967: Japanese Ministry of Agriculture and Forestry Notification 

No. 1841 of December 8, 1967, new standards for softwood and 

hardwood logs. 

Duff G., 1954: Methods of measuring log volume in NZ. New Zealand 

Timber Journal. Vol. 5 (9110) 1954. 

Ellis J.C., 1994: Procedures for the measurement of roundwood. Second 

edition. New Zealand Forest Research Institute, Rotorua. 

Kuchimura, K. 1989: Log business in Japan. Forest Products manual 

series (1). Japan Lumber reports. 1-14-18 Minato, Chuo-ku, Tokyo 

104 Japan. 

Zumwalt Eugene V., 1946: Log scaling in Japan. American Journal of 

Forestry 44(7). 

C.3 JAPANESE AGRICULTURAL STANDARD (JAS) 

KOREAN INDUSTRIAL STANDARD (KIS) 

This method involves measuring small-end diameter inside bark 

and length of individual logs, then reading volume off tables compiled 

from given formulae. The formulae were developed by the 

Japanese Ministry of Agriculture and Forestry. As JAS (KIS) 

measures cubic content (in m3) rather than board content, there is 

a better correlation between this measure and the actual cubic 

content. A correction in the interpretation of this method has 

meant that measurement of small-end diameter 'through the pith' 

is now 'through the centre'. 

C.3.1 Small-end diameter 

1. FOR SMALL-END DIAMETERS LESS THAN 14 CM 

Measure the shortest small-end diameter inside the bark through 

the centre of the log. Round down to the nearest whole centimetre. 

Example: 12.00 - 12.99 cm, record as 12 cm. 

2. FOR SMALL-END DIAMETERS EQUAL TO AND 

GREATER THAN 14 CM 

Measure the shortest small-end diameter inside the bark 

through the centre of the log. Round down to the nearest even 

2-cm interval. 

Example: 16.00 - 17.99 cm, record as 16 cm. 

Measure the longest* diameter inside bark through the centre 

of the log. This need not necessarily be at right angles to the 

shortest diameter. Round down to the nearest even 2-cm interval. 

Note that the commercial convention in NZ is to measure 

the second diameter at right angles to the shortest. 

If the shortest of these two diameters is between 14 and 38 cm 

(inclusive), then for every difference of 6 cm add 2 cm to the 

shortest diameter. 

If the shortest of the two diameters is equal to or greater than 

40 cm then for every difference of 8 cm add 2 cm to the shortest 

diameter. 

Examples: 

"Shortest" "Long" Difference Record as 

13 20 7 13 

16 20 4 16 

16 22 6 18 

16 28 12 20 

38 44 6 40 

40 44 4 40 

40 48 8 42 

C.3.2 Length 

Length is defmed as the shortest distance between the sawn log 

ends. Lengths are measured in metres and tenths of metres and 

rounded down to each fixed-length class. For most export sales 

there is an agreed overcut (about 0.1 metres) to ensure that logs 

are not less than the fmed lengths negotiated with the buyers. 

C33 Volume 

1. FOR LOGS LESS THAN 6 M LONG 

where 

D = shortest diameter 

L = length 

2. FOR LOGS EQUAL TO OR GREATER THAN 

6 M LONG 

where D = shortest diameter 

L = length 

LC = length in metres rounded down to 

nearest whole number 

(LC-4)/2 = a factor for taper. 

Example: 

Therefore 

Short diameter = 26cm 

Long diameter = 32 cm 

Length = 8.1 m 

D = 28,L=8.1,L6=8 

Volumes are calculated to four decimal places and rounded to 

three. 

CONSULTATION 

RECOGNITION 

The following have applied for recognition as general 

forestry consultants in New Zealand and overseas. 

Bruce McVeigh Revington 

Owen Cox 

Neil George Woods 

Ian Marshall Wallace 

Donald Robert Hammond 

Alexander Roberton Rae 

Opotiki 

Wellington 

Auckland 

Gisbome 

Rotorua 

Christchurch 

The following has applied for recognition as a specialist 

forestry consultant in New Zealand and overseas. 

Robert Browne Tennent 

Rotorua 

Under the NZIF constitution, any members of the Institute 

may send objections in writing within 40 days of Journal 

publication to the Registrar, NZIF Consultants 

Committee, PO Box 1340, Rotorua. 

36 N.Z. FORESTRY MAY 1996

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