On the Results of Some Investigations of Errors by Use of Increment Borers

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On the Results of Some Investigations of Errors by Use of Increment Borers

E. Ohtomo

Government Forest Experiment Station

Ministry of Agriculture ,and Forestry, Meguro, Tokyo (Japan)

1. lntroduction

In 1957 the national forest of Japan adopted the sampling method for forest inventory. Two years after füat, the result of such an inventory compared with the value so far obtained, gave a volume of 122 per cent and a growth of 173 per cent of the method used so far. Apart from the volume, the significant increase in the estimate of the growth raised a controversial problem and in 1959, six regional forestry offices in the country examined the accuracy of the survey on the growth by use of increment borers on the important species. The outline of this investigation is described in the following section. Because the writer obtained the data of this investigation only recently, the statistical examination of them could not be made before the submission of t!his paper. The conclusions we made in this paper do not differ much from those of the statistical test. For one part of the design consultation was made with staff-members of the Government Forest Experiment Station. The final design was m~de by members of the P1anning Section of the Forestry Agency. Unfortunately, the design included some inadequacies.

2. Outline of the lnvestigation

In the following table we find the responsible regional forestry offices and the species of investigation:

Regional Office ·

Kitami Sapporo Aomori Tokyo Osaka Kochi

Species

Picea j ezoensis Carr.

Abies Mayriana Miyabe et Kudo.

Thujopsis dolabrata Sieb. et Zucc.

Chamaecyparis obtusa Sieb. et Zucc.

Pinus densiflora Sieb. et Zucc.

Cryptomeria japonica D. Don.

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Stands for the survey were selected of those management units, where sampling survey had been completed in 1958. Each stand consisted of an area of 0.5-1.0 ha.

Trees were measured and classifüed in diameter classes with 2 cm intervals. Site g:riadient for each tree was recorded. Based on this result, the di-ameter dass was further divided into three or four groups and ten trees or more were selected for survey for each group. The site gradient was grouped into even (less than 5), gentle (5-15), medium (15-30), and steep (more than 30) and trees to be surveyed were selected in almost the same number for each gradient. Increment borer was inserted into the selected trees from the both ends of the maximum, minimum and average d.b.h. to fhe center of the trunk and the radius increment for five years was measured in 0.5 mm unit. Such values are denoted as a1, a2, h1, b2, c1, c2, respectively. In this case, the angle between the horizontal plane and the inserting direction of incre1!1ent borer was measured. Also, the gradients of standing trees were measured. After this trees were cut and a disk was taken at that cross section where the increment borer was inserted. 'J1he angle of the iillSertJion of the iborer to the annual ring on the disk was measured. (Refer to the Appendix 3.) More over the radius increments of five years in the maximum, minimum and mean d.b.'h. were measured as a'i, a'2, b'i, b'2, and c'1, c'2 • As the true center of the wood was known on the disk, the true maximum and minimum radius increments were also measur-ed from the center as Ai, A2, B1, B2• The increment in the basal area of the past five years was measured with planimeter and theorebical radius increment d of the same period was calculiated under the assumption that annual rings were circularly shaped. Based on these results, examination was made on rhe following A, B, and C.

A. Comparison of true value with the mean of s1x observations made with mcre- ment borer.

B. Comparison of the above mentioned with

C. Comparison of d with each factor in the above B.

(In these connection, more details - notations and A, B, C - aiie given m the Appendix.)

Stem anailysis was made on cut 1:rees and the volume increment for five years (Z) was determined and comparison was made among the above (Z), the increment obtained from the volume table based on d.b.h. and tree height (Z'), the increment obta-ined from the volume table based on d.b.h. only (Z"), the increment based on growth rate (Z"'), and the increment mentioned in the past forest survey document

(Z'"').

Tue results of the above comparison have to be omitted because of the limited space of this report but the findings of experiments on the above six species based

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on the reports and information submitted by each regional forestry office are summarized as follows:

3. Results of investigation of each major species

i) Picea jezoensis

The number of sample trees was 30 and t!he range of d.b.h. was 22-56 cm.

When the mean values of six observations with increment borer were compared with the corresponding true values, the observation had a tendency to produce small values in general but for 30 sample trees as a whole, values almost agreed.

I d B f S 2 b h ^a¹^{+ ... +}^h² d ^{c, +}c2

n regar to o , ot ₄ an ₂

. d. d h. h 1 (3 5 ) th A, + · · · + Bo

m 1cate 1g er va ues . per cent an ₄ - • As for d (C), A, + -~· + B² d 6 6 11 d ^C,⁺^C2 d a, + ... + h2

prove . per cent sma er an ₂ an ₄ differed only 3.3 per cent.

The insertion angle of increment borer was within the limit of

±

6° against the stem axis and in rare case it was 10° or 22° which however worked almost no effect on observation values as a who,le. In oase of Picea jezoensis, when the increment borer was applied, increment cores extracted from trees had a tendency to be slightly compressed but as the mean compressibility was only 0.05 per cent, there was no serious problem at all.

The volume increment Z", when compared with the true increment Z, was slightly smaller but it was the nearest and Z' was also near but showed a !arger value.

Z"" proved too low to ibe of any signifücance showing about 60 per cent of the true value Z.

ii) Abies Mayriana

'Jlhe number of sample trees was 40. 11he d.b.h. varied between 10-51 cm and the insertion angle of increment borer was almost the same as i). In thi.s case, the mean of increment cores was on the average about 1 per cent higher than that of the true increment values. In this case no tendency of expansion or contraction of increment cores was recognized. The influence of the insertion angle, in view of the deviation of 1 per cent as statet above, a1so offered no problem.

A, + ·

~

^{· +}^Ba was in the average smaller than any of the values. d was smaller than

a1 + ... +h2

4 or and particulary about 9 per cent smaller than

As to the volume increment, Z" was the nearest to Z being !arger by 5 per cent, and Z' was also !arger by 10 per cent and others were smaller by more than 20 per cent.

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iii) Thujopsis dolabrata

The number of sample trees was 30 and the range of d.b.h. was 11-52 cm.

The angle of insertion of increment borer with stem axis was less than

±

4

°.

If the average value of 6 observations was compared with the corresponding true average value, it was by 4 per cent larger.

If compare wrt d . h ^A,^{+ ... +}₄ ^B², t e expressron h . a,

+ ... +

₄ ^h2 was ₈per cent arger an l d the expression

2 was 5 per cent !arger.

If compared with d, all other values were smaller, particularly the expression A,

+ -~· +

B² was the smallest. lt had a difference of -13 per cent. If compared with the volume increment of the stem analysis (Z), all of the estimates were smaller than Z and

Z" was the closest value of -7 per cent and Z' and Z" nearly had the same value.

The value of Z"" in the past forest inventory document was smaller by over 15 per cent.

iv) Chamaecyparis obtusa

The angle of insertion of increment borer with stem axis was all less than

±

2°. Individual mean values of 6 observations were all smaller and the mean smaller by 6.6 per cent.

In this oase it seems that the incr,ement borer did not cut well and cores were thus compressed. W e assume that this is due to the fact that the wood of Chamaecy- paris obtusa is harder than that of other species.

If compared average but

·•h

A, + ...

⁺^B2 h 1 f a,+ ... +h2 1 h .

wie ₄ ^,t e va ue o ₄ was a most t e same m c, ; c² showed a !arger value of 2.8 per cent.

the

If oompared with d, the mean of the six observations values and c,; c² showed a slig'ht 1arger value of 1-2 per cent. lf volume increment was compared with true value (Z), Z' revealed in the average almost no error but Z" was by 11 per cent smaller.

v) Pinus densiflora

Pinus densiflora, if compared with other conifers, tends to grow s1antwise in its nature. The angle of the direction of increment borer to the stem axis was therefore more inaccurate than ~hat of ofuer speoies. lt \'aried mostly Wiithin the range of

±

10

°

and in some extreme cases to -22

°

to +25

°.

^lfthe average of 6 observations and the true average were compared, the mean of the average observation values was larger by 5.3 per cent. This may be due to the fact that the insertion angle, compared with other species, was less perpendicular to the stem ax1s.

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If compare w1t d · h A,

+ ...

₄

+

^B² ^,t e va ue o h 1 f was larger by 11.5 per cent and the expression was by 7.7 per cent larger.

The value of a, + · ~-+ b² was 6.2 per cent larger than that of d, A, + · ~-+ B² -6.0 per cent smaller than d and c, ; c² almost the same with d. In regard to vo1ume increment, the value of Z"" was the closest to the true value (Z). There was unexpectedly almost no error. Z"' and Z" were of too large values, with errors of +9.7 per cent and +17.9 per cent respectively and Z' had an error of -21.3 per cent which is quite a contrast to the results of i) - iv).

vi) Cryptomeria japonica

The number of sample trees was 31 and t:he range of d.b.h. was 7-42 cm.

Because Cryptomeria japonica has a nature of growth straight up and the angle of insertion of increment borer to the stem axis was nearly correct. However, only in the case of this speoies, if tthe angle between the line from the insertion-point to the center (pith) and the insertion-direction of the increment borer was examined, 41 per cent of surveys in number were correct but in other cases, angle of 3 °-24 °, 4.9

°

on the average, was drscovered. If the mean of the averages of 6 observations and that of the true values was compared, the former was slightly smaller than die latter (mean error of -1.6 per cent) which seems to be due to compression if cores were extracted.

A, + ... + B2 d a, + ... + h2

4 an ₄ were almost equal on the average, the latter being 1 per cent larger than the former.

On Vhe contrary, was 1 per cent sma · 11 er t 1an 1 ^A¹^{+ ... +}₄ ^B2 ^A¹+'. .. + B2 4

146 1 ^a,⁺^{... +}^b² ¹⁶¹ d c,+c² 13 1 ^,.,i_ d

was . per cent arger, ₄ . per cent an - -₂- per cent ,arger v.uan . In reference to volume increment, if the •ave:riage of Z is put as 100, Z' was 87, Z" 80 and Z"' 63, each giving a lower estimate value.

4. Conclusion

In regard to the insertion angle of increment bo¹rer, oif a right handed man performed the experiment, the increment borer generally tended to dev~ate to the right side but the angle of •inclination up and down, seems to be generally sma11.

The observation of increment cores proved sometimes smaller or sometimes 1arger than the true value, because of the combined effects of sharpness of increment borer to be used, the compression in the length of cores due to the hardness of wood and the error derived from the angle of insertion of increment borer to the annual

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ring. Therefore, the experiment should be designed to enable to separate these errors.

Because these resulting errors are quite small, it was concluded by the Forestry Agency that the error was negligible. ks, in this oase, many cores were collected from each tree and the mean of average values of them was compared with that of the average true values of all surveyed trees, such conclusion was apparently reached. The lengths of two cores for which increment borer was inserted from both ends of the mean d.b.h. of one tree showed almost no ,difference from each other in Chamaecyparis obtusa and Pinus densiflora but some 10 per cent of the difference was observed in o~her speoies. Accordingly, in the survey •by means of increment borer, with fairly good appro:x!imation we oan extract cores at both ends of the

dbh a¹+ ... + b2

average . . . ₄ is the average lenght of cores at both ends of the maximum and minimum d.b.h. of a standing tree, and the mean radius of the maximum and minimum d.b.h. passing through pith on the ,disk after felling.

Th ere was on y one case 1 f h at ^A,^{+ ...}₄⁺^B2 was equa to t e 1ormer, ut m ot er cases 1 h r b . h

c,+c2 H .

it was always smaller. lt was also always smaller than - -₂- . owever, lt may not be clear what these differences mean.

On 1Jhe assumption that a section me,asured with planimeter was a ciircle ,in form, d was calculated as the radius increment, the relation to which there were various cases, resulting in larger or smaller values. The data ^'SO far available gives such an expLanation that d diiffers significantly from any averages ahove-men1Jioned,

h. h ^A,^{+ ... +}^B2 d c, -t-C2 • d Th . . 'fi

among w 1c ₄ an - -₂- are more approx1mate to . ere 1s no s1gm cant d 'ff 1 erence etween b A, ^-t-^•••₄+ B² an d c, - -+ ₂^-c²^.Th ere ore, - -f c, + c₂^- ²may e use convement y b d . 1 in the fi.eld if basal area growth and o~her conditions are considered. lt can be said that ~he use of increment borer to determine the true volume increment gives in general small value. According to the Forestry Agency, it was found that when Z = 100, Z' = 100, Z" = 97 and Z'" = 76 and the estimate values in the past forest inventory documents weire extremely 1Joo small. While Z" and Z"' can be determined by survey, using increment borer, Z' can not be determined unless height is known in addition to drarrneter. 'I1hus, practioally only Z" and Z"' oan be taken into cons•ideration. Z" is the violume calcuiated from the present d.b.h. minus Vhe volrume ca1culated from the d.b.h. five years ago measured with rincrement borer.

In this case the tarif table was used. Z"' is the method in which volume increment ratio (Refer to Meyer: Forest Mensuration, pp. 226-228) is obtained from d.b.h.

increment ratio and then volume increment is determined. From the resu1t of t!he experiment, it can be said that we can obtain better values by the method of applying the difference of volume (Z") rather than by the method of applying the increment ratio (Z"') and the difference between Z and Z" may be very small.

Summaving if volume increment is estimated by use of increment borer, this may be somewhat underes,timated, but the observation error of d.b.h. growtih will not

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necessarily be a problem. lt would be better to apply the volume difference method for calculating volume increment. In order to prevent error arising from compression, use of sharp increment borer is recommendable.

Appendix 1. Notation

a1, a2, h1, b2, c1 and c2 are observation values of core lengths of d.b.h. in a standing tree.

/ minimum diameter diameter

- maximum diameter

a/, a2', b/, b2', c/ and c2' are observation values, in crossectional cutt at d.b.h., corresponding to a1, a2, b1, b2, c1 and c2.

A1, A2, B1 and B2 are true values of radius increments in five years corresponding maximum and minimum diameters in crossectional cutt

minimum diameter

/

- maximum diameter

Appendix 2. Explanation of three examination A. B and C on page 3.

A) Computation of compression al + a2 + bl + h2 + cl + c2

6

B) Compute as follows 1) al + a2 + bl + b2

4

2) Cl+ C2 Al +¾ +B1 +B2

2 4

3) Al + A2 + Bl + B2 Cl -

4 4) ^Al+ A2 + Bl + B2

c2- 4

6

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C) By means of a planimeter, compute two basal areas in present time and last five years ago.

Find two diameters corresponding to two basal areas, assuming the shape of crossectional cutt is circular. The difference between these two radii is denoted "d". Then, compute as follows

1) A1 +A2+A3+A4 -d 4

2) al + a2 + a3 + a4 -d 4

3) Cl+ C2 - d 2 4,) c1 -d 5) _{c2 -d}

Appendix 3. Boring angle.

Dip angle

Insertion angle

The above angles were measured.