United States 

Department of 

Agriculture 

Forest Service 

An Investigation of Crystalline 

Intensity of the Wood of Poplar 

Clones Grown in Jiangsu Province, 

China 

Southern 

Research Station 

Research Paper 

SRS-11 Bernard R. Parresol and Fuliang Cao 
An Investigation of Crystalline Intensity 

of the Wood of Poplar Clones Grown in 

Jiangsu Province, China 

Bernard R. Parresol and Fuliang Cao 

Abstract 

Observed trends from limited sampling are reported in this paper. Using 

s, differences in wood fiber crystalline intensity 

(CrI%) among four southern-type poplar clones (I-69155,I-63151,I-72/58, 

and 1-2 14) and across four planting spacings (4 m by 4 m, 5 m by 5 m, 6 

m by 6 m, and 7 m by 7 m) were examined. The analyses showed poplar 

clones 1-6315 1 and 1-2 14 have the highest CrIYo, followed by 1-69/55 and 

1-72/58. Crystalline intensity of wood gradually increased across annual 

rings; hence CrI% of sapwood was a little higher than that of heartwood. 

Crystalline intensity of late wood of three of the poplar clones was higher 

than that of early wood (there was no difference in 1-72/58); and as stand 

density increased, CrI% of wood also increased. A fully replicated study 

is needed to firmly establish these trends. 

Ke~ord9: Industrial forests, planting spacing, Populus deltoides, 

Bopulw x eruramericatla, x-ray diffkactograms. 

Introduction 

To establish manmade poplar (Populus spp.) clonal 

forests for industrial uses, two requirements must be met. 

First, forests must have high yield; and second, wood 

fibers must have specific mechanical properties. For 

example, both fiberboard and plywood require fibers with 

a certain stiffiress and strength. In fact, fiber 

characteristics are closely related to the fiber's crystalline 

intensity (CrI%) (Yingtian 1982). 

Cellulose molecules closely linked laterally in aggregates 

of a few hundred are called microfibrils. In general, 

within a microfibril, the lateral linkages between cellulose 

molecules are unifomly ordered. Therefore, the majority 

of the interior of the microfibril consists of a regular 

three-dimensional array of cellobiose units-it is 

crystalline (Wilson and White 1986). Its crystallinity, 

however, is interrupted along its length by numerous 

localized regions where the molecules are less regularly 

packed; the crystalline regions between them being some 

50 to 60 nanometers in length. Because wood cell walls 

contain closely packed and approximately parallel arrays 

of microfibrils, the similarly parallel crystallites within 

the microfibrils act, in the aggregate, to confer on the wall 

as a whole some of the attributes of an overall crystalline 

structure. Thus, wood cell walls can be studied by 

crystallographic methods, such as x-ray diffraction 

analysis, to determine the crystallinity (crystalline 

intensity) of the wood fibers (Boyd 1977, Saka 1993, 

Wilson and White 1986, Yingtian 1982). 

The CrI% of wood affects the properties of the fibers. If 

CrI% increases, tensile strength, Young's modulus of 

elasticity, hardness, density, and stability of size will 

increase. However, tensile ratio, toughness, pliability, 

swelling of wood by water, adsorption to dyes, and the 

rate of chemical reactions will decrease (Zheng 1986). 

Clonal variety and stand density can influence CrI%. 

Crystalline intensity may also vary with early wood 

(EW)-late wood (LW) formation and across annual rings. 

X-ray diffraction analysis was used in this trial study to 

explore the differences in CrI% on four common clonal 

varieties grown in Jiangsu Province. The differences 

across a range of planting densities were also examined. 

The resulting information will aid in effectively using the 

wood of the southern poplar clones. 

Materials and Methods 

Site and Sampling 

Sample trees were taken from 14-year-old experimental 

poplar plantations growing in the Institute of Shuilian 

Forestry Research Center, Jiangsu Province, China, in the 

spring of 199 1. The plantations were established in the 

winter of 1978 using a split-plot design with four types of 

poplar clones as the main plots and four planting densities 

as the subplots done in four blocks or replicates (Cao and 

others 1989). The experimental poplars were P. deltoides 

Bartr. cv. 'Harvard' (1-6315 1 ), P. deltoides Bartr. cv. 

'Lux' (1-69/55), P. x euramericana (Dode) Guiner cv. 

'San Martino' (I-72/58), and P. x euramericana (Dode) 

Cuiner cv. 1-2 14. The planting densities were 204, 278, 

400, and 625 trees per hectare; the corresponding spacings 

were 7 meters (m) by 7 m, 6 m by 6 m, 5 m by 5 m, and 

4 m by 4 m. 
Time and budgetary constraints restricted this 

investigation to a one-replicate pilot study. Four 

randomly picked sample trees--one of each clonal type 

(I-72158,I-69/55? 1-6315 1, and 1-214) from stands planted 

at the 7-m by 7-m spacing-were used to measure 

differences in CrI% among poplar clones. Three 

additional randomly picked trees from clone I-72158--one 

from each of the remaining planting densities-were used 

to determine differences in CrI% among planting 

densities. 

Diffraction 

Diffractogram specimens came from 10-centimeters (cm) 

thick disks removed at breast height from each sample 

tree. Along the upper surface of the disks, EW and LW of 

growth rings 4 through 13 were distinguished, separated, 

and cut into small pieces. The small pieces of wood were 

dried, ground into wood powder, and sifted through a 0.8 

millimeter sieve, 

X-ray diffraction was used for determining CrI% (Boyd 

1977, Xie and Sun 1985). A CX-4B-x-ray diRactor was 

connected to a 2456 diffractometer, and copper x-rays 

were used as the exciting radiation. During use, the 

voltage power of the diffractor was 40 kilovolts; the 

current intensity was 20 milliamperes; and the device 

speed for angle measurement (20) was 5" per minute. 

The diffraction patterns were obtained by collecting 

intensities (Geiger counts per second), I(28), over the 

range from 28 = 5" to 20 = 40". Under normal room 

temperature, the sifted powder was pressed into small 

slices and placed in the aluminum sample holder for 

scanning. For each sample, the resulting intensity curve 

provided two peak values, one at the point where 20 

equaled 22", corresponding to the relatively intense 

reflection of the (002) crystallographic plane of cellulose 

(I,,), and the other at the point where 20 equaled 18", 

corresponding to the amorphous scaaering (Id . Based 

on the Segal method (Xie and Sun 1985), the CrI% was 

determined as: 

Analysis 

An analysis of variance (ANOVA) was performed on the 

CrI% values from growth rings 4 through 1 1 (rings 1 1 

throu* 13 were pooled and labeled 1 1) of the 4 different 

clone trees sampled from the stands planted at the 7-m by 

7-m spacing. Clone means were separated using the 

Ryan-Einot-Orabiel-Welsch multiple F (REGWF) test 

(SAS Institute Inc. 1989). Polynomial trends in CrI% 

over growth rings were tested with orthogonal polynomial 

contrasts. For each clone, we conducted a paired t-test on 

EW-ILW values. Planting spacing or density effects on 

CrI% were analyzed with ANOVA and polynomial 

contrasts. 

Results and Discussion 

Clone, Annual Ring, and EW LW 

Table 1 lists the 64 EW-LW CrI% values of the four trees 

representing each clone at the 7-m by 7-m spacing. The 

CrI% value of a growth ring is the average of its EW and 

LW values. The results of the ANOVA show that CrI% 

differs among clones and that after a decrease in annual 

ring number 5, CrI% increases with annual ring number of 

the tree (table 2, fig. 1). Among the four clones, CrI% of 

the 1-6315 1 clone is the highest (j7 = 47.3), CrI% of 1-214 

follows (j7 = 47.0j, 1-69/55 is third (2 = 454, and the i72/58 clone has the lowest CrI% (2 = 44.2). Based on the 

REGWF test, the clones fa11 into two statistical groups, 

with clones 1-6315 1 and 1-2 14 similar (group A) and 

clones 1-69/55 and 1-72/58 similar (group B), but groups 

A and B differ significantly (a = 0.05). 

From table 2 and figure 1, we can see that there are 

significant linear and quadratic trends in CrI% with 

annual ring of the trees. While the quadratic trend is 

significant, the positive linear trend is by far the 

influential effect. 

381 , I I I I I t t 

4567891011 

Annual ring 

Figure I--Changes in crystalline intensity of four poplar clones with age. 
Table lxrystalfine intensity of early wood and late wood of four poplar 

clones 

Rings fiorn pith (years) 

Clone Item 4 5 6 7 8 9 10 11-13 Average 

EW = early wood; LW = late wood. 

Table 2-Analysis of crystalline intensity of four poplar clones 

(7-m by 7-m spacing) 

Source d f SS MS F P 

Clone 3 50.08 16.69 10.58 0.0002 

Annual ring 7 211.46 30.21 19.15 0.0001 

Error 2 1 33.13 1.58 

Corrected total 31 294.66 

r2 C.V. Root MSE CrI% Mean 

Contrast d f SS MS F P 

Ring: linear trend 1 141.07 140.07 89.43 0.0001 

Ring: quadratic trend 1 29.84 29.84 18.92 0.0003 
That is to say, Cr1?40 appears to be higher in the outer rings 

(sapwood) than in the inner rings (heartwood). One 

possible explanation for the trend is that the gaps between 

the fibers of the heartvvood fill up with a hard 

noncrystallizing pectin-type substance (Butterfield and 

Meylan 1980), which makes CrI% appear to decrease. 

For the age 5 through 1 1 data, the rate of increase in CrI% 

(slope of the linear trend) is 1.33 per year. 

Among the four clones, 1-6315 1 and 1-2 14 have the 

highest CrI% of both EW and LW, 1-49/55 follows, and I72/58 is the lowest (table 1). For clones 1-6315 1,I-214, 

and 1-69/55, there are significant differences (based on 

paired t-tests) between CrI% of EW and LW, with CrI% 

of LW being higher than that of EW (table 3). But for 

clone 1-72/58, EW and LW values do not differ 

significantly. 

Planting Density 

Table 4 lists the 64 EW-LW values of the 4 1-72/58 clone 

trees, 1 fiom each stand density. There are significant 

density and annuaP ring eEects (table 5, figs. 2 and 3). As 

planting spacing increases (density decreases), CrI% of 

wood fibers of 1-72/58 decrease in a linear fashion, with 

the exception of the 7-m by 7-m spacing where CrI% rises 

causing the significant quadratic effect. For the 4-m 

through 6-m spacing data, the rate of decrease in CrI% 

(slope of the linear trend) is 1.80 per m change in spacing. 

The rise at the 7-m spacing could be due to some 

microsite condition or it could be chance variation. 

Crystalline intensity across annual rings, consistent with 

the earlier analysis, has a strong positive linear trend 

(table 5, fig. 3). Clone 1-72/58, regardless of stand 

density, shows no significant differences in CrI% between 

EW and LW (table 6). The 'San Martino' cultivar is 

clearly distinct from the other clones in having uniformity 

of CrI% in the EW and LW of an 

Table &Paired t-tests of early wood vs, late wood 

crystalline intensity values of four poplar clones; 

values paired by growth ring 

Std. Prob 

Clone Mean Error t > ftl 

4x4 5x5 6x6 7 x 7 

Planting spacing (rn) 

Figure 2-Average crystalline intensity of clone 1-72/58 at four planting 

densities. 

381 I I I I I I I 

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Annual ring 

Figure 3-&hanges in crysdfine intensity of clone 1-72/58 with age and 

planting density. 
rystafline intensity of early wood and late wood of clone 1-72/58 

grown at four planting spacings 

Rings from pith (years) 

Spacing Itern 4 5 6 7 8 9 10 11-13 Average 

EW = early wood; LW = late wood. 

Table %Analysis of Crystalline intensity. of clone 1-72/38 at four planting 

spacings 

Source d f SS MS F P 

Clone 3 53.52 17.84 6.57 0.0026 

ual ring 7 116.26 16.61 6.1 1 0.0006 

Error 21 57.04 2.72 

Corrected total 31 226.82 

r2 C.V. Root MSE CrI"h Mean 

Contrast d f SS MS F P 

Spacing: linear trend 1 24.38 24.38 8.97 0.0069 

Spacing: quadratic trend 1 28.03 28.03 10.32 0.0042 

Ring: linear trend 1 62.08 62.08 22.85 0.0001 

Ring: quadratic trend 1 20.74 20.74 7.63 0.01 17 
Table &Paired t-tests of early wood vs. late wood; 

crystalline intensity values of clone 1-72\58 grown at 

four planting spacings; values paired by growth ring 

Std. Prob 

Spacing Mean error t > It1 

Implications 

From this pilot study, the following suppositions are 

offered: (I) based on the CrI% of clones, 1-6315 1 and I214 are the stiffest and strongest, followed by 1-69/55 and 

1-72/58; (2) because CrI% of the four poplar clones 

increases at a linear rate of 1.33 per year, CrI% of 

sapwood is higher than that of heartwood; (3) CrI% of 

LW is higher than that of EW, except in clone 1-72/58; 

and (4) based on the linear increase (slope = 1.80) of 

CrI% in poplar 1-72/58 as planting spacing decreases, 

poplars growing in denser stands should have increased 

fiber strength. While no firm conclusions can be drawn, 

constant monitoring of growth in the Shuilian plantations 

has shown that diameter and height do not differ 

significantly among individual trees in each clonal stand 

(Cao and others 1989), therefore, reasonably small withinclone CrI% variation is expected. 

As pulp-making raw material, poplar wood should possess 

a high cellulose content and a low lignin content (Doupin 

1986). Only the clones with high CrIYo can meet these 

conditions. Because poplar 1-6315 1 has the highest CrI% 

when planted at the 7-rn by 7-m spacing and because 

CrIYo apparently increases as spacing decreases, this 

poplar clone should have the highest CrI% at 4-m by 4-m 

planting spacing, making it the clone with the highest 

quality in pulp and paper-making characteristics. With a 

stand rotation period of 5 to 7 years, the diameter at breast 

height of individual trees can reach more than 20 

centimeters (Cao and others 1989), which meets the 

requirements of the paper-making industry. 

In theory, the quality of fiberboard is a direct hction of 

fiber strength. The strength of fibrous cells are related to 

microfibril angle, CrI%, and the degree of polymerization 

(Northeast Forestry University 198 1, Page and others 

1977, Sun and Xie 1981). Our suppositions suggest that 

clone 1-6315 1 or 1-214 at planting spacings of 4-m by 4-m 

or less, grown for extremely short rotation periods of 4 to 

5 years, will make strong fiberboard. To produce pliable 

fiberboard, fast-growing clones 1-72/58 and 1-69/55 can be 

planted at spacings of 6-m by 6-m and 7-m by 7-m and 

grown for short rotation periods of 8 to 10 years. 

Acknowledgment 

We thank professors Lu Shizing, Huang Minren, Yuan 

Xigen, and Li Dagang, Nanjing Forestry University, for 

their financial support and technical direction. We also 

appreciate the technical assistance of Mr. Gong Shigan 

and Ms. Xu Lin. 
Literature Cited 

Boyd, J.D. 1977. Interpretation of x-ray dimto 

assessments of microfibril angles in fibre cell walls. Wood Science and 

Technology. 1 l(2): 93- 1 14. 

Butterfield, B.G.; Meylan, B.A. 1980. Three-dimensional structure of 

wood: an ultrastruclual approach, 2d ed. New York: Chapman and 

Hall. 103 p. 

Cao, F.; Lu, S.; Xu, X.; Huang, M, 1989. A study on growth 

characteristics of southern type clones. In: Symposium on techniques 

for fast-growth and high yield in southern type poplars. [Date of 

meeting unknown]: [Place of meeting unknown] Beijing, China: 

Academic Book and Periodical Press: 8 1-93. In Chinese. 

Doupin, 2. 1986. Introduction to wood application. Shanghai, China: 

Shanghai Science and Technology Press. In Chinese. 

Northeast Forestry University (NFU). 198 1. Science of fibreboardmaking. Beijing, China: China Forestry Press. In Chinese. 

Page, D.H.; El-Hosseiny, F.; Wier, K; Lancaster, A.P. 1977. Elastic 

modulus of single wood pulp fibers. TAPPI. 60(4): 1 14- 1 1 7. 

Saka, S. 1993. Structure and chemical composition of wood as a natural 

composite material. In: Shiraishi, N.; Kajita, H.; Norimoto, M., eds. 

Recent research on wood and wood-based materialHcmena 

Japanese materials research; Vol. 1 1). Cambridge, England: Elsevier 

Science Publishers Ltd. and The Society of Wterials Science, Japan, 

throu& University Press: 1-20. 

SAS Institute Inc, 1989. SASI'STAT user's guide, version 6,4th ed., 

vol. 2. Cary, NC: SAS Institute Inc. 

Sun, C.; Xie, G. 1981. Study on relative crystalline intensity of fibres of 

P. Massonina. Forestry Science 20(3): 290-299. Beijing, China; In 

Chinese. 

Wion, K; Wte, DAB. 1986. The anatomy of wood: its diversity and 

variability. London, England: Stobart & Son Ltd. 

Xie, G.; Sun, C. 1985, Measurement of microstructure of fibres by means 

of x-ray diffraction. Journal of Nanjing Forestry College. 3: 61 -68. In 

Chinese. 

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Weaving Industry Press. In Chinese. 

Zheng, Y.Z. 1986. Chemistry of wood. Beijing, China: China Forestry 

Press. In Chinese. 
Parresol, Bernard R; Cao, FuLiang. 1998. An investigation of crystalline intensity 

of the wood of poplar clones grown in Jiangsu Province, China. Res. Pap. SRS- 1 1. 

Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research 

Station. 7 p. 

Observed trends from limited sampling are reported in this paper. Using x-ray 

difiactograms, differences in wood fiber crystalline intensity (CrI%) among four southerntype poplar clones (I-69155,I-6315 1,1-72/58, and 1-2 14) and across four planting spacings (4 

m by 4 m, 5 m by 5 m, 6 m by 6 m, and 7 m by 7 m) were examined. The analyses showed 

poplar clones 1-6315 1 and 1-214 have the highest CrI%, followed by 1-69/55 and 1-72/58. 

Crystalline intensity of wood gradually increased across annual rings; hence CrI% of 

sapwood was a little higher than that of heartwood. Crystalline intensity of late wood of 

three of the poplar clones was larger than that of early wood (there was no difference in I72/58); and as stand density increased, CrI% of wood also increased. A fully replicated 

study is needed to firmly establish these trends. 

Keywords: Industrial forests, planting spacing, Populus deltoides, Populus x 

erurarnericana, x-ray difiactograms.