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Variation in Natural Durability of
Seven Eucalyptus grandis 3Eucalyptus
urophylla Hybrid Clones
F. J. N. Franc¸a T. S. F. A. Franc¸a R. A. Arango
B. M. Woodward G. B. Vidaurre
Abstract
Programs aimed at developing clones of hybrid trees are commonly established in Brazil to meet the demands of various
forest-based industries. These programs have continually improved the quality of eucalyptus wood, which has the potential to
reduce deforestation by lowering demand for other high-value species. This is particularly true in the lumber market, but little
is known about the resistance of eucalyptus wood to biodegradation. This study evaluated variation in natural resistance of
seven Eucalyptus grandis 3Eucalyptus urophylla hybrid clones to decay by four wood-rot fungi and feeding by subterranean
termites. In addition to mass loss, the relationship between density and durability was also examined. Results showed
significant differences among the various clones in density as well as in resistance to fungi and termites, although none of the
clones were resistant to Trametes versicolor. Mass loss in wood specimens ranged from 9 to 61 percent in the fungal tests and
from 6.9 to 20.5 percent in termite tests. Average density measurements among clone groups were calculated to be between
461 and 659 kg/m
3
. Among the clones, five of the seven showed resistance to fungal decay and termite feeding, which was
correlated with increased wood density. Based on these results, we suggest that certain clones, particularly those with higher
density values, may be considered for production of various lumber products.
Eucalyptus spp. are commonly used in reforestation
programs in Brazil to meet the demands of various forest-
based industries, with the majority used for pulp and paper
or charcoal. Species of this genus are popular because of
their fast growth, with trees able to be harvested between 6
and 7 years of age (Braz et al. 2014). In Brazil, numerous
cloning programs have been started to improve the quality
of this material, mainly through development of hybrid
species (Bassa et al. 2007, Alves et al. 2011, Brazilian
Association of Planted Forests Producers 2015). In partic-
ular, hybrid trees of Eucalyptus grandis 3Eucalyptus
urophylla represent the most commonly used hybrid by the
pulp and cellulose industry in Brazil (Busnardo 1981).
The crossing of these two Eucalyptus species permits fast
growth, a characteristic of E. grandis, as well as improved
physical properties of the wood (i.e., increased wood density
of between 460 and 650 kg/m
3
), which is characteristic of E.
urophylla. It is also thought that this hybrid is well adapted
to the ecological conditions in Brazil (Carvalho 2000).
Therefore, hybrid clones of E. grandis 3E. urophylla
possess ideal characteristics in terms of both growth and
density, with numerous industries continuing to invest in
research on genetic development of this hybrid (Brigatti et
al. 1983, Ikemori and Campinhos 1983, Bertolucci et al.
1995).
Recently, fluctuations in the price of pulp and paper and
the low value of charcoal have caused many of the major
forestry companies in Brazil to begin considering alternative
uses for eucalyptus wood. Factors such as scarcity and high
cost of native woods, as well as ecological pressures from
overharvesting, have contributed to the growth in utilization
of eucalyptus wood materials, particularly in the flooring
and lumber industry (Scanavaca and Garcia 2003). Al-
though the major properties of wood from E. grandis 3E.
urophylla hybrids have been reported in terms of pulp and
The authors are, respectively, Graduate Research Assistant and
Graduate Research Assistant, Dept. of Sustainable Bioproducts,
Mississippi State Univ., Mississippi State (fn90@msstate.edu,
tsf97@msstate.edu [corresponding author]); Research Entomologist
and Microbiologist, USDA Forest Products Lab., Madison, Wiscon-
sin (rarango@fs.fed.us, bwoodward@fs.fed.us); and Adjunct Profes-
sor III, Dept. of Forestry and Wood Sci., Jerˆ
onimo Monteiro, Federal
Univ. of Esp´
ırito Santo, Esp´
ırito Santo, Brazil (graziela.dambroz@
ufes.br). This paper was approved as journal article SB833 of the
Forest & Wildlife Research Center, Mississippi State University.
This paper was received for publication in June 2016. Article no.
16-00029
ÓForest Products Society 2017.
Forest Prod. J. 67(3/4):230–235.
doi:10.13073/FPJ-D-16-00029
230 FRANC¸ A ET AL.
paper, studies specifically concerning the potential use of
these materials in lumber products are lacking. In particular,
little is known regarding the amount of variation that can
occur among the various hybrid clones and how this
variation can affect susceptibility to biological deterioration.
These types of studies are important as both genetics and
environmental factors can influence the physical properties
of the wood material (Beaudoin et al. 1992, Alzate et al.
2005). Thus, in addition to the studies related to physical
and mechanical properties of E. grandis 3E. urophylla
hybrids, examination of resistance to decay fungi and
termites is also necessary to gain a better understanding of
the possible applications of this material. The main
objective of this study was to evaluate the amount of
variation in hybrid E. grandis 3E. urophylla clones, with
specific focus on density and durability to wood-degrading
organisms, and to provide baseline data that could help
identify potential clones that might be used in production of
higher value products (e.g., lumber).
Materials and Methods
Test samples were obtained from 13-year-old clones of E.
grandis 3E. urophylla hybrid trees harvested from an
improvement test site for pulp production in an experimen-
tal plantation located in Alcobac¸a, Brazil. Clone trees were
planted randomly within the forest, and each tree was
labeled with information relating to clone number and
position within the forest for future reference. In this study,
7 of the 20 different clones were selected based on
dendrometric parameters, such as diameter at breast height,
crown size, and bark thickness, as identified in a previous
study (Franc¸ a 2014).
Samples were cut from each clone in the heartwood
section located directly beneath the bark of a 25-mm-thick
board (Fig. 1). Samples were cut across the center of the
cross section (see Fig. 1 in Choong and Barnes 1969) into
specimens that were 25 by 25 by 9 mm (tangential by radial
by longitudinal). For biological tests, six replicate samples
were selected from each clone for exposure to each of the
four fungi and for termite testing. All sample blocks were
conditioned to a constant weight at 6 percent equilibrium
moisture content (EMC) by maintaining wooden samples
under a constant temperature and relative humidity until
they reached the equilibrium moisture content. This was
done so that accurate measures of density and weight could
be determined before testing. Density was calculated by first
determining the weight of each block at 6 percent EMC and
then measuring block dimensions (cross-section size and
length) with a caliper.
Decay testing followed the ASTM D2017 standard
(ASTM International 2012). Specimens were exposed to a
total of four decay fungi, two brown-rot fungi (Gloeophyl-
lum trabeum and Postia placenta) and two white-rot fungi
(Irpex lacteus and Trametes versicolor), obtained from the
Forest Products Laboratory (Madison, Wisconsin) culture
collection. Southern pine (Pinus spp.) and sweetgum
(Liquidambar styraciflua) sapwood were used as controls
for exposure to brown-rot and white-rot fungi, respectively.
Test samples were exposed to decay fungi for a total of 14
weeks. After this period, blocks were removed from the
culture bottles, carefully brushed free of mycelia, and
allowed to air-dry overnight. Blocks were then conditioned
at 218C and 30 percent relative humidity (6% EMC) and
weighed, and percent mass loss was calculated. Classifica-
tion of decay resistance based on average percent mass loss
was then assigned to each clone group according to the scale
presented in the ASTM D2017 standard (Table 1).
Termite testing followed the American Wood Protection
Association (AWPA) E1-13 standard (AWPA 2014) using
the eastern subterranean termite, Reticulitermes flavipes
(Kollar). Termite species was confirmed both morpholog-
ically and genetically in previous studies (Arango 2015,
Arango et al. 2015). Termite collections were done the day
of test setup from dead logs and cardboard traps set out in a
small wooded area in Janesville, Wisconsin. Southern pine
and sweetgum samples were again used as controls. Test
specimens were placed in a plastic container with 50 g of
sterile, sifted sand and 8.5 mL of sterile water. One gram
(ca. 300 workers and 1% soldiers) of freshly collected R.
flavipes (third and fourth instar) was then added to each dish
and allowed to feed for 4 weeks. After 4 weeks, samples
were removed from the testing arena and cleaned using a
Figure 1.—Schematic cross-section of Eucalyptus grandis 3
Eucalyptus urophylla log identifying sampling locations.
Table 1.—ASTM classification of decay resistance according to
mass loss values.
a
Resistance class Average mass loss (%)
Highly resistant 0–10
Resistant 11–24
Moderately resistant 25–44
Slightly resistant or nonresistant 45
a
Adapted from ASTM International D2017 (2012).
FOREST PRODUCTS JOURNAL Vol. 67, No. 3/4 231
small brush to remove sand particles. The number of live
termites after exposure was also recorded. Samples were
oven-dried overnight and reconditioned to a 6 percent EMC
to obtain a final weight, and then percent mass loss was
calculated. Each sample was also rated based on the visual
evaluation system provided by the AWPA E1-09 standard
(AWPA 2012; Table 2).
For statistical analysis, Pearson correlation coefficient
was used to determine the correlation between density and
percent mass loss for the fungal data and between density,
percent mass loss, and termite mortality for the termite data.
Differences in wood consumption of fungi among clones
and between fungi, as well as the difference in mass loss
between clones for termite tests, were compared using the
Tukey test (a¼0.05; SAS version 9.4, SAS Institute 2013).
Table 2.—American Wood Protection Association (AWPA)
classification for visual rating of test blocks exposed to
subterranean termites.
a
Visual rating classification Rating
Sound 10
Trace, surface nibbles permitted 9.5
Slight attack, up to 3% of cross sectional area affected 9
Moderate attack, 3%–10% of cross-sectional area affected 8
Moderate/severe attack, penetration, 10%–30% of cross-sectional
area affected 7
Severe attack, 30%–50% of cross-sectional area affected 6
Very severe attack, 50%–75% of cross-sectional area affected 4
Failure 0
a
Adapted from AWPA E1-09 (2012).
Figure 2.—Correlation between density and mass loss for the Eucalyptus grandis 3Eucalyptus urophylla hybrid clones against (a)
brown-rot fungi and (b) white-rot fungi.
232 FRANC¸ A ET AL.
Results
Results from decay tests showed mass losses ranging
from 9 to 61 percent and from 53 to 95 percent for clone
specimens and control samples, respectively. Eucalyptus
grandis 3E. urophylla clones E6 and E7 were significantly
less resistant to all fungi tested compared with the other
clones, with the exception of clones exposed to T.
versicolor, where all clones showed significantly lower
resistance compared with the other three fungi tested.
Samples exposed to the other white-rot fungus I. lacteus,
however, showed analogous results with those exposed to
the two brown-rot fungi (Fig. 2). Compared with clones E1
through E5, results showed nearly three to four times higher
average mass loss in clones E6 and E7 (Table 3).
Test blocks exposed to feeding bysubterranean termites had
average mass losses ranging from 7 to 21 percent in clone
specimens, compared with 23 to 30 percent mass loss in
control samples. Termite mortality values ranged from 2.5 to
37 percent in hybrid clones, with 2.5 percent mortality in
control samples (Fig. 3). Based on the visual rating
classification of termite attack, clones E6 and E7 were
classified as having very severe attack and were the clones
most susceptible to termite feeding. Clones E1, E3, and E5
were classified as moderately attacked in the termite test and
had lower mass loss values then the other five clones (Table 4).
Average density values for the hybrid clones ranged from
461 to 659 kg/m
3
, with significantly higher density in clone
E1 and significantly lower density in E6, compared with the
other hybrid clones (Table 3). The relationship between
density and mass loss in decay tests suggests a negative
correlation in samples exposed to G. trabeum (P,0.0001),
P. placenta (P,0.0001), and I. lacteus (P,0.0001). Thus,
clones with higher density values had increased decay
resistance compared with clones with lower densities.
Results from the termite tests were comparable to those
from the decay tests. All hybrid clones were susceptible to
termite feeding, with significantly higher mass losses in
Table 3.—Average density, mass loss, and decay resistance class of the seven Eucalyptus grandis 3Eucalyptus urophylla hybrid
clones exposed to brown-rot and white-rot fungi.
a
Clone Density (kg/m
3
)
Gloeophyllum trabeum Postia placenta Irpex lacteus Trametes versicolor
Mass loss (%) Class Mass loss (%) Class Mass loss (%) Class Mass loss (%) Class
E1 659.6 A (28.2) 16.6 B c (6.8) R 20.7 C b (2.5) R 24.1 B b (7.2) R 50.1 A a (2.7) NR
E2 551.4 CD (50.2) 9.5 B c (4.1) HR 22.9 C b (8.4) R 28.9 B b (14.2) MR 51.4 A a (6.0) NR
E3 619.4 D (20.2) 22.5 B c (11.0) R 24.3 BC c (8.4) R 31.4 B b (6.3) MR 55.2 A a (4.3) NR
E4 542.5 CD (18.2) 14.3 B c (10.3) R 28.4 C b (6.5) MR 30.9 B b (7.4) MR 52.6 A a (2.5) NR
E5 568.2 C (6.5) 11.3 B c (6.1) R 17.5 C b (7.8) R 19.5 B b (5.4) R 49.9 A a (5.1) NR
E6 461.5 E (26.0) 51.8 A b (11.4) NR 55.0 A ab (8.9) NR 60.9 A a (12.3) NR 52.3 A b (4.6) NR
E7 521.0 D (26.0) 40.0 C b (11.4) NR 38.6 B b (8.9) NR 60.9 A a (12.3) NR 52.3 A b (4.6) NR
Avg. 560.6 23.7 29.6 36.7 52.0
SP 747.8 (9.4) 53.1 (1.1) NR 58.6 (1.9) NR — — — —
SG 655.9 (17.5) — — — — 94.7 (1.3) NR 66.8 (1.5) NR
a
Values are the means of six samples (standard deviations in parentheses). Means with the same letter designation are not significantly different (P.0.05),
where capital letters indicate comparisons between clones and lowercase letters indicate comparisons between fungi. Classes of decay resistance are based
on ASTM D2017 categories (ASTM International 2012). HR ¼highly resistant; R ¼resistant; MR ¼moderately resistant; NR ¼not resistant; SP ¼southern
pine; SG ¼sweetgum.
Figure 3.—Correlation between density, mass loss, and termite mortality in Eucalyptus grandis 3Eucalyptus urophylla hybrid clones
exposed to feeding by subterranean termites.
FOREST PRODUCTS JOURNAL Vol. 67, No. 3/4 233
clones E6 and E7. Statistical analysis indicated a negative
correlation between density and mass loss (P,0.0001).
However, no statistical difference was found between clones
in terms of termite mortality, nor was a significant
correlation found between density and termite mortality
(Table 4).
Discussion
Density is often one of the major properties of wood
associated with natural durability (Arango et al. 2006 and
references therein). Because E. grandis 3E. urophylla
clones are commonly used in pulp and cellulose production,
numerous researchers have examined density values, as well
as other characteristics associated with durability, specifi-
cally for this hybrid. In this study, clone density ranged from
462 to 660 kg/m
3
, which is comparable to values reported
from published literature (e.g., Bassa et al. 2007, Gonc¸ alves
et al. 2009). However, in a study on longitudinal variability
in wood density of different E. grandis 3E. urophylla
clones, Alzate et al. (2005) reported slightly lower density
values (Table 5).
Results from both fungal and termite testing in this study
were also comparable to those given by other researchers,
although published literature on decay and termite resis-
tance is limited. Mass loss values reported by Silva et al.
(2014) and Dytz (2014) for G. trabeum and P. placenta are
comparable to those shown here. However, mass loss values
reported by both Silva et al. (2014) and Dytz (2014) after
exposure to T. versicolor were lower than those from the
present study, with specimens classified as moderately
resistant. In one of the only studies on termite resistance of
E. grandis 3E. urophylla clones, Lopes (2014) reported
similar mass loss values, but higher levels of termite
mortality, using the termite species Nasutitermes corniger.
A summary comparing values from published studies with
the results presented here is shown in Table 5.
Natural resistance to termites and decay has often been
correlated to levels of extractives in wood, which has the
potential to explain some of the variation in durability. Low
levels of extractives are ideal for pulp and cellulose
production but likely result in increased susceptibility to
biological degradation (e.g., decay and insect feeding).
Overall, hybrid E. grandis 3E. urophylla clones are thought
to be relatively low in extractives (average total extractives
of ;2.5% in Bassa et al. 2007 and ;3.5% in dos Santos and
Sans´
ıgolo 2007), with higher levels of extractives in
heartwood compared with sapwood (7.6% vs. 3.7%,
respectively; Gominho et al. 2001). Although extractive
content was not measured in this study, Boa (2014) reported
total extractive content of E. grandis 3E. urophylla hybrid
clones to range from approximately 2.08 to 4.82 percent,
with clones E1, E3, and E5 having significantly higher
extractive content compared with the other clones. These
higher levels of extractives might explain the increased
resistance to decay and termite feeding observed in our
study.
Overall, results show that E. grandis 3E. urophylla
hybrid clones vary in terms of biological resistance and
density, suggesting that clone variation is an important
consideration in choosing materials for new markets. In the
United States, natural resistance was determined to be a
major consideration of end users before purchasing lumber
products (Nicholls and Roos 2006). Based on statistical
analyses from this study, it might be possible to estimate
natural durability properties against fungal and termite
attack based on wood density values and then select for
clones with higher densities as potential alternative
materials to be used in the lumber products. Future studies
should focus on the correlation between density and
extractive content to determine if one or both of these
factors significantly improve resistance to biological
deterioration.
Conclusions
This study demonstrated one possible method for
selecting the best clones for lumber production based on
natural resistance to biological deterioration. Although E.
grandis 3E. urophylla hybrids showed variation between
Table 4.—Mass loss, termite mortality, and density of the seven
Eucalyptus grandis 3Eucalyptus urophylla hybrid clones
exposed to feeding by subterranean termites.
a
Clone
Mass
loss (%)
Termite
mortality (%)
Visual
rating
Density
(kg/m
3
)
E1 8.1 B (1.8) 29.6 A (38.0) 8 655.4 (25.7)
E2 9.6 B (2.1) 8.8 A (6.9) 7 541.6 (42.9)
E3 7.5 B (1.5) 36.7 A (36.7) 8 612.7 (23.7)
E4 8.4 B (1.8) 36.7 A (46.4) 7 544.3 (16.1)
E5 6.9 B (1.3) 22.5 A (32.1) 8 567.4 (4.7)
E6 20.5 A (4.4) 2.5 A (0.0) 4 457.8 (24.0)
E7 16.7 A (3.0) 2.5 A (0.0) 4 523.6 (24.1)
Avg. 11.1 19.9 7 557.5
SP 29.2 (0.04) 2.5 (0.0) 0 463.2 (20.4)
SG 23.0 (0.03) 2.5 (0.0) 0 653.04 (11.4)
a
Values are means (standard deviations in parentheses). Means with the
same letter are not significantly different (P.0.05). SP ¼southern pine;
SG ¼sweetgum.
Table 5.—Summary of termite and decay data as well as density values from published literature on hybrid Eucalyptus grandis 3
Eucalyptus urophylla clones.
Reference
Average
density (kg/m
3
)
Average mass loss (%)
Average termite
mortality (%)
Gloeophyllum
trabeum
Postia
placenta
Irpex
lacteus
Trametes
versicolor Termite
Present study 560.1 23.7 29.6 36.7 52.0 11.1 19.9
Alzate et al. (2005) 490.0 — — — — — —
Bassa et al. (2007) 505.0 — — — — — —
Gonc¸alves et al. (2009) 580.0 — — — — — —
Silva et al. (2014) — 26.1 26.8 — 28.6 — —
Dytz (2014) — 37.0 — — 25.7 — —
Lopes (2014) — — — — — 15.7 55
234 FRANC¸ A ET AL.
clones in terms of resistance to fungi and subterranean
termite feeding, two of seven clones did show higher levels
of natural resistance. These results suggest that certain E.
grandis 3E. urophylla clones might have a future potential
use in lumber production, which has more added value than
pulp and paper products.
Acknowledgments
The authors would like to thank the USDA Forest Product
Laboratory for test facilities and technical support and
FIBRIA (Brazil) for providing of wood samples for the
study.
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