Ciência Rural, Santa Maria,
v.47:
e20150895,
2017paraensis through x-ray microdensitometry.
Growth
ring 04,
analysis
of Euxylophora
http://dx.doi.org/10.1590/0103-8478cr20150895
1
ISSNe 1678-4596
PARASITOLOGY
Growth ring analysis of Euxylophora paraensis
through x-ray microdensitometry
Eva Santos de Andrade1 Silvana dos Santos Carvalho Garcia2
Ana Luisa Kerti Mangabeira Albernaz3 Mario Tomazello Fillho4
Victor Hugo Pereira Moutinho5
1
Engenharia Florestal, Universidade Federal do Oeste do Pará (UFOPA), Santarém, PA, Brasil.
Museu Paraense Emílio Goeldi, Av. Perimetral, 1901, Terra Firme, 66077-830, Belém, PA, Brasil. E-mail: silvanasancarcia@gmail.com.
Corresponding author.
3
Programa de Pós-graduação em Biologia Tropical - MPEG, Belém, PA, Brasil.
4
Departamento de Ciências Florestais da Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo (USP), Piracicaba, SP, Brasil.
5
Laboratório de Tecnologia da Madeira, Universidade Federal do Oeste do Pará (UFOPA), Santarém, PA, Brasil.
2
ABSTRACT: Euxylophora paraensis Huber - Rutaceae, popularly known as yellow heart, is a species with a low-density population that has
suffered intense exploitation in recent decades. This has led to its inclusion in the IBAMA list of endangered species. This study aimed to evaluate
the existence of growth rings and their annuity in five trees of Euxylophora paraensis through the x-ray microdensitometry technique, as well as
to compare them using the classical method. Application feasibility of this technique can be deepened through future, broader dendroecological
studies, which may better elucidate the understanding of the species population dynamics and promote more sustainable uses. Wood disks were
collected from the base of five 29-year-old trees from a planting site in the Curua-Una Experimental Station, located in Prainha, Pará State, Brazil.
Samples were polished and sanded for the x-ray microdensitometric analysis. Values of minimum, average, and maximum density (0.581, 0.84,
and 1.077gcm-3, respectively) were obtained. There was a significant difference in density between the studied trees. Growth rings boundaries,
through densitometric pith-bark profile are demarcated by fibrous zones, with density variation between the early wood and late wood. This study
concludes that the growth rings of the studied species are distinct and annual, validating the technique used.
Key words: dendrochronology, yellow heart, density, Amazon.
Análise dos anéis de crescimento de Euxylophora paraensis
por meio da microdensitometria de raios-x
RESUMO: Euxylophora paraensis Huber - Rutaceae, popularmente conhecida como pau amarelo, é uma espécie com baixa densidade
populacional e que sofreu intensa exploração nas últimas décadas. Isso levou à sua inclusão na lista do IBAMA de espécies ameaçadas de
extinção. O presente estudo objetiva avaliar a existência e anuidade dos anéis de crescimento de cinco árvores de Euxylophora paraensis,
por meio da técnica de microdensitometria de Raio-x, e comparar com o uso do método clássico. A viabilidade da aplicação dessa técnica
poderá ser aprofundada por meio de futuros estudos dendroecológicos mais amplos, que poderão melhor elucidar a compreensão da dinâmica
populacional da espécie e promover usos mais sustentáveis. Coletou-se discos do lenho da base de cinco árvores, provenientes de plantio, na
Estação experimental de Curua-Una, em Prainha – PA, com então 29 anos de idade. As amostras foram plainadas e polidas, visando a análise
microdensitometrica de raios x. Foram obtidos valores de densidade mínimos, médios e máximos (respectivamente 0,581, 0,84 e 1,077gcm-3).
Houve diferença significativa na densidade entre as árvores estudadas. Verificou-se, por meio do perfil densitométrico no sentido medulacasca, limites dos anéis de crescimento por zonas fibrosas, com variação da densidade entre o lenho inicial e tardio. Verifica-se que os anéis
de crescimento da espécie estudada são distintos e anuais, validando a técnica utilizada.
Palavras-chave: dendrocronologia, pau amarelo, densidade, Amazônia.
INTRODUCTION
Use of wood resources in the Eastern
Amazon is intense and normally performed in a
non-sustainable way, which may lead to irreversible
damages to the remaining forest, raising fire risk, and
threatening the population of high commercial-value
Received 06.19.15
species (NEPSTAD et al., 1999; PINTO et al., 2002;
FRANCEZ et al., 2007; ALMEIDA et al., 2013).
This is due to unplanned forest harvest, performed
in an intensive and selective way, which turns forests
with high wood stocks and commercial value into
degraded forests with low commercial value and
difficulty restoring biodiversity (PINTO et al., 2002).
Approved 11.17.16
Returned by the author 02.14.17
CR-2015-0895.R2
Ciência Rural, v.47, n.4, 2017.
2
Andrade et al.
Species that have a low natural population
density but high commercial value are those most
affected by population reduction, causing them
to begin the extinction process. An example is
Euxylophora paraensis Huber. Currently, this
species is on national lists of endangered species,
such as the list from the Instituto Brasileiro do Meio
Ambiente (IBAMA) (IBAMA, 2014) and the list
from the state of Pará (SEMA, 2009). Euxylophora
paraensis Huber, which is from the Rutaceae Juss.
family, is popularly known as yellow heart. In
addition, this species is monotypic, belonging to
the Euxylophora genus, which only includes the
Euxylophora paraensis Huber species (PIRANI,
2016). Its occurrence is limited to northern Brazil
(ISIDORO et al., 2012), and it has high silvicultural
and economic value and low population density
(MESSINA, 2016).
According to ALVES et al. (2012) and
WHEELER (2011), Euxylophora does not have
distinct growth rings; however, LOUREIRO &
DA SILVA (1968) and GARCIA (2014) claim
the existence of slightly distinct and distinct
growth rings, respectively. Associated with this
information, BOTOSSO & TOMAZELLO FILHO
(2001), WORBES (2002), and LISI et al. (2008)
asserted that growth rings can be distinguished in
diverse species of the Rutaceae family, to which
Euxylophora belongs.
A growth ring is not necessarily evidence
of an annual formation. WIMMER et al. (2000) and
HIENRICH (2004) ascribe the formation of diverse
false rings in the Amazon region to the lack of a welldefined seasonal climate, compared to temperate
regions. However, annual growth rings have been
reported in flooded forests of Amazon, where the
elevation of the river level causes stress that leads to
differential growth (SCHONGART et al., 2002). More
recently, a study on the Belterra-Pa region indicated the
marking of growth rings in 26 of 64 analyzed species
(TREVIZOR et al., 2015). This region belongs to an
area called the ‘dry corridor’ of the Amazon due to its
well-defined dry season (BUSH, 1994).
X-ray microdensitometry is a growth
ring analysis technique that was developed in the
1960s by Pouge in France (POLGE, 1965), and it
was used for the first time in Brazil by AMARAL
& TOMAZELLO FILHO (1998). Through this
technique, it is possible to verify millimeter by
millimeter the differences of wood densities,
enabling the identification of early wood and
latewood and the check of their densities. According
to TOMAZELLO FILHO et al. (2008), this allows
the delimitation of growth rings through the detailed
building of the apparent density profile of the wood.
In this way, accurate information can be obtained
about the periodicity of the wood formation and the
age that tropical trees reach (BOTOSSO & MATTOS,
2002). For this reason, x-ray microdensitometry is
considered a complementary technique of the classic
dendrochronology.
This research aimed to evaluate the viability
of studying Euxylophora paraensis growth through the
study of growth rings. Since the species is endangered
and it is not possible to have several samples, we
decided to use the x-ray microdensitometry technique
in samples of Euxylophora paraensis, in which the
age is known, in a well-defined seasonality region.
The hypothesis is that the species marks annual
growth rings that can be analyzed through the x-ray
microdensitometry technique. It is expected to
contribute to the development of tools that promote
management of the species compatible with the
conservation of its populations.
MATERIALS AND METHODS
Sampling
Five 29-year-old Euxylophora paraensis
Huber trees were selected. The trees are part of an
experimental planting that started in 1982 in the
experimental station of Curua-Una, which is located in
the Barreirinha Community, city of Prainha-PA, between
the coordinates S02º32’40,1” and W054°05’26,9’’,
which is also located in the so-called ‘dry corridor’ of the
Amazon. Seeds used in the experiment were collected in
the primary forests in the region.
The selection of trees was made
considering individuals without defects and visible
defilements, straight stem, high circumference at
breast height (CBH) and conditions of safe fall, in
order to avoid impact to adjacent trees. Wood samples
were taken as disks from the trunk base in September
2012, when botanic material was also collected for
identification by a specialist of the herbarium of the
Museu Paraense Emílio Goeldi.
Material analysis
In the laboratory, disks were naturally
dried, and then they were planed and sanded with the
variation of granulometry between 60 and 400 mesh,
aiming to improve the visualization of growth rings.
Then, the central region was removed from each disk,
with dimensions of 2 x 1.5cm of width and thickness,
respectively, with variable length, according to the
diameter of the selected material.
Ciência Rural, v.47, n.4, 2017.
Growth ring analysis of Euxylophora paraensis through x-ray microdensitometry.
Wood samples were glued in wood
supports, and their transversal sections were cut
at 2 millimetres of thickness with parallel circular
double blade equipment, resulting in a sample
with 2 millimetres of thickness and 5 millimetres
of width. Then, those samples were stocked
in a climate-controlled room at 20ºC and 65%
relative air humidity for 24 hours to reach the
wood equilibrium humidity of 12% (AMARAL
&TOMAZELLO FILHO, 1998).
X ray microdensitometry
The apparent density profile of the wood
was obtained with the QTRS-01X equipment of
Quintek Measurement Systems in the radial direction
of the samples (pith–bark direction) in each 0.04
millimetres, according to the recommendation of
CHAGAS (2013). Later, the mean values of density
were obtained for each tree, which were submitted
to the Scott-Knott test of mean differentiation at the
probability level of 5%.
At the same time of the x-ray densitometry,
the growth rings were measured by the traditional
methodology. For this measurement, four rays from
each disk were analysed under a Leica stereoscope,
MZ10 model, which has an optical fiber illumination
system. Then, the analyzed rays were scanned by
an HP Scan jet G2710 scanner with 1200dpi of
resolution with a scale for later measurement of
the growth rings’ width using the Image Pro Plus
software. The obtained data were developed in the
COFECHA software, aiming to control quality
and synchronization between trees. Finally, the
densitometry data were compared due to the higher
attenuation of growth rings relative to latewood.
3
RESULTS AND DISCUSSION
The mean, minimum, and maximum
values of apparent density at 12% wood humidity of
yellow heart trees were 0.84, 0.581, and 1.077gcm-3,
respectively. The standard deviation was 0.076, and
the variation coefficient was 9.077% (Table 1).
There was a significant difference between
mean densities; whereas, samples of only two trees
had a statistically equal mean. The difference between
average values of density generally occurs due to the
wood formation and composition of the anatomic
structure of the tree. CASTRO et al. (2014) explain that
the trees with a higher mean value of apparent density
present a higher percentage of latewood, resulting in
an increase of density due to the higher attenuation of
x-rays, whereas trees with a lower apparent density
of wood present a higher percentage of early wood,
decreasing the mean value density. Even though the
studied trees had the same silvicultural treatment, were
of the same age, were grown under the same edaphic
and climate conditions, and had their seeds collected
from the same primary forest, the different genetic
materials seem to be the more plausible explanation
for the variation between individuals.
Considering that density profiles are
related to the anatomic structure of growth rings, it
is suggested that the average of the maximum values
of 1.077gcm-³ for apparent density is related to
latewood; whereas, the average of minimum values
of 0.581gcm-³ is related to early wood. According to
BOTOSSO & MATTOS (2002), this fact occurs due
to the match of early wood to the vegetative period
with a higher physiological activity, when the cell
walls are less thick and have low density. However,
Table 1 - Mean values obtained from apparent density readings of the samples of five Euxylophora paraensis trees from the planting of
Curuá-Una Experimental Station. SD: standard deviation; CV: coefficient of variation; Max: maximum value; Min: minimum
value.
Tree
1
2
3
4
5
Mean
---------------------------------------------------------Apparent Density (g.cm-³)--------------------------------------------------------Mean
0.819 a
0.889 d
0.823 b
0.836 b
0.833 c
0.840
SD
0.072
0.073
0.087
0.072
0.077
0.076
CV (%)
8.760
8.186
10.607
8.562
9.273
9.077
Max
1.080
1.118
1.082
1.057
1.051
1.077
Min
0.579
0.666
0.524
0.575
0.563
0.581
Means followed by the same letter in the column do not show statistically significant differences according to the Scott–Knott test at 5%
significance.
Ciência Rural, v.47, n.4, 2017.
4
Andrade et al.
the latewood corresponds to the end of the vegetative
period, when the cell walls gradually become thicker
and; consequently, have higher density. Higher
density reflects the darker tone than the early wood.
This is clearly emphasized in the wood transversal
section (Figure 1), as verified by CASTRO et al.
(2014), who studied the x-ray micro densitometry in
Pinus caribaea var. hondurensis (Pinaceae).
The diametric apparent density profiles
of the sampled trees showed an increasing density
value in the radial direction and a value decrease in
the sapwood region. This variation model was also
observed by ALVARADO et al. (2010) for Swietenia
macrophylla species, which presented higher density
values due to a higher percentage of adult wood and
the deposition of extractives in the heartwood region;
in the sapwood, the functional region of the xylem, a
reduction of the apparent density of wood compared
to heartwood was reported.
Some samples presented stain fungi in the
sapwood region, making the visualization of growth
rings through the traditional methodology difficult.
However, through the densitometry profile, it was
possible to clearly visualize and associate the right
localization of limits of growth rings in density
peaks. According to TOMAZELLO FILHO et al.
(2008), the action of those xilophagous organisms
can occasion the decrease in density values,
including the minimum, medium, and maximum
values. Moreover, the density decrease in the
regions affected by fungus induced the decrease in
resistance (BRAZOLIN et al., 2011).
It was verified through the profiles that
density peaks are more attenuated in the limits of
growth rings, where it is possible to visualize fibrous
zones with dark coloring, interleaved by the lighter
coloring. According to TOMAZELLO FILHO et
al. (2001), this occurs as a response of the cambial
activity to the seasonality of environmental conditions
(temperature, precipitation, luminosity, etc.), which
reflects in the anatomy and other wood properties.
In the studied case, even the environmental variables
were not measured, and it is believed that the main
influence was the precipitation, since the studied
region has a well-defined dry season; however, the
region does not have a high annual variation of
temperature and luminosity.
The counting and measurement of growth
rings by the traditional methodology returned the age
of 29 years for the studied trees, with a correlation of
0.595 between them and a significance level of 0.515,
corroborating with the planting age. All studied trees
presented the last growth ring as incomplete. In
this regard, it is important to note that the sampling
occurred in September, id est, before the rainy season
had started, preventing the tree from completing the
last growth ring. Thus, that ring cannot be measured
and counted as the others.
Through the densitometry, it was possible
to verify the same quantity of growth rings, beyond the
false rings, which are also reported in the traditional
methodology. The presence of false rings in Amazon
species was also observed by ALVARADO et al.
(2010), who emphasized the importance of identifying
the presence of intra-annual growth rings in growth
studies based on dendrochronology techniques. Both
the densitometry and the traditional method required
quality control to differentiate false rings from
Figure 1 - Radial density profile of a Euxylophora paraensis sample, with the density peaks associated with the darker regions, corresponding
to latewood. On the left is the fungi presence as well as lower readings of wood density for that region.
Ciência Rural, v.47, n.4, 2017.
Growth ring analysis of Euxylophora paraensis through x-ray microdensitometry.
annual rings. Furthermore, by the densitometry, it
was possible to define limits of growth rings by the
density variation, demonstrating the efficiency of that
technique as a methodology.
CONCLUSION
The growth rings of the Euxylophora
paraensis Huber species are distinct and annual.
The x-ray microdensitometry was efficient in the
delimitation of growth ring boundaries of the E.
paraensis. It is possible to associate the density
peaks obtained by the densitometry with the age of
the planting obtained by the traditional methodology
of dendrochronology. The simultaneous use of
two methods enabled a better count calibration,
decreasing the error margin of the age estimate,
which can be caused, for example, by the existence
of false rings.
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