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Palaso et al.
Int. J. Biosci.
2023
RESEARCH PAPER
RESEARCH PAPERRESEARCH PAPER
RESEARCH PAPER
OPEN ACCESS
OPEN ACCESSOPEN ACCESS
OPEN ACCESS
Tree biomass and carbon stock of Falcata (
Falcataria
moluccana
(Miq.) Barneby & J.W. Grimes) along different
altitudinal gradients in the Province of Agusan Del Norte,
Philippines
Roselyn L
.
Palaso
*1
, Nympha E
.
Branzuela
2
, Edgar B
.
Solis
2
1
College of Forestry and Environmental Science, Ca
raga State University, Ampayon,
Butuan City, Philippines
2
College of Agriculture and Related Sciences, University of Southeastern Philippines,
Tagum-Mabini Campus, Apokon, Tagum City, Philippines
Key words:
Aboveground
biomass
, Belowground
biomass
, Carbon
stock
, Altitudinal
gradients
http://dx.doi.org/10.12692/ijb/22.5.88-95 Article published on May 07, 2023
Abstract
Estimation of the tree biomass and carbon stock of
F. moluccana
along different altitudinal gradients was
conducted at Agusan del Norte, Philippines. It followed a non-destructive method of sampling and used the
allometric equation by ERDB 2008 and Cairns et al. (1997) for aboveground biomass and carbon stock, and
belowground computation, respectively. Based on these results, F. moluccana planted at <150 masl had the
highest aboveground biomass with 144.95Mg ha
-1
. The ANOVA at P<0.05 showed no significant difference
in the aboveground biomass at different altitudinal gradients. However, the belowground biomass of F.
moluccana at <150 masl was significantly higher than that of those planted at higher elevations. The
carbon stock of F. moluccana is also highest at <150 masl and lowest at >450 masl with 90.57Mg C ha
-1
and
54.44Mg C ha
-1
, respectively. ANOVA also suggested no significant difference in carbon stocks at different
altitudinal gradients. Furthermore, correlation tests suggested a negative relationship between tree
biomass, carbon stock, and altitudinal gradients.
*
Corresponding Author: Roselyn L. Palaso roselynlina90@gmail.com
International Journal of Biosciences | IJB |
ISSN: 2220-6655 (Print) 2222-5234 (Online)
http://www.innspub.net
Vol. 22, No. 5, p. 88-95, 2023
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Int. J. Biosci.
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Introduction
Biomass quantification is required as the primary
inventory data to understand C pool changes and
forest productivity (Thockhom and Yadava, 2020).
Consequently, forest biomass estimation, its spatial
distribution, changes over time, and strategies for the
increase and conservation of forests have been the
subject of intensive research (Brown & Lugo 1984).
Aboveground biomass stocks vary widely among
tropical forests owing to regional differences in stem
size distribution, soil fertility, topography, and
disturbances (Castilho et al., 2006; Dewalt and Chave
2004; Murthy et al., 2016; Salunkhe et al., In 2016,
Urquiza-Haas et al., 2007). Several environmental
factors change systemically with altitude (Thockhom
and Yadava 2020). Thus, altitudinal gradients are
among the best tools for testing the ecological and
evolutionary responses of organisms to
environmental changes. Information on the allocation
of carbon stocks along different altitudinal gradients
will help predict the responses of regional and global
C balances to future climate change. Additionally, the
altitudinal pattern of biomass and carbon stocks in
forest ecosystems has been reported by several
researchers in different parts of the world (Alves et
al., 2010; Dar and Sundarapandian, 2015; Do et al.,
2017; Ensslin et al., 2015; Gairola et al., 2011; Sharma
et al., 2010; Thockhom and Yadava, 2020).
Similar to tropical forests, plantations play a vital role in
protecting natural forest carbon pools (Chauhan, 2019).
Planting trees to sequester carbon is considered the most
cost-effective, long-lasting, and significant strategy to
address global warming. Carbon sequestration in tree
biomass and subsequent locking of forest-based
products for a long time is considered a viable option for
reducing atmospheric carbon through fast-growing tree
species (Chauhan et al., 2016).
In the Philippines, one of the fastest-growing species
is the F. moluccana (Miq.) Barneby & J.W. Grimes)
(Lantican & Sy, 2010; PCAARRD, 2004). This species
is commonly used in forest plantations, reforestation,
and agroforestry (ERDB 2008). The government and
private sector are establishing small-scale and large-
scale forest plantations to increase the raw material
base of the wood industry while also addressing
ecological concerns through the rehabilitation of
denuded or open lands (Tandug, 2012). However,
there is little data on the tree biomass and carbon
stock of plantation species, specifically F. moluccana,
to account for how much they contribute to carbon
sequestration. However, some studies related to
carbon sequestration rates and biomass were not
specific to conditions at different altitudinal
gradients. Hence, this study was undertaken with the
aim of estimating the tree biomass and carbon stock
of F. moluccana along different altitudinal gradients
and determining the significant effects of different
altitudinal gradients on tree biomass and carbon
stock of F. moluccana.
Materials and methods
Study site
The study was conducted at the 2015 F. moluccana
plantations of National Greening Program-Peoples
Organization (NGP-POs) with a planting distance of
2m x 3m in the province of Agusan del Norte as
shown in Fig.1. Agusan del Norte is situated in
Mindanao's western section of Caraga. It is bordered
on the northwest by the Butuan Bay, northeast by
Surigao del Norte, mid-east by Surigao del Sur,
southeast by Agusan del Sur, and southwest by
Misamis Oriental. It lies at 9° north latitude and 125°-
and 30-minutes east longitude on the northeastern
part of Mindanao Island, Philippines.
It has a total land area of 2,730.24 square kilometers
or 1,054.15 square miles. When Butuan is included for
geographical purposes, the province's land area is
3,546.86 square kilometers (1,369.45 sq mi). The
climate is tropical, with significant rainfall. There was
no definite dry season in this region. Rainfall is
pronounced throughout the year, with the maximum
rainfall occurring from November to January.
According to Köppen and Geiger, this climate was
classified as Af. The province is made up of flat rolling
lands and is surrounded by mountains, the highest of
which is Mt. Hilong-Hilong, 2,012 m above sea level.
The soil types in the province are San Miguel clay
loam covering 10,021.54 hectares, Bolinao silt loam
type with coverage of 14,695.58 hectares, and the
most abundant of all is the Camanesa clay loam
(59,371.39 hectares).
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Fig. 1. Map showing the sampling sites.
Sampling
Three 20m x 50m plots were laid out for each
identified altitudinal gradient: (a) <150 masl, (b)
150masl-300 masl, (c) 301masl-450masl, and (d)
>450 masl, totaling 48 plots for the four sampling
sites (Fig.1).
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This study used non-destructive sampling. Diameter-
breast-height (DBH) which is 1.3m from the surface,
and the total tree height of all trees inside the plot
were measured using a diameter tape and clinometer,
respectively. The units for DBH and tree height were
in centimeters and meters, respectively, and
measured at (±0.1).
Data Analysis
The aboveground biomass of F. moluccana was
computed using the allometric equations of ERDB
(2008), adopting Tandug (1986). That is, AGB = 10 ^
[0.9836 + 1.8036 x log (D) 0.8702 x log10 (H)].
where AGB for Fresh biomass (kg per tree), D is the
DBH (cm), and H is tree height (m). In the absence of
a specific allometric model of Belowground Biomass
(BGB) for plantation forests, the equation for tropical
forests by Cairns et al. (1997) was used. That is, BGB
= Exp [-1.0587 + 0.8836*Ln (AGB)]. where BGB is
the belowground biomass (kg ha
-1
), LN is the natural
logarithm, and AGB is the aboveground biomass (kg
ha
-1
). The Carbon stored in each tree, expressed as kg
C per tree, was determined by multiplying biomass
per tree with a conversion factor of 48.30% average
carbon content of F. moluccana in percent using ERDB
(2008). That is, C =%C * B. The total tree biomass and
carbon stock of trees were determined using the same
computation per hectare expressed in megagrams per
hectare (Mg ha
-1
). Furthermore, one-way Analysis of
Variance (ANOVA) in Randomized Complete Block
Design (RCBD) and linear comparison of treatment
means by Duncan Multiple Range Test (DMRT) were
used. A paired t-test of correlation was used to identify
the relationship between tree biomass, carbon stock, and
altitudinal gradients.
Results
Aboveground biomass
Aboveground tree biomass was calculated using the
allometric equation developed by ERDB (2008). Fig.
2 shows a graphical representation of the
aboveground tree biomass of F. moluccana. Based on
these results, F. moluccana planted at <150 masl had
the highest aboveground biomass with 144.95Mg ha
-1
.
It is followed by AG4 (>450 masl) with 128.14Mg ha
-
1
, AG3 (301-450 masl) with 115.11Mg ha
-1
. and AG2
(150-300 masl) at 104.24Mg ha
-1
.
Fig. 2. Aboveground Biomass, Belowground
Biomass, and Carbon Stock of F. moluccana along
different Altitudinal Gradients.
On the other hand, Table 1 shows that the effects of
altitudinal gradients (AG1, AG2, AG3, and AG4) on
the aboveground biomass of F. moluccana were not
significantly different. This result suggests that the
aboveground wood biomass of the trees was not
significantly different, even when they were planted at
different altitudes.
Table 1. Analysis of Variance for aboveground biomass of F. moluccana.
Source of Variation
SS
df
MS
F
P
-
value
F crit
Blocks
99989186
3
33329728.68
2.372187117
0.138151
3.862548
Treatments
36887113.7
3
12295704.58
0.875125996
NS
0.489301
3.862548
Error
126451896
9
14050210.64
Total
263328196
15
NS
means not significant at P<0.05 level of significance.
The t-test for aboveground biomass in Table 2 shows a
weak correlation between altitudinal gradients and the
corresponding tree biomass. The non-significant t-
statistics also show this trend.
The t-test results conformed with the ANOVA results
for aboveground biomass. A graph of stand density and
basal area is shown in Fig. 3. Trees at the lowest
altitude (<150m) had the highest stand density.
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Table 2. Paired t-test for aboveground biomass of F.
moluccana.
t
-
Test: Paired Two S
ample for
Means
Variable
1 Variable 2
Mean
217.7954
215.6499065
Variance
26668.75
31926.43379
Observations
30
30
Pearson Correlation
0.251436
Hypothesized Mean
Difference 0
df
29
t Stat
0.056071
ns
P(T<=t) one
-
tail
0.477835
t Critical
one
-
tail
1.699127
P(T<=t) two
-
tail
0.95567
t Critical two-tail 2.04523
NS
Not Significant.
Fig. 3. Stand density and basal area of F. moluccana
along altitudinal gradients.
However, in terms of basal area (m
2
ha
-1
), AG3 had
the highest basal area because of the larger trees
compared to the other sites. Furthermore, the high
biomass content at lower altitudes may be attributed
to the stand density and basal area. Altitude is one of
the important physiographic factors that affect plant
growth and development since functional traits could
show great variance depending on the altitude level.
Trees growing at low altitudes have taller stems
because they are more inclined to grow vertically in
order to capture more light. However, trees growing
at higher altitudes have thicker stems because the
temperature is colder at higher altitudes. Therefore,
stems are more likely to grow radially (Briceà ± o et
al., 2000; Cavieres, 2000; Keles, 2020).
Belowground Biomass
Belowground biomass was computed using the formula
proposed by Cairns et al. (1997). It uses the results of the
aboveground biomass. Based on the result, the
belowground biomass of 6-year-old F. moluccana
plantations ranges from 13.36Mg ha
-1
to 25.70Mg ha
-1
.
Trees planted at altitudes of <150 masl had the highest
total belowground biomass. As shown in (Fig.2), the
trend line also suggests a decrease in the average
amount of biomass with increasing altitude.
Meanwhile, Table 3 shows that altitudinal gradients
have significant effects on the belowground biomass
of F. moluccana, suggesting that soil depths at
different altitudes might have affected the volume or
biomass of roots. The results of the Duncan Multiple
Range Test (DMRT) shown in Table 4 indicate that
trees at the lowest altitude (<150 masl) have the
largest belowground biomass than those at higher
altitudes. This means that the biomass of trees at
<150 masl was significantly different from that at
higher altitudes.
Although there was a significant difference (P < 0.05),
the results in Table 5 show a weak correlation between
altitudinal gradients and their corresponding
belowground tree biomass. The t-statistics also showed
the weak effects of varying altitudes on tree biomass.
Table 3. Analysis of Variance for belowground biomass of F. moluccana.
Source of Variation SS df MS F P-value F crit
Blocks 2528878 3 842959.2 2.910828273 0.093326 3.862548
Treatments 3927525 3 1309175 4.520721799* 0.03392 3.862548
Error
2606348
9
289594.3
Total
9062751
15
* means significant at P<0.05 level of significance.
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Table 4. Summary of Duncan Multiple Range Test
(DMRT) for belowground biomass of F. moluccana.
Y
AG
1
(<150 masl)
2570.071 a
AG
2
(150
-
300 masl)
1500.931 b
AG
3
(301
-
450 masl)
1468.023 b
AG
4
(>450 masl)
1335.572 b
Pr > F(Model)
0.069
Significant
No
Carbon Stock
The carbon stock was computed using the ERDB
(2008) carbon stock equivalent for F. moluccana,
which was 40.20% for the whole tree. Based on the
result, trees planted at <150 masl have the highest C
content with 90.57Mg C ha
-1
(Fig. 2). Table 5, found
below, is the Analysis of Variance (ANOVA) for the
carbon stock that shows no significant difference in
the amount of carbon stock with the different
altitudinal gradients.
Table 5. Analysis of Variance for carbon stocks of F. moluccana.
Source of Variation
SS
df
MS
F
P
-
value
F crit
Blocks
1409.4818
3
469.827291
1.1358913
0.38564
3.86254
Treatments
3127.5716
3
1042.52387
2.52048755
NS
0.12362
3.86254
Error
3722.5793
9
413.619923
Total
8259.63279
15
NS
means not significant at P<0.05 level of significance.
Discussion
Aboveground Biomass
The aboveground standing crop biomass of woody
vegetation is frequently regarded as a major carbon
sink in the world (Sheikh et al., 2011). The
aboveground biomass values of woody vegetation
observed in this study varied from 104 to 144Mg ha
-1
(AG1). These values were closer to those reported by
Sarmiento et al. (2015). Few studies have found that
aboveground biomass declines with increasing
elevation (Moser et al., 2007; Leuschner et al., 2007,
as cited by Khadanga & Jayakumar, 2020). Other
studies have reported that biomass and C increase
with increasing altitude (Yadava et al., 2015; Yadava
et al., 2017). The study proved otherwise, as a result,
showing a multimodal pattern of biomass along
different altitudinal gradients. The statistics (Table 3)
suggest that different altitudes had weak effects on
the aboveground biomass of the trees planted therein.
This result is supported by the study of Khadanga and
Jayakumar (2020), as biomass has no correlation
with altitudinal gradients.
Trees can adopt various morphological, anatomical,
and physiological characteristics. Trees can
morphologically adjust to different altitudinal
gradients by varying their stem height and diameter,
quantity and size of leaves and needles, internode
length, and bark thickness (Poorter, 2001; Huber et
al., 2009). F. moluccana trees are nitrogen-fixers,
being leguminous plants. Nitrogen-fixing bacteria
usually associate mutually with rootlets, which are
usually formed in the upper soil horizon. Despite
variations in soil depth, nitrogen promotes vegetative
growth. This fact may explain the non-significant
difference in the aboveground biomass of the trees
despite the differences in altitude.
Belowground Biomass
Belowground biomass and litter are the smallest
fractions of total carbon in most forests (Brown
2002). Deep soil at lower altitudes promotes the
formation of a higher volume of roots than at higher
altitudes, with shallower soil depths brought about by
erosion. This explains why the belowground biomass
differs across different altitudes. This result is also
affected by specific factors such as site quality and
silviculture treatment (Rodríguez-Soalleiro et al.,
2018). Additionally, we found that the proportion of
root biomass decreased gradually with increasing tree
diameter. This was caused by natural pruning of the
root component. The primary function of the root
system is to absorb water and other nutrients. When
the root grows older, it regenerates naturally to
guarantee water and nutrient absorption (Jing et al.,
2018). This finding satisfies the assumption that trees
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Int. J. Biosci.
2023
with larger basal areas have less belowground
biomass than those with smaller basal areas. This
outcome is similar to that of previous studies
conducted in different forest locations (Mendoza-
Ponce & Galicia, 2010, as cited by Pandu et al., 2020).
Carbon Stock
Deep-rooted crops such as trees positively affect the
conservation of natural resources, including carbon
sequestration (Kell 2011). The carbon stock of F.
moluccana plantations contributed a generous amount
of carbon sequestration, given its value varied from
58.58Mg C ha-1 to 90.57Mg C ha
-1
. These values are
comparably larger than those reported by Tandug
(2006), 66.1Mg C ha
-1
for F. moluccana plantations of
ages 5-25 years old. However, compared to other
plantation species such as Samanea saman, the C
stored in F. moluccana is comparatively lower
(314.28Mg /ha, which appears at six years old), and the
lowest value was 193.31Mg/ha) (Fajariani et al., 2020).
Conclusion
The study revealed that the biomass and carbon stocks
showed distinct variation along different altitudinal
gradients. However, the different altitudinal gradients
did not play a significant role. It was concluded that
aboveground biomass and carbon stocks at different
altitudinal gradients did not differ significantly. In
contrast, belowground biomass is significantly higher at
<150 masl or at lower elevations.
Acknowledgement
The authors are grateful to the Caraga State
University College of Forestry and Environmental
Science for their financial support in this study.
Conflict of interest
The authors declare no conflicts of interest regarding
the publication of this manuscript.
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