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B I O D I V E R S I T A S
ISSN: 1412-033X
Volume 25, Number 9, September 2024 E-ISSN: 2085-4722
Pages: 3286-3294 DOI: 10.13057/biodiv/d250951
Unveiling the prevalence of invasive alien plant species in multiple-use
zone of Initao-Libertad Protected Landscape and Seascape, Misamis
Oriental, Philippines
LARRY C. HERBITO JR.1,, JAIME Q. GUIHAWAN1, CHRISTINE MARIE V. CASAL2,
DAISY LOU L. POLESTICO3, ARMI G. TORRES1
1Department of Environmental Science, School of Interdisciplinary Studies, Mindanao State University-Iligan Institute of Technology. Andres Bonifacio,
Tibanga, 9200 Iligan City, Philippines. Tel.: +63-063-221-4056, email: larry.herbito@g.msuiit.edu.ph
2School of Environmental Science and Management (SESAM), University of the Philippines Los Baños. Batong Malake, Los Baños, 4031 Laguna,
Philippines
3Center for Computational Analytics and Modeling, Premier Research Institute of Science and Mathematics, Mindanao State University-Iligan Institute
of Technology. Andres Bonifacio, Tibanga, 9200 Iligan City, Philippines
Manuscript received: 22 May 2024. Revision accepted: 26 September 2024.
Abstract. Herbito Jr. LC, Guihawan JQ, Casal CMV, Polestico DLL, Torres AG. 2024. Unveiling the prevalence of invasive alien plant
species in multiple-use zone of Initao-Libertad Protected Landscape and Seascape, Misamis Oriental, Philippines. Biodiversitas 25:
3286-3294. Invasive Alien Plant Species (IAPS) threaten Protected Areas (PAs) globally, causing habitat degradation, biodiversity
reduction, and ecosystem disruption. In the Philippines, data on invasive species in PAs is limited. This study aimed to investigate the
prevalence, abundance, and diversity of IAPS in multiple-use zone of Initao-Libertad Protected Landscape and Seascape (ILPLS),
Misamis Oriental, Philippines. Using belt-transect method, a total of 15 nested plots (20×20 m for trees, 5×5 m for herbs and shrubs, and
1×1 m for grasses and lianas) were established. Twenty-nine plant species from 18 families were identified, comprising 18 Native
Species (NS), seven Non-Invasive Alien Species (NIAS), and four IAPS. The IAPS identified were Gmelina arborea, Leucaena
leucocephala, Lantana camara, and Swietenia macrophylla which had the highest relative abundance of 96.83%. The Shannon-Weiner
diversity indices showed very low to low diversity of 0.30 to 2.17, and an unbalanced to semi-balanced species evenness of 0.17 to 0.70.
The Wilcoxon signed-rank test showed a significant difference in relative abundance between NS and IAPS (p = 0.01576). The
Wilcoxon rank-sum test indicated significant differences in species diversity and evenness of p = 0.03359 and 0.03343, respectively.
These findings are crucial for developing IAPS control strategies in the ILPLS in the future.
Keywords: Initao-Libertad Protected Landscape and Seascape, invasive alien plant, diversity, Sustainable Development Goal 15
Abbreviations: IAS: Invasive Alien Species; IAPS: Invasive Alien Plant Species; ILPLS: Initao-Libertad Protected Landscape and
Seascape; NS: Native Species; NIAS: Non-Invasive Alien Species
INTRODUCTION
Biodiversity encompasses the variety of life on earth,
including plants, animals, and microorganisms, which are
crucial for sustaining ecosystems. It provides essential
services like food production, pollination, disease
regulation, cultural enrichment, influencing human health
and well-being (Gora et al. 2023; Jain 2023). Despite its
benefits, biodiversity is declining globally due to several
factors, such as land and ocean use changes, climate
change, pollution, overexploitation of organisms, and the
introduction of Invasive Alien Species (IAS) (Brondizio et
al. 2019), which is the main concern in this case. Invasive
Alien Plant Species (IAPS), part of the IAS, are non-native
plants that can outcompete native flora, reduce
biodiversity, disrupt ecosystems, and cause economic and
ecological harm. Key characteristics of IAPS include rapid
growth, high reproductive capacity, effective seed dispersal
mechanisms, and the ability to adapt to various
environmental conditions (Dawson et al. 2017; Langmaier
and Lapin 2020).
The proliferation of IAPS has become an urgent
concern in managing Protected Areas (PAs) (Bomanowska
et al. 2017; Foxcroft et al. 2017). PAs serve as sanctuaries
for biodiversity, where natural ecosystems can flourish free
from human disturbances and the encroachment of invasive
species (Holenstein et al. 2021; Martínez-Vega and
Rodríguez-Rodríguez 2022). However, several studies have
unveiled a concerning trend of IAPS infiltrating the PAs
globally, such as Braun et al. (2016), Padmanaba et al.
(2017), Foxcroft et al. (2019), Paclibar and Tadiosa (2019),
and Huda et al. (2022). Meanwhile, among the 18 mega-
diverse countries, the Philippines ranks fifth in plant
species diversity and hosts 5% of the world's flora, but is
now one of the most threatened forest areas (Keong 2015;
Ramachandran 2023; CBD 2024). Biodiversity decline in
the country is driven by the introduction of IAS, habitat
loss, climate change, overexploitation, and pollution
(BMB-DENR 2016). In response, the government has
created more than 240 PAs under Republic Act 11038, the
Expanded National Integrated Protected Areas System
(ENIPAS) Act, to safeguard and conserve the country's
HERBITO JR. et al. – Invasive alien plants in protected area
3287
terrestrial and aquatic biodiversity. The country also
established a National Invasive Species Strategy and
Action Plan (NISSAP) 2020-2030 to mitigate IAS threats
and reduce pressure on local biodiversity.
Only a few PAs in the Philippines have undergone
assessments for IAPS like the ecological niche modeling of
IAPS in Quezon Protected Landscape (QPL), Southern
Luzon (Paclibar and Tadiosa 2019), and the distribution
and management of Swietenia macrophylla G.King in Mt.
Banahaw de Nagcarlan, Luzon Island (Coracero 2023).
Additionally, the species richness of trees in Mt. Apo
Natural Park, Mindanao Islands (Zapanta et al. 2019), the
native and alien plant species inventory and diversity in Mt.
Manunggal and Cebu Island (Garces 2019) also highlight
the occurrence of IAPS within these PAs. Meanwhile, the
biodiversity assessment of flora and fauna (Canencia and
Daba 2015) revealed some IAPS in the Initao-Libertad
Protected Landscape and Seascape (ILPLS).
There is no full account of the composition and
diversity of IAPS in the ILPLS yet. Hence, this study is
committed to assessing the prevalence of IAPS in the
ILPLS. Specifically, this study aimed to identify the IAPS
within the ILPLS and assess their abundance, diversity, and
evenness. The findings from this study hold significance
for Sustainable Development Goal (SDG) Target 15.8 -
introduce measures to prevent invasive species and reduce
their ecosystem impact, and serve as a useful guide by the
Protected Area Management Board (PAMB) of the ILPLS
and Municipal Environment and Natural Resources Office
(MENRO) Initao for developing management strategies
aimed at mitigating the proliferation of IAPS, preserving
native biodiversity, and maintaining the ecological balance
of the ILPLS.
MATERIALS AND METHODS
Entry protocol
The research proposal was submitted to the PAMB and
MENRO Initao for approval. Subsequently, a gratuitous
permit was obtained from the Department of Environment
and Natural Resources (DENR) Region 10 Office in
Cagayan de Oro City, Misamis Oriental, in compliance
with Republic Act No. 9147 - Wildlife Resources
Conservation and Protection Act.
Study area
The study was conducted in the multiple-use zone of the
Initao-Libertad Protected Landscape and Seascape
(ILPLS), Misamis Oriental, Philippines (Figure 1). ILPLS
spans 1,425 ha, with 57 ha of landscape and 1,368 ha of
seascape. It lies between Initao and Libertad, adjacent to
Iligan Bay, at the coordinates 8.1846°N,124.2571°E on
Mindanao Island, with 6.1 m above sea level (m asl.)
(Canencia and Daba 2015). ILPLS is one of over 240
national parks and protected areas designated under
Republic Act No. 11038 - Expanded National Integrated
Protected Areas System (ENIPAS) Act of 2018.
Procedures
Field sampling and data collection
Field sampling took place from December 2023 to
January 2024. Five 100-m transects were spaced roughly
100 m apart using a belt transect method, covering an area
of 5 ha (50,000 m2). Within each transect, three nested
plots, totalling 15 nested plots were designated: 20×20 m
for trees, 5×5 m for herbs and shrubs, and 1×1 m for
grasses and lianas, following the study of Paclibar and
Tadiosa (2020) with modification. Moreover, plant species
frequency and height were recorded, photographed, and
categorized as habitus, such as trees, shrubs, and lianas.
Figure 1. Map showing the Initao-Libertad Protected Landscape and Seascape (ILPLS), Misamis Oriental, Philippines. Note: Red dots
are sampling plots
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25 (9): 3286-3294, September 2024
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Identification and classification of invasive alien plant species
The identification of IAPS utilized data from the Global
Invasive Species Database (GISD)
(https://www.iucngisd.org/gisd/) and Global Register of
Introduced and Invasive Species (GRIIS)
(https://www.gbif.org/). Plant specimens were cross-
checked with existing reports, scientific literatures, and
websites such as Co’s Digital Flora of the Philippines
(https://www.philippineplants.org/), Catalog for Life
(https://www.catalogueoflife.org/), and Plants of the World
Online (https://powo.science.kew.org/) for further validation.
Identified species were categorized into habitus: trees,
shrubs, and lianas.
Size classes, height, and canopy cover of tree species
Tree species size classes are based on research by
Coracero (2023). Tree species were analyzed for Diameter
at Breast Height (DBH), height, and canopy cover using a
transect tape and range finder. DBH, measured at 1.3 m
above ground, approximates breast height. The diameter (in
cm) was calculated by dividing the circumference (in cm)
by 3.1416 (Yimam and Kifle 2020). Furthermore, the data
were presented in tabular format.
Data analysis
Species richness and distribution were estimated using
Shannon-Wiener Diversity Index described by Shannon
(1948) as follows:
Where :
H' : Species Diversity Index
s : Number of species
pi : Proportion of (n/N) of individuals of one
particular species found (n) divided by the total number of
individuals found (N)
Whereas, evenly species and/or individuals distributed
within a plot or quadrat were calculated using evenness
index described by Pielou (1966) as follows:
Where :
H' : Species Diversity Index
s : Number of species
Species diversity and evenness were calculated using
PAST Software (v.4.03). Additionally, the descriptive
values used are presented in Table 1.
Table 1. Descriptive value for plant species diversity and
evenness indices (Napaldet 2023)
Diversity
Evenness
Values
Description
Values
Description
>3.50
Very high
0.96-1.00
Balanced
3.00-3.49
High
0.76-0.95
Almost balanced
2.50-2.99
Moderate
0.51-0.75
Semi-balanced
2.00-2.49
Low
0.26-0.50
Less balanced
<1.99
Very low
0.00-0.25
Unbalanced
The relative abundance of IAPS was determined using
the formula described by Achacoso et al. (2016) as follows:
Where :
Pi : Relative abundance
ni : Number of individuals of the same species
N : Total number of individuals for all species
The Wilcoxon signed-rank test, a non-parametric test,
was used to compare the relative abundance between
Native Species (NS) and Invasive Alien Plant Species
(IAPS) across the 15 plots, with a significance level set at
0.05. Meanwhile, the Wilcoxon rank-sum test at a
significance level of 0.05 was applied to assess differences
in species diversity and evenness between NS and IAPS
(Renner et al. 2011). Moreover, heatmaps were utilized to
present and compare the species relative abundance,
diversity, and evenness across plots.
RESULTS AND DISCUSSION
Species identification and classification
Twenty nine distinct species comprising 18 Native
Species (NS), 7 Non-Invasive Alien Species (NIAS), and 4
Invasive Alien Plant Species (IAPS) in the Philippines are
documented (Table 2). The four IAPS identified are
mahogany (S. macrophylla), Gmelina (Gmelina arborea
Roxb. ex Sm.), Ipil-ipil (Leucaena leucocephala (Lam.) de
Wit), and Koronitas (Lantana camara L.) (Figure 2). These
IAPS are further categorized into habitus, namely trees and
shrubs. The IAPS categorized as trees are S. macrophylla,
G. arborea, and L. leucocephala, while the shrub group is
L. camara. Notably, no IAPS, NIAS, and NS belonging to
the herb and grass groups are observed within the ILPLS.
In terms of conservation status, most of the identified
Native Species (NS) were Least Concern (LC) based on the
2024 IUCN Red List of Threatened Species
(https://www.iucnredlist.org/). Only two species,
Rhaphidophora korthalsii Schott (Other Threatened
Species (OTS)) and Caryota mitis Lour. (Near Threatened
(NT)) have been evaluated locally based on the DENR
Administrative Order (DAO) 2017-11. The R. korthalsii
was designated with OTS status locally through DAO 2017-
11. However, it has not yet been evaluated by the IUCN.
Therefore, assessment of its conservation status using the
IUCN Red List categories and criteria should be considered.
Notably, no conservation status has been designated to
NIAS and IAPS, as they are targeted for control and
eradication rather than conservation.
Swietenia macrophylla, a member of the family
Meliaceae indigenous to the Americas, including Mexico
and South America, is renowned for its rapid growth and
environmental adaptability. Its introduction to the Philippines
dates back to 1911, primarily for reforestation and timber
production (Pinol et al. 2018). The leaf litter of S. macrophylla
is known to hinder the growth of native species (Galano
and Rodriguez 2021). Moreover, due to its allelopathic
property, S. macrophylla can suppress other plants' growth
under its canopy (Mukaromah et al. 2016). The G. arborea is
HERBITO JR. et al. – Invasive alien plants in protected area
3289
a fast-growing tree species belonging to the family
Lamiaceae that is native to Pakistan, China, and northern
Indo-China (Warrier et al. 2021). Its introduction to the
Philippines aimed to bolster pulpwood and furniture
manufacturing as early as 1960 (Pinol et al. 2018; Alipon et
al. 2019). The species was categorized as a long-lived pioneer
species, displaying opportunistic characteristics. It can
potentially disturb the natural succession of ecosystems in
areas where it spreads, thereby outcompeting native plant
communities (Sandoval 2016).
The L. leucocephala, a legume species in the family
Fabaceae, is native to Southern Mexico and Central
America (Pinol et al. 2018; Kato-Noguchi and Kurniadie
2022). Its arrival in the Philippines can be traced back to
natural dispersal and human-mediated introduction around
1910 (Pinol et al. 2018). The International Union for
Conservation of Nature (IUCN) has identified it as one of
the 100 worst invaders globally. This species has a negative
impact on infrastructure and inhibits the growth and
germination of other plants due to its allelopathic properties
(Kato-Noguchi and Kurniadie 2022). Finally, L. camara, a
flowering plant species from the family Verbenaceae native
to the American tropics (Kumar et al. 2022), likely reached
the Philippines through anthropogenic means as early as
1930 (Pinol et al. 2018). Known for its allelopathic
properties, L. camara can disrupt the structure and
composition of native plant vegetation (Singh et al. 2014).
In addition, it also threatens livestock productivity due to
its toxicity, especially in cattle and sheep (Ntalo et al.
2022).
Species diversity, evenness, and relative abundance
A total of 2,649 individual plants were identified in
plots that had been designated at ILPLS, of which 1,429
individuals (53.94%) were NS, 54 individuals (2.04%)
were NIAS, and 1,166 individuals (44.02%) were IAPS.
Among the existing plots, plot 3 had the highest IAPS with
583 individuals, followed by plot 2 (451 individuals) and
plot 14 (39 individuals), whereas no IAPS were recorded in
plots 7 to 10 (Table 3). Among the identified IAPS, S.
macrophylla was the most dominant species with a relative
abundance of 96.83%, followed by G. arborea (2.14%), L.
leucocephala (0.86%), and L. camara (0.17%) (Figure 3).
Native species, although relatively abundant, showed
varying degrees of distribution across plots. On the other
hand, NIAS groups, although less numerous than natives,
also showed their presence in some plots. Meanwhile,
IAPS shows a large number of individuals recorded. These
findings are consistent with research highlighting the
widespread impact of invasive species on ecosystems
(Galano and Rodriguez 2021).
The diversity values across all plots ranged from 0.30 to
2.17 wherein Plot 3 has the lowest and Plot 6 has the
highest diversity index value. Based on the descriptive
values provided (Napaldet 2023), Plot 3 is considered very
low diversity, while Plot 6 is considered low diversity.
Meanwhile, the species evenness values across all plots
ranged from 0.17 to 0.70 wherein Plot 3 is the lowest,
while Plot 11 is the highest. These values are considered
unbalanced and semi-balanced, respectively (Napaldet
2023). The dominance of IAPS individuals, particularly S.
macrophylla, resulted a very low diversity observed in
plots 2 and 3. In contrast, the very low diversity values
observed in other plots can be attributed to the dominance
of large native trees, which limit the establishment and
growth of other species in the region. Meanwhile, evenness
values across plots may indicate an imbalance in the
distribution of species abundances, with some species
being much more abundant than others (Taiwo et al. 2021).
Moreover, plots with higher proportions of IAPS exhibited
lower diversity and evenness, indicating potential disruption
to ecosystem stability (Pyšek and Richardson 2017).
Statistical analysis
The relative abundance of Native Species (NS), Non-
Invasive Alien Species (NIAS), and Invasive Alien Plant
Species (IAPS) in the 15 plots are shown in Figure 4.
Notably, NS showed varying levels of abundance across
plots, ranging from 4.9% to 100%. Plots 7 and 10 consist
exclusively of NS. In contrast, NIAS and IAPS show
different patterns. NIAS shows its presence sporadically,
with values below 10%, indicating a small contribution to
the overall abundance. In contrast, IAPS shows a wider
distribution range from 0% to 94.8%. Plots 2 and 3,
particularly, are distinguished by a marked dominance of
IAPS. These plots were located on the perimeter of the
ILPLS, and the large number of IAPS individuals recorded
in these plots may have been influenced by the encroaching
presence of several mature S. macrophylla trees near the
area (outside the perimeter fence) from ILPLS, as
highlighted by the parallel study of Herbito Jr. et al. (2024).
This finding is consistent with other studies highlighting
the invasiveness of S. macrophylla, which suppresses the
growth of native plants through its allelopathic properties
(Mukaromah et al. 2016; Coracero 2023). Moreover,
further investigation is needed to explore the observed
gaps. Therefore, to achieve this aim, a statistical test was
conducted to ascertain if the median differences between
the relative abundance of NS and IAPS, matched by the
plot, significantly deviate from 0, with a significance level
set at 0.05. Given the presence of outliers in the relative
abundance observed in Plots 2, 3, 7, and 10, the Wilcoxon
signed-rank test with continuity correction was employed.
The resulting test statistic, V = 103, yielded a
corresponding P-value of 0.01576. These results indicate a
significant difference in the relative abundance between NS
and IAPS across the sampled plots.
The species diversity and evenness distribution in the
15 plots are shown in Figure 5. Plots 2 and 3 showed the
lowest diversity and evenness indices than the others.
Furthermore, these plots had the highest prevalence of
IAPS compared to the other plots (Table 3). Therefore, to
investigate whether species diversity and evenness had the
same distribution for NS and IAPS vegetation types, the
Wilcoxon rank sum test was used at a significance level of
0.05 (Table 4).
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25 (9): 3286-3294, September 2024
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Table 2. List of identified plants in Initao-Libertad Protected Landscape and Seascape, Misamis Oriental, Philippines
Family
Conservation status
Scientific name
Common name
Local name
Habitus
DAO
2017-11
IUCN Red
List (2024)
Native Species (NS)
Araceae
Rhaphidophora korthalsii Schott
Dragon tail plant
Tibatib
Liana
OTS
-
Arecaceae
Caryota mitis Lour.
Fishtail palm
Lubi-lubi
tree
NT
LC
Arecaceae
Cocos nucifera L.
Coconut
Lubi
tree
-
-
Apocynaceae
Tabernaemontana pandacaqui Lam.
Banana bush
Kampupot
shrub
-
LC
Burseraceae
Garuga floribunda Decne.
Garuga tree
Bogo
tree
-
LC
Calophyllaceae
Calophyllum sp.
-
-
tree
-
-
Capparaceae
Crateva religiosa G.Forst.
Spider tree
Banugan
tree
-
LC
Combretaceae
Terminalia catappa L.
Tropical almond tree
Talisay
tree
-
LC
Elaeocarpaceae
Elaeocarpus monocera Cav.
One-hundred
quandong
Margapali
tree
-
-
Euphorbiaceae
Macaranga tanarius (L.) Müll.Arg.
Parasol leaf tree
Binunga
tree
-
LC
Euphorbiaceae
Mallotus sp.
-
tree
-
-
Euphorbiaceae
Melanolepis multiglandulosa (Reinw. ex.
Blume) Rchb. & Zoll.
Chawan
Alim
shrub
-
LC
Malvaceae
Pterocymbium tinctorium (Blanco) Merr.
Winged boot tree
Taloto
tree
-
LC
Malvaceae
Pterospermum sp.
-
tree
-
-
Meliaceae
Aglaia argentea (Reinw.) Blume
Silver boodyara
Ilo-ilo
tree
-
LC
Moraceae
Artocarpus blancoi (Elmer) Merr.
Tipolo
Antipolo
tree
-
LC
Moraceae
Streblus asper Lour.
Siamese rough bush
Kalyos
tree
-
LC
Rhamnaceae
Ziziphus sp.
-
Malabayabas
tree
-
LC
Non-Invasive Alien Species (NIAS)
Araceae
Syngonium podophyllum Schott
Arrowhead
-
liana
Arecaceae
Chrysalidocarpus lutescens H.Wendl.
Golden cane palm
-
tree
Bignoniaceae
Tabebuia rosea (Bertol.) Bertero ex A.DC.
Trumpet tree
-
tree
Fabaceae
Bauhinia purpurea L.
Butterfly leaf
Alibangbang
tree
Lamiaceae
Tectona grandis L.f.
Teak
Teak
tree
Nyctaginaceae
Bougainvillea glabra Choisy
Paper flower
Bogambilya
shrub
Sapotaceae
Chrysophyllum cainito L.
Star apple
Caimeto
tree
Invasive Alien Plant Species (IAPS)
Fabaceae
Leucaena leucocephala (Lam.) de Wit
River tamarind
Ipil-ipil
tree
Meliaceae
Swietenia macrophylla G.King
Mahogany
Mahogany
tree
Lamiaceae
Gmelina arborea Roxb. ex Sm.
Beechwood
Gmelina
tree
Verbenaceae
Lantana camara L.
Coronet
Koronitas
shrub
Table 3. Coordinates, vegetation composition, diversity, and species evenness in observed plots
Coordinates
Plot
NS
NIAS
IAPS
TI
H'
SE
Description by Napaldet (2023)
Latitude (N)
Longitude (E)
H'
SE
8° 32' 31.815"
124° 19' 3.183"
1
345
1
20
366
1.46
0.43
VL
LB
8° 32' 33.014"
124° 19' 1.455"
2
81
14
451
546
0.80
0.19
VL
U
8° 32' 33.986"
124° 19' 0.109"
3
30
2
583
615
0.30
0.17
VL
U
8° 32' 33.755"
124° 19' 4.872"
4
112
1
6
119
1.55
0.34
VL
LB
8° 32' 35.052"
124° 19' 3.396"
5
80
20
10
110
2.03
0.45
L
LB
8° 32' 36.131"
124° 19' 1.919"
6
80
10
18
108
2.17
0.59
L
SB
8° 32' 36.959"
124° 19' 7.067"
7
188
0
0
188
1.42
0.59
VL
SB
8° 32' 37.853"
124° 19' 5.822"
8
91
2
0
93
1.46
0.48
VL
LB
8° 32' 38.638"
124° 19' 4.426"
9
88
1
0
89
1.95
0.64
VL
SB
8° 32' 39.948"
124° 19' 9.408"
10
90
0
0
90
1.88
0.66
VL
SB
8° 32' 41.460"
124° 19' 8.256"
11
62
0
4
66
1.95
0.70
VL
SB
8° 32' 42.683"
124° 19' 6.887"
12
55
0
3
58
1.19
0.55
VL
SB
8° 32' 42.624"
124° 19' 13.540"
13
22
1
16
39
1.21
0.67
VL
SB
8° 32' 44.012"
124° 19' 13.202"
14
54
2
39
95
1.16
0.46
VL
LB
8° 32' 45.711"
124° 19' 12.809"
15
51
0
16
67
1.81
0.68
VL
SB
Total
1429
54
1166
2649
Note: NS: Native Species; NIAS: Non-Invasive Alien Species; IAPS: Invasive Alien Plant Species; TI: Total Individual; H': Diversity
Index; SE: Species Evenness; VL: Very Low; L: Low; SB: Semi-Balanced; LB: Less Balanced; U: Unbalanced
HERBITO JR. et al. – Invasive alien plants in protected area
3291
Swietenia macrophylla Gmelina arborea
Leucaena leucocephala Lantana camara
Figure 2. Invasive Alien Plant Species (IAPS) present in Initao-Libertad Protected Landscape and Seascape (ILPLS), Philippines
Figure 3. A. Relative abundance of different plant individuals; and B. Relative abundance of identified IAPS
Figure 4. Relative abundance heatmap by vegetation type across the 15 plots
A
B
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Table 4. Wilcoxon rank sum test results for Species Evenness
Index (SE) and Diversity Index (H')
Variable
W Statistic
P-value
Diversity Index (H')
0*
0.03359
Species Evenness Index (SE)
0*
0.03343
Table 5. Size classes of IAPS categorized as trees
Size class
Diameter (cm)
Swietenia
macrophylla
Gmelina
arborea
Leucaena
leucocephala
Seedlings/
Saplings
1≤Diameter<5
1,117
8
10
Poles
5≤Diameter<30
3
1
0
Adults
≥30
9
16
0
Total
1,129
25
10
Figure 5. Heatmap by IAPS across the 15 Plots of: A. Species
diversity; and B. Evenness
The results show with 95% confidence that there are
significant differences in species diversity and evenness
between IAPS and NS vegetation types. This could mean
that plots predominantly occupied by IAPS show lower
diversity and evenness values than plots dominated by NS.
However, NS-dominated plots tended to show low levels of
diversity, albeit with varying degrees of evenness, often
showing signs of depression or instability in species
evenness. The findings indicate that the high prevalence of
IAPS can contribute to the reduction of biodiversity
(Dawson et al. 2017; Pyšek and Richardson 2017;
Langmaier and Lapin 2020), while diverse native plant
communities may limit the invasion of IAPS on small-scale
observations (Petruzzella et al. 2018).
Tree size classes, height, and crown cover of IAPS
The distribution of size classes for the three tree species
is presented in Table 5. Most individuals of S. macrophylla
are classified as seedlings/saplings (1,117 individuals),
followed by adults (9 individuals) and poles (3
individuals). Meanwhile, G. arborea has the highest
number of adults (16 individuals), with 8 seedlings/saplings
individuals and just 1 pole. Moreover, L. leucocephala is
solely represented by seedlings/saplings (10 individuals),
with no individuals recorded in the pole or adult-size
classes. Adult individuals of S. macrophylla have heights
ranging from 13 to 18 m, with crown cover ranging from 4
to 7 m. In contrast, adults G. arborea exhibit heights
ranging from 15 to 19.5 m, with crown cover varying from
2.3 to 9 m.
The predominance of seedlings/saplings in S.
macrophylla indicates successful recruitment and
regeneration processes in the area. This observation aligns
with previous studies highlighting the species' ability to
establish and thrive in various forest environments (Galano
and Rodriguez 2021; Coracero 2023). Additionally, the
widespread use of S. macrophylla in reforestation projects,
such as the Philippine government's National Greening
Program (NGP), has led to its prevalence within PAs. The
S. macrophylla is the most planted tree in the country under
NGP until 2011 (Torres 2018). Furthermore, the abundance
of S. macrophylla underscores its invasiveness,
emphasizing the necessity for efficient management
strategies to alleviate its impact on native biodiversity
(Galano and Rodriguez 2021). Meanwhile, G. arborea has
a notably higher number of adult individuals than S.
macrophylla. This observation aligns with the fact that G.
arborea is known for its rapid growth rate, making it a
popular choice for reforestation programs in tropical and
subtropical regions (Sandoval 2016). The broader range of
heights and crown covers observed among adult G.
arborea trees suggest greater variability in canopy structure
and potential niche differentiation within the species
(Hakamada et al. 2023). In contrast, only seedlings/saplings
of L. leucocephala may indicate ongoing establishment and
colonization by this species in the study area. The absence
of individuals in the pole and adult size classes may
suggest that L. leucocephala populations are in earlier
stages of development or experiencing limitations in
reaching maturity, possibly due to biotic or abiotic factors
(Sharma et al. 2022).
Assessing the prevalence of invasive species in this
region is a critical step in supporting the country’s efforts
to meet SDG 15.8, which focuses on preventing,
controlling, and eradicating invasive alien species.
A
B
HERBITO JR. et al. – Invasive alien plants in protected area
3293
Moreover, policymakers and conservationists can identify
the areas most affected, understand the species causing the
greatest harm, and develop targeted management strategies.
In conclusion, the multi-use zone of Initao-Libertad
Protected Landscape and Seascape (ILPLS) has a variety of
plant species, with 29 species consisting of 18 native
species, seven non-invasive alien species, and four IAPS.
Thus, 2,649 individual plants were identified, consisting of
1,429 native individuals, 54 non-invasive alien individuals,
and 1,166 IAPS individuals. This shows the high
prevalence of IAPS in ILPLS; S. macrophylla (Mahogany)
was the most abundant IAPS, with a relative abundance of
96.83%. The Shannon-Wiener diversity index ranged from
0.30 to 2.17, indicating very low to low diversity. In
contrast, the evenness value ranged from 0.17 to 0.70,
indicating an unbalanced and semi-balanced species
community and species abundance distribution. Relative
abundance between native species and IAPS showed
significant differences in species diversity and evenness.
This indicates that plots dominated by IAPS showed lower
levels of diversity and reduced evenness compared to plots
dominated by native species. In recommendation,
conservation efforts must prioritize controlling and
eradicating IAPS to reduce its negative impacts on native
ecosystems. Ongoing monitoring and research are also
essential to track changes in vegetation dynamics within
the area. Additionally, comprehensive assessments of IAPS
in the landscape zone of ILPLS should be conducted to
inform effective management strategies.
ACKNOWLEDGEMENTS
The first author would like to express his gratitude to
the Department of Science and Technology - Accelerated
Science and Technology Human Resource Development
Program (DOST-ASTHRDP), Philippines, for the graduate
research grant. We also thank the Protected Area
Management Board (PAMB) and Department of
Environment and Natural Resources (DENR) - Community
Environment and Natural Resources Office (CENRO)
Initao, Philippines, for granting the permission to conduct
the study, and DENR Region 10 Office for granting the
Gratuitous permit. Special thanks are extended to Faulyn
Bernardo, Juceil Habagat, Dan Menard Aguaviva, Archie
Quitos, Chin Manginsay, and Shaina Lampad for their
assistance in field sampling.
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