Population Structure and Spatial Pattern of Critically Endangered Dipterocarpaceae Tree Species in Mt. Malindang Range Natural Park, Mindanao, Philippines ()
1. Introduction
Dipterocarpaceae is the most well-known and dominant tree in the tropic regions [1] with economic and ecological importance. It particularly grows and is abundant in lowland within elevation ranges from 300 to 1200 masl and with an annual mean rainfall of 1000 mm to 2000 mm [2]. The dipterocarps are highly valuable timber products in Southeast Asian countries [3] [4]. They are also the source of minor forest products such as resins, camphor, dammars, and tannin [5], which most of the upland dwellers are dependent on for their survival [6]. Intense exploitation of dipterocarps trees caused their rapid decline and eventually became globally threatened.
The Philippine forest is rich in dipterocarps, especially in lowland forests. However, these areas experienced massive exploitation such as logging, land conversion and fragmentation that endangered local floral species. Philippine dipterocarps species are distributed to five habitat types namely: tropical lowland evergreen rain forest, tropical semi-evergreen rain forest, tropical lower montane rain forest, forest over limestone and peat swamp forest [7]. The philippines has around 50 species of dipterocarps in 6 genera, 21 are endemic to the country [2] [8], and 31 species are considered threatened [9] [10]. Furthermore, in 2011, an assessment conducted in Mt. Hamiguitan Range, Davao del Sur had identified 5 threatened endemic species of dipterocarps with high priority protection and conservation [11]. Furthermore, the preliminary assessment of threatened plants in the country assessed by [9] listed 686 taxa of vascular and mosses that are indigenous to the Philippines, which are considered threatened plants as well. Of the 686 taxa, 472 (69%) belonged to angiosperm of which the family Dipterocarpaceae is contributing 31 (6.5%) to the national list of threatened plants which 14 (45%) species are considered critically endangered.
Mt. Malidang Range Natural Park (MMRNP) is located in the Northern Part of Mindanao. On June 19, 1971, the area was proclaimed as Mount Malindang National Park by virtue of Republic Act 6266. Under the establishment of the National Integrated Protected Areas System (NIPAS) in 1992, the park was reclassified and was renamed Mount Malindang Range Natural Park on August 2, 2002, through Proclamation No. 228. It has an area of 53,262 hectares with 34,464 as Strict Protect Zone and 18,798 hectares as Multiple Use Zone [12]. It is part of the Key Biodiversity Areas (KBAs) and was declared an ASEAN Heritage Park in 2012 because of its immense value and high endemicity. The park was included in the list of one of the conservation priority areas in the country; however, the park is facing constant threats of illegal poaching, unsustainable farming practices, and weak law enforcement [13] [14]. Furthermore, in the 2013 Management Effectiveness and Capacity Assessment of the park, utilization of portions of the park for agricultural crops and logging and wood harvesting were considered as high threats to the park values [15].
The comprehensive study made during the Biodiversity Research Program (BRP) for Mindanao in the northern part of Mt. Malindang focused on tree diversity and abundance of which 85 species were recorded with 57% endemism [16]. In MMRNP, there were four (4) identified Dipterocarps species: Shorea contorta, Shorea polysperma, Shorea squamata, and Shorea negrosensis, which are listed as critically endangered in DAO-2007-01 and IUCN Red List [17]. However, the population structure and spatial tree pattern of the critically endangered dipterocarp trees have not yet been studied.
Given the large area of MMRNP, it is recommended that future studies be made on tree species richness and diversity for the rest of the park. There is also a need to assess the health status of the remaining forest cover in Mt. Malindang, especially the critically endangered species for propagation, conservation, protection, and policy development. Hence in order to address the following research objectives were provided: 1) describe tree composition, population structure and distribution patterns; 2) analyse the relationship of the spatial distribution of the critically endangered dipterocarp trees with Physico-chemical properties and topographic conditions; 3) identify sources of disturbances present in the area.
2. Materials and Methods
2.1. Description of the Study Area
This study was conducted in the northern part of Mount Malindang Range Natural Park (MMRNP), Misamis Occidental (Figure 1). It is within geographic coordinates 123˚31'45'' to 123˚55'30'' East longitudes and 8˚30'30'' to 8˚45'55'' North latitudes. MMRNP has a total area of 53,262 hectares with a Strict Protection Zone of 34,464 hectares and Multiple Use Zones of 18,798 hectares. It has an altitude range of 600 meters to 2404 m asl. It has 7 peaks namely: South Peak, Mt. Malindang peak itself, Mt. Labag, North Peak, Mt. Sumalarong, Mt. Ampiro, and Mt. Balabag [14] [18]. The climate of the MMRNP is wet and moist, slightly moderate dry season and has an average rainfall of about 2500 mm and above. Rainfall is fairly distributed throughout the area. The mean minimum monthly temperature is 27.7˚C with mean annual relative humidity is 82%. The soil is generally clay loam in the upland area with a pH value range of 4.6 - 6.0. The habitat types of the park includes: dipterocarp forest, grassland, lower montane forest, mossy forest and upland wetland. The northern portion Mount Malindang covers municipality of Concepcion, Calamba, Oroquieta, Lopez Jaena and parts of Don Victoriano.
2.2. Sampling Design and Vegetation Data Collection
Entry protocol made to the DENR- MMRNP Protected Area Office, Municipalities and Barangays covered in the study area, seeking their approval to penetrate the area for security reasons and presentation to the PAMB (Protected Area
Management Board) for seeking their approval for allowing the researcher to conduct and acquire permit gratuitous permit for the collection of voucher specimens of unidentified trees.
Three permanent 2-kilometer transect lines were established in different elevation ranges (300 masl to 700 masl, 701 masl to 900 masl, and 901 masl to 1500 masl) in the North-east portion of MMRNP following the method of the Biodiversity Monitoring System (BMS) of DENR in establishing a permanent plot for monitoring of a protected area [19] (Figure 2).
A total of 29 20 m × 20 m plots were laid down alternately in a 2-kilometer transect line at a regular distance of every 250 meters.
All trees with a diameter breast height (DBH) of at least 5 cm inside the quadrats were identified, measured, geo-tagged, and recorded. In addition, voucher specimens of each species were collected, photographed, labelled, pressed, and identified using different taxonomic keys from floras and monographs
![]()
Figure 2. Topography of the three sites in the Northeastern part of Mt. Malindang Range.
of [20] - [25], Herbarium comparison, Co’s Digital Flora in the Philippines [26], and sent to plant expert for further verification.
In each quadrat, threats and disturbances were recorded through direct observation in the study area. Threats determined were recorded as present and absent and identified the types of threats. Physico-chemical properties were recorded, such as soil moisture and pH in each quadrats using a Kelway Soil Tester, light intensity using the calibrated android App (Physics Toolbox v.1.8.9), a free app developed by Vieyra Software [27] installed in Samsung Galaxy J7 Prime mobile phone. The app was calibrated in LI-COR Model LI-250. The geographical locations of individual trees inside the quadrats were recorded using a Garmin e-Trex 30.
2.3. Data Analysis
Analysis of density, frequency and abundance followed the standard methods of [28] and [29].
Density = Total no. of individuals of a species/Total no. of quadrats studied;
Relative Density (%) = Number of individuals of species/Number of individuals of all species × 100;
Frequency = Number of sampling units species occur/Total no. of sampling units;
Rel. Frequency (%) = Frequency of a species/Frequency of all species × 100;
Rel. Basal Area (%) = Basal area of a species/Basal area of all species × 100.
The Basal Area of trees was calculated using this formula:
Basal Area = 0.7854 * d2.
Where, d = diameter at breast height in meter.
Importance Value (IV) was used to measure to determine the productivity of species in a community. Species Importance Value Index (IVI) was calculated by summing the Relative Density, Relative Frequency, and Relative Basal Area following [30]. The abundance and Frequency ratio of each species were also calculated to determine the population dispersion pattern. The ranges of values in determining dispersion pattern were: regular (<0.025), random (0.025 - 0.05) and contiguous (>0.05) given by [31].
Tree diversity indices such as Shannon-Wiener Index, and Simpson’s Diversity Index were calculated using PAST version 3.23 software package for education and data analysis [32]. The Shannon diversity index (H’) is also known as the Shannon-Wiener index, Shannon-Weaver index and Shannon entropy. The H’ value of the Shannon diversity index is a function of the number of species present in a plot and the degree of evenness of the total population that is distributed equally among species. Simpson’s diversity index is used to measure diversity taking into account the common or dominant species. Moreover, the similarity of dipterocarps tree species along elevational gradient was calculated with the Bray-Curtis index of similarity.
The following formulae were used in calculating the different indices:
1) Shannon-Wiener Index (1963)
ni = Total number of individuals per species,
N = Total number of individuals per quadrat.
2) Simpson’s Diversity Index (1949)
For Simpson’s index of diversity is the value of 1 − D.
Shannon diversity index was used because it is more sensitive to small samples as compared to other indices while the Simpson diversity index was used for comparison. The classification of [33] was used for the interpretation of the Shannon diversity index (Table 1).
Demographic characterization of trees including the critically endangered dipterocarp trees, individuals were classified as seedlings (no measurable
![]()
Table 1. Diversity indices classification developed by [33].
dbh 1.3 m); juveniles (with dbh < 20 cm); reproductive (with dbh > 20 cm) according to [34]. Dipterocarp trees that have measurable dbh of <10 cm were grouped into different size classes of 5cm of each group following by [35]. Basal area was calculated using the DENR formula: BA = 0.7854(D)2, where D is a diameter at breast height in meters.
The assessment of the conservation status of tree species was based on the national list of threatened Philippines plants [36] [37] [38] [39].
3. Results and Discussion
3.1. Tree Composition and Distribution Patterns
The present study recorded 638 individuals belonging to 86 species, 62 genera, and 54 families from the three (3) sampling sites (Table 2) in the North-western part of Mt. Malindang Range Natural Park. Out of these 27 families comprising 41 genera, 50 species and 215 individuals were recorded in Site 1; 28 families representing 35 genera, 58 species, and 300 individuals were recorded in Site 2. Site 3 contributed 123 individuals belonging to 43 species among 32 genera and 23 families. Site 1 is dominated by Moraceae (Ficus sp.), site 2 is dominated by Dipterocarpaceae (Anisoptera thurifera), and Melastomataceae and site 3 is also dominated by Dipterocarpaceae (Shorea contorta) in terms of basal density. Other relatively abundant families are Moraceae, Fagaceae, and Myrtaceae. The values of the Shannon-Weiner diversity index ranged from 3.30 to 3.54, with the value from Site 1 being the highest and site 3 as the lowest. On the other hand, Simpson’s value ranged from 0.94 to 0.95 for all sites (Table 2). Using the classification scheme developed by [33], the diversity of the North-western part of Mt. Malindang in three study sites was considered high to very high. The result of this study is higher species diversity of [40] in the southern portion of the park and of [41] in upland farming communities of Nueva Viscaya, Benguet and Quezon. Furthermore, the values of Simpson’s diversity index corresponded to the other reports on tropical forests [42] [43].
Understanding species composition and tree diversity are essential in determining forest community stability, tree population status, regeneration, and diversity [44] [45]. The previous study in the northern part of Mt. Malindang found 1284 species of plants belonging to 472 genera and 187 families [46], and southern part, there were 275 individuals belonging to 46 species and 28 families
![]()
Table 2. Floristic richness, number of individuals, and diversity indices for the three sites.
[40]. The present findings account for 6.6% of the total species found in the comprehensive floral inventory in the Northern part of Mt. Malindang, and a higher number of tree species found in the southern portion of the park since the study in the southern part had only one (1) 2-kilometer transect in this study.
The number of plant families in the three different elevation sites was 54 taxonomically well-represented families (Table 3). Moraceae and Myrtaceae had the most species-rich families (8 species each), followed by Dipterocarpaceae and Anacardiaceae (7 species each); Fagaceae (6 species each). Dipterocarpaceae had the maximum number of species (127 species each), followed by the family Moraceae (107 species each). Correspondingly, the most species-rich genera are Ficus & Syzygium (Moraceae and Myrtaceae (8 species), Lithocarpus Fagaceae (6 species), and Shorea (Dipterocarpaceae (5 species). Twelve (1.94%) undescribed tree species were collected because of the lacking of diagnostic features.
Dipterocarpaceae was analysed with the Importance Value Index (IVI = 50.98) in the present study as the ecologically most dominant and significant family. The other co-dominant families were Moraceae (IVI = 40.54), Rubiaceae (IVI = 20.87), Melastomataceae (IVI = 19.15), Myrtaceae (IVI = 18.81), and Fagaceae (IVI = 16.36) (Table 3). The greater importance value of dipterocarp trees in this study indicated that the dipterocarps are still dominated in Mt. Malindang, and this substantiated the forest types of the park and in other dipterocarp forests in tropical countries [47] [48].
There were seven (7) dipterocarps tree species recorded, representing three (3) genera, contributing 8.8% of total tree species diversity (86 species) of which one (1) species was identified up to genera level belonging to Shorea (Table 3). This accounts for (14 percent) of the total number of dipterocarps species in the
![]()
![]()
Table 3. Dominant families for the 3 sites based on number of individuals, species, genera, and family importance value index.
Note: 12 unidentified tree species.
Philippines [2] Seven (7) recorded dipterocarps species are Anisoptera thurifera (Blanco) Blume, Dipterocarpus grandiflorus (Blanco), Shorea contorta S Vidal, Shorea negrosensis Foxw., Shorea polysperma (Blanco) Merr, Shorea squamata (Turcz), and Shorea sp. This also corresponds to the findings of the previous study in the southern part of Mt. Malindang found 4 Shorea species: Shorea polysperma, Shorea negrosensis, Shorea contorta, and Shorea squamata [40]. Shorea contorta, Shorea negrosensis, and Shorea polysperma are listed as critically endangered listed in [49] and [36]. Dipterocarpus grandiflorus (Blanco) is listed in [36] as vulnerable and endangered in [49]. Shorea squamata syn. Shorea palosapis is listed in the [38] as critically endangered. Anisoptera thurifera is listed as vulnerable in [37].
The most important species across three sites were A. thurifera indicated with a value of 15.66 followed by Astrocalyx calycina (S.Vidal) M (11.27); S. contorta S. Vidal (9.32); Neonauclea formicaria (Elmer) Merr. (9.25) and Ficus fistilulosa Reinw.ex Blume (8.72). The other dipterocarps species, such as S. polysperma (Blanco) Merr. had 8.61 IVI, S. squamata (Turcz.) Benth. (4.49), Dipterocarpus grandiflorus (Blanco) (4.12), and S. negrosensis Foxw and Shorea sp. both had 1.08 SIV (Table 4). The present findings are unique to other studies conducted inside Mt. Malindang. In the previous study in the Southern part of the park, [40] reported S. contorta was abundant species of the Dipterocarpaceae family. This is because the Southern part is less disturbed than the Northern part, where the present study is.
Spatial patterns of Dipterocarps species across three sites are varied differently, Anisoptera thurifera (Blanco) Blume species distribution pattern is clumping in all sites, Dipterocarpus grandiflorus (Blanco) which is present only in Site 3 the distribution is also clumping, Shorea contorta S.Vidal is random in Site 2 and contiguous in site 3, Shorea negrosensis, present in site 2 only is regular in distribution pattern, Shorea polysperma (Blanco) Merr. Foxw is contiguous in site 1 and regular in both site 2 and 3. Shorea sp. is regular only in sites 3 and Shorea squamata (Turcz.) Benth. & Hook.f. ex DC is both regular in distribution pattern in sites 2 and 3 (Table 5).
Dipterocarp species in this study exhibit both clumping and uniform distribution pattern; this is similar to the study in the tropical evergreen forest of West
Legend: SIVI-Species Importance Value Index; IUCN & DAO 2017-11 & -07 Criteria: CR (Critically Endangered), Vu (Vulnerable), En (Endangered), OTS (Other Threatened Species), OWS (Other Wildlife Species), NL (Not Listed).
![]()
Table 5. Distribution analysis of Dipterocapaceae tree species at three forest sites of Northern part of Mt. Malindang.
India that dipterocarps species showed clumping or uniformed distribution patterns [50]. According to [51], a clumped distribution pattern is the most common in nature. In contrast, random distribution occurs in a homogeneous environment, and a regular pattern occurs when there is severe competition between individuals. It means that the secondary forest community of Mt. Malindang is highly patchy in nature. The clumping of individuals may be due to a lack of mode of seed dispersal in the area, or maybe after the logging, the removal of a mature tree creates a large gap in the forest, which encourages regeneration and growth of numerous seedlings as in the present studied dominated with a single stand of trees like the Shorea contorta.
3.2. Population Structure
Individual plants of dipterocarps species ranged in number from 1 (Shorea negrosensis Foxw and Shorea sp.) to 57 (Anisopthera thurifera (Blanco) Blume) (Table 5). The abundance of S. negrosensis Foxw and Shorea sp. are the lowest among the seven (7) species of dipterocarps found in three (3) study sites in a different elevation range. Abundance ranked in increasing order as Shorea negrosesis Foxw (1) = Shorea sp. (1) < Dipterocarpus grandiflorus (Blanco) Blanco (5) < S. squamata a (Turcz.) Benth. & Hook.f. ex DC. (7) < S. polysperma (Blanco) Merr. (24) < Shorea contorta S. Vidal (29) < Anispothera thurifera (Blanco) Blume (57). The total basal area of Anisoptera thurifera (Blanco) Blume was significantly larger than that of the other seven dipterocarp species, and the mean DBH and height of S. polysperma (Blanco) Merr. was notably largest than other Dipterocarpaceae species. Non-dipterocarps species mean dbh and height are lowest compared to dipterocarps species (Table 6).
Diameter-class distribution of dipterocarps species in all sites showed irregular population structure trends (Figure 3). Species like Anisoptera thurifera showed a distinct reverse J-shaped distribution and were represented mainly at lower-sized classes with higher density at juvenile and seedling stages (Figure 4). A. thurifera grows from >300 to 1200 masl with normal to slightly acidic, low relative light intensity, and high moisture environment. This means that A. thurifera recruitment is good and is regenerating even in both disturbed and undisturbed areas. However, with only one adult stage found and poaching present in the area, it indicates that the population is declining.
The rest of the dipterocarps species, i.e., Shorea contorta, Shorea polysperma, and Shorea squamata, were represented by an irregular trend in size class distribution with high density at the mature stage except for Shorea polysperma which has a higher density at the juvenile stage. Dipterocarpus grandiflorus showed uniform but uneven distribution in the size class. Shorea negrosensis and Shorea sp. both species are in the juvenile stage with single species. Dipterocarps species found in this study were mostly in the reproductive stage. The declining population is evident in both types of the structure since the seedlings of critically endangered dipterocarps are in short supply. There would be an inadequate number of seedlings or saplings to maintain their population in the
![]()
Figure 3. Diameter-class distribution of dipterocarps and non-dipterocarps species by density.
future. Furthermore, according to [52], a species is on the verge of extinction if its population is represented by a high size class diameter. Anthropogenic activities observed in the area like poaching, slash and burn, land conversion can
![]()
Figure 4. Dipterocarps species with their seedlings, saplings, and mature tree abundance pattern by [34].
greatly influence the recruitment of dipterocarps in the area. The larger stem of Shorea contorta is still present in Site 3 and thus is susceptible to high disturbance.
The overall population of critically endangered dipterocarps species in Mt. Malindang Park (e.g., S. contorta, S. polysperma, S. squamata, Dipterocarpus grandiflorus, S. negrosensis are decreasing and at high risk of local extinction. Thus, conservation and protection priority in the park need to be strengthened and strictly imposed.
Plant structure and diversity in any site are subjective by their abundance pattern, species distribution, topography, soil, geographical location, and climate
![]()
Table 6. Population structure of seven (7) Dipterocarpaceae and non-Dipterocarps tree species in three different elevation range in the north-east portion of Mt. Malindang.
[53] [54]. In this study Anisoptera thurifera structure in all sites showed good regeneration from the management perspective, thus in the future, its population will maintain.
3.3. Spatial Pattern
Figure 5 and Figure 6 show the spatial distribution of the individual tree species highlighting the dipterocarps species. The map also gives a particular location and elevation distribution of dipterocarps species, especially the critically
![]()
Figure 5. Spatial distribution pattern of dipterocarps species in relation to the topography of the study sites.
![]()
Figure 6. Distribution pattern of dipterocarps and non-dipterocarps.
endangered species such as Shorea contorta S. Vidal, Shorea negrosensis Foxw. and Shorea polysperma (Blanco) Merr. and other associated tree species. The plots containing the critically endangered or threatened dipterocarps species should be prioritized for conservation and protection. However, areas located outside the strict protection zone with dipterocarps species should be declared priority conservation areas for reforestation programs DENR or become local conservation areas of LGUs or barangays where the critically endangered dipterocarps are located and become a seed source area for ex-situ and in-situ conservation.
The distribution of Anisoptera turifera in some plots in different elevation ranges is aggregated; however, it is also observed that it has a regular pattern because of disturbances. Dipterocarpus grandifluros has a regular pattern in an elevation ranging from 300 - 700 masl. Shorea contorta is aggregated in an elevation ranging from 300 to 900 masl. Shorea polysperma is randomly distributed in an elevation of 701 - 900 masl and regular distribution in the lower elevation (300 to 700 masl). Moreover, Shorea squamata, Shorea negrosensis, Shorea sp. are regularly distributed in the elevation range of 700 to 900 masl; this may be influenced by the disturbance present in those areas. The different patterns observed in this study, such as random, regular, and aggregated, tend towards regularity patterns among the adult trees found in [55] and randomness in [56] study Xuan Nha Nature Reserve, Vietnam.
Cluster analysis was carried out using the Bray-Curtis similarity index between dipterocarps tree species and elevation gradients. The dendrogram showed the similarity between elevation gradients and dipterocarps tree species forming 3 clusters. D. grandifluros, Shorea sp. and S. squamata was found in the lower elevation and mid-elevation (300 - 900 masl), S. polysperma, A. thurifera and S. contorta can grow from lower to high elevations (300 - 1200 masl) whereas S. negrosensis formed a unique cluster among the dipterocarps and was found the middle elevation (700 - 900 masl) with one singles species recorded, but S. negrosensis is preferably growing up to 1000 masl (Figure 7).
3.4. Physicochemical Properties
Limited or uniformed environmental homogeneity leads to a regular pattern of individual organisms [57]. However, different environmental factors and seed dispersal mechanisms lead to aggregated individual organisms [58]. Soil moisture, pH, light, nutrient availability, herbivory, and pathogen pressure lead to variations in species diversity [59]. Details of the soil of the three study site’s physicochemical properties are given in (Table 7). Actual soil moisture content was highest in Site 1 (65.91) and lowest in Site 3 (58.0), while a maximum pH value was at Site 1 (6.8) and minimum pH at Site 2 and 3 (6.7). Relative light was highest in Site 3 (7.91) and was lowest in Site 2 with 0.71.
To understand the relationship between environmental factors and the critically endangered dipterocarps species correlation test was carried out (Table 8). The basal area of four (4) dipterocarps species is affected by environmental
![]()
Table 7. Physicochemical properties of the three sites in north western portion of Mt. Malindang.
Note: Values in parentheses show standard error.
![]()
Table 8. Pearson correlation coefficients between Dipterocarpaceae trees basal area and height and physico-chemical and topographic variables.
Legend: value with (*) indicates significant value of p = 0.05: (*) – p = 0.5, (**) – p = 0.03, (***) – p = 0.000 to p = 0.001.
![]()
Figure 7. Dendrogram of dipterocarps tree species between elevations generated through UPGMA using bray-curtis similarity index. Bootstrapping was done n = 0; correlation = 0.8578.
factors such as light intensity, soil moisture, and elevation. The basal area of A. thurifera was significantly correlated with soil moisture and inversely correlated with light in both basal and height. S. polysperma is significantly correlated with light intensity and elevation. D. grandiflorus and S. negrosensis cannot be correlated to environmental factors in this study because of the single species found in one plot. In this study, dipterocarps species showed different responses to light. Plants are influenced by light in terms of their growth; however, it introduces stresses and vulnerabilities when there is high light exposure; though it allows rapid growth, it increases water and nutrient demand in soil.
3.5. Threats and Disturbances
Despite being classified as a protected area, the study area is still vulnerable to both natural and human disturbances that could threaten the vegetation of Mt. Malindang. The three study sites are in secondary forests belonging to the lowland dipterocarp and montane forest classification of Mt. Malindang (Figure 8). Anthropogenic activities were noticeable in Site 1 and very widespread in Sites 2 and 3. Timber poaching, particularly to Anisoptera thurifera species in Site 2, is extensive. The sampling sites were previously selectively logged areas in the year 1960s [60]. Poaching and kaingin were present in Site 2. In contrast, in Site 3,
![]()
Figure 8. Sample picture of different disturbance observe in sampling sites.
the disturbance is mainly caused by agricultural conversion since it is located within the park's buffer zone where human activities are allowed. Site 1 is free from human disturbance at present; however, it was a logged area. The presence of a logging road near the sampling plots was observed during the field sampling. Evidence of grazing was also apparent in all plots of Site 2, which may be affecting the dipterocarp trees' growth, especially during the seedling stage. Based on the interviews of some residents living at the foot of Site 3, there had been no cutting allowed since 2000 because of the strict enforcement and regular patrolling of DENR in the area. Another threat found in the study area is the presence of non-native plants Gmelina arborea, Falcataria mollucana and Sweitennia macrophylla, however, their effects on the population of dipterocarp species are not yet established.
4. Conclusions and Recommendations
A recent study recorded 638 individual trees recorded belonging to 86 species, 54 families, and 64 genera. The distribution of tree species is contiguous in less disturbed and regular distribution patterns in disturbed areas. There were seven dipterocarps species registered in this study, namely: Anisoptera thurifera, Dipterocarpus grandiflorus (Blanco), Shorea negrosensis, Shorea polysperma (Blanco) Merr. Foxw, Shorea squamata (Turcz.) Benth. & Hook. f. ex DC, and Shorea sp. Four are listed as critically endangered, and one is vulnerable in IUCN and DAO 2017-11.
The population of dipterocarps species in MMRNP is declining. These results imply that even though Mt. Malindang is a protected area, tree species with economic value are degraded over time due to threats and disturbances in the area because of poaching, slash and burn, settlements, agricultural activities, roads, and infrastructure, especially in the park's low elevation.
Among the environmental variables (soil pH, moisture, light, and elevation), light and elevation are the major factors that influences the growth of dipterocarps species in the area.
The present study has provided valuable information on the structure and spatial pattern of critically endangered dipterocarps species in Mt. Malindang Range Natural Park that would be used as an input for effective conservation and protection of the area.
Acknowledgements
The authors are very thankful to the United States Agency for International Development (USAID)—DAI, through its Protect Wildlife Project, the Commission on Higher Education (CHED), for the financial assistance. To Mt. Malindang Range Natural Park—Protected Area Management Board (PAMB), Protected Area Management Office (PAMO), Armed Forces of the Philippines (AFP)-10th Infantry Battalion, National Commission on Indigenous People (NCIP), the Local Government of Municipality of Calamba and Concepcion for allowing the authors to conduct her study in Mt. Malindang. To Misamis University through Misamis University Community Extension Program (MUCEP) headed by EnP. Grace V. Villanueva for their moral support and encouragement.