Biodiversity considers all types and kinds of organisms existing in the planet including plants, animals and other microorganisms [8]. It has been observed that there is a continuous reduction in the world’s biodiversity. Statistics found out a total declination of 40% in the average species abundance, 50% in inland water species, and 30% in the population of marine and terrestrial species [9]. These numbers were brought by the drastic change due to rapid reduction of tropical forests and the increase in human population which both threatened plant and animal species of the world. Despite the decreasing biodiversity level, an evident increase in the number of described species continues to show which means that there is still a large number of species yet to be discovered.

Philippines was one of the many countries largely covered by forest. In the past, the country was covered with about 90 percent or 27 million ha of lush tropical rainforest [10]. It was in 1521 when the Spaniards colonized the Philippines and as the spread of commercial crops begun during their regime, deforestation started. In the year 1900, two years after the Spaniards left, the Americans came while still about 70 percent or 21 million of the country’s land is forested until they introduced the first modern logging operations in 1904 and the Philippines became one of the main exporters of Dipterocarp lumbers in the world. Continuous deforestation and cutting of trees happened. The least forest cover that the country has experienced was around 1988 with only 6.5 million ha of forested lands. It increased by 0.3 million ha by 2010 making the forest cover 23 percent of the land area or 6.8 million ha [11]. According to DENR, the forest cover of the country is about 8.205 million ha in 2015 [12]. The continuous decrease in the forest cover of the Philippines shall be a concern and drive to perform studies for conservation and rehabilitation of forests in the country.

Philippines as one of the megadiversity countries and biodiversity hotspots has a significant story to tell when it comes to its floral and faunal composition and status [13]. The country’s biodiversity together with its forest areas continues to decrease. Only through the efforts of different studies and research groups can the concern on the matter be addressed.

The number of threatened floral species in the country increased from the 2007 record of 526 to 984 in the year 2017 [14]. It can be said that there is really continuous declination due to certain factors including the anthropogenic and natural factors. It dictates the need to perform activities related to the conservation and rehabilitation of the Philippine forests.

In the conduct of the study, different materials were used starting from site establishment until the preservation of the voucher specimens. Meter tapes, nylon rope, pegs, and bolo were used in establishing the quadrats and transect belts. For the collection of voucher specimens and listing of species and its measurements, pencil, meter tape, datasheets, clipboard, specimen tags, bolo, pruning shears, polyethylene bags, and sacks were used. Transect belts and quadrats were located using a GPS device in obtaining the coordinates and elevation. Lastly, in the preservation of the voucher specimens, herbarium bags, denatured alcohol, pruning shear, newspapers, sacks and packing tape were used.

Three 2-km transects following the existing trails were established in three different locations (Figure 1). A 20 × 20-meter quadrat was established at every 250-meter interval along each transect at the left and right of the existing trail (Figure 2). Hence, a total of 27 quadrats were established.

Trees with diameter at breast height (DBH) of at least 5 cm inside the quadrats were identified and recorded. The total height (TH) and merchantable height (MH) were also measured. Voucher specimens of each species were collected photographed and placed inside the herbarium bags for identification and verification purposes. Identification of voucher specimens was performed through

different taxonomic references such as Co’s Digital Flora of the Philippines, Lexicon of Philippine Trees by Rojo, and Philippine Vascular Plants Checklist by Leonard Co. Also, digital photo database of fresh plants [15] and herbarium specimens of Pastor L. Malabrigo, Jr. were used in comparison with our pressed specimens and its photos for identification and verification.

Diversity indices (i.e. Shannon, Simpson evenness) were also computed using the Paleontological Statistics Software Package for Education and Data Analysis (PAST v.3.14) [16]. Shannon Index measures the diversity using species richness and distribution. Simpson Evenness measures diversity in terms of evenness in the distribution of species and individuals per quadrat [17]. Diversity indices were interpreted using the scheme of Fernando Biodiversity Scale [18] (Table 1). Endemism, conservation status, and distribution record of each species were assessed and verified. For the conservation status, worldwide category was based on the International Union for Conservation of Nature Redlist [19]. While for the Philippine scheme, the local list of threatened species under DAO 2017-11 was used [12]. Importance values were also computed using the data collected

during the collection: individual count per species, frequency of plot occurrence, and dominance (using DBH) [20]. Below are the formulas for IV computation.

· Dominance equals to (0.7854) × Diameter²

· Relative dominance equals to (dominance of a species/sum of the dominance of all species) × 100

· Frequency equals to (total number of quadrats in which species occurred/total number of quadrats studied)

· Relative frequency equals to (frequency of a species/sum of frequency of all species) × 100

· Density equals to (Total number of individuals of species/ Total number of individuals of all species)

· Relative density equals to (density of a species/sum of density of all species) × 100

· IV equals to Relative dominance + Relative frequency + Relative density

A total of 139 morpho-species were recorded along the tree transects with a total of 2239 individuals from 87 genera and 46 families. Number of tree individuals per quadrat varies from 38 to 132. Diameter of trees ranges from 5 cm to 130 centimeters. Only four individuals of trees exceeded 100 cm-diameter which belong to only one species, Dangula (X. philippinensis), belonging to the family of myrtles or Myrtaceae. Majority of the species was measured to have DBH of less than 50 cm indicating that the forest is secondary growth.

The importance values (IVs) of the species were computed as the sum of the relative dominance, relative density, and relative frequency. Based on the computed IVs, the five most important species in terms of dominance, frequency, and density are Dangula (T. ahernianum) (35.29), Bagoadlau (X. philippinensis) (31.49), Yakal malibato (S. malibato) (16.60), Bitanghol (C. blancoi) (15.51), and Malabetis (M. oblongifolia) (11.01) (Table 2). These species belong to five different families. All these species except Bitanghol and Dangula are threatened both in the IUCN Redlist and the Philippine Redlist of Forest Plants. Dangula was found to be the most important species in the area which according to studies is still abundant in tropical areas particularly in Asia [21].

The computed diversity indices of Sitio Dicasalarin falls on the category of a very highly diverse area (Shannon diversity = 4.096, Evenness = 0.9735) (Table 3). Transect 3 has the highest diversity with Shannon diversity of 3.856 and Simpson’s Evenness value of 0.967 which are both very high values. There were only minimal disturbances (e.g. fallen trees) observed in the site which has potentially no to low effect on the diversity as the diversity index values showed. Studies showed that disturbing activities such as excessive and improper logging can lessen the richness of species in an ecosystem [22].

In terms of diversity per quadrat, 14 fell under the classification of having high diversity: 5 from Transect 1, 4 from Transect 2, and 5 from Transect 3 (Table 4). Quadrat 8 in Transect 1 has the highest diversity (Shannon = 3.367, Simpson = 0.9554). The remaining quadrats fell in the category of having moderate diversity. Considering the small dimensions of the quadrats, it is assuring to know that there is still a relatively high diversity since studies showed that Shannon Index values typically ranges from 1.5 to 3.5, while areas with Shannon values of 4 are very rare [23].

As part of the tree diversity assessment, there is a need to look for noteworthy species such as the endemic tree species in the country and those species which

are critically important in terms of their conservation status. This information is essential to be able to manage an area’s conservation and rehabilitation.