Open Journal of Forestry, 2020, 10, 445-459 https://www.scirp.org/journal/ojf ISSN Online: 2163-0437 ISSN Print: 2163-0429 Species Composition and Stand Structure of Primary and Secondary Moist Evergreen Forests in the Tanintharyi Nature Reserve (TNR) Buffer Zone, Myanmar Idd Idd Shwe Zin1*, Ralph Mitlöhner2 1University of Forestry and Environmental Science, Yezin, Nay Pyi Taw, Myanmar 2Department of Tropical Silviculture and Forest Ecology, Georg-August University, Goettingen, Germany How to cite this paper: Zin, I. I. S., & Abstract Mitlöhner, R. (2020). Species Composition and Stand Structure of Primary and Sec- The habitat structure and floristic composition examined for this study are of ondary Moist Evergreen Forests in the great importance, providing a scientific baseline of information for develop- Tanintharyi Nature Reserve (TNR) Buffer ing a biodiversity database and in supporting crucial information for the Zone, Myanmar. Open Journal of Forestry, 10, 445-459. management decision-making process of the buffer zones. The primary ob- https://doi.org/10.4236/ojf.2020.104028 jective of this study was to examine the current status of species composition and stand structure of moist evergreen forests distributed in the TNR buffer Received: August 27, 2020 zone. Forest inventory was conducted in the primary moist evergreen forest Accepted: October 27, 2020 Published: October 30, 2020 (~1 ha) and secondary moist evergreen forest (~1 ha). In the TNR buffer zone, 83 species belonging to 31 families in the primary moist evergreen for- Copyright © 2020 by author(s) and est and 86 species belonging to 32 families in the secondary moist evergreen Scientific Research Publishing Inc. This work is licensed under the Creative forest were found. The most dominant families in the primary moist ever- Commons Attribution International green forest were Dipterocarpaceae, Sapindaceae, Meliaceae, Myrtaceae, and License (CC BY 4.0). Myristicaceae; at species level; this forest was composed of Nephelium lappa- http://creativecommons.org/licenses/by/4.0/ ceum, Myristica malabarica, Nephelium laurium, Aglaia andamanica, and Open Access Diospyros peregrine. The most dominant families in the secondary moist evergreen forest were Myrtaceae, Sapindaceae, Euphorbiaceae, Myristicaceae, and Lauraceae, while Nephelium lappaceum, Syzygium claviflorum, Syzy- gium sp-1, Eugenia oblate, and Myristica angustifolia were the most domi- nant at the species level. The results of Sörensen’s similarity index based on common species (Ks) and the similarity index based on species dominance (Kd) were observed at about 55% and 75% between the primary and second- ary moist evergreen forests. The basal area (51.39 m2∙ha−1) of the primary moist evergreen forest was higher than that (44.50 m2∙ha−1) of the secondary moist evergreen forest. Between these two forest types, the Shannon-Wiener, DOI: 10.4236/ojf.2020.104028 Oct. 30, 2020 445 Open Journal of Forestry I. I. S. Zin, R. Mitlöhner the Simpson and the Evenness indices were not significantly different at (p < 0.05). The total number of trees per hectare (n/ha) of the primary and sec- ondary moist evergreen forests were 910 (±184) and 991 (±183). Keywords Tree Density, Basal Area, Floristic Similarity Index, Floristic Composition, Moist Evergreen Forest 1. Introduction Tropical rain forests occur in the southernmost portion of Myanmar. These are the most structurally complex plant communities and are the richest in species in Myanmar (Kermode, 1964). The primary objective of this study is to highlight tree species diversity, species composition and stand structure of tropical rain forests which support the sustainable forest management in Myanmar. Forest types and their distribution are dominated by geological factors (soil and slope), rainfall regimes, and species associations (Kyaw, 2003). Due to hu- man intervention, agricultural expansion and biogeography, species diversity in tropical forests differ greatly from location to location (Whitmore, 1998). Floris- tic inventory is a prerequisite to assess the current diversity to inform the con- servation of forest biodiversity (Jayakumar et al., 2011). The expression of stand density across different diameter class distributions showed how the forest is adapting to dynamic environmental conditions. For a more detailed analysis of stand structure, more information is needed on the actual distribution of diame- ters in the stand and the absolute distribution of stem numbers per diameter class (Apel, 1996). 2. Materials and Methods 2.1. Study Area This study was carried out in the ecologically and administratively distinct areas of Tanintharyi Nature Reserve, the Tanintharyi Division (Figure 1). Tanintharyi Nature Reserve is situated between latitudes 14˚20'50'' and 14˚57'55'' North and between longitudes 98˚5'10'' and 98˚31'32'' East. Tanintharyi Nature Reserve (TNR) was legally established by the Ministry of Environmental Conservation and Forestry (MOECAF) in 2005 as a protected area. It is situated between the Dawei River and the Myanmar-Thailand border. It includes 170,000 ha with primarily pristine tropical evergreen forest and some mixed deciduous forest. It lies in the Ecoregion of Tenasserim-South Thailand Semi-Evergreen Rain Fo- rests and harbors globally outstanding levels of species richness (WWF, 2002). In the Tanintharyi Division, forest inventory was conducted in the buffer zone of Tanintharyi Nature Reserve (TNR). We highlighted the species composition and stand structure of primary and secondary forests in the TNR buffer zone areas. DOI: 10.4236/ojf.2020.104028 446 Open Journal of Forestry I. I. S. Zin, R. Mitlöhner Figure 1. Location of the study sites in Tanintharyi Nature Reserve, Southern Myanmar. Source: GIS, Forest Department (FD). Based on the past ten years of climatic data from the Department of Meteor- ology and Hydrology (Meteorology Department of Dawei Township, 2014), the mean annual temperature was 28˚C with the hottest in March and the coldest in January, while the mean annual rainfall was 5519 mm. This area is among the most abundant rainfall areas in Myanmar because the climate is seasonal and monsoon type. 2.2. Field Surveys In Figure 1, two different sites were chosen in the buffer zone areas of TNR. DOI: 10.4236/ojf.2020.104028 447 Open Journal of Forestry I. I. S. Zin, R. Mitlöhner There were 25 sample plots measuring 20 m × 20 m (one hectare) with equal in- tervals (200 m in distance) in each site due to the heterogeneity of sites in the nature reserve. The aim was to obtain the representative tree species in the dif- ferent ecosystems and to support a quantitative estimate of plant species diversi- ty. Height and diameter at breast height (DBH ≥ 5 cm) of all trees were meas- ured in each plot for the two study sites. 2.3. Data Analysis All data were put into Microsoft Excel 2013 spreadsheets and later transferred to Statistica software version 12.5. The relative abundance, relative frequency, and dominance were used to calculate the Importance Value Index at the family and species levels, characterizing the composition and diversity of tree species (Cur- tis & McIntosh, 1951; Greig-Smith, 1983; Mori et al., 1983; Lamprecht, 1989). Sörensen’s Coefficient of Similarity method was applied to identify the similarity ratio among forest stands (Magurran, 1988; Lamprecht, 1989). The species richness is the number of species appearing within a specific for- est area (Magurran, 1988). The Simpson index (1 − D') gives was calculated ac- cording to Magurran (1988) as follows: −=−′ S 2 (11DP) ∑i=1 i (1) where: S: the number of species and Pi: the proportion of individuals belonging to each species The Shannon-Wiener index (H') is the most widely used index for compar- ing diversity between habitats (Clarke & Warwick, 1994). The Shannon-Wiener index was calculated according to (Clarke & Warwick, 1994) as follows: ′ =−×S H∑i=1 PPiiln (2) where: Pi: the density of a species and P: sum of total density of all species in that forest type and S: the number of species. The Evenness index (J') expresses how evenly individuals are distributed among different species (Khan, 2006); it was calculated according to Pielou (1966) as follows: H ′ J ′ = (3) ln (S ) where: H' = Shannon-Wiener index and S = the number of species. 3. Results 3.1. Species Areas Relationship The species-area curve is the best statistical indicator for detecting the habitat diversity within the survey area (He & Legendre, 1996), and was used to deter- mine a minimum plot-size needed to survey a community adequately (Lam- DOI: 10.4236/ojf.2020.104028 448 Open Journal of Forestry I. I. S. Zin, R. Mitlöhner precht, 1989). In this study, species-area curves (Figure 2) were drawn based on trees that attained ≥1.3 m in height and ≥5 cm dbh and the total area was one hectare for each forest type. In the buffer zone, the curves of primary forest and secondary forest were greater and reached as high as 4800 m2. After that the secondary forest increased more than primary forest at 7600 m2 and its curve appeared constant from the point of 9200 m2. Because of human interventions in the secondary forest, different sizes of gaps are formed and different tree species are known to respond to or regenerate in these areas. Moreover, the primary forest gradually increased and become constant at 9600 m2. As suggested by Cain (1938) and Lamprecht (1989), the minimum area is acceptable when the occurrence of new species remains below 10% with a 10% expansion in the sam- ple area. The trend curves of all forests indicated that the total survey area (one hectare) can be regarded as a representative for tree flora in the buffer zone of TNR. 3.2. Species Richness and Diversity The species richness of trees (DBH ≥ 5 cm) showed that the secondary forest occupied the greatest number of species (86) and families (32) in the buffer zone of TNR whereas the primary forest possessed the number of species (83) and families (31) (Table 1).