Silviculture COMPARISION OF STAND STRUCTURE AND TREE SPECIES DIVERSITY BETWEEN MEDIUM AND RICH FORESTS OF TRUONG SON FORESTRY COMPANY, QUANG BINH PROVINCE Cao Thi Thu Hien, Nguyen Hong Hai Vietnam National University of Forestry SUMMARY Results from this study showed several characteristics of structure, composition and tree species diversity of the medium and rich forests in the tropical moist evergreen forests of the Truong Son Forestry Company, Quang Binh province. A total of 4 plots of 100m × 100m each placed in two forest states were surveyed and all stems ≥ 6 cm DBH were measured. 3661 live stems ≥ 6 cm DBH were encountered, representing 40 families and 70 tree species. The density, mean DBH, mean height and total basal area of the medium forest ranged 809 trees/ha - 839 trees/ha, 14.55 cm – 15.05 cm, 10.80 m – 11.06 m and 19.35 m2/ha – 22.42 m2/ha, while these numbers in the rich forest were 1003 trees/ha - 1010 trees/ha, 15.55 cm – 15.64 cm, 11.79 m – 12.60 m and 28.22 m2/ha – 29.00 m2/ha, respectively. These key characteristics were significant difference between two forest states. The Exponential and Weibull distributions could provide good fit for the tree diameter and height data. The most dominant families in both two forest states were Fabaceae, Burseraceae, Lauraceae and Meliaceae, and the most important species found in both two forest states were Garuga pierrei, Ormosia balansae and Litsea glutinosa. Based on the diversity profile, there is no intrinsic diversity ordering between the medium and the rich forests. Keywords: Diversity indices, diversity profile, forest structure, species composition, tree species diversity. 1. INTRODUCTION products. It is therefore essential to understand Geographically, tropical rain forests are the structures and species diversity of tropical currently found in Southeast Asia, Central and forests in order to find a way to maintain, South America, and Central and West Africa protect, and develop those ecosystems. (Richards, 1996; Whitemore, 1998), with However, the majority of researching Southeast Asia containing the second largest tropical forests in developing countries are still tropical rain forest with an area of about 2.5 limited, consequently, the stand structures and million km2 (Whitemore, 1998). Globally, species diversity of those forests are often around 52% of the total forests are in tropical insufficient for management. Sustainable regions and they are known to be the most management of these forests requires a good important areas in terms of biodiversity (Lewis knowledge of all the natural forest resource; et al., 2009). this knowledge could be reliable only through Tropical forests play a crucial role in three studies of the forest environment. respects regarding the well-being of mankind. In this study, the forest structures, Tropical forests provide many goods and composition and tree species diversity of the ecosystem services, such as prevention of soil tropical moist evergreen forests of Truong Son erosion and preservation of habitats for plants Forestry Company, Quang Binh Province were and animals (Anbarashan M. and Parthasarathy analyzed. The specific objectives of this N., 2013). Socially, millions of people who are research paper are to (1) analyze stand living in or around tropical forests depend on structure, (2) identify tree species composition them for the many forest products and and (3) assess tree species diversity between environmental services gained (Naughton- the medium forest and rich forest in terms of Treves and Weber, 2001). Economically, they timber volume in the tropical moist evergreen possess a main source of energy in the form of forests. fuel wood, wood, and traditional medicines; 2. RESEARCH METHODOLOGY they also provide timber and non-timber forest 2.1. Study site JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 7 (2019) 35 Silviculture The study was carried out within the disturbances and are representatives of tropical tropical moist evergreen forests belonging to moist evergreen forests in Truong Son Forestry the Truong Son Forestry Company. The zone Company according to field surveys. Each plot of study covers a total of 26,490.13 ha natural was divided into 100 contiguous 10 × 10 m forest. It lies between 17010’00’’ and subplots as workable units. All free-standing 17040’00’’N of northern latitude and between woody plants in the plot with diameter at 106000’00’’ and 107000’00’’E of longitude. breast height (DBH) ≥ 6 cm were investigated. The annual climate is divided into 2 distinct The species names, dbh and total tree height seasons: dry season from March to August, within each subplot were recorded. All tree rainy season from September to February. The species were assigned to species. average temperature is about 230C - 240C. 2.3. Data analysis Annual rainfall is between 2,500 and 3,000 2.3.1. Forest structure mm. Rainfall is distributed unevenly in the - Several general information on forest year, mainly in October and November, structure were computed for each sample plot, accounting for 60 - 70% of the total annual including: Number of trees per plot, mean rainfall. Average humidity is 86%. In the study diameter at breast height (DBH), mean total area, soil can be divided into two main groups: tree height, total basal area, number of tree The lowland ferralite soils develop on granite, species, number of families. sandstone, Shale, and limestone; The - Frequency distributions: In the present mountainous humus soils develop on granite, study, the Exponential and Weibull functions limestone. (two parameters) were used to model absolute Flora of Truong Son company has 663 frequency distributions of the dbh and total species of 131 families and 408 genera of 4 tree height. vascular plant phylum: Lycopodiophyta, - Comparison of key characteristics between Polypodiophyta, Pinophyta (Gymnospermae), medium forest and rich forest: We used Z test Magnoliophyta (Angiospermae) (Source: to determine differences in diameter, height, Report on Flora Survey of Truong Son basal area, and density of trees between two Forestry Company in Quang Binh by Vu Anh forest states. To combine two plots in each Tai, Ho Van Cu). The most abundant species is forest state into one larger plots, Kolmogorov– Magnoliophyta and the poorest of the species Smirnov test was used. The frequency is Pinophyta. There are 27 plant species in the distribution of stem density in various size Forestry Company are endangered species. classes in two forest states was compared using 2.2. Plot set-up and censuses Kolmogorov–Smirnov one-sample test (Zar, The tree sampling for the data collection 1999). was performed in four plots of 100 × 100 m 2.3.2. Tree species composition each randomly placed in two different forest Family relative diversity, relative density, states of the study area: medium forest and rich relative dominance and family importance forest. values (FIV) were calculated according to the Forests in these four plots have less human formulae of Mori et al. (1983): . (. %) = . 100 (1) . . (%) = . 100 (2) . (%) = . 100 (3) (.) (.) (.) = (4) 36 JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 7 (2019) Silviculture In addition, we quantified basal area, dominance and importance value indices (IVI) relative density, relative frequency, relative following Curtis and Cottam (1956): (%) = 100% (5) (%) = 100% (6) (%) = 100% (7) (.)(.)(.) = (8) The IVI varies from 0% to 100%; the larger was equally likely), equal to: the importance value, the more important a = − ∑ . = (11) species is within that particular community. J' is constrained between 0 and 1. The less The families and species with FIV% and evenness in communities between the species IVI% are equal or higher than 5% in our study (and the presence of a dominant species), the were listed. lower J' is. And vice versa. 2.3.3. Measuring biodiversity - Simpson index (): a measure of species a) Diversity indices dominance. The Simpson index is defined as The following diversity indices were used in (Magurran, 1988): this study. = 1 − ∑ (12) - Species richness (S): is the total number of Where p is the is the proportion of species. importance value of the ith species. - Shannon diversity index (’): as a = (13) measure of species abundance and richness to th quantify diversity of the tree species. This ni is the number of tree of i species and N index takes both species abundance and is the number of trees of all species. species richness into account: As biodiversity increases, the Simpson index decreases. = − ∑ . (9) Where: equals the number of species and b) Diversity profile equals the ratio of individuals of species Diversity profiles have been used to assess divided by all individuals of all species. The tree species diversity in uneven-aged forest Shannon diversity index ranges typically from stands. Patil and Taillie (1979, 1982) discuss 1.5 to 3.5 and rarely reaches 4.5 (W.L. Gaines two kinds of rarity measures, the dichotomous et al., 1999). type and the rank type, which lead to two - Species evenness (J’): refers to how close different diversity profiles. Examined more in numbers each species in an environment is. closely, these types are defined as follows: Mathematically it is defined as a diversity - Dichotomous type: ∑ index, a measure of biodiversity which ∆= ∑ = , ≥ −1 (14) quantifies how equal the community is numerically. In this paper, we used Pielou's where for = -1, ∆-1 is the species richness, evenness index (Magurran, 1988): for = 0, ∆0 is the Shannon-Wiener index and for = 1, ∆1 is the Simpson index. = , (10) - Rank type Where H’ is the number derived from The intrinsic diversity profile of a the Shannon diversity index and H’max is the community is given by the pairs (Tj): maximum possible value of (if every species = ∑ j = 1, …., s-1 (15) JOURNAL OF FORESTRY SCIENCE AND TECHNOLOGY NO. 7 (2019) 37 Silviculture where: Ts = 0 and T0 = 1.