Summary of the dissertation: Effects of peatland and submergence regime on biomass of melaleuca forest in the U Minh Ha national park, Ca Mau province

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Research objectives: Assessing thickness and quality of peatland on biomass of the melaleuca forest; determining levels of submergence and water quality on biomass of the forest; evaluating levels of peatland thickness and submergence on biomass and CO2 of the melaleuca forest.

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Nội dung Text: Summary of the dissertation: Effects of peatland and submergence regime on biomass of melaleuca forest in the U Minh Ha national park, Ca Mau province

MINISTRY OF EDUCATION CAN THO UNIVERSITY SUMMARY OF THE DISSERTATION Major: Land and Water Environment Code: 62440303 TRAN THI KIM HONG EFFECTS OF PEATLAND AND SUBMERGENCE REGIME ON BIOMASS OF MELALEUCA FOREST IN THE U MINH HA NATIONAL PARK, CA MAU PROVINCE Can Tho, 2017
THE DISSERTATION IS COMPLETED AT CAN THO UNIVERSITY Principal Advisor: Duong Van Ni, PhD Co-advisor: Nguyen Van Be, PhD The dissertation was defended at the doctoral committee at University level Venue: Dissertation Defense Room (Meeting Room No. 3, 2nd Floor, Administration Building) Campus II – Can Tho University.  At date: Examiner 1: Examiner 2: Examiner 3: Revision confirmed by The chairman The dissertation can be found at the library: Learning Resource Center, Can Tho University Viet Nam National Libary
PUBLISHED PAPERS Trần Thị Kim Hồng, Nguyễn Bình Long, Dương Văn Ni, Nguyễn Văn Bé, 2015. Khảo sát sự sinh trưởng cây tràm (Melaleuca cajuputi) ở các độ dày than bùn Vườn quốc gia U Minh Hạ, tỉnh Cà Mau. Tạp chí Khoa học Đại học Cần Thơ. Số 40/2015. Trang 92-100. Trần Thị Kim Hồng, Nguyễn Văn Bé, Dương Văn Ni (2016). Sinh khối rừng tràm và chất lượng nước ở các điều kiện ngập khác nhau tại Vườn quốc gia U Minh Hạ, tỉnh Cà Mau. Tạp chí Khoa học Đất. Số 49/2016. Trang 134-139.
Chapter 1: INTRODUCTION 1.1. The necessary of the dissertation While climate change is global issue, trees play an pivital role in mitigation of negative impacts through the absorption of CO2 (IPCC, 2003). The main characteristics of melaleuca trees are its ability to withstand submergence, drought, slight salinity or acidic environments (Da, 2012; Sam and Binh, 1999; Okubo et al., 2003). For those reasons, several studies have been focosed on adaptation of melaleuca trees to climate change. However, effect of maintaining water level on growth and biomass of melaleuca forest has not been addressed. The natural condition of U Minh Ha National Park, Ca Mau province is that melaleuca forest is found on the peatland where its thickness is differently distributed in various locations. Thus, the quality of peatland as well as thickness of peatland layers are required to be considered in addition to controlling water to prevent forest fire. The study on whether maintaining water over years in the melaleuca forest to prevent fire has affected the density of melaleuca and whether melaleuca trees that existed permanently generating a suitable environment for biodiversity conservation, an intergrated study on conditions of land and water environments is essential for sustainable and long-term forest management. Therefore, the research entitled "Effects of peatland and submergence regime on biomass of melaleuca forest in U Minh Ha National Park, Ca Mau Province" was conducted. 1.2. Research objectives - Assessing thickness and quality of peatland on biomass of the melaleuca forest. - Determining levels of submergence and water quality on biomass of the forest. - Evaluating levels of peatland thickness and submergence on biomass and CO2 of the melaleuca forest. 1.3. Scope of the study -1-
The study was conducted at U Minh Ha National Park, Vo Doi Village, Tran Hoi Commune, Tran Van Thoi District, Ca Mau Province. Data of peatland, water quality and melaleuca trees were surveyed and collected in plots 13 and 14 of sub-zone II; plots 23, 24, 26 and 27 in sub-zone 4 and plot 3 of sub-zone 75 in the core zone of U Minh Ha National Park. 1.4 Significant contributions of the study Identified relationships between peatland and biomass of melaleuca forest at different thicknesses of peatland: Peatland was rich with nitrogen (0.58 – 1.23%N) but it was not optimal condition for growth of melaleuca forest. As the peatland is highly sensitive to fire, maintaining certain level of water in the forest to prevent firing has made the forest deteriorated which was clearly observed via the density of melaleuca trees. The higher the thickness of peatland, the lower the tree density. The biomass of melaleuca forest ranged from 72.3 to 95.9 tons/ha and the biomass tends to decrease as the peatland thickness increases. At peatland thickness of 20 - 40 cm, biomass of melaleuca forest was 95.9 ton/ha. In the peatland thickness of 40 - 60 cm and 60 - 80 cm, biomass of melaleuca forest were 81.1 ton/ha and 72.3 ton/ha, respectively. Identified relationships between levels of submergence and biomass of melaleuca forest: The density of melaleuca trees in the treatment of the lowest level of submergence (
Water quality parameters including pH, DO, BOD5, N-NO3-, N-NH4+ and soil quality factors such as bulk density, pH, total nitrogen, total phosphorus and N-NH4 of the peatland layers were tested using multivariate regression analysis. The results indicated that pH, DO, N-NH4+ in water and pH, total phosphorus and N-NH4+ of the peatland layers did not clearly show significant influence on the melaleuca forest biomass. However, levels of submergence, BOD5 and N-NO3- in water and bulk density, and organic matter in soil, and seasonal variation showed influence on the biomass of the melaleuca forest. 1.5 Practical significance This study provides useful information and scientific data for the management and sustainable development of melaleuca forest in U Minh Ha National Park, Ca Mau Province. Conservation of the melaleuca wetland ecosystem on peatland is a long-term task, and requires integrated solutions for the management of special-use forests. For melaleuca forest on peatland if managed by permanently submerged the forest over years and increased depth of submergence to prevent fire would result in decreasing density and increasing death of melaleuca trees. In order to prevent forest fire and ensure sustainable biomass growth of melaleuca trees, the optimal depth of peatland and level of submergence should be at 20 - 40 cm and lower than 30 cm, respectively. -3-
Chapter 2: CONTENT AND METHODOLOGY 2.1 Contents - Determination of thickness of peatland in U Minh Ha National Park, Ca Mau Province and soil quality at different thicknesses of peatland. - Examination of submergence levels and water quality at various submergence levels at U Minh Ha National Park, Ca Mau Province. - Survey, enumeration of growth parameters of melaleuca trees at different levels of submergence and depths of peatland thickness. - Assessment of melaleuca trees’ biomass and CO 2 absorption at different levels of submergence and depth of peatland thickness. - Recommendation for management practices for U Minh Ha National Park, Ca Mau Province. 2.2 Methodologies 2.2.1. Standard plots setup in the field Eighteen standard plots including nine plots in the melaleuca forest on peatland at three different depths of thickness (20 - 40 cm, 40 - 60 cm, 60 - 80 cm) and nine plots in the the melaleuca forest at three levels of submergence (< 30 cm, 30 - 60 cm, > 60 cm) were established at the U Minh Ha National Park, Ca Mau Province. There were three standard plots (10 m x 10 m = 100 m2 for each) at every level of submergence and depth of peatland thickness. Table 2.1 Parameters and niumbers of samples collected at U Minh Ha National Park, Ca Mau province Sites Parameters No. of Sampling Total Grand total samples times Soil samples Bulk 9 4 36 216 samples density TN 9 4 36 TP 9 4 36 OC 9 4 36 N-NO3- 9 4 36 N-NH4+ 9 4 36 pH 9 2 18 Water samples DO 9 5 45 198 Samples BOD 9 5 45 N-NH4+ 9 5 45 N-NO3- 9 5 45 pH 9 2 18 Melaleuca 18 18 standard samples plots -4-
2.2.2 Soil and water sampling methods - Bulk density: was collected using metal augur with the volume of 100 cm3. Using force from hands to push the auger into the soil until auger was filled with soil. Then the auger containing soil was closely covered and transported to the laboratory for analysis. - Samples for analysis of nitrogen-ammonium (N-NH4+), nitrogen-nitrate (N- NO3-), total nitrogen (TN), total phosphorus (TP), pH, organic carbon (OC) were collected by using soil borer to obtain one kilogram of peatland, then placed it into nylon bags which were then transported to the laboratory for analysis. - Dissolved oxygen (DO): was collected separately (without any air bubbles in the collected water sample). The collected samples were immediately fixed in the field by using 1 ml MnSO4 and 1 ml KI-NaOH (for every 125-ml bottle), stored at 40C in the dark. - N-NH4+, N-NO3-, biological oxygen demand (BOD5): water samples were collected and stored in 2-L plastic bottles. The bottles with caps opened were hold down into the water at the middle and against the water current, then closed the caps tightly. The water bottles were stored at 4oC until analysis. 2.2.3 Soil samples analysis methods Table 2.2 Methods for analysis of soil quality parameters No. Parameters Methods 1 Buld density Dried at 105oC 2 N-NH4+ Colorimetric development 3 TN Kjendhal method 4 TP Colorimetric development 5 pH Measured at field 6 N-NO3- Colorimetric development 7 OC Furnace Table 2.3 Methods for analysis of water quality parameters No. Parameters Methods 1 DO Winkler modified method 2 BOD5 Oxitop method 3 N-NH4+ Ion chromatographyThermor 1100, USA 4 N-NO3- SnCl2 method 5 pH Measured at field -5-
2.2.4 Methods for measurement and enumeration of melaleuca trees in the standard plots - Density: counted numbers of trees per one standard plot, converted to numbers of trees per hecta - Diameter at breast height (DBH): used ruler-clamp to measure diameter of the tree at the height of 1.3 meters from the soil surface. - Height under the branches (Hdc): the height that measured from the soil surface to the point where a tree protrude its first branch using surveying ruler or meter. - Height to the top of the trees (Hvn): the height that measured from the soil surface to the top of a tree using surveying ruler or meter. 2.2.5 Data analysis - The statistical analysis of the obtained data was performed using IBM SPSS statistics for Windows, Version 19.0 (IBM Corp., Armonk, NY, USA). - The following equations were selected for calculation of the biomass and CO2. o Wtotal dry weight = 0,144 * D1,3 2,160 o Ct = 0,066 * D1,3 2,1267 o CO2= C*44/12 (tons/ha) - The factors influencing on the melaleuca biomass were studied using multivariate regression analysis of data of soil parameters at various thickness layers and water indicators at different submergence levels and the data of biomass of melaleuca forest. - Descriptive statistics: calculation of means, standard deviations, standard errors, minimum and maximum values of the experimental data. - Ducan test was used after analysis of variance (ANOVA) to compare difference of diameters, height, density, biomass and CO2 at different peatland thickness and submergence levels. -6-
- Duncan test was also used for comparison of difference of water quality on at various levels of peatland thickness and submergence. - Significant difference of quality of soil and water was tested using Duncan test. - The correlation between season*thickness of peatland and season*levels of submergence and quality of soil and water was tested using multivariate analysis. -7-
Chapter 3: RESULTS AND DISUSSION 3.1 Soil quality at different depths of peatland thickness 3.1.1 Bulk density of peatland Densities of soil at three different peatland thicknesses including 20 – 40 cm, 40 – 60 cm and 60 – 80 cm at U Minh Ha National Park were relatively low ranging from 0.19 – 0.37 g/cm3. Density of peatland tended to decline when the thickness of the peatland increases. Of three surveyed levels of thickness, the highest bulk density was found at the depth of 20 - 40 cm in which the bulk density ranged from 0.24 g/cm3 ± 0.02 to 0.34 g/cm3 ± 0.03. The lowest bulk density was found at the depth of 60 - 80 cm (0.20 g/cm3 ± 0.01 – 0.23 g/cm3 ± 0.02). The bulk density in U Minh Ha National Park in the treatments having melaleuca trees with peatland thickness of 20 - 40 cm was significantly different (P < 0.05) from those from the depths of 40 - 60 cm and 60 - 80 cm. This difference could be due to effects of slow degradation of organic matters in submerged environment. It could be possible that the deeper of the peatland depth leads to slowly degrade organic matters. (Note: Period 1: 9/2014, Period 2: 11/2014, Period 3: 1/2015, Period 4: 9/2015) Figure 3.1 Bulk densities of peatland in treatments Among observed seasons (Period 1-4), the period 3 (middle of dry season) soil showed the highest bulk density. This could be because peatland is soil-rich organic matters and slowly degraded in flooded environment and sampling of peatland samples -8-
in Period 3 at the depths of 20 - 40 cm and 40 - 60 cm in period 3 when the peatland were not submerged in the middle of dry season (January) when organic matters were rapidly degraded. 3.1.2 pH of peatland Peatland at the surveyed melaleuca treatments is acidic indicated by low pH values ranging from 3.67 ± 0.58 to 4.46 ± 0.58. Values of pH in peatland at three different levels of thickness were insignificantly different indicating highly acidic environment which could largely influence on growth and development of melaleuca trees. Melaleuca trees highly tolerate with acidic soil but they are not in favored of acidic condition. Therefore, soil with low pH could influence on solubility and forms of avaiblable nutrients thus limiting growth of melaleuca trees. (Note: Period 1: 9/2014, Period 2: 11/2014, Period 3: 1/2015, Period 4: 9/2015) Figure 3.2 pH of peatland 3.1.3 Content of organic matters in peatland Organic matter content in peatland in U Minh Ha National Park, Ca Mau province was high. At three levels of peatland thickness, the organic matter content ranged from 83.71 to 94.00%. Organic matters in the peatland at three levels of thicknesses of 20 - 40 cm, 40 - 60 cm and 60 - 80 cm showed insignificant differences. The vegetation in the surveyed areas was relatively similar. However, at peatland thickness of 60 - 80 cm, the organic content was highest (90.81 ± 0.87 to 92.75% ± 0.54), at the thickness of 40 - 60 cm was from 86.72 ± 3.06 to 91.75% ± 0.91 and at the -9-
thickness of 20 - 40 cm was 88.21 ± 3.56 to 91.36% ± 3.37. Since peatland was high in organic matters, this type of soil was highly porous and low compression. Low compression of peatland may result in negative effect on stable standing of meleleuca trees, making it easily vulnerable to external forces. (Note: Period 1: 9/2014, Period 2: 11/2014, Period 3: 1/2015, Period 4: 9/2015) Figure 3.3 Organic matters of peatland at different treatments The high content of organic matter in peatland was due to soils in melaleuca forests formed by decomposition of plant matters under assistance of activity of microorganisms taking place in hundreds or thousands of years (Tran Manh Tri et al., 2010). Highly organic content in the surveyed areas may also be because soil was in the low-lying area, with low pH. It was previously reported that organic matters were often poorly degraded under submerged and acidic conditions. 3.1.4 Total nitrogen in peatland The total nitrogen content in peatland was relatively high. At the thickness of peatland of 20 - 40 cm, 40 - 60 cm, 60 - 80 cm total nitrogen contents were in the ranges of 0.58 - 1.23%N, 0.69 - 0.07%N, and 0.69 - 0.98%N, respectively. According to Do Anh (2003), soils with TN of greater than 0.2% are nutrient-rich soils. The findings in this study indicated that peatland in U Minh Ha National Park, Ca Mau Province was of high fertility because of decompostion of debris in melaleuca forest, creating favorable conditions for the growth and development of forest trees. The total nitrogen contents at three levels of thickness of 20 - 40 cm, - 10 -
40 - 60 cm and 60 - 80 cm were not significantly different. Total protein contents showed positive correlation with the contents of soil organic matters in the manner that total nitrogen content was high as soil organic content was high and vice versa. The analytical results of the contents of organic matters in peatland in the observed plots showed that the contents of organic matters were high and they were insignificant difference between the three levels of peatland thickness. Therefore, the total nitrogen content in the peatland in the surveyed plots was also high and there was no difference in the treatments. (Note: Period 1: 9/2014, Period 2: 11/2014, Period 3: 1/2015, Period 4: 9/2015) Figure 3.4 Total nitrogen in peatland at different treatments 3.1.5 Content of N-NH4+ of the peatland At three levels of peatland thickness, N-NH4+ content was not significantly different except the Period 4. The concentrations of N-NH4+ tended to increase at higher peatland thickness. N-NH4+ is formed by the ammonification process in both aerobic and anaerobic conditions. At peatland thickness of 20 - 40 cm, N-NH4+ content was the lowest among three treatments (3.04 - 11.9 mg/kg), N-NH4+ content at the thickness of 40 - 60 cm was higher (1.74 - 16.08 mg /kg) and N-NH4+ content at the thickness of 60 - 80 cm was the highest (3.49 - 17.03 mg/kg), which may be due to certain proportion of N-NH4+ was oxidized into nitrate, reducing the amounts of N- NH4+ in the peatland. - 11 -
(Note: Period 1: 9/2014, Period 2: 11/2014, Period 3: 1/2015, Period 4: 9/2015) Figure 3.5 The content of N-NH4+ in peatland at different treatments 3.1.6 Content of N-NO3- in the peatland The content of nitrate (N-NO3-) in peatland varied from 0.23 to 2.85 mg/kg. Nitrate in the soil is formed by nitrification process due to the activity of aerobic microorganisms. Content of N-NO3- tends to decrease at higher peatland thicknesses. Among three levels of peatland thickness observed, the content of N-NO3- was significantly different, possibly due to the effect of reducing-oxidizing conditions. The deeper the peatland thickness, the lower oxygen content in the soil, leading to soil changes from aerobic to anaerobic condition, thereby reducing oxidation and increasing reduction. Thus, N-NO3- in the peatland tends to decrease as the peatland thickness increases. For the sampling period in the wet season, melaleuca forest was flooded, so N-NO3- content in the peatland was found to be lower than that in dry season. 3.1.7 Total phosphorus in the peatland In general, total phosphorus did not differ significantly and fluctuation of phosphorus in peatland was relatively low. At the peatland thicknesses of 20 - 40 cm, 40 - 60 cm and 60 - 80 cm, total phosphorus contents were 0.03 - 0.12% P2O5 and 0.03 - 0.07% P2O5, respectively. According to Le Van Can (1968) in Đo Anh (2003) soils with the content of % P2O5 less than 0.06, 0.06 - 0.10, and greater than 0.10 are the soil with poor, average, and rich in phosphorus, respectively. The findings from the present - 12 -
study showed that peatland has averaged content of phosphorus. According to E.Detrunk (1931) in Do Anh (2003), phosphorus-rich soil exhibits high fertility, whereas high fertility soil contains high phosphorus. Total phosphorus content and plant productivity are positively correlated. The obtained results showed that fertility of peatland was at medium level. (Note: Period 1: 9/2014, Period 2: 11/2014, Period 3: 1/2015, Period 4: 9/2015) Figure 3.6 Content of total phosphorus at different treatments However, among the sampling periods, the signicant difference in total phosphorus was found in the sampling period 3. Total phosphorus had the lowest value (0.03 - 0.05% P2O5) in the sampling period 2. This difference may be due to the influence of mineralization of organic phosphorus. Peatland in the study area is primarily formed from residues of plant debris and vegetation. Thus, phosphorus presented in peatland is mainly organic phosphate which would be converted into inorganic phosphorus (that could be utilized by plants) because of microbial activity. However, the findings showed that total phosphorus and pH in the peatland were low, leading to low availabe phosphorus, which may affect the growth and development of melaleuca trees. - 13 -
3.2 Growth and biomass of melaleuca trees at three levels of peatland thickness 3.2.1 Density of melaleuca trees The findings showed that melaleuca trees in the standard plots at different levels of peatland thickness ranged from 1,100 - 2,000 trees/ha. The data suggested that melaleuca forest in U Minh Ha National Park, Ca Mau Province has the density at medium level. Figure 3.7 Density of melaleuca trees at three levels of peatland thickness Comparison of melaleuca forest densities in three different treatments showed that melaleuca density tended to decrease in the treatments with higher peatland thickness. For example, denisities at peatland thickness of 20 - 40 cm, 40 - 60 cm, 60- 80 cm was 1,623 ± 327 trees/ha, 1,048 ± 120 trees/ha and (936 ± 131 trees/ha), respectively. This was in line with the previous study by Nguyen Van Them (2008) reported that effect of soil on the forest is to support trees stand firmly. However, the higher thickness of peatland, the higher porosity. The high porosity of high thickness of peatland could result in collapse of trees under rainstorms or strong winds leading to death of melaleuca trees. 3.2.2 Diameter at breast height (DBH) and height (Hdc, Hvn) In the higher density of melaleuca tree, the living space is narrowed so that the individual trees have to rise to compete for sunlight and the higher the density results in smaller diameter and higher height of melaleuca trees. On the other hand, with lower - 14 -
density, melaleuca trees have sufficient light to grow so it would develop more on its diameter affecting average diameter of the trees in the treatments. The treatment of the melaleuca trees with the thickness of 20 - 40 cm showed the averaged diameter of 15.93 cm ± 3.35 which was lower and significantly different from those of the higher levels of peatland thickness. Melaleuca trees showed the highest diameters at the thickness of peatland of 40 - 60 cm (17.95 cm ± 4.33), while the medium diameters of the melaleuca tree were found at the thickness of peatland of 60 - 80 cm (17.85 cm ± 4.06). Compared with the results of density, the diameter values results showed a reverse tendency: the diameters of melaleuca trees at the peatland thickness of 20 - 40 cm (with the density was higher than those from the other two peatland thickness) were lower than those of 40 – 60 cm and 60 – 80 cm. This can be explained by the higher the density of the melaleuca forests, the narrower the living space, so the melaleuca trees have to rise in height to compete for light. As a result, the melaleuca trees were dense and the diameters of the trees were small. The height to the top of the trees (Hvn) and the height under the branches (Hdc), showed no difference at three levels of peatland thicknesses. This may be due to the density of trees in this group is medium density and sparse so the development of individual trees are not very competitive in light and nutrients so the heights of the trees were relatively similar. The heights under the branches at the peatland thickness of 20 - 40 cm, 40 - 60 cm, and 60-80 cm ranged from 6 -14 m, 4 -14 m, and 5 - 14 m, respectively. There were no differences in heights among the treatments but the height of the trees in every standard plot varied considerably. The heights to the top of the trees at the peatland thickness of 20 - 40 cm, 40 - 60 cm, and 60 - 80 cm were 13.6 m ± 2 (medium), 14.3 m ± 2 (highest), and 13.8 m ± 1.9 (lowest), respectively. 3.2.3 Melaleuca trees biomass and melaleuca forest biomass at U Minh Ha National Park The dry biomass of melaleuca plants at U Minh Ha National Park, Ca Mau province at the peatland thickness of 20 - 40 cm was significantly different from those in the other thicknesses. At peatland thickness of 20 - 40 cm, dry biomass of melaleuca trees was lowest and ranged from 60.7 kg/trees. In the peatland thickness of 40 - 60 cm and 60 - 80 cm, dry biomass of melaleuca were 78.9 kg/tree and 77.4 kg/tree, respectively. Melaleuca trees in these two treatments have larger diameters at breast height leading to heavier biomass. The biomass of melaleuca trees is mostly from the contribution of the stem and the higher the age of melaleuca trees the higher the - 15 -
biomass. This result is also consistent with the previous studies reporting on yield and biomass of wood species in Vietnam and in the world. Figure 3.8 Biomass of melaleuca forest at different treatments Forest biomass was highly dependent on the biological parameters of melaleuca and density of melaleuca trees in the study area. It was found that the biomass of melaleuca forests ranged from 72.3 to 95.9 tons/ha and the biomass tended to decrease as the peatland thickness increases. Although the biomass of individual trees at the peatland thickness of 20 - 40 cm was lowest but the density of the trees was highest which was statistically different from those of the other two treatments leading to high forest biomass. 3.2.4 Plant species in melaleuca forests in different levels of peatland thickness The survey on the composition of plant species in the melaleuca forest in U Minh Ha National Park, Ca Mau revealed that there were 27 plants species. The number of species increases as the peatland thickness increases. For instance, the numbers of species at the depths of peatland thickness 20 - 40 cm, 40 - 60 cm, and 60 - 80 cm were 9, 12, and 14 species, respectively. This could be explained because the density of melaleuca trees was high at low thickness of peatland, other types of trees have less capability to compete with melaleuca trees for light, nutrients and space leading to lower in number of species. Once the thickness of peatland increases, density of melaleuca trees decreases in combination with moisture and porosity increases generating favorable conditions for plant species, bushes, and vegetation climbing species to be gradually dominant (Thai Van Trung, 1998). The woody plants comprised - 16 -
of Melaleuca cajuputy, Acacia auriculiformis, Eugenia zeylanica, Ilex thorelli and Alstonia spathulata accounted for 18.5% of the surveyed species. The group of species including Phragmites karka, Sturocholena palustris, Blechnum serrulentum, Cyperus compactus, Flagellaria indica, and Leersia hexandra occupied by 22.2% of total observed species. Climbing groups of vegetation comprised of Gymnopetalum integrifolium, Lygodium microphylum, Cissus modeccoides, Cayratia trifolia accounted for the largest proportion of 40.7%. The species of shrubs including Annona glabra, Evodia lepta, Glochidion littorale accounted for 18.5% of the total species. At different peatland thicknesses, level of species diversity was also different: highest species diversity at the peatland thickness of 60 - 80 cm (H = 3.95), followed by peatland thickness of 40 - 60 cm (H = 2.77) and the lowest diversity was found at the peatland thickness of 20 - 40 cm (H = 1.5). Thus, as the higher the peatland thickness, the lower density of melaleuca trees while the number of species of shrubs and climbing vegetation species would be higher. 3.2.5 Multivariate regression of melaleuca forest biomass at different peatland layers and soil quality Analysis of multivariate regression of melaleuca forest biomass at different peatland layers and soil parameters such as bulk density, pH, total nitrogen, total phosphorus, organic matter, N-NO3- and N-NH4+ indicated that bulk density and organic matter significantly influence on melaleuca biomass (p