EVALUATION OF THE ECOLOGICAL ROLE OF Acacia confusa IN URBAN ECOSYSTEMS IN HONG KONG BY LAI TAT WA STUDENT NO.:_14676990_ 環境及資源管理社會科學學士 (榮譽)學位 課程 BACHELOR OF SOCIAL SCIENCES (HONS) IN ENVIRONMENT AND RESOURCES MANAGEMENT April/2016 畢業論文 PROJECT i EVALUATION OF THE ECOLOGICAL ROLE OF Acacia confusa IN URBAN ECOSYSTEM IN HONG KONG BY LAI TAT WA STUDENT NO.: 14676990 AN HONOURS PROJECT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF BACHELOR OF SOCIAL SCIENCES (HONOURS) IN ENVIRONMENT AND RESOURCES MANAGEMENT HONG KONG BAPTIST UNIVERSITY April/2016 ii HONG KONG BAPTIST UNIVERSITY April / 2016 We hereby recommend that the Honours Project by Mr LAI TAT WA entitled "Evaluation of the ecological role in the urban ecosystems in Hong Kong" be accepted in partial fulfilment of the requirements for the Bachelor of Social Sciences (Honours) in Environment and Resources Management. Dr. K.L. Karen Chow Chief Adviser Second examiner Overall Grade : iii Acknowledgement I would like to express my gratitude sincerely to my chief supervisor Dr. K.L. Chow, Karen, for her supervision, guidance and kindly help. She was very patient and supportive to me in my entire study period these two years. I wish to thank Dr. H.C. Chiu for his hard work for clarification of the requirement of the Honours Project. ______________ Student’s signature Date: _________ iv Abstract Acacia confusa was one of the exotic tree species commonly used for plantation in Hong Kong. The aim of this study was to evaluate the ecological role of Acacia confusa in urban ecosystems and impacts of urbanization on it. 9 study sites were selected. A. confusa in urban area did not lead to acidification of soils and not cause any effect on electrical conductivity of soils. The existence of it did not alter the invertebrates’ richness. The soil textural classes of the soil samples were dominated by loamy sands and sandy loam. A. confusa can make the soil to become suitable topsoil for cultivation. The moisture content of soil increased with the level of urbanization, the most urbanized district (13.49%), the medium urbanized district (17.97%) and the least urbanized district (20.06%). A. confusa was threatened by urbanization. In addition, there was a decreasing trend of soil temperature from the most urbanized district to the medium urbanized district and an increasing trend from medium urbanized district to the least urbanized district. Urbanization provides more available nutrients to A. confusa. A. confusa were generally aging. Most of the DBH of A. confusa recorded were larger than 24 cm. It ranged from 23.04 cm to 60.51 cm. There was the risk for these A. confusa to be infected by fungi and collapse. Moreover, there was a moderate negative v correlation between the DBH and the health index of A. confusa. Finally, Syzygium hancei, Schima superba and Castanopsis fissa were the three common native tree species recommended to replace the aging and aged A. confusa due to their similar properties with A. confusa. (Total word count: 9735) vi Table of Contents Acknowledgement ............................................................................................ iv Abstract .............................................................................................................. v Table of Contents ............................................................................................. vii List of Tables ...................................................................................................... ix List of Figures ..................................................................................................... x Chapter 1: General Introduction ........................................................................ 1 1.1 Background of Acacia confusa ............................................................. 1 1.2 Plantation History ................................................................................ 3 1.3 Characteristics ...................................................................................... 4 1.4 Problems facing .................................................................................... 5 1.5 Hypothesis ............................................................................................ 6 1.6 Objectives ............................................................................................. 7 Chapter 2: Literature Review ............................................................................. 7 2.1 Overview .............................................................................................. 8 2.2 Role of Acacia confusa ......................................................................... 8 2.3 Tree survey ......................................................................................... 11 2.4 Impact of Urbanization on trees ........................................................ 12 2.5 Aging problem .................................................................................... 15 Chapter 3: Methodology .................................................................................. 16 3.1 Study area .......................................................................................... 16 3.1.1Study sites description ............................................................. 16 3.2 In-situ inspection ................................................................................ 18 3.2.1 Soil sampling ........................................................................... 18 3.2.2 Tree analysis ............................................................................ 19 3.3 Laboratory analysis ............................................................................ 20 3.3.1 Soil texture .............................................................................. 20 3.3.2 Soil pH & Electrical conductivity ............................................. 21 3.3.3 Soil moisture ........................................................................... 22 3.4 Statistical analysis .............................................................................. 22 Chapter 4: Results and Discussions .................................................................. 23 4.1 Ecological role of Acacia confusa ....................................................... 24 4.1.1Soil properties .......................................................................... 24 4.1.1.1 Soil pH .................................................................................. 24 4.1.1.2 Soil electrical conductivity ................................................... 27 4.1.2 Effects of Acacia confusa on soil texture ................................ 30 4.1.3 Number of invertebrates’ species ........................................... 34 vii 4.2 Urbanization problems of and effect on A. confusa .......................... 38 4.2.1 Soil moisture ........................................................................... 38 4.2.2 Soil temperature ..................................................................... 42 4.3 Aging problems .................................................................................. 45 4.3.1 Health Index ............................................................................ 45 4.3.2 Diameter at breast height (DBH) ............................................ 47 4.4 The ecological role of A. confusa in urban ecosystems and .............. 50 Chapter 5: Conclusion ...................................................................................... 53 5.1 Summary of findings .......................................................................... 53 5.2 Limitations of the study ..................................................................... 54 5.3 Future study recommendations ......................................................... 55 Appendix .......................................................................................................... 57 References ........................................................................................................ 59 viii List of Tables Table 1. The general parameters of the A. confusa in different sampling sites, the height, canopy width and frequency. ......... 23 Table 2. Data results for soil pH values and EC values of all sampling points and the standard deviation ............................. 29 Table 3. The soil texture classes of the 9 sampling sites and their relative soil composition percentage ........................................ 32 Table 4. Data result of number of invertebrates’ species of different sampling sites and the standard deviation ................................ 36 Table 5. Data result of soil moisture of different sampling sites and the standard deviation .............................................................. 40 Table 6. Data result of soil temperature of different sampling sites and the standard deviation ....................................................... 44 Table 7. Data result of health index of A. confusa of different sampling sites and the standard deviation ................................ 46 Table 8. Data result of DBH of A. confusa of different sampling sites and the standard deviation ....................................................... 48 ix List of Figures Figure 1. The distribution of the 9 sampling sites in Hong Kong .... 18 Figure 2. The comparison of pH value among the different sites and the correlation between the frequency of A. confusa and the pH values of the sites ....................................................................