Secondary successions after shifting cultivation in a dense tropical forest of southern Cameroon (Central Africa) Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften vorgelegt beim Fachbereich 15 der Johann Wolfgang Goethe University in Frankfurt am Main von Barthélemy Tchiengué aus Penja (Cameroon) Frankfurt am Main 2012 (D30) vom Fachbereich 15 der Johann Wolfgang Goethe-Universität als Dissertation angenommen Dekan: Prof. Dr. Anna Starzinski-Powitz Gutachter: Prof. Dr. Katharina Neumann Prof. Dr. Rüdiger Wittig Datum der Disputation: 28. November 2012 Table of contents 1 INTRODUCTION ............................................................................................................ 1 2 STUDY AREA ................................................................................................................. 4 2.1. GEOGRAPHIC LOCATION AND ADMINISTRATIVE ORGANIZATION .................................................................................. 4 2.2. GEOLOGY AND RELIEF ........................................................................................................................................ 5 2.3. SOIL ............................................................................................................................................................... 5 2.4. HYDROLOGY .................................................................................................................................................... 6 2.5. CLIMATE ......................................................................................................................................................... 6 2.6 VEGETATION ..................................................................................................................................................... 7 3 SHIFTING CULTIVATION IN SOUTHERN CAMEROON …………………………………………………..…9 3.1 GENERAL DESCRIPTION .............................................................................................. 9 3.1.1 DIFFERENT STEPS OF SHIFTING CULTIVATION ......................................................................................................... 9 3.2 SHIFTING CULTIVATION IN SOUTHERN CAMEROON .................................................. 10 3.2.1 SELECTION ................................................................................................................................................... 10 3.2.2 CLEARING .................................................................................................................................................... 11 3.2.3 BURNING .................................................................................................................................................... 11 3.2.4 CROPPING ................................................................................................................................................... 12 3.3 LAND TENURE .......................................................................................................... 13 4 METHOD …………………………………………………………………………………………………………………… 14 4.1. TRENDS IN VEGETATION STUDY .............................................................................. 14 4.1.1 THE DISCONTINUITY TREND ............................................................................................................................. 14 4.1.1.1 The Zürich Montpellier school .......................................................................................................... 14 4.1.1.2. The Scandinavian school ................................................................................................................. 15 4.1.1.3. The Russian school .......................................................................................................................... 15 4.1.1.4 The Anglo-Saxon school ................................................................................................................... 15 4.2 THE TREND OF CONTINUITY .................................................................................... 15 4.3 CHOICE OF A METHOD ............................................................................................ 15 4.4 DATA COLLECTION .................................................................................................. 16 4.4.1 Approaches in study of secondary successions ................................................................................... 16 4.4.2 Searching of fallows and their ages .................................................................................................... 16 4.4.3 Soil texture .......................................................................................................................................... 17 4.4.4 Degree of canopy closure .................................................................................................................... 17 4.4.5 Floristic composition ........................................................................................................................... 17 i 4.4.6 Diameter classes ................................................................................................................................. 18 4.4.7 Precipitations ...................................................................................................................................... 18 4.4.8 Auto ecological characters of recorded species .................................................................................. 19 4.4.8.1 Life-forms ...................................................................................................................................................... 19 4.4.8.2 Types of phytogeographic distribution ......................................................................................................... 19 4.4. 8.3 Types of diaspore dispersal .......................................................................................................................... 20 4.5 DATA ANALYSIS ...................................................................................................... 21 4.5.1 Data processing .................................................................................................................................. 21 4.5.2 Multivariate analyses .......................................................................................................................... 22 4.5.2.1 Ordination ..................................................................................................................................................... 22 4.5.2.2 Classification ................................................................................................................................................. 23 4.5.2.3 Diagnostic species and fidelity measures ...................................................................................................... 23 4.5.2.4 Diversity indices and other structural parameters ........................................................................................ 24 4.5.5.5 Ecological behaviour and forest types .......................................................................................................... 25 5 RESULTS OF ORDINATION AND CLASSIFICATION ANALYSES .......................................... 27 5.1 ORDINATION ANALYSIS ............................................................................................ 27 5.1.1 IMPORTANCE OF ENVIRONMENTAL FACTORS ....................................................................................................... 27 5.1.2 VEGETATION GROUPS .................................................................................................................................... 28 5.1.3 CATEGORIAL FACTORS .................................................................................................................................... 31 5.1.3.1 Previous vegetation type ................................................................................................................. 31 5.1.1.2 Vegetation around fallows ............................................................................................................... 32 5.1.1.3 Number of farming cycles in the plots ............................................................................................. 33 5.1.1.4 Type of soil ....................................................................................................................................... 34 5.2 CLASSIFICATION ANALYSIS ....................................................................................... 36 6 PHYTOSOCIOLOGICAL STUDY OF SUCCESSION ………………………………………………………….. 40 6.1 REGULARLY DISTURBED FALLOWS OR CHROMOLAENA THICKETS ............................. 40 6.1.1 ENVIRONMENTAL FACTORS ............................................................................................................................. 40 6.1.2 PHYSIOGNOMY AND STRUCTURE ...................................................................................................................... 40 6.1.3 PHYTOSOCIOLOGICAL CHARACTERIZATION OF CHROMOLAENA THICKETS ................................................................... 43 6.1.3.1 Species cover and constancy degree ................................................................................................ 43 6.1.3.2 Diagnostic species ............................................................................................................................ 44