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CONTENTS.
VI
III. Initial Causes - Continued
Climatic Causes
- Róle 55
- Bare areas due to climatic factors directly 55
- Bare areas due to drouth 56
- Bare areas due to wind 56
- Bare areas due to snow, hail, and frost 56
- Bare areas due to lightning 57
- Bare areas due indirectly to climatic factors 57
- Sudden changes of climate 57
Biotic Causes
- General relations 58
- Action and effect 58
- Bare areas due to destruction of vegetation alone 59
- Bare areas with dry or drier soils 59
- Bare areas with wet soils or water 60
Primary and Secondary Areas
- Distinction 60
- Sterility of primary and secondary areas 60
- Denudation 61
- Methods of denudation 61
- Depth of removal or deposit 61
- Rate and extent of removal 62
Ecesic Causes
- Nature 63
Aggregation
- Concept and róle 63
- Effects of simple aggregation 63
- Relation to denuded areas 64
- Interaction of aggregation and migration 64
Migration
- Concept 64
- Mobility 64
- Seed-production 65
- Influence of the organ used 65
- Influence of the migration contrivance 66
- Role of migration agents 67
- Destructive action of agents 67
- Direction of migration 67
Ecesis
- Nature and róle 68
- Germination 69
- Fate of seedling 70
- Growth 71
- Reproduction 71
- Ecesis in bare areas 71
Competition
- Nature 72
- Competition and dominance 72
- Competition in air and in soil 73
- Róle of competition in succession 73
Invasion
- Nature and róle 75
- Kinds of invasion 75
- Manner of invasion 76
- Barriers 77
- Biological barriers 77
- Changes in barriers 78
Reactions
- Concept and nature 79
- Róle in succession 80
- Previous analyses of reaction 80
- Kinds of reactions 81
Soil Formation
- Manner 81
- Reaction by accumulating plant bodies or parts 81
- Reaction by accumulating plant concretions 83
- Reaction by producing weathering 83
- Reaction upon wind-borne material 84
- Reaction upon water-borne detritus 85
- Reaction upon slipping sand and gravel 86
Soil Structure
- Reaction by adding humus 86
- Reaction by compacting the soil 87
- Reaction by preventing weathering or erosion 88
Water-Content
- Reaction by increasing water-content 88
- Reaction by decreasing water-content 89
Nutrients and Solutes
- Reaction by adding nutrients or foodstuffs 89
- Reaction by decreasing nutrients 89
- Reaction by producing acids 90
- Reaction by producing toxins 90
Soil Organisms
- Reaction by means of parasites 91
- Reaction by means of saprophytes 92
Air Reactions
- Reaction upon light 92
- Reaction upon humidity, temperature, and wind 94
- Reaction upon local climate 94
- Reaction upon aërial organisms 95
- Correlation of reactions 96
- Quantitative study of reactions 96
Stabilization and Climax
- Stabilization 98
- Causes of stabilization 98
- Relation to the climax 98
- Degree of stabilization 99
Life-History Stages
- Nature
- Kinds of stages 100
- Role of life forms 100
- Reasons why plants disappear 100
- Reasons why plants appear at certain stages 100
- Reasons why plants appear before their proper time 103
- Initial stages 103
- Medial stages 105
