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THE FLORISTIC COMPOSITION OF PRIMARY TROPICAL RAIN FOREST
Author(s) -
RICHARDS P. W.
Publication year - 1945
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/j.1469-185x.1945.tb00310.x
Subject(s) - floristics , temperate rainforest , geography , rainforest , temperate climate , ecology , climax , temperate forest , tropical and subtropical dry broadleaf forests , species richness , forestry , biology , ecosystem
Summary (i) The tropical rain forest is a formation‐type or pan‐climax. Its outstanding characteristic is the enormous wealth of species of which it is composed. (2) The investigation of the floristic composition of the rain forest presents special difficulties owing to the inaccessibility of the tree‐tops, non‐seasonal flowering and the backward state of taxonomy in tropical regions. For these reasons little definite information has been forthcoming on the subject until recently and the rain forest in each of the main geographical regions has been regarded as forming a vast assemblage of species varying in composition from place to place and not differentiated into distinct forest types comparable to the associations and consociations of temperate forests. (3) The floristic composition can best be studied by counting the trees on sample plots, identifying them first of all by their vernacular names with the help of native ‘tree‐finders’. With sufficient precautions this method can be made to give results of scientific value. (4) Primary lowland rain forest may be either Mixed Forest with numerous dominants or one dominant may form a large proportion of the stand. (5) Mixed rain forests may contain up to 100 species of trees 8 in. diameter and over in a sample plot 400times400 ft. The majority of the species in such a plot are represented by one or very few individuals, the average number of individuals per species ( Mischungs‐quotient )for trees 8 in. diameter and over being sometimes as low as 2–7. The evidence suggests that in any one geographical area there is only one mixed association whose composition fluctuates in both space and time. (6) Forests in which one species forms a large proportion of the whole stand are found in all the major tropical regions, but occupy small areas compared with the mixed associations. Some of these single‐dominant types are comparable with the consociations of temperate forest climaxes, while others should probably be regarded as societies of a gregarious species. In South America and Africa the majority of the dominants of consociations belong to the Leguminosae. (7) Most, perhaps all, of these single‐dominant communities occupy special soils or habitats and it is suggested that they tend to be restricted to non‐optimal soils while the mixed association occupies optimum soils. On similar soils in geographically widely separated areas there tends to be a parallel differentiation of edaphic forest types. (8) The single‐dominant forests can probably be regarded as what Braun has termed ‘association‐segregates’. If this is so the tropical rain forest, like the ‘Mixed Mesophytic Forest’ of North America, would consist of undifferentiated climax associations together with association segregates which are consociations, i.e. associations with a tendency to single‐species dominance. I would like to express my gratitude to Mr T. A. W. Davis and Mr T. G. Tutin for communicating unpublished data, and to Dr H. Godwin and Mr T. G. Tutin for kindly reading and criticizing the manuscript.