Vegetative architecture in the tropical forest
Tropical trees and forests, by F. Halle R.A.A. Oldeman and P.B. Tomlinson. Springer-Verlag, Heidelberg, New York: 1978, 441 p. (price not quoted)
The topic of vegetative architecture has evoked interest in widely different disciplines, such as taxonomy, morphogenetics, plant physiology and bio-geography. This book is a comprehensive study of vegetative architecture in tropical trees and forests. It includes a conceptual model and a classification that allow one to analyse and identify trees not according to the usual taxonomic system but by their vegetative architecture. The concept of identifying trees according to vegetative architecture originates with these authors.
The volume opens with a brief phytogeographic analysis of tropical and temperate floras, the former being rich in woody plants. Then the authors present broad outlines of the morphology and growth and development of plants, providing a background for the subsequent analysis of the vegetative architecture of the tree. How do the authors define vegetative architecture? The visible morphological expression of a tree at any one time is called its architecture. A selection of these forms or points of reference constitutes the architectural model of a tree.
A discussion of tree architecture accounts for nearly half the text of the book. Here the authors present a new method of describing and identifying trees according to their architecture. The method is based on morphological expressions of the genetic blueprint and a means for storing in a retrievable manner information on the more than 500 000 species of plants that cover the earth.
Overall organization exists in large long-lived woody plants as much as in herbs, the authors say. They add that organizational diversity is best studied in humid tropics where generally there is a uniformly favourable climate for growth of an enormous number of species and wide array of growth expressions.
Elaborating their proposed method of analysing trees, the authors state that trees have a genetically determined growth programme. At any one time a tree in an optimal environment that permits it to grow precisely according to its genetic plan revealing its genetic potential has a real and observable form, designated "momentary architecture," representing an ephemeral phase in the development of the tree. The architectural mode], however, is commonly obscured in trees growing in a stressed environment because it necessitates constant adjustment to it.
In order to explain the plan in the growth of trees, the authors have made, a selection of successive momentary architectural phases, each representing a different age. These points of reference constitute the "architectural model" of the tree. The authors point out that their model does not involve size, and diminutive herbs and giant forest trees may exhibit precisely the same architecture. The many thou sands of identified tree species of the world fit into only 23 models, according to the authors. There is a short description of each model illustrated by species that show the model well. The description concludes with a concise list of species by family and for many of them the general geographic distribution is also given. The emphasis is on tropical species. Woody climbing plants and herbs are included to a limited extent.
Having discussed the form of the tree and its potential growth activity in a more or less optimal environment, the authors consider tree growth in -the competitive environment of the :Forest itself. In nature, trees in the forest rarely exist in the idea] state since numerous factors such as microclimatic conditions, insect and fungal attack and forest density affect their development. Nevertheless, architectural models can be applied to the development of all trees and provide an analytical key to understanding why a tree takes the shape that it does. There is a detailed discussion of architectural and related properties of individual trees growing in forest sites, such as the process of architectural adjustment by which the tree accommodates itself to its environment and to its own energy distribution.
In the concluding chapter the authors discuss the architecture of forest sites within a forest and of whole forests. In this context, the rode of individual trees as building elements and the overall architecture of the forest are also treated. Floral 1 taxonomy has been the accepted norm for identification and classification of trees since Linnaeus, and for good reason. The idea of identifying trees according to vegetative architecture may, therefore, sound retrograde to some readers. The same critics may also complain that vegetative architecture is somewhat too theoretical. Nonetheless, it is a fascinating point of view that Halle, Oldeman and Tomlinson put forth and one worth considering especially in regard to the tropics ... at least theoretically.
P. ARGAL
