Ingrid Roth:

Leaf structure of a Venezuelan cloud forest

In relation to the microclimate

1990. XI, 244 pages, 122 figures, 16 tables, 17x24cm, 700 g
Language: English

(Encyclopedia of Plant Anatomy, Band XIV Teil 1)

ISBN 978-3-443-14018-2, bound, price: 76.00 €

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VenezuelaBlattstrukturWaldcloud forestleafmicroclimate


English description top ↑

By the expansion of the population and the refinement of techniques, tropical vegetation is more and more endangered. Particularly the tropical forests are destroyed by the spreading of the indigenous agriculture as well as by the clearance of forests to obtain timber for various purposes. For thousands of years the indigenous population lived in a stable equilibrium with the environment, maintaining the existing ecosystem. In our modern times, however, the whole world seems to be involved in a rapid destruction of what has been left of the humid tropical forests. But our knowledge of an adequate management of these forests in order to maintain their natural characteristics as well as their productivity is very limited. Just as poor is our awareness of the real economic value of the humid tropical forests. However, exploited reasonably they may constantly yield forest products of different kinds, such as wood, fiber, resin, latex, cork, oil, medicinal drugs, chemical products and others.

Humid tropical forests, the richest manifestation of plant and animal life in the world, have evolved under relatively uniform environmental conditions so that an exuberant vegetation with a large variety of species but a small number of individuals per species has developed. It is estimated that 50--200 species may be found on a hectare, but only a few individuals of a given species. These «living laboratories» represent the most important gene pool of the world. However, they may easily become extinct when exploited without care. Many species are endemic, many sensitive to environmental changes. Seeds have usually a short viability. Interrelations between plants and animals are of great importance, particularly in the dispersal of seeds and fruits.

It thus seemed worthwhile to dedicate a series of volumes of the Encyclopedia of Plant Anatomy to the structure of tropical plants to demonstrate the relationship between plant structure on the one hand, and environmental conditions on the other. A variety of ecological habitats in Venezuela have been studied by the present author in this connection. The present author has been teaching and doing research at Venezuelan universities for more than 20 years. Contacts have been maintained through many years and an exchange of Venezuelan and German scientists is still sustained. This interrelationship should be maintained for the benefit of future botanical studies in the neotropics. The cloud forest of the Parque Nacional Henri Pittier is one of the best known forests in Venezuela and probably in the whole of South America. It comprises a mountainous area of not less than 107800 ha. Its particular climate, the almost constant presence of mist and the occurrence of diffuse light generated a variety of structural adaptations of the «mist shade plants», such as funnel-shaped photosynthetic cells, chloroplasts with thylakoids pointing in different directions, a larger chlorophyll a/b proportion, a weaker venation, formation of special water-storing tissues, a weaker radical system and many other peculiarities.

Because it is so well known in the scientific world, we decided to begin our series with the cloud forest of Rancho Grande.

Contents top ↑

Introduction 1
Topography 1

Climate 2
Soil 5
Vegetation 5
The transitional cloud forest 6
The cloud forest proper 9
The upper cloud forest 12
Origin of the flora 14
Identification of species 15
Forest structure and diversity 16
Diversity 16
Forest structure 19
Mosaic structure of the forest 21
Forest stratification and some ecophysiological observations 22
Flowering 23
Leaf growth 24
Forest stratification and distribution of the biomass 24
Specific leaf area 25
Chlorophyll and nitrogen content 26
Light compensation point . 27
Leaf morphology and anatomy of 80 species belonging to four different strata
of the cloud forest 31
Material and methods 31
Vertical forest stratification and sampling 32
Species studied 32
Layer I: 5-40/60 m 32
Layer II: 1.30-5 m 35
Layer III: 1.30 m 38
Layer IV: 0-1.30 m 41
Leaf size in the different strata 43
Leaf shape in the different strata 49
Compound leaves 49
Simple leaves 50
The drip tip 51
Leaf symmetry 52
Stomata size and density in the different strata 53
Stomata density 53
Stomata size 56
Leaf anatomy in the different strata 89
Layer I 89
Layer II 94
Layer III 98
Layer IV 104
Discussion 114
15 monocotyledons of the undergrowth in stratum III and stratum IV 119
Species studied 119
Araceae 119
Arecaceae 119
Cyclanthaceae 120
Marantaceae 120
Musaceae 120
Leaf structure of the 15 monocotyledons 120
Araceae 120
Arecaceae 122
Cyclanthaceae 131
Marantaceae 133
Musaceae 134
Discussion of the results 134
Comparison with the 80 species studied in the four different forest
layers 136
Stomata density and stomata! size 136
Mesophyll structure 137
Other important characteristics 137
Position of the leaf blade 138
Anatomical data of the 15 monocotyledons studied 139
The so-called "sleeping position" of the Ctenanthe leaves, an
adjustment to minimal lightintensities? 142
Four species of Heliconia studied by NAPP-ZINN & FRANZ 144
Besleria disgrega, a herb of the undergrowth 146
Bauhinia, a liana of the cloud forest 149
Gyranthera caribensis, the highest emergent tree in Rancho Grande 152
20 tree species of dicotyledons 158
Description of the species studied 158
Leaf surface area of the 20 dicotyledonous tree species 164
Leaf shape of the 20 arboreous species 165
Structural characteristics of the leaves of the 20 tree species
studied 166
Description of the leaf anatomy of the 20 dicotyledonous tree species 189
Leaf structure as related to the height category of the tree 196
Giant herbs 196
Shrubs 196
Trees of medium height (10-20/25 m) 197
High trees (30-40/60 m) 199
Lianas 200
Hemi-epiphytes 201
Leathery consistence of leaves 201
Young and adult plants - shade and sun leaves 202
Structural characteristics due to the generic relationship 203
Slimy inner walls 205
Species of Cecropia and neoteny 205
Faculeative invadors and the refuge theory 206
General discussion 207
Leaf size 209
Leaf shape 211
Position of the leaf blade 212
Stomata: density and size 213
Guttation 215
Inner leaf structure 218
The "omnipresent" leathery leaf? 221
Leaf consistence 222
Xero- and hygromorphy- sun and shade leaf type 223
Leaf of youth and leaf of the adult tree 226
Forest stratification and heterophylly 227
Comparison of the leaves of a low herb with those of the highest tree 227
Genetic characteristics 228
Leaf structure and the microclimatic gradient 230
Bibliography 234
General index 240
Author index 240
Index of scientific plant names 242