Dominant Tropical Ecosystems - Rainforest & Savanna
Tropical rainforest and tropical savanna are the two most widespread tropical ecosystems. This course specifically focuses on these ecosystems, however, many of the management issues and the management techniques discussed for rainforest and savanna ecosystems are relevant to the other types of tropical ecosystems.
Definitions & Description of Tropical Rainforest & Savanna
Tropical Rainforest
The definition of tropical rainforests varies around the world depending on the classification scheme used. Within Australia, the Specht vegetation system (Specht 1970) is commonly used. This classification system is based on canopy cover and the height and form of the dominant vegetation.
Based on Specht’s classification, tropical rainforest falls within the general vegetation type “closed forest”. Therefore, tropical rainforest in Australia are closed forests located within the tropical climatic regions.
There are a number of general structural characteristics and more specific physiognomic features of tropical rainforest plants that are useful for identifying tropical rainforests. These include;
Structural features
- multilayered canopy
- predominance of vines
- diverse and abundant epiphytes
Physiognomic features
- predominance of leathery, glossy leaves
- distinctive “drip tip” on up to 90% of leaves
- Leaf size relatively large (this also depends on position in canopy)
- Many trees will flower and fruit on the branches and/or trunk
- Abundance of trees with horizontal root spread, development of “buttress” or “plank roots”
Tropical Savanna
The vegetation classification “Savanna” is generally used to identify plant communities with a continuous grass layer and scattered trees. A widely used definition describes a savanna ecosystem as one consisting of a continuous or near continuous C4 grass dominated understorey, with a discontinuous woody overstorey (Hutley and Setterfield 2005). Thus tropical savannas are these grass and scattered tree communities within the tropical regions of the world.
The distinction between savannas and grasslands and between forests and savannas are unavoidably arbitrary. However, scientific usage of the term is generally restricted to tropical and subtropical formations where;
- the grass stratum is continuous and important, and occasionally interrupted by tress and shrubs
- where fires occur from time to time
- where the main growth patterns are closely associated with alternating wet and dry seasons
A complicating factor in defining and classifying savannas is that the physiognomy of vegetation may be the result of natural process, human activities, or both. Human activities have extended the range of natural savannas so that savanna communities occur under many edaphic and climatic conditions.
Next topic - Distribution of the World's Tropical Rainforests & Tropical Savannas
Topics in this module