The Lowland Equatorial Monsoon Ecozone
black-water rivers, creating narrow sub-ecozones of flood plain and swamp forest, and was dotted with small permanent and seasonal lakes as a result of isolated impervious sub-soil clay deposits.
We know that it grew largely on free-draining, deep Oxisols and that the forest was only likely to become waterlogged between May and September (when an average of 2300mm of rain falls on the area).
These factors would be reflected in the physical dimensions of the forest.
5.6.1 VERTICAL DIMENSIONS
Excessively high rainfall prevents trees reaching their maximum height, but the deep Oxisols will nonetheless have favoured tall, deep-rooting tree species. With the exception of forest bordering on lakes and rivers, a vertical section of the forest would show recognisable layers as follows:
#Upper Tree Layer
Above 25 metres, composed of emergent trees, woody climbers and epiphytes.
#Middle Tree Layer
From 10 to 25 metres, made up of large trees and woody climbers.
#Lower Tree Layer
Between 5 and 10 metres, made up of small trees and woody saplings
#Shrub Layer and tree seedlings
#Herb Layer
Smaller tree seedlings and ferns covering no more than 10% of the ground (absent in some areas).
#Upper Root Layer
From the surface down to about 5 cms deep and made up of a compact root-mass in the topsoil.
#Middle Root Layer
From 5 to 50 cms deep, having a less abundant root-mass in the subsoil
#Lower Root Layer
Scattered roots below 50 cms, with occasional deep taproots down to 5m.
Although not exclusive to a given layer, different animal communities are associated with different levels.
5.6.2 HORIZONTAL DIMENSIONS
Looking at an overhead plan of the forest, different phases can also be seen.
#Mature Phase
The most extensive, within which the other phases exist. Stable, and dim under an unbroken canopy, it is actually quite easy to navigate through mature rainforest.
68
