Plants - Not All Forests are The Same

There are some general characteristics by which rainforests are readily identified. They usually have moisture loving, closely spaced trees whose dense leafy tops close over, limiting the light which makes it to the forest floor. Often palms and tree seedlings poke up from a sparsely covered ground while convoluted vines weave their way from one tree trunk to another. Branches may be heavily weighed by birds nest ferns and orchids growing on them. But these are just the most general descriptions of a rainforest. There are actually specific types of forest which, in turn, will support particular types of animals, fungus and insects.

In 1975, Geoff Tracey and Len Webb developed a structural classification system for rainforests for the Wet Tropics. The system consists of 13 main types of forest and some of these are divided into sub-types. For example, class 3a forest has a dominance of Feather palms whereas class 3b is dominated by Fan palms.

 
Some general descriptions of the major forest types are presented here:

Rainforests reach their peak development as complex mesophyll vine forests on the very wet and wet lowlands and foothills on soils which include basalts, basic volcanics, mixed colluvia and riverine alluvia. These communities have an uneven canopy ranging from 20 to 40 metres (65 to 130 feet) in height. There is a lot of stratification and many of the tallest trees that stand prominently higher than the top of the continuous canopy (called emergents) have large spreading crowns. Species composition and the variety of life forms are the most complex of any vegetation type found on the continent. Plank buttressing is common, robust woody lianes, vascular epiphytes and palms are typical, and fleshy herbs with wide leaves (such as gingers and aroids) are prominent.

When comparing complex mesophyll vine forest communities, there are obvious structural differences such as an increase in palms on sites with poor drainage, and gingers and aroids in gullies and along creek banks which are permanently saturated with water.

The notophyll vine forest categories include a diverse group of communities. They occur on small areas of basic volcanic soils on cool wet uplands and highlands and on a range of drier sites at various elevations, on sandy beach ridges in drier coastal zones and exposed sites backed by foothills. These communities, while extraordinarily variable, are characterised by a canopy range of 12 to 45 metres (39 to 147 feet) in height, rattans or palm lianes, strangler figs, frequently conspicuous epiphytes and variable amounts of ferns, walking stick palms and fleshy herbs.

On the summits and upper slopes of the higher peaks which are frequently covered by cloud and often exposed to strong winds, simple microphyll fern forests or thickets dominate. Aerially suspended mosses are often found here (these forests are also referred to as 'cloud' or 'wet montane' forests).

Many sites which experience significant water stress during the dry season have closed forest/thicket communities which include semi-deciduous to deciduous vegetation. Semi-deciduous mesophyll vine forest is largely restricted to the foothills between the Bloomfield River and Cooktown. The canopy is comparatively even to a height of 25 to 32 metres (82 to 105 feet) with deciduous emergents as high as 36 metres (119 feet). Figs, including both cluster (cauliflorous) and strangler types, and lianes (rather than rattans) are relatively conspicuous and epiphytes are much less common.

Vine forest with sclerophyll emergents represent different stages of post-disturbance succession (such as fire, logging or cyclones). Their composition varies greatly with each sub-type characterised by the dominance of certain sclerophyll species such as eucalypts and wattles.

 
The material on this page is from 'Repairing the Rainforest' by Dr Steve Goosem and Nigel Tucker. This book is available from the Wet Tropics Management Authority >