Tropical rain forest in Australia is often overlooked in international comparisons. It is often considered as an area of ‘outlier’ tropical rain forest and not as well developed as the Neotropical, Asian, or African forests. There are various reasons for this lowered status, including it’s position towards the edge of the equatorial region, the discontinuous yearly rainfall with a definite ‘drier’ season (Winter and Atherton 1987) and because the annual range of temperature exceeds 5 degrees Celsius (Tracey 1987).. However, despite the relatively tiny area it covers, Australian tropical rain forest has been found to have special significance.
Classifying Australian Tropical Rainforest
The Specht system
Within Australia, a system designed by Specht is commonly used. It is based on canopy cover and the height and form of the dominant vegetation. In this classification, much of the tropical rain forest comes under the general vegetation type ‘closed forest’ (Adam 1997). But this may also include much of the mangrove communities found along the coast line of Australia, a community with a very distinct and different species composition with incredibly different physiology and basic ecological different, such as herbivory and seed dispersal strategies. And yet rainforest also occurs in other categories, such as the low closed forest, which would include the stunted rainforests at higher altitudes, such as on Mt.Lewis or Bartle Frere/Bellenden Ker. It can also be a very difficult system to actually measure, with some of the measurements of foliage cover being either subjective to use, or very complicated if proper technique is followed.
'Ecofloristic' or 'Phytogeographical rainforest zones' within Australia
One of the first ways to classify tropical rain forest within Australia is to divide based on distribution. This was done in a casual way by many different explorer naturalist early on, with most assuming the northern tropical rainforests to be merely 'invasive' elements from south east Asia. The Australian ecologist Webb than later attempted a more formal systems diving the basic types of rainforest in Australia up roughly based on distribution, a system different from the more specific system discussed below. He actually accomplished this through a floristic survey throughout Australia, but geography, latitude, altitude and associated environmental factors such as temperature and rainfall defined much of the final classification. It ended up classifying Australia's rainforest into three main provinces, largely correlating with the idea 'tropical/monsoonal', 'subtropical' and 'temperate'. There was also a rough but logical correlation between altitude and latitude that assists in classifying different types of rainforest both in Australia and overseas. That is, the higher in altitude, the more like a higher latitude rainforest it is. This is, of course, mainly due to the temperature dropping as either altitude or latitude values increase. So higher altitude forest becomes more like sub-tropical rain forest, and higher still, it becomes more like temperate rain forest. So parts of province C (subtropical) poked into province B (tropical) in the higher altitude areas of, for example, the Atherton Tableland.
This system works well on a national scale, and is useful for academic comparisons of distribution of rainforest in Australia, and comparisons to overseas. However, it couldn't be used much in applications for land management. Within the provinces were very obviously different rainforest types. Thus, the same author also worked on more specific classifications systems at a finer scale.
The Tracey and Webb classification
A system made for specifically for diving up rainforest in North Queensland is the Tracey and Webb classification. This has been developed by ecologists Webb, Hitchcock, and most especially Tracey, in the last few decades.
One culmination of the development of this classification is a small book called the “Vegetation of the Humid Tropical region of North Queensland” (Tracey 1987). It seems to be commonly known and used by land planners, botanists and environmental consultants in the region, and has even been utilized in popular books (e.g.; Breeden 1999). For many of these professionals, it is the ‘bible’ and it is commonly sourced in national and international texts.
This classification uses altitude as well as many other different characteristics to divide the rainforests of the Australian Wet Tropics. These may include canopy height and evenness, leaf size and leaf fall, rainfall and soil type. The system also takes note of special features, such as lianas, epiphytes, bryophytes, ferns and if there are any particular dominant species.
The rainforests of the Australian Wet Tropics are thus divided into at least 13 different classes. These are numbered, with some then further divided into sub classes, which are assigned smaller case letters. The lower the number, the better ‘developed’ the rain forest. Thus, type 1a; “represents the optimum development of rain forest in Australia under the most favourable conditions of climate and soil on the tropical humid lowlands” (Tracey 1987). The higher numbers begin to grade into less complex subtropical and temperate rain forest as they increase in altitude.