Australia: The Land Where Time Began

A biography of the Australian continent 

Closed Forest Formation

There are 3 divisions of this formation - tall closed forest, closed forest and low closed forest, that are differentiated on the basis of their tallest component vegetation.

All closed forests have dense canopies in the upper level, 70-100 % cover, that allows little sunlight to penetrate to lower levels. The upper level varies in height from 5 to 40 m, occasionally with a scattering of emergent trees. The lower strata may contain a considerable amount of complexity. In northern Australia many mangrove forests can be described as closed-forest. In a small area there can be considerable variation in structure, so these communities are dealt with under the heading of Vegetation of Extreme Habitats.

Along the east coast of Australia, from Cape York to Tasmania, there are pockets of closed-forest, usually in small wet areas. In the coastal regions of the Northern Territory there are small isolated areas of depauperate communities. This extensive disjunct distribution supports palynological evidence that these isolated communities are relicts of an earlier more extensive, more continuous distribution of these communities over much of eastern and north Australia.

Australian closed forests typically contain 2 distinct assemblages of plant species. One with a strong Indo-Malaysian affinity, the other, the Antarctic element - is also represented in New Zealand and South America. The geographical distribution of these assemblages overlap. From Cape York, north Queensland, pockets of Indo-Malaysian-derived elements extend westward across the coastal fringe to the Northern Territory, and south to Wilson's Promontory in Victoria. The Antarctic element is found in Tasmania, southern Victoria, in the highlands near the New South Wales-Queensland border and in New Guinea highlands.

Structure and component species vary considerably over the wide geographical range. In the driest limit of their distribution there is likely to be depauperate stands of low closed forest.

There are a number of diagnostic features  used to classify the closed forest types. These characteristics include degree of deciduousness, leaf size of dominant trees, the presence of emergents such as Araucaria, or of lianes (vines), palm, epiphytic ferns and mosses, or plank buttresses at the foot of tree trunks. 

Sources & Further reading

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading