ABSTRACT
No abrupt change in vegetation type is found where the deciduous seasonal forests of America and Asia are flanked by even drier regions. Quite often, as the dry season becomes longer and the mean annual rainfall becomes less, the dominant deciduous trees decrease in stature and adopt a more gnarled and spreading habit. Also more and more species disappear from the stands so that, although the communities still compose a closed-canopy forest, this is very low-growing and floristically depleted. Ultimately, through an ecotone of greater or lesser width, the deciduous forest gives way to a different formation-type. Though this is lower-growing it is still dominated by woody plants. This type of community is dominated by low, bushy trees and tall shrubs 1 many of which have small leaves; consequently this type of vegetation has been referred to as 'microphyllous forest'. The term 'thorn forest' has also been applied to this kind of community in many places, and this is certainly appropriate in Africa and the Americas where most of its dominant plants are normally armed with a fearsome array of thorns and spines. It is inappropriate in Australia however; consequently the former term is now thought to be the most suitable one for the formation-type as a whole.
