The type of vegetation found on the Ridge is known as Adinandra belukar, as Adinandra dumosa is its characteristically most commonly found tree, and 'belukar' is Malay for secondary forest. Secondary forest is forest that grows on ground that has been previously cleared of its original vegetation (primary forest) or disturbed significantly. It is different from primary vegetation in many ways. For example, the species of plants growing in secondary forests are different from those in primary forests, and are more adapted to life in its different conditions. These different conditions include increased light intensity, lower humidity, higher temperatures, etc. In order to survive and be successful, plants in secondary forests also have to grow quickly and be easily and widely dispersed, so that they may colonize newly disturbed ground before other plants do. Adinandra belukar is found on degraded land, whereas another type of belukar, Trema belukar, dominated by Trema sp. and similar plants is found in naturally occurring gaps in primary forest, where the soil is still rich in nutrients and not degraded.
Adinandra belukar was first qualitatively described by Holttum (1954a), and later by Sim et al (1992). Wee and Corlett (1986) have given a semi-popular account of secondary vegetation in Singapore, and Corlett (1991) has described the various stages of development in Singapore's secondary vegetation based on studies in the Central Catchment area. In general, belukar has several distinct differences from primary forest. Firstly, its floristic diversity is much lower, with more plants per species per unit area than primary forest. Secondly, temperature and humidity fluctuations are much greater. The belukar is highly exposed to the elements, hence in the day it is very warm and during the night it is very cool. It is much drier too, for the belukar's average minimum relative humidity is 62% whereas primary forests experience at least 76%. Thirdly, the soil is much poorer, lacking various nutrients due to its previous uses. Rain and other erosive agents wash away humus and organic material as well. In short, belukar is hotter, drier, and poorer than primary forests. Its various aspects are explored in detail below.