There are many exotic plants that have invaded the Ridge belukar. Many of these are pan-tropical weeds of the Compositae (Asteraceae), as well as alien grasses and sedges that have been introduced. This might be due to Kent Ridge being enveloped in an urban area, and since Singapore was, and still is, a busy trading port, many of these may have followed traders in from overseas. Woody alien plants are also present. The most prominent of these, and also the most successful, is Acacia auriculiformis, the Wattle, which is a native of northern Australia, the Torres Straits, and southern Papua New Guinea. It was brought to this region as a horticultural plant and also as a source of timber, and Nicholson (1965) calls it "...a very useful tree, especially for replanting waste areas...." Hill (1977) notes that it was planted in Kent Ridge itself along the Gap. The tree was also used as a wayside tree by the government before being abandoned because of its excessively vigorous growth and rapid dispersal. Other trees along Kent Ridge Road are also possibly planted as wayside trees, for example Adenanthera pavonina, the Saga tree, as well as Causuarina equisetifolia, which is found naturally on sandy shores. But Acacia is still the most common exotic, and this is due to several factors. Firstly, it is well suited to the dry and exposed environment of the belukar, and also has tough leaves like native belukar plants. Secondly, its growth is fast, and it matures rapidly, competing with the natives for light and nutrients. Thirdly, being a legume, its associated root nodules can fix nitrogen and give it an edge in growth. Fourthly, its brightly coloured yellow aril attract birds which feed on its numerous seeds that are produced year round and hence disperse the plant. As can be seen, even though it is an exotic that has evolved in a different area from this region, it shares many characteristics and adaptations with belukar plants and hence is able to compete favourably with them.
As mentioned above, horticultural plants and food plants have "escaped" from peoples' gardens to grow wild on the Ridge. It was quite surprising for the author to stumble upon a patch of Sanseviera sp. growing wild in the shade of the belukar trees. Epipremnum, the money plant, can also be seen climbing up trees together with the native Smilax spp. These weeds may compete with the native plants and smother them out, or compete with them for nutrients, and hence reduce plant diversity. Veldkamp (2001) complained about how tropical flora is becoming increasingly homogenized, and in the belukar, where plant diversity is already significantly less than primary forest, the threat of exotics is quite great. However, the exotics are established mostly at the edge of the forest, where human disturbance is the greatest, and the conditions are the best for their growth. It can be observed that even plants as successful as Acacia still have not penetrated to the core of the belukar forest, though in time they may.
Other foreign invaders include Mimosa pudica, the sensitive plant, and Lantana camara, one of the top ten weeds worldwide. With the increased exposure of the Ridge to external influences and urbanization, the belukar will be increasingly infiltrated by plants that 'should not be there'. At present the belukar natives are holding their own, but the future is somewhat uncertain. According to Mudaliar (1987), two-thirds of belukar plant species are natives. While it compares favourably with other forms of land use, e.g. urban green space, residential, etc., it is much less than primary forests.