Been working in Brunei Darussalam recently, including having a look around the Temburong National Park. The park is notable for its extensive pristine tropical forest on hill country, with some interesting inhabitants, including the endangered Proboscis monkey. The trees in the park are numerous in terms of numbers of species and size. The average height of the taller trees rarely exceeds 50 to 60 metres, though individual trees may grow up to 90 metres tall.
Buttress roots are a fascinating feature in tropical forests and I saw some great examples in Brunei. Unlike temperate forests where soils are frequently deep and rich in nutrients tropical forest soils are generally thin and contain few nutrients. Because of this tree roots do not extend down very far into the soil, but instead spread outward just below the surface of the ground to absorb available nutrients.
So because tropical trees are tall, they need extra support to keep them from toppling over. Buttress roots perform this function, growing like stilts from the base of trees, often very thick, they prop up trees giving them added strength and stability. Also they as useful places to rest and shelter from the sometimes frequent and heavy cloud bursts.