from the day this exhibit opened i thought - "but why skimp on the arboreal space?" since then the few dead eucalyptus trees they had in the exhibit have slowly rotted and crumbled away leaving what you see here. the monkeys spend virtually all the time on the ground. bet the zoo eventually rectifies this by installing unattractive ropes and plastic toys.
Vervet monkeys are mostly ground dwelling anyway so I think the gum trees are all they need and an enriching floor of the exhibit with grasses and bushes is more important. You can see this exhibit on zoolex.