In the Trees — Pauline Fisk

All around him, the smell of trees rose from the ground, earthy and dank, just the way he'd smelt it that first day. And he'd heard a voice that day, which he'd thought was calling out a welcome. But really it had been calling out for help.'

Kid Cato's come to Belize, on the Caribbean coast. He's left behind his life in London and is looking for his dad. But what he finds instead is a group of gap year volunteers. They're just the boring, do-good types he's always hated, but he's stuck with them. Stuck with the jungle too - but, by the time it's done with him, he'l never be the same. And neither will Kid's new companions. Living in the trees will change them all.
'Forest are like lungs. They breathe life into us and make us one. Here we are from worlds apart. And thanks to the forest we're sharing one life. Where we come from doesn't matter, or what we once were in the past. It's what we are now that matters. It's what we make of ourselves.'