 I often lie in bed at night thinking about trees. Trees are just like the people in your life. All of them are unique. And sometimes they can be hard to predict, right? Especially when life gets stressful. Some people get anxious or flaky. Others stay calm and reliable. Well, trees are like this too. We know surprisingly little about how trees respond to the world around them. And this is a big problem. Because trees are the building blocks of forests. And forests guzzle up carbon dioxide and keep our climate clean. Getting to know trees is the focus of my research. If we can come to know how trees act when life gets stressful, we could manage, restore and use forests to help save the world. Trees build their bodies from carbon in the air. And that makes forests amazing allies, because on balance forests take up more carbon than they release. And we call this a carbon sink. Forests have not been so reliable lately. Tropical forests even in places untouched by humans are now taking up less carbon than they used to. We don't know why forests are acting this way. Or whether Australia's tropical forests are also going through this setback. So this year I set out to find answers. I hiked to remote parts of the Australian rainforest to visit some trees that scientists have been tracking for 50 years. This is the third generation of scientists coming to meet these characters. Some of them grow on impossibly steep mountains up in the clouds. And others on coastal plains where the forest can be so dense, it can take half an hour just to find one tree. We visited 4,000 trees and took a census of each of them. Their height, diameter and notes on who had died. Now I can read the growth charts and death records for thousands of trees alongside climate data going back 50 years. My modelling of this huge data set shows that the carbon sink in Australia's tropical forests is acting unreliable. But in ways that make our forests very unusual. By reconstructing past changes in the carbon sink and getting to know individual trees to slight people, my research will help tell us how we can best use forests to support the future that we choose to create.