How happy do you feel right now? The question is asked by an app on my phone, and I drag the slider to the space between “not much” and “somewhat”. I’m about to start a walk in the woods that is part of a nationwide research project to investigate how better to design the forests of the future. Volunteers are being sought to record their feelings before and after eight walks on a free app, Go Jauntly, which could reveal what kind of treescapes most benefit our wellbeing and mental health. …Scores of peer-reviewed studies have identified the myriad benefits of wooded landscapes on everything from improved cardiovascular and immune system health to depression. …But it appears the type of forest may be important too: intriguingly, several studies suggest that more biodiversity has a bigger boost on people’s mental health.