Disturbance and its fingerprint on the structure of the world’s forests

A bird’s eye view of a forest fragment (right) adjacent to an oil palm plantation (left) in Sabah, Malaysian Borneo, captured using high-resolution airborne LiDAR. Tall, emergent trees reaching upwards of 70m appear in bright yellow, while canopy gaps are in dark purple.

There is long-standing debate about whether a falling tree makes any sound if no one is around to hear it. Sound or no sound, what we know for sure is that when a tree dies in a forest, in its place a gap is left in the canopy – a fingerprint of disturbance. Ecologists are fascinated by canopy gaps and the processes that create them, as these disturbance events drive forest dynamics. By letting light flood the forest floor, they kick-start a vertical race for space among understorey trees hoping to take advantage of an opening at the top. This process ultimately shapes the 3D architecture of forest canopies, the primary interface between the biosphere and the atmosphere when it comes to exchanging carbon, water and energy. By taking a snapshot of the number and size of canopy gaps in a forest, we can therefore build a detailed picture of how environmental constraints shape the structure and function of forests.

However, because the disturbance events that create gaps are rare and haphazard, locating canopy gaps from the ground is immensely challenging. One solution to this problem has been to use remote sensing technologies to identify canopy gaps from above. In particular, airborne laser scanning (LiDAR) – the same technology that enables driverless vehicles to ‘see’ their surroundings – has revolutionised our ability to map canopy gaps at scale. By using LiDAR to generate extremely detailed 3D models of entire forest landscapes, we can now map the location and size of 100,000s of gaps using just a few lines of code. And yet despite the growing availability of this data, we are still missing a global picture of how and why canopy gaps vary across the world’s forests. Moreover, we have no framework for linking canopy gaps to the types of attributes that ecologists typically measure in the field, including how much carbon is stored in a forest.

To tackle this challenge, our project will bring together airborne LiDAR and field data from thousands of sites across world. Combining recent advances in theoretical ecology, remote sensing and computer modelling, we aim to integrate canopy gaps into existing theories of forest dynamics and will test whether they reflect a globally coherent fingerprint of disturbance on canopy architecture. In doing so we hope to shed new light on the processes that shape the 3D structure and function of the world’s forests.