Gaps in the Canopy - One Year On

At the start of 2021, the FODEX experiment was on a bit of a knife edge. With fieldwork impossible due to Covid-19 for most of the previous year, the processes of logging and regrowth were charging ahead in our plots, but without us there to collect the data!

Without flying our lidar drone before and after logging, we would have had none of the crucial change data that is central to the project. While mapping the biomass of a forest at one time has been done many times before, mapping biomass change is still a significant challenge.

We got very lucky. With Covid cases in Gabon low, we were granted permission to come to the country this January - one year on from when a number of trees were logged in our forest plots. 

Where each tree was felled, the most striking thing is the light streaming in from the huge "hole in the ceiling". It is not normal to see blue sky from a tropical forest! These canopy gaps are glaringly obvious when looking up from the forest floor, as the following picture shows.

However, that doesn't mean our task of measuring these gaps in the forest is easy. The influx of light to the forest floor had rapidly turned the brown wreckage of the logging into a green burst of new life. The following two pictures show the same scene in 2020 (above) and 2021 (below)...

This "re-greening" of the forest means that the canopy gap ends up being a very similar colour to the surrounding canopy. That is, in an optical image, it isn't so obvious how dramatic a change has taken place. The image below was taken from a height of 120 m. Fancy picking out that canopy gap from space?

This year we collaborated with Medard Obiang, a Gabonese researcher who took the picture above and the video that follows using a light, quadcopter drone. In the video, the camera faces downwards as the drone ascends through the canopy gap. The question for FODEX is: how can we estimate the biomass lost in these logging events using satellite data?