Tropical forests are greatly important stores of carbon and biodiversity, covering a huge land area (about 15% of the planet's land surface) but nonetheless having an outsized impact on the Earth System, regulating our climate and supporting livelihoods and populations everywhere. Given their importance and area, we know surprisingly little about how they are changing. We know, in broad terms, that people are deforesting an ever increasing proportion of tropical forests, and have evidence to suggest that they are damaging (degrading) a much larger area through selective logging, small-scale agriculture, and the extraction of resources, but we do not have a good idea of where these disturbances are happening or at what intensity. This is a tragedy, as it prevents the targeting of policies and resources to stop deforestation and forest degradation.
Further, we know that the tropical forest areas that have been left largely alone, or that are recovering from past disturbance, are doing a really important job in stabilising the climate. Over half the carbon we release into the atmosphere by burning fossil fuels and cutting down forests does not remain in the atmosphere, but is in fact taken up immediately by the Earth system. This 'missing sink' has helped us out greatly during the recent past, meaning that climate change has occurred much more slowly than it would have done if all that carbon had been allowed to remain in the atmosphere, warming the planet through the greenhouse effect. We do not know well where this 'missing sink' is located, but we believe it is a combination of capture in the oceans, and capture in the world's forests. Being able to map this sink is crucial, as it is really important for humanity to know where it is so we can strengthen protection on those forests that are protecting us most, and predict how this sink will change with time.
Over the past decades the NASA, the European Space Agency (ESA), and the European Union, among others, have invested in collecting more and more satellite data. These data are increasingly sophisticated in terms of their spatial resolution (the size of pixel sizes on the ground), the range of data being collected, and their temporal frequency (once we only 'saw' the planet every month or two with most higher resolution sensors, now it's often more than once a week). And, critically, the data are increasingly released in a free and open way, meaning scientists and companies can take advantage of hundreds of thousands or even millions of scenes, with only computing costs to worry about as data volumes increase. Combined with the big data revolution and massive developments in artificial intelligence and machine learning, this should mean that by now we have good systems of using these satellite data to monitor the forests of the tropics.
However, this revolution in satellite monitoring of forests has not really happened. Data on monitoring deforestation have definitely improved. But data on forest degradation, where only some trees are removed from an area, and regrowth, are still very poor. We believe that a major reason for this has been a lack of good 'ground truth' data on forest change. While there are scientific field plots where every tree is measured, enabling the calibration of static forest carbon maps, these plots are typically in protected areas and are very rarely disturbed or cleared. This makes it hard to calibrate products that are directly trying to measure this change.
Collecting suitable ground data to develop forest degradation and regrowth data is therefore the aim of this project, FODEX. We have set up permanent forest plots in two logging concessions, in contrasting forest types, one in Peru, and one in Gabon. In both of these we set up our plots and measured all the trees in 2019, including collecting laser scanner data from the ground so we had exact 3D models of every tree, and collecting LiDAR data from our drone so we could map millions of trees in the surrounding area. Then the plots were logged at different intensities. We have remeasured these plots in Gabon, and are still waiting to remeasure the Peru plots (our field campaign due in May 2020 has been delayed due to COVID). Ultimately, we will remeasure the plots again twice during their regrowth from disturbance, so each plot will have been measured four times, with substantial changes in biomass at each point.
We have used these data to develop and test new algorithms for mapping forest degradation across the tropics. We have so far developed a new algorithm based on the Sentinel-1 Synthetic Aperture Radar satellites, that provides, for the first time, the timing and magnitude of disturbance events. We have tested this across Peru and Gabon, and published large scale maps based on these showing the relative impact of illegal logging and commercial logging, and allowing comparisons to deforestation. Publications showing further developments using other sensors, and developing these maps more widely, are ongoing. The raw data from FODEX has also been shared and provides a unique resource for other scientists.
