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Tropical Forest Degradation Experiment

Periodic Reporting for period 4 - FODEX (Tropical Forest Degradation Experiment)

Berichtszeitraum: 2022-07-01 bis 2023-12-31

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.
We have completed four field campaigns in each of Gabon and Peru. These include before and after logging, and during two periods of recovery, and involved measuring all the trees in four large field plots in each site, as well as collecting LiDAR data from our UAV and a Terrestrial Laser Scanner. The timing of some of these campaigns was not ideal due to the impact of the Covid-19 pandemic, and one Peru campaign had to be completed in a more limited way by local scientists due to travel restrictions. But overall the datasets we set out to collect have been collected, and have been released as open data to the wider scientific community.

We have processed these data and published papers about the detail or how to process TLS and LiDAR data when multiple datasets exist at different times for the same plots, with some changes (in our case, some trees being logged); and on how these perform using different Synthetic Aperture Radar (SAR) and optical satellite datasets. On the way we made developments particularly in SAR data processing, producing better understandings of how to detect changes over slopes when data are available from both east- and west- looking directions, and on how to use dense time series of satellite data. These have resulted in major new maps of degradation and deforestation in Peru and Gabon, and will ultimately lead to the production of pantropical maps of disturbance.
We have collected entirely novel data at this point: we are the first group to ever collect Terrestrial Laser Scanner and LiDAR data over forest before and after logging, and then during recovery. These have been made available to the scientific community, and will be widely used to test and train algorithms.

We have discovered a way of using dense stacks of Sentinel-1 data to map the occurrence and magnitude of forest degradation. This will be widely used for monitoring forests, for example for compliance purposes under zero deforestation legislation (e.g. the EU's Deforestation Regulation, EUDR), and for the carbon markets.

We have developed methods that show the optimum resolution for optical satellite data to be used to map forest degradation, showing that around 5m resolution is better than both coarser and higher resolution options. This will have impacts on future satellite sensor funding and design.
Some exciting visitors found in one of our Gabon plots
Presentation on FODEX from our senior PhD student, Chiara Aquino
An example slice through one of the Peru plots (before logging), collected from our LiDAR drone