Historical aerial surveys map long-term changes of forest cover and structure in the Central Congo basin

Given the impact of tropical forest disturbances on atmospheric carbon emissions, biodiversity, and ecosystem productivity, accurate long-term reporting of Land-Use and Land-Cover (LULC) change in the pre-satellite era (<1972) is an imperative. Here, we used a combination of historical (1958) aerial photography and contemporary remote sensing data to map long-term changes in the extent and structure of the tropical forest surrounding Yangambi (DR Congo) in the central Congo Basin. Our study leveraged structure-from-motion and a convolutional neural network-based LULC classifier, using synthetic landscape-based image augmentation to map historical forest cover across a large orthomosaic (similar to 93,431 ha) geo-referenced to similar to 4.7 +/- 4.3 m at submeter resolution. A comparison with contemporary LULC data showed a shift from previously highly regular industrial deforestation of large areas to discrete smallholder farming clearing, increasing landscape fragmentation and providing opportunties for substantial forest regrowth. We estimated aboveground carbon gains through reforestation to range from 811 to 1592 Gg C, partially offsetting historical deforestation (2416 Gg C), in our study area. Efforts to quantify long-term canopy texture changes and their link to aboveground carbon had limited to no success. Our analysis provides methods and insights into key spatial and temporal patterns of deforestation and reforestation at a multi-decadal scale, providing a historical context for past and ongoing forest research in the area

Historical forestry research from the Belgian colonial period in the Democratic Republic of Congo

Globally, forests influence climate change through complex, often nonlinear, forest-atmosphere interactions, such as carbon sequestration, decreased surface temperature through reduced solar irradiance and evaporative cooling. Likewise, climate change impacts forests in myriad ways, including shifts in plant phenology, changes in ecosystem productivity, and alterations in the geographic distribution of plant species. Trees are thus a unique living document of past and current climatic influences. The UNESCO biosphere reserves Yangambi and Luki are situated within the Congo Basin rainforest, which is the second largest rainforest in the world and presently a persistent carbon sink. Given its role as mitigator for global warming, reliably predicting how the Congo Basin rainforest will respond to climate change is key. Such predictions are complicated, however, by an apparent lack of eco-climatological baseline data for Central Africa. This data gap reflects the inaccessibility of such data, not the unavailability. In fact, forestry research in the Democratic Republic of Congo dates back to 1937, when the Institut National pour l’Etude Agronomique du Congo Belge (INEAC) created its Forestry Division. Particularly noteworthy are the long series of unpublished detailed phenologicalobservations and daily climatological data records, both of which are unique on a global scale. Historical collections, located at the Royal Museum for Central Africa, the Botanic Garden Belgium, the National Belgian Archives, and in local herbaria in the DRC, provide data and insight into the dynamics of tropical forests and their resilience after disturbance. Here we report on current efforts to digitise and valorize data from forestry research carried out in the DRC between 1900-1960. We will address in particular the creation of the Forestry Division, as recorded in archival documents. We will also present an overview of the methodologies used by INEAC to collect phenological observations of trees, and arboreal samples

Contributions of the Belgian Congo archives to contemporary research questions

Agricultural Research in the Democratic Republic of Congo, Rwanda and Burundi dates back to the beginning of the Belgian colonization (1901-1960). Initially, state plantations and experiment stations were built throughout the Belgian territories. In 1933, these facilities were expanded with the creation of INEAC (Institut National pour l’Etude Agronomique du Congo Belge, 1933 – 1962). The INEAC headquarters were based at Yangambi on 25.000 ha, surrounded by a 200.000 ha reserve. The data archives are diverse, with a large temporal and geographical spread. They include daily weather records, specific observations of seasonal changes in forest growth, countless herbarium specimens and detailed photographic documentation. With a network of 36 research stations spread across the three territories, INEAC was the largest tropical agricultural research institute in Africa until 1960. In 1962, following independence, INEAC was abruptly disbanded. Today the INEAC archives are stored in three Belgian institutes: the Botanic Garden of Meise, the Royal Museum for Central Africa and the National Archives of Belgium. The agronomic, climatic, biodiversity and edaphic legacy data hold great potential and relevance for current and future applied and basic research in the Congo Basin and Albertine Rift. Their scientific value resides in the extent of the data collected in a region where the availability of reliable baseline measurements are practically absent. By their nature, the archives also invite a re-interpretation of our colonial heritage, through the revelation of sometimes controversial histories, such as the life story of Panda Farnana

Climate data rescue from the Belgian colonial archives : helping to close the data-gap over Central Africa

During the first half of the twentieth century, climate data was rigorously collected throughout the Belgian Congo. Yet today this data is practically absent from (international) data repositories and not included in (re-analysis) climate models. The historical archives of La régie des plantations de la colonie (REPCO) and the Institut National d’Etudes Agronomique du Congo Belge (INEAC) archives hold vast amounts of (eco-) climatological data, with great potential and relevance for basic and applied research in the central Congo Basin. They are currently stored at the State Archives of Belgium, the Royal Museum for Central Africa and the Botanic Garden Meise in Belgium. In 2017, the “Congo basin eco-climatological data recovery and valorization” (COBECORE) 4-year project was launched with the aim to valorize this legacy data by making it accessible for contemporary research through computer vision, machine learning and citizen science approaches. Here we report on the completion of scanning activities during the first year of data recovery for 575 climatological stations spread throughout the Congo Basin, equivalent to 4300 site-years (50 000 scans). We provide an overview of the climate stations where this data was collected during colonial times, as well as the parameters and timeframe for which we have data

Century‐long apparent decrease in iWUE with no evidence of progressive nutrient limitation in African tropical forests

Forests exhibit leaf- and ecosystem-level responses to environmental changes. Specifically, rising carbon dioxide (CO2) levels over the past century are expected to have increased the intrinsic water-use efficiency (iWUE) of tropical trees while the ecosystem is gradually pushed into progressive nutrient limitation. Due to the long-term character of these changes, however, observational datasets to validate both paradigms are limited in space and time. In this study, we used a unique herbarium record to go back nearly a century and show that despite the rise in CO2 concentrations, iWUE has decreased in central African tropical trees in the Congo Basin. Although we find evidence that points to leaf-level adaptation to increasing CO2-that is, increasing photosynthesis-related nutrients and decreasing maximum stomatal conductance, a decrease in leaf delta C-13 clearly indicates a decreasing iWUE over time. Additionally, the stoichiometric carbon to nitrogen and nitrogen to phosphorus ratios in the leaves show no sign of progressive nutrient limitation as they have remained constant since 1938, which suggests that nutrients have not increasingly limited productivity in this biome. Altogether, the data suggest that other environmental factors, such as increasing temperature, might have negatively affected net photosynthesis and consequently downregulated the iWUE. Results from this study reveal that the second largest tropical forest on Earth has responded differently to recent environmental changes than expected, highlighting the need for further on-ground monitoring in the Congo Basin