Historical tree phenology data reveal the seasonal rhythms of the Congo Basin rainforest

Tropical forest phenology directly affects regional carbon cycles, but the relation between species-specific and whole-canopy phenology remains largely uncharacterized. We present a unique dataset of historical tropical tree phenology collected in the central Congo Basin, before large-scale impacts of human-induced climate change.

Historical data was recovered from a phenological study carried out between 1937 and 1956 in the central Congo Basin at the Yangambi Research Station (N00°48’, E24°29’) in what is now the Democratic Republic of Congo (DRC). The data were retrieved from the archives of the INERA (Institut National pour l'Etude et la Recherche Agronomique) herbarium at the Yangambi Research Station.

Ground-based phenological observations of local tropical trees were made four times each month on a rotating schedule (resolution of 7.2 days on average) from 1937 until 1956 by the forestry division of the INEAC (Institut National pour l'Étude Agronomique du Congo). The sampling protocol was recovered at the State Archives of Belgium, including details on the observation methods, the observational routes and the training and schedules of the observers. Canopy leaf senescence was defined as a distinct period during which leaves fall and trees remain bare, while canopy turnover was defined as a period during which leaf-fall comes in peaks with concomitant flushes of new leaves (INEAC archives). Summarised data sheets of these long-term observations were digitized using 12 MP resolution cameras. The hand-written notes and annotations depicting phenophases during the observational period were digitized to binary data (yes or no phenophase event at each time-step) through an online citizen science project ‘Jungle Rhythms’ (Hufkens & Kearsley 2023, https://www.zooniverse.org/projects/khufkens/jungle-rhythms). 

A selection of species found in the historical forest inventories (Pierlot 1966) are presented, representing 96.0% of the basal area within these inventories. The phenological data comprises 668 individuals covering 140 species (representing 112 genus and 38 families) for a total of 5011 individual observation years (overview of species in Supplementary Table S1). We did not include individuals that were only identified to genus-level.

This data accompanies the publication ‘Kearsley, E., Verbeeck, H., Stoffelen, P., Janssens, S. B., Yakusu, E. K., Kosmala, M., De Mil, T., Bauters, M., Kitima, E. R., Ndiapo, J. M., Chuda, A. L., Richardson, A. D., Wingate, L., Ilondea, B. A., Beeckman, H., van den Bulcke, J., Boeckx, P., & Hufkens, K. (2024). Historical tree phenology data reveal the seasonal rhythms of the Congo Basin rainforest. Plant-Environment Interactions, 5, e10136. https://doi.org/10.1002/pei3.10136’.

ReferencePierlot, R. (1966). Structure et composition de forêts denses d’Afrique Centrale, spécialement celles du Kivu. Academie Royale des Sciences d’Outre-Mer. Classe des Sciences naturelles et medicales. N.S. XVI-4, Bruxelles, p. 367.