In total ~6000 still growing trees and lianas across ~600 species were observed for phenological purposes (Capon 1947). These obervations include the timing of flowering, fruit development and dispersion and leaf drop. The emphasis on species changed over time when observations were transferred from the botanical division (Division Botanique) to the forestry department (Division Foresterie), which retained mostly commercial species toward the end of the observation period. Many trees with observations before 1937 were cut for wood biological studies and received a database number (Tw) for the collection of Louis (appendix A). These changes over time through anthropogenic or natural causes are noted by both the non sequential nature of trees in the weekly planning (Figure 2) and the recovered data values.
The observed plants covered the wide Yangambi region from the islands in the Congo river to the plateau to the north of Yangambi (Figure 2). We identified nine key areas, mainly (1) Parc Isalowe (“Parc Forestier”), (2) along the river Isalowe, (3) around the building of the forestry division, (4) at the phyto-technical department (current abandoned buildings of the IFA), (5) near experimental sites, (6) along the river Lusambilla, (7) along roads to Yangambi from Kisangani, Isangi or NGasi (“Arbres eloignees” or far removed trees) (8) on islands of the Congo river, and (9) in front of the Yangambi reserve (Tofende, Lomondje, Tutuku, Esali). This wide distribution has considerable importances with respect to phenology as it mediates both soil properties and water availability during the dry season.
Observations of fruiting were limited to those species which drop fruit. Capon (1947) acknowledges that observations near water or fruits desirable by humans or animals (in large quantities) might be biased. Similarly, Capon further notices that spotting flowers on larger trees took considerable practice where to author felt skilled after observing roughly 3000 trees in various circumstances. In this early study by Capon geographic differences were already noted. For example, Lannea Welwitschii fruits appeared continuously on the islands in the Congo river, while on a far longer cycle in other locations.
Witboek/Livre blanc - wetenschappelijke bijdrage van België tot de ontwikkeling van Centraal-Afrika - apport scientifique de la Belgique au développement de l’Afrique centrale, 2. Sciences naturelles et médicales / Natuur- en Geneeskundige Wetenschappen. (506-956-XVI pp., 1962)