We are studying the factors of spatial distribution of light-demanding tree species in an undisturbed natural forest to contribute to the elucidation of the enigma of the persistence of light-demanding tree species in the canopy of the Congo Basin rainforests. Our objective was to analyze the current spatial distribution combined with the spatial autocorrelation of light-demanding stems species and to carry out a Canonical Correspondence Analysis (CCA) to discuss the role that different factors may have played in determining the observed spatial pattern. These species were subdivided into three regeneration guilds, based on their growth speed and longevity: short-lived pioneer (SLP), long-lived pioneer (LLP), and non-pioneer light-demanding (NPLD) species. We also compared the distribution of these species to that of Gilbertiodendron dewevrei, a typical extremely aggregative and locally hyperdominant shade-tolerant species. For this purpose, we carried out a selective inventory of all stems (at least 10 cm DBH) of light-demanding species in the forest around the Moni River, an area rich in individuals of light-demanding species. This inventory was carried out along eight transects equidistant by 450 m. The total length of these transects was 50.125 km (an area of 250.625 ha). The sampling units consisted of contiguous plots (200 m x 50 m) centered on the transect (long side parallel to the transect). Each plot was divided into 8 sub-plots of 25 m x 50 m. The parameters directly measured in the field were diameter at breast height (DBH), wetland indicators, topography, and slope. The last three parameters were measured in each sub-plot. The wetland indicators were spring, stream (stream 1 to about 3 m wide that can be forded), river (stream more than 3 m wide and that cannot be forded), temporary or periodically flooded swamp, permanent swamp, and absence of wetland. The modalities of the topography parameter were ridge, plateau, slope break, upward slope, downward slope, and lowland. The slope was measured using the SUUNTO clinometer. The longitude and latitude were deduced from the Cartesian coordinates (X and Y) of each tree, which were measured directly during the inventory. The altitude and distance from the nearest watercourse were deduced from the Geographic Information System (GIS). The altitude was derived from the digital terrain model of the Yangambi region, while the distance to the nearest watercourse was derived from a distance to watercourses map of the Yangambi region.

Data F1 Spatial Analysis, column headings correspond to:

Tag No.: unique number written on an aluminium tag nailed to the tree.

Transect: identification of the transect in all the transects.

Segmented transect: Segment of the transect that starts from the Moni river. This river divides each transect into two. Segment A is east, and Segment B is west.

Plot: number of the inventory plot.

Subplot: number of the inventory subplot.

Regeneration guild: SLP, short-lived pioneer species, LLP, long-lived pioneer species, and NPLD, non-pioneer light-demanding species.

POM (m): Point of Measurement expressed in meters.

DBH (cm): Diameter at breast height expressed in centimeters.

Long (m): longitude of the tree expressed in meters.

Lat (m): latitude of the tree expressed in meters.

Data F2 and F3; columns correspond to:

Transect: identification of the transect in all the transects.

Segmented transect: Segment of the transect that starts from the Moni river. This river divides each transect into two. Segment A is east, and Segment B is west.

Plot: number of the inventory plot.

Subplot: number of the inventory subplot.

Slope: slope of the subplot (measured on the transect with the SUUNTO clinometer) expressed in percentage.

DistanceMilHum: distance in meters between the tree and the nearest watercourse.

MilHum: wetland indicator.

Topo: topography in the subplot.

Altitude: altitude in meters of the subplot

The remaining columns concern either the abundance of each regeneration guild (Data F2) or the abundance of each species (Data F3).