Variabilité Structurale Des Peuplements D’arbres En Forêt De Montagne Du Parc National De Kahuzi-Biega Et Ses Environs, RD. Congo

This work aims to determine the change in the diametric structure, density, basal area, height and dominance of trees dbh ≥ 10 cm depending on altitude range or forest types. The study was conducted in 30 ha in Kahuzi Biega National Park and surrounding areas in DR Congo. In total, 16,797 individual trees were surveyed. The number of family, genus and species regress following the altitudinal gradient as the density increases. Mountain ecosystems in Kahuzi-Biega and its surroundings are dominated by Meliaceae, Euphorbiaceae, Moraceae, Fabaceae and Rubiaceae families. The Chi square analysis showed that the diametric structure of vegetation succession following a progressive dynamic and varies according to altitude gradient. The average basal area was 35 m²/ha. The analysis of variance (ANOVA) and post hoc Tukey test does not prove the impact of altitude on the basal area. But it becomes low in elevation due to the reduced diameter of the trees. The vertical structure was analyzed according to the classification IUFRO (International Union of Forest Research Organizations). The maximum height was 48 m and becomes lower in altitude. The tree height diameter relationship varies according altitude range so that the models H/D in this area should be developed for each forest type. We determine that the dominance of woody species following the altitude effect; only Strombosia scheffleri and Xymalos monospora dominated by its basal area, abundance and frequency of the various altitude horizons

Etude De La Variabilite Structurale Et Floristique Des Forets Sur Terre Ferme En Chefferie De Bahema-Boga (Province De L’ituri, RDC)

The knowledge of the structural and floristic variability of forest is the principal tool which makes it possible to know the floristic composition of forest in an area. This paper focuses on analyzing the structural and floristic variability between compounds of forest on firm earth in chieftainship Bahema-boga in Ituri Province in Democratic Republic of Congo (DRC). The study provides knowledge and education to those responsible for environmental protection and those who are concerned with the forest based on the floristic potential for the conservation and the sustainable management of the forests. The structure and the floristic composition vary from one forest to another. The quantity of carbon stoke also vary due to the function of structures and floristic composition of forests. The forests play an important role in the reduction of CO2. The inventories of trees whose diameter is ≥ 10 cm have allowed us to collect the data to analyze this structural and floristic variability in a sample of 3 ha (plots) of forests in firm earth. The results obtained indicate that 812 inventoried individuals (trees) are extended in 16 species, 11 kinds, and 8 famillies. The total earth surface of inventoried individuals is 32,06 m2 /ha. The species of Cynometra sessiliflora dominated those forests with 408 individuals (50,25%). The diametric class of the most  elevated inventoried plants are located between 10-20cm (63,17%). The family of the Fabaceae is better represented in those forests (73,65%)

Caractérisations Structurale, Floristique Et Biomasse Ligneuse Du Peuplement À Hagenia abyssinica Du Parc National De Kahuzi-Biega (Rift Albertin, RDC)

Hagenia abyssinica is a characteristic species of mountain forests in the Albertine Rift. In Kahuzi Biega National Park, the species is found between 2000 and 2600 m altitude. This study intended to characterize Hagenia monospecific forest by providing an account for its floristic composition, structure and biomass. Data were collected from 9 different plots of 1 hectare each located in 3 different sites (Tshivanga 2000-2250m asl; Mugabe and Kasirusiru 2400-2600m asl). Parameters including tree diameter ≥ 10cm, height, dead individuals and young shoots of Hagenia abyssinica were wetting the plot. The results showed that species richness was significantly low, varying between 8-24 species (p < 0.05, Df = 35); while the specific density was 565 ± 121 individuals. The Richness decreased with the increment of the species density of Hagenia. The similarity analysis revealed the influence/impact of the site/altitude on the species composition. The diametric structure showed a regressive dynamism within the population found between 2000 and 2200 m altitude, in which Hagenia specimens were replaced by the specimens of secondary forest species such as Sapium ellipticum, Macaranga neomilbraediana, Neoboutonia macrocalyx. Whereas, between 2400-2600 m altitude, there was a progressive dynamism with several Hagenia young shoots, with no mortality (χ2 = 487, p < 0.001). The average woody biomass was estimated at 108t / ha. This increased as Hagenia density decreased and vegetation became heterogeneous. Human disturbance and climate change effects in the region, could be the causes of variability observed in this population in the Kahuzi-Biega National Park

Contrasting nitrogen fluxes in African tropical forests of the Congo Basin

The observation of high losses of bioavailable nitrogen (N) and N richness in tropical forests is paradoxical with an apparent lack of N input. Hence, the current concept asserts that biological nitrogen fixation (BNF) must be a major N input for tropical forests. However, well-characterized N cycles are rare and geographically biased; organic N compounds are often neglected and soil gross N cycling is not well quantified. We conducted comprehensive N input and output measurements in four tropical forest types of the Congo Basin with contrasting biotic (mycorrhizal association) and abiotic (lowland-highland) environments. In 12 standardized setups, we monitored N deposition, throughfall, litterfall, leaching, and export during one hydrological year and completed this empirical N budget with nitrous oxide (N2O) flux measurement campaigns in both wet and dry season and in situ gross soil N transformations using N-15-tracing and numerical modeling. We found that all forests showed a very tight soil N cycle, with gross mineralization to immobilization ratios (M/I) close to 1 and relatively low gross nitrification to mineralization ratios (N/M). This was in line with the observation of dissolved organic nitrogen (DON) dominating N losses for the most abundant, arbuscular mycorrhizal associated, lowland forest type, but in contrast with high losses of dissolved inorganic nitrogen (DIN) in all other forest types. Altogether, our observations show that different forest types in central Africa exhibit N fluxes of contrasting magnitudes and N-species composition. In contrast to many Neotropical forests, our estimated N budgets of central African forests are imbalanced by a higher N input than output, with organic N contributing significantly to the input-output balance. This suggests that important other losses that are unaccounted for (e.g., NOx and N-2 as well as particulate N) might play a major role in the N cycle of mature African tropical forests