Productivité herbacée des savanes de la Cuvette congolaise (Congo-Brazzaville)

La savane à Hyparrhenia diplandra Stapfet celle à Loudetia simplex C.E. Hubbard ont été étudiées dans la Cuvette congolaise (Nord du Congo-Brazzaville), sur le plan de la production herbacée. Les sites retenus pour l’étude sont Ollombo, Owando et Makoua. L’étude a démarré à partir des feux de la saison « sèche ». L’objectif de cette étude était d’évaluer la phytomasse aérienne herbacée et sa productivité, en vue d’aider à la prise de décision sur le choix des espaces à occuper pour des activités agricoles et pastorales. Laphytomasse aérienne herbacée a été mesurée par la méthode de la récolte et sa productivité primaire nette réelle par la méthode de la différence entre le moment où la phytomasse est maximale et le moment où elle est minimale dans un cycle annuel. Les échantillons de sols ont été prélevés sous ces deux types de savanes. Leurs analyses granulométrique et chimiques révèlent que ces sols sont dans l’ensemble très sableux, acides et pauvres en matière organique. Le taux en argiles est légèrement supérieur dans le sol sous savane à H. diplandra (jusqu’à 14%) que dans celui sous savane à L. simplex (1% au maximum). La phytomasse aérienne totale maximale est enregistré à dix mois après les feux, en mai : 9,48 – 10,44 t MS ha-1 pour la savane à H. diplandra et 3,43 – 4,52 t MS ha-1 pour la savane à L. simplex. La productivité de la phytomasse varie de 9,29 – 10,04 t MS ha-1an-1 pour la savane à H. diplandra et de 3,09 – 4,64 t MS ha-1an-1 pour la savane à L. simplex. La savane à H. diplandra serait donc à recommander pour des activitésagricoles et pastorales que celle à L. simplex.Mots-clés : savanes, sols, phytomasse, strate aérienne herbacée, productivité, cuvette congolaise.Productivity of Congolese Basin savannas (Congo-Brazzaville)The Hyparrhenia diplandra Stapf and the Loudetia simplex C.E. Hubbard savannas have been studied in the Cuvette congolaise (the North of Congo-Brazzaville) on the herbaceous production level. The selected sites for this research are: Ollombo, Owando and Makoua. The study started with the fires of the dry season. The objective of this survey was to evaluate the aerial herbaceous phytomass and its productivity, in order to help the decision taking concerning the choice of the areas for agricultural and pastoral activities. Theherbaceous aerial phytomass has been examined within the harvesting framework and the net primary productivity of the phytomass is determined by the method of difference between the time when the phytomass is maximal and when it is minimal in an annual cycle. The soil samples have been taken from these two types of savannas. The granulometric and chemical analyses of soils reveal that the soils of the studied savannas are generally very sandy (79, 94-98, 38 %), acidic and poor in organic materials. The clay rate is slightly superior in the soil of the H. diplandra savanna (up to 14%) than in that of L. simplex (1% maxi). The maximal total aerial phytomass is recorded ten months after the fires, in may: 9, 48-10, 44 t MS ha-1 for H. diplandra savanna and 3, 43-4, 52 t MS ha-1 for L. simplex savanna (Figures 1 and 2). The phytomass productivity varies from 9, 29-10, 04 t MS ha-1an-1 for H. diplandra and from 3, 09-4, 64 t MS ha-1 an-1 for L. simplex. The H. diplandra savanna is more productive than the L. simplex savanna. The former should be recommended for agricultural and pastoral activities than the latter.Keywords : savannas, soils, phytomass, herbaceous aerial stratum, productivity, congolese cuvette

Évaluation de la diversité floristique en herbacées des savanes de la cuvette congolaise (République du Congo)

Les savanes de la République du Congo sont exploitées pour des fins agricoles et pastorales. Dans la Cuvette congolaise (nord du Congo), les savanes sont encore peu étudiées. La gestion durable de ces savanes nécessite leur connaissance sur le plan floristique. C’est ainsi qu’une étude floristique a été menée dans les savanes de la zone. Elle avait pour objectif d’évaluer l’intérêt pastoral des savanes de cette cuvette. A cet effet, des relevés floristiques ont été réalisés par la méthode des points quadrats alignés, afin d’inventorier la diversité floristique et les principales espèces fourragères. Ainsi, 37 espèces réparties en 33 genres et 10 familles ont été recensées dans la savane à Hyparrhenia diplandra (Hack.) Stapf , et 27 espèces réparties en 22 genres et 8 familles dans la savane à Loudetia simplex (Nees) C.E. Hubbard. Dans l’ensemble, les familles les plus riches en espèces étaient les Poaceae, les Fabaceae et les Cyperaceae. L’indice de diversité de Shannon et l’équitabilité de Piélou avaient des valeurs moyennes de 2,23 bits et 0,57 pour la savane à H. diplandra, et entre 2,1bits et 0,61 pour la savane à L. simplex. Il y a donc une diversité floristique non négligeable, dans ces savanes. Elle varie en fonction des stations d’étude et des phytocénoses. Une gestion planifiée de ces formations permettrait d’assurer une meilleure planification pour des fins pastorales.Mots-clés : savanes, phytodiversité, herbacée, pastoralisme, cuvette congolaise.Evaluation of herbaceous floristic diversity of Congolese basin savannahs (Republic of Congo)The savannas of the Republic of Congo are exploited for agricultural and pastoral. In the Congolese Basin (northern Congo), savannas are still poorly studied. Sustainable management of these savannas requires knowledge in terms of flora. Thus, a floristic study was conducted in the savannah area. It aimed to assess the value of pastoral savannas of the basin. To this end, the floristic surveys were conducted by the method of quadrat points aligned to inventory plant diversity and major forage species. Thus, 37 species, 33 kinds and 10 families were identified in the savannah of Hyparrhenia diplandra (Hack.) Stapf and 27 species, 22 kinds and 8 families in the savannah of Loudetia simplex (Nees) CE Hubbard. Overall, the richest families in species were Poaceae, Fabaceae and the Cyperaceae. The Shannon diversity index and equitability of Pielou had average values of 2.23 bits and 0.57 for the savannah of H. diplandra, and between 2.1 bits and 0.61 for the savannah of L. simplex. So there is substantial plant diversity in these savannas. It varies from study sites and phytocenoses. Planned management of such training would ensure better planning for pastoral purposes.Keywords : savannas, plant diversity, herbaceous, pastoralism, congolese basin

Adaptation d’un cultivar de Niébé (Vigna unguiculata (L.) Walp.) aux conditions pédoclimatiques de Boundji (République du Congo)

L’étude réalisée sur un cultivar de niébé dans la zone de Boundji en République du Congo se justifie par la recherche des plantes fourragères à utiliser pour l’amélioration des pâturages. L’objectif de cette étude estd’avoir des données préliminaires sur la croissance et la production de ce cultivar de niébé en rapport avec les conditions pédoclimatiques de la zone. Le pouvoir germinatif des graines a été évalué, avant le semis etaprès la récolte. Le semis a été fait en ligne sur des buttes avec un espacement de 75 cm x 50 cm. Les résultats obtenus montrent que le niébé a un bon pouvoir germinatif (92 %), la croissance est normale, laproduction foliaire moyenne est bonne à deux mois après le semis (888 kg/ha) et celle de graines sèches récoltées à trois mois est faible (184 kg/ha). Ce cultivar s’adapte bien aux conditions écologiques de la zone.La production élevée de feuilles pourrait faire de ce cultivar une plante fourragère à prendre en compte dans des programmes d’aménagement des pâturages au Congo et ailleurs.Mots-clés : Niébé, croissance, production foliaire, production en graines, zone de Boundji

Hyphenated living: between longing and belonging, an exposition of displacement as liminality in the transnational condition

This thesis explores a complex concept of home with respect to issues of belonging and displacement from both a personal and transnational1 perspective, which deals with the here in New Zealand and there in the Netherlands. Through the visual and the poetic, in printmaking, book art, digital photography and installation--drawing on auto-biographical experiences of migration, as well as contextual research--I have been investigating the concept of "home" as a hyphen. This hyphen motif aptly performs the migrant condition of between here and there, a liminal space of betweenness and transition, where internal and external worlds, here and there, past and present, intersect. This intersection point, marked by hyphenation, always performs across multiple borders and thereby emphasises a spatial-temporal liminal register experienced by many transnational. In textual practice a hyphen is a punctuation sign that connects and separates two different entities. As such, here the hyphen begins to evoke an interesting spatial-temporal paradigm for transnational, who are placed between two or more divided geographies, sociographies and cultural identities. As well as being a link between multiple series of dual entities and conditions, the hyphen can simultaneously signify an ambiguous area of liminality--a psychological space of neither here nor there, an undecidability of identity and belonging, which, on various levels, is symptomatic for many transnational. This project explores how this hyphenated position influences a sense of identity and belonging and its relation to our postmodern world

Above-ground carbon stocks, species diversity and fire dynamics in the Bateke Plateau

Savannas are heterogeneous systems characterised by a high spatial and temporal variation in ecosystem structure. Savannas dominate the tropics, with important ecological functions, and play a prominent role in the global carbon cycle, in particular responsible for much of its inter-annual variability. They are shaped by resource availability, soil characteristics and disturbance events, particularly fire. Understanding and predicting the demographic structure and woody cover of savannas remains a challenge, as it is currently poorly understood due to the complex interactions and processes that determine them. A predictive understanding of savanna ecosystems is critical in the context of land use management and global change. Fire is an essential ecological disturbance in savannas, and forest-savanna mosaics are maintained by fire-mediated positive feedbacks. Over half of the world’s savannas are found in Africa, and over a quarter Africa’s surface burns every year, with fires occurring principally in the savanna biome. These have strong environmental and social impacts. Most fires in Africa are anthropogenic and occur during the late dry season, but their dynamics and effects remain understudied. The main objective of this research is to understand the floristic composition, carbon storage, woody cover and fire regime of the mesic savannas of the Bateke Plateau. The Bateke Plateau is savanna-forest mosaic ecosystem, situated mainly in the Republic of Congo, with sandy Kalahari soils and enough precipitation for potential forest establishment (1600 mm/yr). Despite occupying 89,800 km2, its ecology and ecosystem functions are poorly understood. This study combines two approaches: firstly experimental, setting up long term field experiments where the fire regime is manipulated, and then observational, using remote sensing to estimate the carbon storage and study the past history of the fire regime in the region. I established four large (25 ha) plots at two savanna sites, measured their carbon stocks, spatial structure and floristic composition, and applied different annual fire treatments (early and late dry season burns). These treatments were applied annually during 3 years (2015, 2016 and 2017), and the plots were re-measured every year to estimate tree demographic rates and the identification of the key processes that impact them, including fire and competition. Field data were combined with satellite radar data from ALOS PALSAR, and the fire products of the MODIS satellites, to estimate carbon stocks and fire regimes for the entire Bateke Plateau. I also analyse the underlying biophysical and anthropogenic processes that influence the patterns in Above-Ground Woody Biomass (AGWB) and their spatial variability in the Bateke landscape. The total plant carbon stocks (above-ground and below-ground) were low, averaging only 6.5 ± 0.3 MgC/ha, with grass representing over half the biomass. Soil organic matter dominate the ecosystem carbon stocks, with 16.7 ± 0.9 Mg/ha found in the top 20 cm alone. We identified 49 plant species (4 trees, 13 shrubs, 4 sedges, 17 forbs and 11 grass species), with a tree hyperdominance of Hymenocardia acida, and a richer herbaceous species composition. These savannas showed evidence of tree clustering, and also indications of tree-tree competition. Trees had low growth rates (averaging 1.21 mm/yr), and mortality was relatively low (3.24 %/yr) across all plots. The experiment showed that late dry season fires significantly reduced tree growth compared to early dry season fires, but also reduced stem mortality rates. Results show that these mesic savannas had very low tree biomass, with tree cover held far below its climate potential closed-canopy maximum, likely due to nutrient poor sandy soils and frequent fires. Results from the remote sensing analysis indicated that multiple explanatory variables had a significant effect on AGWB in the Bateke Plateau. Overall, the frequency of fire had the largest impact on AGWB (with higher fire frequency resulting in lower AGWB), with sand content the next most important explanatory variable (with more sand reducing AGWB). Fires in the Bateke are very frequent, and show high seasonality. The proportion of fires that occurred in the late dry season, though smaller predictor, was also more important than other factors (including soil carbon proportion, whether or not the savanna area was in a protected area, annual rainfall, or distance to the nearest town, river or road), with a larger proportion of late dry season fires associated with a small increase in AGWB. The results give pointers for management of the savannas of the Bateke Plateau, as well as improving our understanding of vegetation dynamics in this understudied ecosystem and help orient policy and conservation

Hyphenated living: between longing and belonging, an exposition of displacement as liminality in the transnational condition

This thesis explores a complex concept of home with respect to issues of belonging and displacement from both a personal and transnational1 perspective, which deals with the here in New Zealand and there in the Netherlands. Through the visual and the poetic, in printmaking, book art, digital photography and installation--drawing on auto-biographical experiences of migration, as well as contextual research--I have been investigating the concept of "home" as a hyphen. This hyphen motif aptly performs the migrant condition of between here and there, a liminal space of betweenness and transition, where internal and external worlds, here and there, past and present, intersect. This intersection point, marked by hyphenation, always performs across multiple borders and thereby emphasises a spatial-temporal liminal register experienced by many transnational. In textual practice a hyphen is a punctuation sign that connects and separates two different entities. As such, here the hyphen begins to evoke an interesting spatial-temporal paradigm for transnational, who are placed between two or more divided geographies, sociographies and cultural identities. As well as being a link between multiple series of dual entities and conditions, the hyphen can simultaneously signify an ambiguous area of liminality--a psychological space of neither here nor there, an undecidability of identity and belonging, which, on various levels, is symptomatic for many transnational. This project explores how this hyphenated position influences a sense of identity and belonging and its relation to our postmodern world

Évaluation du profil minéral des èspeces fourragères et de la capacité de charge des savanes de la Cuvette congolaise (République Du Congo)

Les potentialités fourragères ont été évaluées dans la Cuvette congolaise, à partir des teneurs en éléments minéraux des fourrages et de la capacité de charge des savanes au Nord du Congo (Ollombo, Boundji, Owando, Makoua). Les échantillons de fourrages ont été récoltés dans des parcelles retenues dans chaque type de savanes puis analysés pour leur  composition minérale. La capacité de charge de chaque savane a été évaluée à partir de la phytomasse maximale. Les résultats obtenus  montrent que les espèces fourragères de la Cuvette congolaise sont dansl’ensemble riches en Mg (1,42-4,28 g/kg, pour Hyparrhenia diplandra et 1,51-2,37 g/kg, pour Loudetia simplex), K (5,67-11,6 g/kg, pour H. diplandra et 6,00-9,85 g/kg, pour L. simplex), Mn (83,3-121 mg/kg, pour H. diplandra et 61,2-131 mg/kg, pour L. simplex) et Fe (160-657 mg/kg, pour H. diplandra et 103 mg/kg pour L. simplex), car les valeurs trouvées sont au dessus des normes. Ces teneurs peuvent satisfaire les besoins de croissance et de reproduction des bovins et non ceux de production de lait. Une complémentation minérale est donc nécessaire dans la gestion de l’élevage dans cette zone. La charge de 1,21 ± 0,52 ha/UBT/an est la charge théorique moyenne que peuvent supporter les savanes étudiées.Mots clés : Savanes, fourrages, éléments minéraux, capacités de charge, Cuvette congolaise.EVALUATION OF MINERAL PROFILE OF FORAGE AND CARRYING CAPACITY OF SAVANNAHS CONGOLESE BASIN (REPUBLIC OF CONGO)The forage potentialities have been evaluated in Congolese Basin using mineral profile of forages and carrying capacity of savannahs in Ollombo, Boundji, Owando and Makoua from the northern of Congo. The forage samples were collected from selected plots in each type savannah and analyzed for their mineral composition. The carrying capacity of each savannah has been evaluated from the maximal phytomass. Result showing that the forages of the Congolese Basin are rich in magnesium(1.42 to 4.28 g / kg, for Hyparrhenia diplandra and 1.51 to 2.37 g / kg, for Loudetia simplex), potassium (5.67 to 11.6 g / kg, for H. Diplandra and 6.00 to 9.85 g / kg, for L. simplex), manganese (83.3 to 121 mg / kg for H . diplandra and 61.2 to 131 mg / kg for L. simplex) and iron (160-657 mg /kg for H. diplandra and 103 mg / kg for L. simplex), because the values are found above the norms. These levels can meet the needs of growth and reproduction of cattle and not those of milk production. A mineral supplement is therefore relevant for the management of breeding in this area. The carrying capacity of 1.21 ± 0.52 ha / TLU / year is the theoretical average than savannas can withstand studied.Keywords : Savannahs, forages, mineral contents, carrying capacity, Congolese Basin

Analyse De La Diversite Floristique Du Sous-Bois De La Palmeraie De Mbobo Dans La Cuvette Congolaise (Republique Du Congo)

Dans la Cuvette congolaise, les palmeraies sont implantées dans des zones forestières pour des besoins d’huile de palme. Cependant, leur sous-bois connait une exploitation limitée comme pâturage et sa diversité floristique n’est pas assez connue. C’est ainsi que la présente étude a été réalisée avec pour objectif général d’évaluer l’intérêt pastoral du sous-bois de la palmeraie de Mbobo. Spécifiquement il s'agit de : (1) inventorier la diversité floristique ; (2) identifier les espèces fourragères. L’inventaire floristique a été réalisé par la méthode de transects et la diversité floristique évaluée à partir des indices de diversité de Shannon-Weaver et d’équitabilité de Pielou. Les résultats obtenus montrent que le sous-bois de la palmeraie de Mbobo présente 93 espèces réparties en 76 genres et 39 familles, sur une superficie de 900m2 représentant l'ensemble des trois parcelles prospectées. Les espèces fourragères représentent 25 % de l'ensembles des espèces recensées. Elles sont dominées par les Poaceae et les Cyperaceae. Les indices de diversité (4,8-5) et de régularité (0,6-0,9) sont très élevés. Le sous-bois de la palmeraie présente donc une richesse floristique élevée et une qualité fourragère importante qui permettrait de l’exploiter comme pâturage.Mots clés : Cuvette congolaise, palmeraie, sous-bois, diversité floristique, pâturageIn the Congolese Basin, the palm groves are located in forest areas for oil palm production. However, their undergrowth knows as limited for grazing and their floristic diversity is not well known. Thus, the present study whose main objective was to assess the pastoral value of undergrowth of palm grove of Mbobo was conducted. The specific objectives were to: (1) inventory the floristic diversity, (2) identify the forage species. The floristic inventory was performed by the transect method and plant diversity was estimated by the Shannon-Weaver index and Pielou evenness index. The forage species were identified by the food tracking sheep in the palm grove. The undergrowth vegetation of the palm grove of Mbobo is composed of 93 species in 76 genus and 39 families. The most representative families in number of species are Poaceae (10 %), Fabaceae (7 %), Rubiaceae (7 %), Verbenacea (7 %), Cyperaceae (5 %) and Malvaceae (5 %). Forage species represent 25 % and are dominated by Poaceae and Cyperacea. Diversity (0.6 - 0.9) and evenness (4.8 - 5) indices are very high. The undergrowth of this palm grove exhibits a high floristic diversity and important forage quality, and it could therefore be exploited as pasture. Forages spcies could be introduced under the palm grove to encourage the development of agropastoralism.Key words : Congolese Basin, palm grove, undergrowth, plant diversity, grazingArticle in Frenc