The Ethnography of Landscape: GIS and Remote Sensing in the Study of Forest Change in West African Guinea Savanna

In this paper we explore the application of Amazonian forest change models to the Guinea savanna environment of western Africa. In particular, we examine recent research documenting the growth of peri-village forest islands in the area of Kissidougou, Guinea, which purports to challenge the pervasive view of Guinea savanna deforestation brought about by human activity. As a more systematic approach to the analysis of human/environmental interactions, we propose an "ethnography of landscape," in which the findings of detailed, local ethnographic and ecological case studies are combined with remotely sensed information on what the wider region looks like as it changes over time. In pursuing this research, we employ aerial photography and Geographic Information Systems (GIS) techniques to examine our study area of Kilimi in northwestern Sierra Leone. We show that a Kissidougou-type model of peri-village forest island growth is not applicable to this region, where other environmental change processes are underway. In future work, we propose to employ Landsat satellite image archives to examine, monitor, and compare processes of ecological change throughout the Guinea savanna. [deforestation, ecological anthropology, remote sensing, Sierra Leone, West Africa]     

Climate, life forms and species distribution on the Loma Montane grassland, Sierra Leone

The Loma Mountains (2090 m), situated in lowland south Guinea savanna in Sierra Leone, are shown to have a cooler and more mesic climate than the savanna region. A temperature lapse rate of 7.5^o C/1000 m is calculated using means for the dry, dry/wet, wet and wet/dry seasons of the year. In the montane grassland the life forms of the species are predominantly hemicryptophytic, and the biological spectrum is closer to that of temperate grasslands than to the savanna type, although the adverse conditions are still dry-season drought and fires. The phytogeographical distribution of the flora indicates a 44% widespread, truly montane to montane/savanna element and a 43% West African endemic element. In the Guinean highlands, the Loma/Tingi group shows about 10% disjunction of its grassland flora with other African mountains outside West Africa.     

Serpulids on living Eocene larger foraminifer <Emphasis Type="Italic">Discocyclina</Emphasis>

About 70% of the groundnut (Arachis hypogaea L.) produced in Ghana is from the Guinea savanna. However, low soil nutrients, especially N, together with erratic rainfall distribution have often resulted in poor grain yield. The aim of this study was to evaluate plant growth, N₂-fixing efficiency, N contribution, water-use efficiency and pod yield of 21 elite groundnut genotypes in the Guinea savanna of Ghana, using the ¹⁵N natural abundance technique. The data revealed significant variations in plant growth, symbiotic N contribution, and pod yield among the 21 genotypes tested at each field site. Average N contribution by groundnut genotypes ranged from 48 to 108 kg N ha^?1. Also, mean pod yield ranged from 0.58 to 2.1 t ha^?1. Genotypes ICGV-IS 08837, ICG 6222, ICGV 03315 and NKATIESARI demonstrated superior plant growth, symbiotic N contribution and greater pod yield. In fact, ICGV-IS 08837 yielded almost 2.5 fold more than CHINESE which is the most widely cultivated variety in the region. Genotypes ICGV-IS 08837, ICG 6222, ICGV 03315 and ICGV 99247 are therefore recommended for development into varieties for the Guinea savanna of Ghana. Genotypes ICG (FDRS) 4, ICGV00362 and ICGV99247 exhibited increased water-use efficiency, but were low in N₂ fixation and N contribution, and would therefore be good parental material in breeding programs aimed at enhancing water-use efficiency in high N₂-fixing genotypes.     

Reproduction and growth in three species of West African fruit bats

This study outlines the reproduction periods of the African fruit bats Epomops buettikoferi, Epomophorus garnbianus , and Micropteropus pusillus at two West African savanna sites: a wet southern Guinea savanna and a drier southern Sudanese savanna. At both sites the two annual birth periods were timed such that both lactation by only one weaning period coincided with the rainy season peaks in fruit availability. On this basis we propose that lactation rather than weaning was the important determinant of the timing of reproduction. There was no evidence of cycling of testes size in males corresponding with the seasonal mating periods. E. buettikoferi and M. pusillus females mated at six months and gave birth at the age of 12 months. Males of the two species reached puberty by 11 months and seven months, respectively. Growth rates did not differ between cohorts growing through the wet and dry season and E. buettikoferi and M. pusillus grew at rates of 276 mg/day and 116 mg/day, respectively.     

Swidden cultivation in forest and savanna in lowland southwest Papua New Guinea

Ecological aspects of traditional swidden cultivation by Bine- speaking groups in wetland areas of lowland southwest Papua New Guinea are examined. A notable feature of the area is the coexistence of extensive, polycultural forest cultivation and more intensive, specialized savanna cultivation. Both agrosystems occur on soils of inherently similar properties. The savanna vegetation is secondary in character and, once established, is better suited to more intensive swidden cultivation based on taro (Colocasia esculenta). The agrosystems in question represent stages in the local development of agriculture, and, although multiple causes of intensification may be involved, the study confirms that lowland, as well as highland, areas of New Guinea have provided development opportunities for traditional cultivators.     

Structure, floristic composition, and vegetation forming factors of three vegetation types in Senegal

Six 1 ha plots were established in a coastal savanna, called Fathala Forest, in Delta du Saloum National Park, Senegal. Two plots were placed in woodland, two in wooded grassland, and two in transition woodland in order to describe structure and floristic composition of the vegetation. All trees ≥ 5 cm dbh were sampled. The three selected vegetation types showed distinct differences in structure as well as in species composition. Woodland had high density (440–449 individuals per ha), many small trees, and high basal area (13.4 m²per ha). Transition woodland was characterised by low density (54–118 individuals per ha) but many large trees and a relatively large basal area (8.6–12.8 m² per ha). Wooded grassland was characterised by medium sized trees, it had low density (86–102 individuals per ha) and low basal area (3.8–5.7 m² per ha). Species richness ranged between 17 and 27 species per ha in the six plots. Only two species were found in all plots, Daniellia oliveri (Caesalpiniaceae) and Prosopis africana (Mimosaceae). Legumes dominated all plots. Wooded grassland and transition woodland had many characteristics of fire-affected vegetation in contrast to woodland. Today wooded grassland encroaches on woodland and transition woodland. Management of the latter two vegetation types should be given priority as they maintain structural and floristic characteristics that are essential to conserve biodiversity and original features of the vegetation, and they are also important for local people who are allowed to make sustainable use of the vegetation.     

A Holocene record of savanna vegetation dynamics in southern lowland Papua New Guinea

Vegetation History and Archaeobotany - The southern lowlands of Papua New Guinea (PNG) are biogeographically distinct. Vast tracts of savanna vegetation occur there and yet most palaeoecological...     

A survey of the vegetation in Zaria Province,N. Nigeria

Summary Eighteen plant associations characteristic of the Northern Guinea savanna in N. Nigeria are described from Zaria Province.The dominance of the species in each association is assessed on the Domin scale.The inter-relationships between the associations are discussed with reference to the geomorphological features of the area and the availability of water. There is a clear distinction between the northern and southern parts of the area and the possibility of defining an upper and lower Northern Guinea zone is considered.     

Vegetation history of the savanna corridor between the Guinean and the Congolian rain forest during the last 150,000 years

Pollen and spores from a deep-sea core located west of the Niger Delta record an uninterrupted area of lowland rain forest in West Africa from Guinea to Cameroon during the last Interglacial and the early Holocene. During other periods of the last 150 ka, a savanna corridor between the western — Guinean — and the eastern — Congolian — part of the African lowland rain forest existed. This so-called Dahomey Gap had its largest extension during Glacial Stages 6, 4, 3, and 2. Reduced surface salinity in the eastern Gulf of Guinea as recorded by dinoflagellate cysts indicates sufficient precipitation for extensive forest growth during Stages 5 and 1. The large modern extension of dry forest and savanna in West Africa cannot be solely explained by climatic factors. Mangrove expansion in and west of the Niger Delta was largest during the phases of sea-level rise of Stages 5 and 1. During Stages 6, 4, 3, and 2, shelf areas were exposed and the area of the mangrove swamps was minimal.     

Seasonal variation in the protein content and the grazing of some tropical savanna grasses

This paper presents the effects of seasonal variation on the protein contents of four grass species examined in the experimental fire plots at Kainji Lake National Park in the Northern Guinea savanna zone of Nigeria. Also reported is the proportion of grass utilized on year-long basis. Tropical savanna grasses generally have higher protein contents at the beginning of the growing season than at the end when they become tall, coarse and unpalatable. It is also shown that the percentage of grass species utilized by game follow the seasonal changes in their protein contents; utilization being highest when the protein content of grass is optimum. It is stressed that trees, shrubs and forbs should not be totally eliminated from grazing lands because of the great contribution they make to animal feeding during the dry season when the grasses become dry and coarse with low nutritive value.     

Periodicity of Wood Formation in Twigs of some Tropical Trees in Nigeria

The periodicity of wood formation was studied in twigs of treesgrowing in three ecological areas in Nigeria, namely lowlandrainforest, Southern Guinea savanna and mangrove swamp. Initiationof cambial activity was correlated with bud break, and wheremultiple vegetative bud formation occurred in the lowland rainforestand the Southern Guinea savanna, the number of growth ringscorresponded with the number of times the vegetative buds opened.In the mangrove swamp, although there may be a clear correlationbetween vegetative bud growth and wood formation in 1 to 2 year-oldtwigs of Drepanocarpus lunatus and Ormacarpum verrucosum therewas no such correlation in Dalbergia ecastaphyllum. Short axillarybranches and inflorescences which developed irregularly in plantsof the mangrove swamp induced multiple growth ring formation.In D. ecastaphyllum, the pattern of unfolding of young leavesseems to play a major role in the formation of multiple growthrings. In each of the areas multiple growth ring formation couldbe induced by injury. In Daniellia oliveri there was periodicdeposition of prismatic crystals. The crystals were depositedeach time wood formation stopped. In plants in which flowersopened before the opening of the vegetative buds, there wasinitiation of cambial activity by the opened flowers in thetwigs on which the flowers were borne.     

THE RELATIONSHIP OF THE SOUTHERN NIGERIAN AVIFAUNA TO THOSE OF UPPER AND LOWER GUINEA

The composition of the forest avifauna of Southern Nigeria is analysed in the light of the most recent work in the region. It is found that east of the Niger the affinities are with Lower Guinea: at Lagos with Upper Guinea; in the Ondo-Benin area not definitely with either. A discussion of the barriers between the two sub-regions follows, and it is claimed that, whereas the Lagos-Accra savanna gap and the Cameroon montane area can each account for about one quarter of the total change, factors within Nigeria were almost twice as important in causing differentiation. It is suggested that these factors were a combination of climatic conditions and northward position of the coastline in late or post-Pliocene times, giving rise to a condition similar to that we find today between Lagos and Accra.     

Resource availability and distribution patterns, indicators of competition between Macrotermes bellicosus and other macro-detritivores in the Comoé National Park, Côte d'Ivoire

Interspecific competition has rarely been demonstrated in field studies. For it to occur a resource must be in limited supply and potential competitors must be concurrently active in time and space. We studied the availability of plant litter during the course of the year and the activity and distribution of macro‐detritivores (termites, diplopods and earthworms) in two habitats in a Guinea savanna (Côte d'Ivoire), to test whether interspecific competition might be important. Plant litter was limited during the rainy season in the savanna, but was never limited in the gallery forest. The termite Macrotermes bellicosus, the dominant macro‐detritivore in this area, and other detritivorous termites (e.g. Microtermes spp., Ancistrotermes spp., Odontotermes spp.) were active all year round with a peak during the rainy season, when diplopods and earthworms were also active. In the savanna at the beginning of the rainy season when food became limiting, other detritivorous termite species were more active in the absence of M. bellicosus than in its presence. This complementary activity pattern of M. bellicosus and other termites indicates that interspecific competition among detritivorous termites may be occurring. However, the spatio‐temporal distribution of diplopods and earthworms suggests that interspecific competition with M. bellicosus is of minor importance.     

ABUNDANCE AND SEASONALITY OF THE SAVANNA AVIFAUNA AT PORT MORESBY, PAPUA NEW GUINEA

The results of 156 transect counts carried out over 30 months in savanna of the Coastal Hill Zone, Port Moresby, Papua New Guinea, are analysed. The avifauna is depauperate compared to similar habitats in New Guinea and temperate Australia. Twelve common species of the Port Moresby savannas were not so in the Coastal Hill Zone and reasons for their rarity are given. Most species present are solely savanna forms but some are dependent upon the presence of small patches of monsoon forest. Average density of birds was estimated at 55 per 10ha, a very low figure compared to New Guinean rainforests. Carnivores and mixed-feeders make up two thirds of numbers present but frugivores, because of their large individual size, are a significant proportion of biomass. There was little significant seasonal difference in overall numbers except for granivores which decline in numbers during the wet season. However, individual species show regular seasonal fluctuations reasons for which are postulated. A correlation exists between flowering of trees and numbers of certain species, and also between the annual grass-fires and numbers of certain grassland species. Merops ornatus, Lalage sueurii and Coracina novaehollandiae, considered in the literature to be wintering migrants, are also shown to be breeding residents. Breeding records for 462 species were analysed. Most breeding of insectivores and mixed-feeders occurs in the Austral spring during the dry season and ends before the onset of heavy rains. Granivores breed in the late wet season. The few records for frugivores indicate a wet season peak.     

The distribution of two major malaria vectors, Anopheles gambiae and Anopheles arabiensis, in Nigeria.

The distribution of Anopheles gambiae and An. arabiensis across the ecological zones of Nigeria (arid savanna in the north gradually turns into humid forest in the south) was investigated. Results of the present study were compared to the distributions determined from samples of indoor-resting females reported by an earlier study over 20 years ago. Larvae were sampled in the rainy seasons of 1997 and 1999 from 24 localities, 10 of which were sampled in both years. Specimens were identified by the polymerase chain reaction method. Results showed that species composition changed significantly among the 10 localities in both years (chi2=13.62, P = 0.0002), but this change was significant in only four of the 10 localities. The identity of the prevalent (more abundant) species changed between 1997 and 1999 in only three of 10 localities. An. arabiensis was prevalent in several localities in the southern Guinea savanna, an area where it was virtually absent over 20 years ago. The data suggest that An. arabiensis has extend its range, although differences in sampling technique (larval sampling versus adult collection) can not be ruled out as a possible explanation.     

Large Bird Declines with Increasing Human Pressure in Savanna Woodlands (Burkina Faso)

The impacts of human pressure, habitat changes, and efficiency of conservation measures on the non-passerine bird community were assessed in the Sudanian belt of Burkina Faso. Three regions with increasingly large protected areas and higher conservation status were compared. In each region, natural savanna woodlands were also compared to traditionally cultivated areas. Six groups of diurnal raptors and six groups of other large bird species were counted along 167 5-km transect counts during the dry season. Within savanna woodlands, the only significant and consistent declines from the little disturbed Eastern National Parks to the more populated and exploited Western forest reserves were those of the largest terrestrial game birds (Guinea fowl, Bustard, Ground Hornbill), eagles and vultures, which became virtually extinct in the least protected areas. Although some species groups maintained substantial, if not higher populations in cultivated areas (rollers, non-game terrestrial birds, several raptors), the overall abundance of both raptor and non-raptor species declined markedly (50–65%) from natural savanna woodlands to tree-dotted cultivated and fallow fields. Again large game birds, eagles and vultures were absent from every agricultural areas censused. Yet, all of them were still commonly recorded in the same natural and cultivated areas during surveys I conducted in the same regions from 1968 to 1973. The main factors correlated with large bird extinctions or declines from national parks to mere forest reserves and from natural woodlands to fields were first related to hunting, then to habitat degradation and fragmentation through intensive cattle grazing and wood cutting and extension of cultivated areas.     

Influence of rainfall and grazing on herbage dynamics in a seasonally dry tropical savanna

Species composition and herbage dynamics in relation to rainfall variability and cattle grazing were studied in permanently protected, grazed, and temporarily fenced treatments on three sites in a seasonally dry tropical savanna. Permanently protected sites, established between 1979 and 1984, were 55–79% similar with each other in species composition, and 14–25% similar with grazed sites during the period 1986–1988. Similarity among grazed sites was only 36–43%. Number of species was greater in the grazed treatment than in the permanently protected treatment. The percentages of annual grasses and non-leguminous forbs were greater in grazed savanna than in permanently protected savanna. Species diversity was higher in grazed savanna than in the corresponding permanently protected savanna. Species the two annual cycles studied, peak live shoot biomass was 614 g m^-2 in permanently protected savanna, 109 g m^-2 in grazed savanna, and 724 g m^-2 in temporarily fenced savanna. Live shoot biomass in temporarily fenced savanna was 18 to 44% greater than in permanently protected savanna. Peak canopy biomass ranged from 342 to 700 g m^-2 in permanently protected savanna. It was related with total rainy season rainfall, and was particularly sensitive to late rainy season rainfall. On the other hand, peak canopy biomass in grazed savanna ranged from 59 to 169 g m^-2 and was related to grazing intensity rather than either total rainy season rainfall or late rainy season rainfall. Coefficient of variation of green biomass in permanently protected savanna was related with rainfall variability indicating it to be a pulsed system which responds quickly to rainfall events. Biomass of woody species ranged from 2466 to 5298 g m^-2 in permanently protected savanna and from 744 to 1433 g m^–2 in the grazed savanna. Green foliage biomass was 3.7 to 6.4% of the woody biomass in permanently protected and 5.6 to 5.9% in grazed savanna, and supplements substantially the fodder resource during the dry periods of the year.     

Edge influence on plant litter biomass in forest and savanna in the Brazilian cerrado

Edge influence, characterized by differences in ecosystem characteristics between the edge and the interior of remnants in fragmented landscapes, affects a variety of organisms and ecosystem processes. An important feature that may be affected by edges is the amount of plant litter, which provides important habitat for a large variety of organisms and influences ecological processes such as fire dynamics. We studied edge influence on plant litter and fine woody debris in the cerrado of São Paulo state, south‐eastern Brazil. We collected, sorted, dried and weighed plant litter along 180 m‐long transects perpendicular to three savanna and eleven forest edges adjacent to different anthropogenic land uses, with four to five transect per edge. There tended to be less biomass of the finer portions of fine woody debris at both savanna and forest edges. Graminoid litter at savanna edges was greater than in the corresponding interior areas, whereas other litter portions were either unaffected by edges or did not show consistent patterns in either savanna or forest. Edge influence was usually restricted to the first 20 m from the edge, was not influenced by edge characteristics and exhibited no clear differences between savanna and forest areas. Several mechanisms may have led to the variable patterns observed including variation in the plant community, plant architecture, and invasive species. The edge‐related variation in plant litter may putatively lead to, for example, increased fire frequency and intensity at the savanna edges and altered trophic dynamics at forest edges; the mechanisms and consequences of this edge influence should be addressed in future studies.     

Seasonal variation in leaf traits between congeneric savanna and forest trees in Central Brazil: implications for forest expansion into savanna

The ecology of forest and savanna trees species will largely determine the structure and dynamics of the forest–savanna boundaries, but little is known about the constraints to leaf trait variation imposed by selective forces and evolutionary history during the process of savanna invasion by forest species. We compared seasonal patterns in leaf traits related to leaf structure, carbon assimilation, water, and nutrient relations in 10 congeneric species pairs, each containing one savanna species and one forest species. All individuals were growing in dystrophic oxisols in a fire-protected savanna of Central Brazil. We tested the hypothesis that forest species would be more constrained by seasonal drought and nutrient-poor soils than their savanna congeners. We also hypothesized that habitat, rather than phylogeny, would explain more of the interspecific variance in leaf traits of the studied species. We found that throughout the year forest trees had higher specific leaf area (SLA) but lower integrated water use efficiency than savanna trees. Forest and savanna species maintained similar values of predawn and midday leaf water potential along the year. Lower values were measured in the dry season. However, this was achieved by a stronger regulation of stomatal conductance and of CO₂ assimilation on an area basis (A _area) in forest trees, particularly toward the end of the dry season. Relative to savanna trees, forest trees maintained similar (P, K, Ca, and Mg) or slightly higher (N) leaf nutrient concentrations. For the majority of traits, more variance was explained by phylogeny, than by habitat of origin, with the exception of SLA, leaf N concentration, and A _area, which were apparently subjected to different selective pressures in the savanna and forest environments. In conclusion, water shortage during extended droughts would be more limiting for forest trees than nutrient-poor soils.     

Phylogeography of the Guinea multimammate mouse (Mastomys erythroleucus): a case study for Sahelian species in West Africa

Aim To investigate the phylogeographical structure of the Guinea multimammate mouse, Mastomys erythroleucus (Temminck, 1853), a widespread murid rodent in sub‐Saharan (Sahel and Sudan) savannas, for a better understanding of the impacts of geographical and historical factors on the evolutionary history of this species, in the context of the growing database of phylogeographical studies of African savanna mammal species. Location Sahel and Sudan savannas, Africa. Methods We sequenced the whole cytochrome b gene in 211 individuals from 59 localities distributed from Senegal to Ethiopia. Sequence data were analysed using both phylogenetic (several rooted tree‐construction methods, median‐joining networks) and population genetic methods (spatial analyses of molecular variance, mismatch distributions). Results Haplotypes were distributed into four major monophyletic groups corresponding to distinct geographical regions across a west–east axis. Diversification events were estimated to have occurred between 1.16 and 0.18 Ma. Main conclusions Vicariance events related to the fragmentation of savanna habitats during the Pleistocene era may explain the phylogeographical patterns observed. Genetic structure was consistent with a role of major Sahelian rivers as significant barriers to west–east dispersal. Recent demographic expansions probably occurred during arid phases of the Holocene with the southward expansion of savannas.