Wet Savanna Research Articles

Resource competition and fire‐regulated nutrient demand in carnivorous plants of wet pine savannas

AbstractQuestion: What are the mechanisms by which fire reduces competition for both a short‐lived and a long‐lived species in old‐growth ground‐cover plant communities of wet pine savannas (originally Pinus palustris, replaced by P. elliottii)?Location: Outer coastal plain of southeastern Mississippi, USA.Methods: I reviewed previous competition experiments and proposed a new hypothesis to explain the relationship between fire, competition, and species co‐existence in wet longleaf pine savannas. The first study is about growth and seedling emergence responses of a short‐lived carnivorous plant, Drosera capillaris, to reduction in below‐ground competition and above‐ plus below‐ground competition. The second study deals with growth and survival responses of a long‐lived perennial carnivorous plant, Sarracenia alata, to neighbour removal and prey‐exclusion to determine if a reduction in nutrient supply increased the intensity of competition in this nutrient‐poor system.Results: Fire increased seedling emergence of the short‐lived species by reducing above‐ground competition through the destruction of above‐ground parts of plants and the combustion of associated litter. Prey exclusion did not increase competitive effects of neighbours on the long‐lived species. However, because the experiment was conducted in a year without fire, shade reduced nutrient demand, which may have obviated competition for soil nutrients between Sarracenia alata and its neighbours.Conclusion: Repeated fires likely interact with interspecific differences in nutrient uptake to simultaneously reduce both above‐ground competition and competition for nutrients in old‐growth ground cover communities in pine savannas. Restoration practitioners should consider the possibility that the composition of the plant community is just as important as fire in ensuring that frequent fires maintain species diversity.

Resource competition and fire-regulated nutrient demand in carnivorous plants of wet pine savannas

Resource competition and fire-regulated nutrient demand in carnivorous plants of wet pine savannas

Rainwater Chemistry and Wet Deposition over the Wet Savanna Ecosystem of Lamto (Côte d'Ivoire)

From the IGAC-DEBITS Africa network (IDAF), data sets on precipitation chemistry collected from the ‘wet savanna ecosystem’ site of Lamto (Cote d'Ivoire), are analyzed (1995–2002). Inorganic (Ca2 +, Mg2 +, Na+, K+, NH4 +, Cl−, SO4 2 −, NO3 −) and organic (HCOO−, CH3COO−) ions content were determined using Ion Chromatography. The analyzed 631 rainfall events represent 8420.9 mm of rainfall from a 9631.1 mm total. The precipitation chemistry at Lamto is influenced by four main sources: natural biogenic emissions from savanna soils (NO x and NH3), biomass burning (savanna and domestic fires), terrigeneous particles emissions from dry savanna soils, and marine compounds embedded in the summer monsoon. The inter-annual variability of the weighted volume mean concentration of chemical species linked with wet deposition fluctuates by ∼ 20% over the period. Ammonium concentration is found to be the highest (17.6 μ eq.l− 1) from all IDAF sites belonging to the West Africa ecosystems. Ammonia sources are from domestic animals, fertilizers and biomass burning. In spite of the high potential acidity of 30.5 μ eq.l− 1 from NO3 −, SO4 2 −, HCOO− and CH3COO−, a relatively weak acidity is measured: 6.9 μ eq.l− 1. The 40% acid neutralization is explained by the acid gas – alkaline soil particles interaction. The remaining neutralization is from inclusion of gaseous ammonia. When results from Lamto, are compared with those from Banizoumbou (dry savanna) and Zoetele (equatorial forest), a regional view for wet tropospheric chemistry processes is obtained. The high concentration of the particulate phase in precipitation emphasizes the importance of multiphases processes between gases and particles in the atmospheric chemistry of the West Africa ecosystems. For example, the nss Ca2 + precipitation content, main indicator of terrigeneous particles, goes from 30.8 μ eq.l− 1 in dry savanna to 9.2 μ eq.l− 1 at Lamto and 8.9 μ eq.l− 1 in the Cameroon forest. A similar gradient is obtained for rainfall mineral particles precipitation content with contribution of 80% in dry savanna, 40% in wet savanna, and 20% in the equatorial forest.

Ethnogenesis, Regional Integration, and Ecology in Prehistoric Amazonia

This paper critically reviews reconstructions of cultural development in prehistoric Amazonia and argues for the primacy of regional and interregional exchange in generating the complex distributions of ethnolinguistic identities traced by linguists and archaeologists in the area. This approach requires an explicit abandonment of notions of migrating peoples in favor of modern anthropological understandings of ethnicity and ethnogenesis. Further, the paper discusses the significance of such a regional system perspective on Amazonian ethnogenesis for the ongoing debate on the extent of social stratification and agricultural intensification on the floodplains and wet savannas of lowland South America. It concludes that the emergence of Arawakan chiefdoms and ethnic identities in such environments after the first millennium BC signifies the occupation of a niche defined in terms of both ecology and regional exchange but also that it transformed both these kinds of conditions. In these processes, ethnicity, social stratification, economy, and ecology were all recursively intertwined.

Flora and Soils of Wells Savannah, an Example of a Unique Savanna Type

Wells Savannah is a unique wet pine savanna located in the Lower Coastal Plain of North Carolina. It consists of two utility rights-of-way and a fire-suppressed pond pine (Pinus serotina) woodland. The objectives of this study of Wells Savannah were to characterize its soils, inventory its vascular flora, and compare its soils and flora with those of reference sites. Soil drainage, texture, and redoximorphic features were described at all locations. Wetland indices were calculated to represent the degree to which the plant communities were adapted to wet substrates. We identified 209 species in 107 genera and 48 families at Wells Savannah. Eight community associations were recognized. Wetland indices for Wells Savannah were significantly lower than those for the reference savannas. The unique combination of fine textured, very wet soil and plant species composition present at Wells Savannah has not been identified in previous studies of savannas in the region.

Genotype � environment interactions in symptom development and yield of cassava genotypes with artificial and natural cassava bacterial blight infections

Thirty-seven cassava genotypes from Benin, including advanced breeding lines, were tested for their reaction to bacterial blight in the forest–savanna transition, wet savanna and dry savanna zones of Benin. Sixteen genotypes were repeated in 12 environments. In year 1998, genotypes RB92164, RB92022, TMS30572, BEN86004, RB92033 and Dangbo2, and in year 2000, genotypes RB92202, RB92151, RB92132 and TMS30572 were resistant in one ecozone. Among the more resistant genotypes, CAP94030, BEN86040, RB89509, RB92132 and TMS30572 showed low interaction across environments and were most stable in disease reaction. Ten genotypes were classified as high yielding across environments. Among the more resistant group of genotypes, only TMS30572 and RB89509 were high yielding, with RB89509 being unstable in yield across environments. Selection of genotypes proved reliable only after artificial inoculation. Comparing environments, artificially inoculated treatments in the wet savanna zone and in the forest–savanna transition zone with stable high symptom severity proved most suitable for screening of genotypes, while the wet savanna zone with low natural infection in year 1998 was suitable for production of propagation material, and the site in the dry savanna zone with natural infection in year 1998 was the best environment for cassava production. The correlation between disease severity and root yield was significant only for the non-inoculated treatment in the dry savanna zone in year 2000 (R = −0.58), but not in any other environment. Among the 37 genotypes tested, several genotypes can be recommended to farmers in specific ecozones, and genotype TMS30572 revealed as relatively stable in disease resistance and in high yield across ecozones.

Seed Bank Viability in Disturbed Longleaf Pine Sites

Abstract Some of the most species‐rich areas and highest concentrations of threatened and endangered species in the southeastern United States are found in wet savanna and flatwood longleaf pine (Pinus palustris Mill.) communities. Where intensive forestry practices have eliminated much of the natural understory of the longleaf ecosystem, the potential for reestablishment through a seed bank may present a valuable restoration opportunity. Longleaf pine sites converted to loblolly pine plantations and non‐disturbed longleaf sites on the Coastal Plain of North Carolina were examined for seed bank presence and diversity. Conducting vegetation surveys and examining the seed bank using the seedling emergence technique allowed for verification of the seed bank presence, as well as evaluation of the quality of the seed bank on disturbed longleaf pine sites. Forty‐three species and over 1,000 individuals germinated, and the seed banks of both the disturbed and non‐disturbed stand types contained species not noted in the vegetation survey. Although many of these species were considered weedy and typical of disturbance, numerous taxa were indicative of stable longleaf pine communities. This study confirms both the presence and quality of seed banks in highly disturbed former longleaf pine sites, suggesting that the seed bank may be an important tool in restoration efforts.

Characterization of microsatellite markers from capybaras, Hydrochoerus hydrochaeris (Rodentia: Hydrochoeridae)

Fourteen microsatellite loci were isolated from capybaras (Hydrochoerus hydrochaeris), which are large, diurnal social rodents that occur in the wet savannas of South America. Five of these loci were monomorphic. The remaining nine loci were polymorphic (two to seven alleles per locus), with observed levels of heterozygosity ranging from 0.063 to 0.800 (n = 17 animals). The latter loci provide a valuable tool for assessing patterns of parentage and kinship within capybara social groups.

Grass populations control nitrification in savanna soils

Summary Nitrification plays a key role in the functioning of many natural ecosystems. It is directly involved in plant nitrogen nutrition and soil N losses through leaching and denitrification. The control of this process by plants is poorly understood, although modifications of nitrification would allow plants to manipulate competition for N and induce changes in ecosystem N balance. In a wet tropical savanna ecosystem (Lamto, Côte d’Ivoire), the soil N cycle is characterized by distinct high‐ and low‐nitrification sites. Previous publications showed that nitrification was positively or negatively correlated with root densities of the dominant grass covering these sites. These contrasting sites were chosen to investigate the extent to which vegetation controls long‐term nitrification. In situ experimental plots were created where grass individuals originating from high‐ or low‐nitrifying soils were transplanted into both soils. Nitrifying enzyme activity (NEA) was measured up to 24 months after transplanting. Grasses from both sites significantly modified NEA up to rates similar to those at their respective control sites. The level of individual plant control (inhibition and stimulation) was correlated with grass biomass. The potential mechanisms of this control is discussed, along with its consequences for ecosystem N cycling (such as N losses), as the denitrifying enzyme activity (DEA) is much higher in the high‐nitrification site. Such results suggest that plant species can have important consequences for N cycling at the population level.

Landscape analysis of Aboriginal fire management in Central Arnhem Land, north Australia

AbstractAim To describe the spatial and temporal pattern of landscape burning with increasing distance from Aboriginal settlements.Location Central Arnhem Land, a stronghold of traditional Aboriginal culture, in the Australian monsoon tropics.Methods Geographical information system and global positioning system technologies were used to measure spatial and temporal changes in fire patterns over a one decade period in a 100 × 80 km area that included a cluster of Aboriginal settlements and a large uninhabited area. The major vegetation types were mapped and fire activity was assessed by systematic visual interpretation of sequences of cloud‐free Landsat satellite images acquired in the first (May to July) and second (August to October) halves of the 7‐month dry season. Fire activity in the middle and end of one dry season near an Aboriginal settlement was mapped along a 90‐km field traverse. Canopy scorch height was determined by sampling burnt areas beside vehicle tracks.Results Satellite fire mapping was 90% accurate if the satellite pass followed shortly after a fire event, but the reliability decayed dramatically with increasing time since the fire. Thus the satellite mapping provided a conservative index of fire activity that was unable to provide reliable estimates of the spatial extent of individual fires. There was little landscape fire activity in the first half of the dry season, that was mostly restricted to areas immediately surrounding Aboriginal settlements, with burning of both inhabited and uninhabited landscapes concentrated in the second half of the dry season. The mean decadal fire indices for the three dominant vegetation types in the study area were three in the plateau savanna, two in the sandstone and five in the wet savanna. The spatial and temporal variability of Aboriginal burning apparent in the satellite analyses were verified by field traverse surrounding a single settlement. Fires set by Aborigines had low scorch height of tree crowns reflecting low intensity, despite generally occurring late in the dry season.Conclusions Our findings support the idea that Aboriginal burning created a fine‐scale mosaic of burnt and unburnt areas but do not support the widely held view that Aboriginal burning was focused primarily in the first half of the dry season (before July). The frequency and scale of burning by Aborigines appears to be lower compared with European fire regimes characterized by fires of annual or biennial frequencies that burn large areas. The European fire regime appears to have triggered a positive feedback cycle between fire frequency and flammable grass fuels. The widely advocated management objective of burning in the first half of the dry season burning provides one of the few options to control fires once heavy grass fuel loads have become established, however we suggest it is erroneous to characterize such a regime as reflecting traditional Aboriginal burning practices. The preservation of Aboriginal fire management regimes should be a high management priority given the difficulty in breaking the grass‐fire cycle once it has been initiated.

Use of the Topex–Poseidon dual-frequency radar altimeter over land surfaces

The capability of NASA radar altimeter Topex for land surface studies at regional or global scale is investigated. The analyzed data, available since mid-1992 consist of dual-frequency backscattering coefficients values (Ku and C band) estimated at the nadir pointing angle along the satellite tracks between 66°S and 66°N and averaged in 0.75° ground resolution cell. Mean global backscatter images of the entire land surfaces are presented in Ku, C band and the difference C–Ku. Statistics and major temporal signals over nine entire years are also presented at a global scale. Finally, temporal profiles of backscatters are extracted for main land types (desert, tropical forest, wet and dry savanna, boreal regions, ice sheet) to validate the dataset and to analyze radar response to land surface variability through 9 years. Results indicate the high capabilities of Topex–Poseidon (T–P) radar altimeter data for monitoring snow-covered regions at global and regional scale. The use of dual-frequency measurements can also improve methods developed with single frequency radar altimeter over complex vegetated areas. The complementarities for future synergy with wind-scatterometer or satellite imagery data over continents look also promising because of the T–P 10-day repeat cycle, a 10-year span dataset and a future better spatial resolution with combination of other dual-frequency altimetry missions such as ENVISAT or Jason.

The herpetological collection from Bolivia in the “Estación Biológica de Doñana” (Spain)

The collection consists of 822 specimens, of which 529 are amphibians, all of them anurans (5 families, 17 genera and 51 species) and 293 specimens are reptiles (10 families, 28 genera and 49 species). The collection has around 25% of the amphibians species known to occur in Bolivia and about 19% of the reptile species. They come from 55 localities of the Bolivian Departments of Beni, Chuquisaca, Cochabamba, La Paz, Potosi and Santa Cruz and represent the following bioregions: Puna, Chaco, Chiquitanian Forest, Wet Savannas, Ceja de Montana, Yungas, Interandean Dry Valleys and Humid Lowland Forest. The specimens of Scinax chiquitanus and Phrynopus kempffi are paratypes. The record of Pleurodema borelli is the first for the Santa Cruz Department and second for Bolivia. Liolaemus dorbignyi also constitutes the second report for the country and Tropidurus melanopleurus is cited for the first time for the Beni Department.

Trace elements and major species in precipitation at African stations: concentrations and sources

Abstract The chemical composition of rainwaters is important in obtaining information on the aerosols and gaseous species present in the atmosphere. Original data on the concentrations of trace elements and major species in the dissolved and particulate fractions of rainwater samples collected in intertropical Africa were used to determine the potential sources of chemical species. The photographic and mineralogical characterization of rainwater particles using scanning electron microscopy allow to identify the various origins of aerosols and the associated chemical elements: (i) the crustal source characterized by clay minerals, kaolinite (Al, Si), illite (Al, Si and K) and Fe, Ti, and Mn oxides, (ii) vegetation relicts: Mg, Si, Cl, Mn and Zn have been identified in these biogenic particles and (iii) carbonaceous particles (mainly Si) emitted during vegetation fires. Ionic charge balance calculation for the stations located in the rain forest and wet savanna zones (Cameroon, Centrafrican Republic and Ivory Coast) exhibit an anion deficit from 20 to 50 % (between 7 and 9 μeq.l−1). Measured total organic carbon concentrations (between 0.5 and 3.3 mg.l−1), are much higher than acetic and formic acid. The presence of mimic and/or fulvic substances emitted from the vegetation can explain this anion deficit. The results obtained in this study confirm the existence of three important sources of atmospheric compounds in intertropical Africa: (i) the silicate upper crust source: Sc, Ti, Fe, Y, Zr, Nb, Cs, La, Ce, Nd, Yb, Th and U exhibit enrichment factors very close to 1, (ii) the biogenic and biomass burning source characterized by the following elements: Mg, Cl, K, Ca, Mn, Zn, Rb, Sr, and (iii) two minor sources; marine (Mg, Na, Cl) and anthropogenic (Cr, Co, Zn, Ba and Pb). For the stations located in the rain forest zone, all these sources appear strongly linked. High correlations are observed between elements of various origins. This suggest a strong interaction between terrigenous, biogenic, marine and anthropogenic aerosols. The deposition of aerosols onto vegetation and the re-mobilization of the chemical species through natural emissions or biomass burning could explain these correlations and the observed chemical fractionation of marine origin elements such as Cl and Na.

A demographic analysis of fire‐stimulated seedling establishment of Sarracenia alata (Sarraceniaceae)

Recurring fires are thought to be critical to maintaining populations of carnivorous plants in wet pine savannas. Nevertheless, the impact of fire on population dynamics of these unique and sometimes rare plants is poorly understood. In this study, I analyzed stage-structured matrices for Sarracenia alata. To examine the effects of fire-stimulated increases in seedling establishment, five matrices were constructed, which differed in fecundity rates associated with different fire frequencies (annual fires, 1/3, 1/7, 1/20, and 0/20 yr). In addition, I analyzed the sensitivity of population growth and dynamics to changes in other vital rates. Fire-stimulated increases in fecundity were not necessary to maintain viable populations of Sarracenia alata. Although increases in fecundity increased population growth rate, all five fire frequencies (including the "no-fire" scenario) produced either stationary or increasing populations. Adding year-to-year stochasticity in vital rates did not alter these general trends. Population growth and decline were much more sensitive to reductions in the survival of large adult ramets (which were projected to have a life expectancy of 59 yr). Population growth was also more sensitive to changes in juvenile persistence than to juvenile growth, suggesting that conservative use of captured resources by juveniles has a greater impact on fitness than rapid growth and maturation. Given that a previous study showed that modest variation in fire frequency had no impact on either adult or juvenile survival, I conclude that Sarracenia alata relies on fire-regulated plasticity in allocation to pitchers to increase the survival and lifetime fecundity of iteroparous ramets.

Gene flow in a facultative apomictic poacea, the savanna grass Hyparrhenia diplandra.

The genetics of the poacea Hyparrhenia diplandra was studied in four natural populations from an ecological station in West Africa, where it makes up 80% of grasses from wet savanna and constitutes a dense continuum of randomly distributed individuals. DNA content and cytogenetical observations suggest it is an allotetraploid. Using two highly variable microsatellites (heterozygosity H = 0.615-0.616), we show that this species is an apomict with rare sexual reproduction events that account for approximately 0.5% of seeds pollinated in the wild. Hexaploid individuals were also produced, corroborating the observation of aberrant genotypes in the wild. The spatial extent of asexual clones in the field was low in comparison with the predominance of apomixis, thus indicating a low dispersal of seeds from their parent. Heterozygosity and departure from Hardy-Weinberg predictions were similar in the four populations, revealing a high apparent selfing rate s = 0.599 among sexually produced seeds. This is an overestimate since we could not distinguish true selfing from reciprocal outcrosses between neighboring individuals from the same apomictic clone. Gene flow by pollen could be substantial, possibly explaining the absence of isolation by distance in the studied area.

The effects of gap size and disturbance type on invasion of wet pine savanna by cogongrass, Imperata cylindrica (Poaceae)

Cogongrass is a nonindigenous species perceived to threaten native communities of the southeastern United States through modification of species composition and alteration of community processes. To examine how gap size and disturbance type influence the invasion of wet pine savannas by cogongrass, we performed three field experiments to evaluate the response of cogongrass seeds and transplanted seedlings to four different gap sizes, four types of site disturbance, and recent burning of savanna vegetation. Cogongrass germinated, survived, and grew in all gap sizes, from 0 to 100 cm in diameter. Similarly, disturbance type had no effect on germination or seedling and transplant survival. Tilling, however, significantly enhanced transplanted seedling growth, resulting in a tenfold increase in biomass over the other disturbance types. Seedling survival to 1 and 2 mo was greater in burned savanna than unburned savanna, although transplant survival and growth were not affected by burning. Results of this study suggest that cogongrass can germinate, survive, and grow in wet pine savanna communities regardless of gap size or type of disturbance, including burning. Burning of savanna vegetation may enhance establishment by improving early seedling survival, and soil disturbance can facilitate invasion of cogongrass by enhancing plant growth.

Aircraft assessment of trace compound fluxes in the atmosphere with relaxed eddy Accumulation: Sensitivity to the conditions of selection

The Relaxed Eddy Accumulation (REA) technique, implemented aboard aircraft, may be used to measure a wide variety of trace gas fluxes at a regional scale. Its principle is rather simple: air is sampled at a constant rate and the flux is calculated by multiplying a constant β (0.58 in field experiment and 0.62 in simulations) by the standard deviation of the vertical velocity and by the difference between the average concentrations of the scalar (trace gas) for updrafts and downdrafts. The storage of the chemical compound in reservoirs allows for trace gas analysis in laboratory, when in situ measurement with fast response and high sensitivity sensors are not available. The REA method was implemented on the Avion de Recherche Atmosphérique et de Télédétection aircraft during the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO) campaign. The main requirement for accurate flux determination is the measurement of the vertical component of wind velocity in real time. A simulation technique was developed to evaluate the performance of an aircraft REA. The influence of the time lag between the vertical velocity (W) measurement and REA control was tested, as well as the offset of W, the threshold, and the filtering imposed on W. Correction factors, used in a deployment of aircraft REA, were deduced from this study. An additional simulation was performed to evaluate the influence of spatial or temporal drifts on the scalar. The simulation showed that the REA method is not more disturbed than the Eddy Correlation method by low frequencies of physical origin, such as topography. The REA method was used during EXPRESSO for the measurement of isoprene fluxes over the wet savanna and the evergreen rain forest.

Dynamic and thermodynamic structure of the lower troposphere above rain forest and wet savanna during the EXPRESSO campaign

This paper focuses on the energy budget of atmospheric surface and boundary layers over the wet savanna and the rain forest during the Experiment of Regional Sources and Sinks of Oxidants (EXPRESSO). It assesses dynamic features at the transition between savanna and forest at the beginning of the dry season. The experimental zone was still influenced by the monsoon flow with water vapor mixing ratio of about 16 g/kg. Thermodynamic characteristics of the savanna and forest ecosystems are similar. However, for an equivalent net radiation, evaporation is greater over the forest and leads to lower Bowen ratios (0.2 over the forest, 0.45 over the savanna). Low horizontal winds with no mean direction are observed, due to the proximity of the Intertropical Convergence Zone (ITCZ). However, in spite of low horizontal winds, the momentum flux is high, owing to high drag coefficients and roughness lengths. Some differences appear in the turbulent kinetic energy budget: dynamic and thermal production terms over the forest are nearly half those over the savanna. As a consequence, turbulent exchanges are more efficient over the savanna. Entrainment velocities are deduced from the latent heat flux values at the top of the atmospheric boundary layer (ABL) and from the jump in water vapor mixing ratio between the ABL and the free troposphere. Entrainment velocities are of the same order as subsidence velocities deduced from European Centre Medium‐Range Weather Forecasts statistical analyses. High pollution levels are observed in the forest ABL (CO concentration is around 280 ppb). Pollutants, produced by savanna fires, are transported from the free troposphere into the forest ABL by entrainment. Furthermore, horizontal exchanges between the savanna and the forest, induced by large eddies, may occur, increasing the pollution of the forest ABL. Through this study, the ITCZ appears to be an exchange zone rather than a barrier to the transfer of pollutants.

Stable coexistence of contrasted nitrification statuses in a wet tropical savanna ecosystem

1. Wet tropical savannas are characterized by strong environmental constraints—particularly low soil nutrient availability—associated with high plant productivity. Nitrogen recycling, and especially nitrification, is supposed to be a strong determinant of the balance between conservation and loss of nutrients at the ecosystem level. Savanna facies dominated by the grass Hyparrhenia diplandra (Andropogoneae) are known to exhibit low levels of nitrification and thus avoid nitrate losses. 2. By comparing two sites in the Lamto area (Côte d’Ivoire, West Africa) with similar soil physico‐chemical characteristics and equally dominated by H. diplandra (80% of the grass cover), it was demonstrated that, within this facies, nitrification is highly heterogeneous, with a 240‐fold variation in potential nitrification within a specific site. 3. In order to test whether these differences can be considered as permanent in this ecosystem, nitrate reductase activities were compared on H. diplandra plantlets from the two sites, cultivated under identical conditions in the presence of nitrate. The leaves of plants originating from the high nitrification site were always able to reduce nitrate at a significantly higher rate than those from the low nitrification site. This observation indicates a long‐term adaptation of the plants and stable nitrification behaviour. 4. Lamto can thus be considered as a contrasted dual ecosystem relative to its nitrogen cycle. The two sites studied therefore constitute useful models to assess the determinism of nitrification in wet savannas and the role of this process on nitrogen retention in such ecosystems.

Flesh availability and bone modifications in carcasses consumed by lions: palaeoecological relevance in hominid foraging patterns

Competing explanations of early human behavior concerning animal carcass acquisition and exploitation are currently some of the most debated topics in the study of human evolution. Various hypotheses depict hominids as either hunters and flesh-eaters, or as scavengers who mainly consumed marrow and brains. One of the main arguments advanced to support the scavenging hypothesis is that flesh-bearing medium-sized carcasses (weighing between 150 kg and 350 kg) at early sites could have been obtained from large felid kills. This paper presents the results of a preliminary study, in which I have analyzed lion-killed carcasses with respect to the availability and disposal of flesh and conspicuous carnivore-inflicted bone damage patterns, so as to have a reference that can be applied both to archaeofaunas and to actualistic experiments that try to model early human behavior. Bone damage made by lions overlaps the damage patterns caused by other carnivores, such as canids and hyenids, although it is not as intense. Scraps of flesh available after consumption are rare and show a typical anatomical distribution. The scavenging hypothesis is thus testable by comparing the distribution of cut marks on fossil archaeofaunas to the location of flesh in lions' kills. Comparisons between carcasses in different environments show that scraps of flesh can be obtained in open habitats. Carcasses consumed by lions in closed habitats are flesh depleted. The application of this referential framework to archaeological bone assemblages can help to identify hominid foraging strategies, and indirectly, trophic dynamics on savannas: scavenging in open habitats is only feasible in wet savannas with a slightly marked seasonality and lack of migratory biomass [M. Tappen (1992) Ph.D. Thesis, Dept. Anthropology, Harvard Univ., Cambridge, MA]; scavenging in closed habitats can only be made in semi-arid seasonal savannas whose biomass is subjected to migratory processes [R.J. Blumenschine (1986) B.A.R. Int. Ser. 283, Oxford].