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

Alcohol consumption and body composition in a population-based sample of elderly Australian men

Background: Alcohol is calorie dense, and impacts&nbsp;activity, appetite and lipid processing. The aim of this&nbsp;study was to therefore investigate the association between&nbsp;alcohol consumption and components of body composition&nbsp;including bone, fat and lean tissue.Methods: Participants were recruited from a randomly&nbsp;selected, population-based sample of 534 men aged&nbsp;65 years and older enrolled in the Geelong Osteoporosis&nbsp;Study. Alcohol intake was ascertained using a food&nbsp;frequency questionnaire and the sample categorised as nondrinkers or alcohol users who consumed B2, 3&ndash;4 or C5&nbsp;standard drinks on a usual drinking day. Bone mineral&nbsp;density (BMD), lean body mass and body fat mass were&nbsp;measured using dual energy X-ray absorptiometry; overall&nbsp;adiposity (%body fat), central adiposity (%truncal fat) and&nbsp;body mass index (BMI) were calculated. Bone quality was&nbsp;determined by quantitative heel ultrasound (QUS).Results: There were 90 current non-drinkers (16.9 %),&nbsp;266 (49.8 %) consumed 1&ndash;2 drinks/day, 104 (19.5 %) 3&ndash;4&nbsp;drinks/day and 74 (13.8 %) C5 drinks/day. Those consuming C5 drinks/day had greater BMI (?4.8 %), fat mass&nbsp;index (?20.1 %), waist circumference (?5.0 %), %body&nbsp;fat (?15.2 %) and proportion of trunk fat (?5.3 %) and&nbsp;lower lean mass (-5.0 %) than non-drinkers after adjustment for demographic and lifestyle factors. Furthermore,&nbsp;they were more likely to be obese than non-drinkers&nbsp;according to criteria based on BMI (OR = 2.83, 95 %CI&nbsp;1.10&ndash;7.29) or waist circumference (OR = 3.36, 95 %CI&nbsp;1.32&ndash;8.54). There was an inverse relationship between&nbsp;alcohol consumption and QUS parameters and BMD at the&nbsp;mid forearm site; no differences were detected for BMD at&nbsp;other skeletal sites.Conclusion:&nbsp;Higher alcohol intake was associated with&nbsp;greater total and central adiposity and reduced bone&nbsp;quality.<br /

The charcoal trap: Miombo forests and the energy needs of people

<p>Abstract</p> <p>Background</p> <p>This study evaluates the carbon dioxide and other greenhouse gas fluxes to the atmosphere resulting from charcoal production in Zambia. It combines new biomass and flux data from a study, that was conducted in a <it>miombo </it>woodland within the Kataba Forest Reserve in the Western Province of Zambia, with data from other studies.</p> <p>Results</p> <p>The measurements at Kataba compared protected area (3 plots) with a highly disturbed plot outside the forest reserve and showed considerably reduced biomass after logging for charcoal production. The average aboveground biomass content of the reserve (Plots 2-4) was around 150 t ha^-1, while the disturbed plot only contained 24 t ha^-1. Soil carbon was not reduced significantly in the disturbed plot. Two years of eddy covariance measurements resulted in net ecosystem exchange values of -17 ± 31 g C m^-2y^-1, in the first and 90 ± 16 g C m^-2in the second year. Thus, on the basis of these two years of measurement, there is no evidence that the <it>miombo </it>woodland at Kataba represents a present-day carbon sink. At the country level, it is likely that deforestation for charcoal production currently leads to a per capita emission rate of 2 - 3 t CO₂y^-1. This is due to poor forest regeneration, although the resilience of <it>miombo </it>woodlands is high. Better post-harvest management could change this situation.</p> <p>Conclusions</p> <p>We argue that protection of <it>miombo </it>woodlands has to account for the energy demands of the population. The production at national scale that we estimated converts into 10,000 - 15,000 GWh y^-1of energy in the charcoal. The term "Charcoal Trap" we introduce, describes the fact that this energy supply has to be substituted when woodlands are protected. One possible solution, a shift in energy supply from charcoal to electricity, would reduce the pressure of forests but requires high investments into grid and power generation. Since Zambia currently cannot generate this money by itself, the country will remain locked in the charcoal trap such as many other of its African neighbours. The question arises whether and how money and technology transfer to increase regenerative electrical power generation should become part of a post-Kyoto process. Furthermore, better inventory data are urgently required to improve knowledge about the current state of the woodland usage and recovery. Net greenhouse gas emissions could be reduced substantially by improving the post-harvest management, charcoal production technology and/or providing alternative energy supply.</p

Ecologie génétique de populations halophytiques d'<i>Aster tripolium</i> L. dans l'estuaire de l'Yser (Belgique)

info:eu-repo/semantics/publishe

Elodea nuttallii

Angiosperm