[Show abstract][Hide abstract] ABSTRACT: Miombo woodlands cover the transition zone between dry open savannas and
moist forests in Southern Africa. They cover about 2.7 million km2 in
southern Africa and provide many ecosystem services that support rural
life, including medical products, wild foods, construction timber and
fuel. In Zambia, as in many of its neighbouring countries, miombo
woodlands are currently experiencing accelerating degradation and
clearing, mostly with charcoal production as the initial driver.
Domestic energy needs in the growing urban areas are largely satisfied
by charcoal, which is less energy-efficient fuel on a tree-to-table
basis than the firewood that is used in rural areas, but has a higher
energy density and is thus cheaper to transport. This study uses data
from inventories and from eddy covariance measurements of carbon
exchange to characterize the impact of charcoal production on miombo
woodlands. We address the following questions: (i) how much carbon is
lost at local as well as at national scale and (ii) does forest
degradation result in the loss of a carbon sink? On the basis of our
data we (iii) estimate the per capita emissions through deforestation
and forest degradation in Zambia and relate it to fossil fuel emissions.
Furthermore, (iv) a rough estimate of the energy that is provided by
charcoal production to private households at a national level is
calculated and (v) options for alternative energy supply to private
households are discussed.
[Show abstract][Hide abstract] ABSTRACT: This study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems in Sub-Saharan Africa, as measured using eddy covariance (EC) technology. The ecosystems for which data were available ranged in mean annual rainfall from 320mm (Sudan) to 1150mm (Republic of Congo) and include a spectrum of land cover types (savannas, woodlands, croplands and grasslands). Data were analysed across the network, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments. In addition to the spatial pattern, the temporal pattern that connects carbon fluxes with water relations in savanna ecosystems were studied in detail in a savanna ecosystem at Kruger National Park, South Africa and a miombo woodland in Western Zambia. Temporal variability: The regulation of canopy conductance was temporally changing in two ways: changes due to phenology during the course of the growing season and short-term (hours to days) acclimation to soil water conditions. The most constant parameter was water use efficiency. It was influenced by humidity (VPD) during the day, but the VPD response curve of water usage only changed slightly during the course of the growing season, and decreased by about 30% during the transition from wet to dry season. The regulation of canopy conductance and photosynthetic capacity were closely related. This observation meets recent leaf-level findings that stomatal closure triggers down-regulation of photosynthesis during drought. Our results may show the effects of these processes on the ecosystem scale. Spatial variability: The same pattern was found at large spatial scales. Maximum carbon assimilation rates were highly correlated with mean annual rainfall (r2=0.74) and were also positively correlated with satellite-derived fAPAR. Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000 mm of rain per year. All the ecosystems studied that were dominated by C3-plants showed a strong decrease in the 30-minute assimilation rates at low humidity (VPD > 2.0 kPa), while ecosystems dominated by C4-plants did not.