Soil sampling in the Miombo woodlands
The overall aim is to reconstruct vegetation dynamics and to quantify carbon
dynamics in the Savanna landscape of Eastern Tansania. Our approach is based
on the isotopic differences of C4-grasses and C3-woodlands. Analysis of the
natural 13C abundance and the radiocarbon age of soil organic matter will allow
to estimate how the dominant vegetation has changed during the last centuries.
Old photographs, field observations and a simulation model suggest that during the last decades, forested areas increas on the slopes (Bloesch, 2002). The absence of elephants and rhinoceroses and prevailing cool early dry season fires allowed the coalescence of expanding thicket clumps within a shrub savanna matrix on slope thereby building small forest formations. These forests are not relicts of previously large forests as supposed by former researchers (see e.g., Lebrun 1955; Troupin 1966; Rodgers et al. 1977) but are dynamic parts of the savanna landscape whereby their expansion or regression mainly depend on the intensity of browsing by mega herbivores and the type of fire regime. On the other hand, thicket clumps within a seasonally waterlogged grass savanna matrix on plain (Planisols / Vertisols) are limited to termitaria. The longevity of the mounds and the mutualism between termitaria and vegetation lead to high persistence of the vegetation mosaic
Working hypotheses:
1) Currently forested hillsides (C3 vegetation) were formerly covered with
savannas (C4 vegetation). Therefore, SOM will have a C4-dominated isotopic signature.
2) Thicket clumps within a grass savanna matrix on plains and gully forests
along temporary watercourses on slopes are long-term components of the landscape.
As a consequence, SOM of the uppermost soil horizons will be characterised by a C3-dominated isotopic
signature.
Soil sampling in the Miombo woodlands