Senna spectabilis is a tree native to South and the unmanipulated plot. In contrast, the abundance of native tree species increased markedly in the plots where Central America. Thirty-five years ago it invaded the Mahale Mountains National Park in western Tanzania S. spectabilis had been removed or killed, with higher densities in the girdled rather than the felled plot. where it presently covers c. 225 ha. We quantified its occurrence relative to that of sympatric species of native S. spectabilis appears to suppress the recruitment of native trees in the Park, and its removal can encourage trees, and compared girdling and felling as methods for its control in three 0.25 ha plots. Within invaded areas of regeneration of the degraded forest without the need for artificial seeding. forest this exotic species was both the most abundant and dominant of the 26 species of tree recorded. During 4 years of monitoring the experimental plots the abundance Keywords Caesalpiniaceae, control, exotic species, invasive tree, Senna spectabilis, Tanzania. of S. spectabilis declined markedly in the plots where control methods were practised, but increased slightly in Mountains National Park, located c. 17 km south of the
Above-and below-ground production and morphological characteristics of papyrus wetlands were measured at monthly intervals from July 2005 to June 2006 at Rubondo Island, Lake Victoria, Tanzania. The average value of live culm biomass (5,789 ± 435 g DW m -2 ) was higher than that of umbel biomass (2,902 ± 327 g DW m -2 ) by 50%. Root to rhizome means biomass value ratio was 1:1.8, rhizome biomass (4,144 ± 452 g DW m -2 ) being higher than roots biomass (2,254 ± 314 g DW m -2 ) by 45%.Direct proportion was observed between shoot density and culm-unit (culms and umbels) biomass. The average value of detritus/litter biomass (1,306 ± 315 g DW m -2 ) was less than total aerial biomass by 86%.The values of biomass are average of 12 sampling months from
The dissolved oxygen concentration (DO) was sampled during a diurnal cycle in three water holes heavily used by wildlife and with distinctive biological features along the Seronera River. The DO fluctuated widely (by up to 11.5 mg l À1 ) as a function of time, mechanical stirring and aeration by animals, and the presence of fringing wetlands. The DO cycle was successfully modeled (within 0.3 mg l À1 ) by assuming that the four dominant processes were photosynthesis and respiration by algae near the surface, trapping by wetlands, decomposition of dead organic matter on the bottom, and stirring/aeration by hippos. The rate of DO decline from the decay of dead organic matter was equal to the rate of DO removal by algal respiration at night.
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