Dominant species' resprout biomass dynamics after cutting in the Sudanian savanna-woodlands of West Africa: long term effects of annual early fire and grazing

The potential of forest to regenerate after harvesting is a key element for sustainability of the ecosystem. For semi-arid tropical savanna environments, managing resprouts after tree cutting is ideally suited because of the natural ability of many indigenous species to regenerate vegetatively. Regeneration in this ecosystem is, however, prone to many disturbance factors such as fire and grazing by livestock. In this paper, we used a factorial experiment to examine the long-term effects of annual early burning and grazing on dominant species' resprout biomass dynamics after selective cutting in the Sudanian savanna-woodlands of Burkina Faso, West Africa Burning decreased shoot mortality of Crossopteryx febrifuga while grazing increased that of Detarium microcarpum. Burning, in later measurement years, reduced resprouts' size of Acacia macrostachya, C. febrifuga and D. microcarpum while an increased basal area was observed for Combretum glutinosum. There was no significant evidence of grazing hampering growth. Moderate livestock grazing could be integrated in the forest management prescriptions in Burkina Faso for the sake of multi-purpose uses, while more attention should be paid to burning practices to lower fire severity, as complete fire exclusion is utopian in this savanna ecosystem

Interaction effects of seed mass and temperature on germination in Australian species of Frankenia (Frankeniaceae)

The seed size and number theories have been proposed to explain the advantages of having many small versus a few large seeds in plants. In particular, seed germination is predicted to be shaped by temperature, and may differ for small and large seeds. In this study, we experimentally test germination at different temperatures in 12 species of arid zone plants in the genus Frankenia L. that differ in seed mass. Seed mass was categorized as "smaller-seeded species" versus "larger-seeded species" for analysis (six species per category). Many of these species co-occur geographically and hence experience similar abiotic conditions (unpredictable rainfall, extremes in temperature, poor soil conditions). The results demonstrated differences in germination as a result of the temperature*seed mass(species) interaction effect. There were significant differences in germination rates across seed mass categories during the first eight days of germination. Germination rates were higher in the larger-seeded species than the smaller-seeded species. Smaller-seeded species had lower germination success but had higher germination rates at lower temperatures, and had a more stringent temperature as a germination cue. These findings are discussed in the context of life-history strategies in arid zone plants. © Institute of Botany, Academy of Sciences of the Czech Republic 2008.Lyndlee C. Easton, Sonia Kleindorfe