Fire behaviour and the invasion of Acacia sieberiana into savanna grassland openings

Following the recent decline in browsing and grazing pressures and changed fire regimes in Queen Elizabeth National Park, Uganda, Acacia thickets have encroached on grassland habitats important for grazing mammals. The objective of this research was to test experimentally the effects of fire behaviour, using simulated and natural fuel loading conditions, on A. sieberiana seedling and sapling regeneration. A high fire intensity (3200 kW m^-1) in natural fuels stimulated high seedling emergence (172 seedlings m^-2) compared to 6 seedlings m^-2 without fire. Also a highly significant linear regression was established between percentage top-kill of seedlings and fire intensities. High fire intensities during late dry season fires were more effective in controlling sapling height growth than early dry season fires of low intensities. A conceptual diagram was developed to show the major factors and possible pathways leading to successful invasion by A. sieberiana into grassland openings of the savanna.     

Biomass Allocation of Erythronium americanum Populations in Different Irradiance Levels

The forest herb Erythronium americanum was collected from threeNew Jersey habitats and grown in 100%, 43%, or 23% glasshouselight to determine if biomass allocation responses to irradiancediffered between populations. Shaded plants had longer petioles,produced fewer runners, and had greater specific leaf areasthan unshaded plants; these responses did not differ significantlyamong populations. All populations produced smaller bulbs whengrown in shade. Over all light treatments, mean leaf area ofplants from a stable, established site was greater than thatof plants from others. In 100 % light, these plants had thegreater bulb growth. The simple architecture of Erythroniummay constrain morphological responses to the light environment. Erythronium americanum(Ker.), forest herb, biomass allocation, light intensity