Effects of burn size and burn patterns on the above ground net primary production on savanna ecosystem, Laikipia Kenya.

Abstract

This study investigated the separate and combined influences of fire and herbivores on herbaceous layer primary production in burn treatments of various scales and patchiness. The study was conducted in savanna ecosystem of central Laikipia in Kenya. The treatments included a nine hectare and one hectare burn, each size had two continuous burns (CB), two patchy burns (PB) and one control which was unburnt. Standing biomass, primary productivity and herbage utilisation in each treatment was measured from April to August 2005 following rains after burn using movable cage method. The results showed a significant difference (p<0.05) for net primary production and standing biomass between burned and unburned treatments. Burn treatment, recorded the highest net primary production (418.6 gm2) which was four times more than that recorded in the unburn treatment while mean standing biomass for burn treatment (54.5 gm2) was three times lower that recorded in unburned (214.2 gm2) treatment. Burning had an effect on both standing biomass and net primary production. Burn treatment resulted in a higher net primary production and lower standing biomass (due to increased intensity of grazing herbivores.) Daily herbage utilization was high in the burn which could be one of the factors contributing to the low standing biomass and high net primary production compared to unburnt treatments. Large burn treatments had a lower standing biomass where else small burn treatments had more standing biomass. The reason might have been that large burns were highly utilized to small burns. They might also have been preferred by grazers as predators "watch spots" in case a predator approaches it could be spotted from far. Vl The standing biomass obtained in this study in burn pastures suggest there is a high preference to grazing in the burn thus keeping the herbaceous layer shorter. Burn treatments attracted grazers and thus reducing the standing biomass (grass size), this could be due to the fiash and nutritious regrowth after the burn. Utilization was highest in the larger burn (9 hectare) treatment which differed significantly (p>0.05) with other treatments except for the smaller burn treatment. Utilization in 1 hectare burn was high but not significantly difference to any of the other smaller treatments. Larger burn treatments (9 hectares) contributed 71.0% and 59.4%( primary production measures) while smaller burn treatment (1 hectare) contributed 29% and 40.6% of total net primary productivity in the burn, burn and unburn (unburn and control) treatments respectively, In spite of high net primary production, larger burn treatments recorded herbage removal of 30.1% while smaller burn treatment recorded 22.8% of total burn and unburn herbage removal. On the other hand, 52.9% of all treatment net primary production was utilized in the burns compared to 47.1% removal in unburn treatments. The mean daily aboveground net primary production was 18.0±4.6 gm2 and 10.7±2.8gm2 in treatments patchy Burn and continuous Burn respectively with no significant difference between them. Utilization and standing herbage biomass was relatively higher in treatment Patch Burn than treatment continuous Burn. Treatment continuous Burn had a relatively low standing biomass to treatments patchy Burn irrespective of burn size. However larger burns for both continuous Burn and patchy Burn had lower standing biomass relative to the smaller burns but significantly higher production.