Effects of fire history and N and P fertilization on seedling biomass, Specific Leaf Area, and root:shoot ratios in a South African savannah

Fire exerts clear direct effects on savannah vegetation dynamics, but the indirect effects of fire, for example via changes in soil fertility, are less clear. In fire-dominated nutrient-poor savannahs, there is little evidence that fire affects plant-available nutrients, but plant performance on soils with contrasting fire histories has not been investigated. A bioassay experiment was conducted in Kruger National Park, South Africa, to test for effects of long-term fire manipulation on the ability of soils to influence tree growth. Combretum hereroense, a common savannah species, was used as a phytometer species in an experiment that combined fire history with N and P fertilization treatments. The results suggested no effect of fire history on a number of seedling traits after seven months of growth. Root mass and shoot:root ratios responded to P addition, with seedlings exhibiting lower allocation to root tissue under elevated P, particularly in the presence of N, suggesting some N and P co-limitation. Overall, it is concluded that there is little evidence that fire degrades or alters soil chemistry in a way that is likely to influence vegetation structure and dynamics in nutrient-poor savannah ecosystems.

► No effect of fire treatment on soil was found on several seedling traits.
► Seedlings responded to P addition, particularly in the presence of N.
► There was no evidence of fire effects on seedlings via indirect effects on soil.