Fire history and fire ecology of Northern Kruger (KNP) and Limpopo National Park (PNL), southern Africa

This paper explores the general correlations between fire and grass/tree relationships, as represented by fossil charcoal and pollen, from different vegetation types in the savanna ecosystems of the neighbouring Kruger (KNP) and Limpopo (PNL) national parks. Our analysis suggests that the basic presumption that fire is a main driver of vegetation dynamics in the savanna ecosystem by suppressing tree seedlings and encouraging grasses needs to be re-examined. An improved approach is to understand how fire may act both as a negative and positive feedback in different vegetational phases and both as a driver and responder in transitions between phases. The correlation between arboreal pollen (AP) percentages and charcoal influx suggests that in the grassland phase (< 5% AP), fire acts as a driver of woody recruitment and as a positive feedback, i.e. potentially driving the system to shift into a savanna phase. In the savanna phase (5-10% AP) fire limits woody recruitment and acts as a negative feedback in maintaining the savanna. Thus, in the savanna phase other factors than fire alone drive the transition from savanna to woodland-forest. In the riparian phase, where evidence of farming is present particularly from AD 1600 onwards, fire appears to facilitate tree recruitment where AP ranges between c. 10 and 20% AP. Though a decline in AP abundance can be seen contemporaneously with charcoal peaks, our analysis suggests that overall, human-induced fires do not seem to have a negative impact on woody cover. Our results have implications for fire management as riparian-dominated phases and savannas with a sufficient woody cover are less sensitive to changes in fire policies than open grasslands that may, with a change in fire frequency, change into another state.