Forest tree and fern species as indicators of an unnatural fire event in a southern Cape mountain forest

Abstract

Afromontane forests in the southern Cape are typically surrounded by fire prone fynbos. Although the impact of fire on fynbos has been extensively studied, little is known about the impact of fire on adjacent forest. Fire swept through a mountain forest in the southern Cape in 1996. Our study indicated that this fire was one of at least two fires that influenced the recent history of this forest; the other fire was probably the great fire of 1869.We consider the latter fire typical of fires that burn mountain forest and suggest a return period for these fires of between a 100 and 200 years. In contrast to the 1869 fire, evidence from our study suggests that the 1996 fire was unprecedented in the recent history of the forest. This fire changed a large proportion of Ocotea bullata in the margin from single stemmed to multistemmed trees and reduced the number of Cyathea capensis in the margin by 68%. Using these species as indicators, we argue that similar fires will reduce the structure and diversity of mountain forests as a whole. The 1996 fire was fuelled by abnormally high fuel loads associated with surrounding pine plantations and mountain fynbos invaded by woody aliens. Given that large areas of mountain fynbos are invaded by woody aliens, that large areas of the southern Cape are afforested and that global climate change is likely to lead to an increase in the conditions favouring intense fires, we consider effective management of Afromontane mountain forests essential.