Short-term response of the encroacher shrub Seriphium plumosum to fire

Abstract

Quantification of the short-term impact of burning in terms of the encroacher shrub Seriphium plumosum and grass tuft mortality, seed germination of the shrub (field and seed bank), aboveground phytomass production, plant density and basal cover of the grass sward was conducted in semiarid grassland following an accidental fire. These variables were determined along a terrain morphological unit where S. plumosum density increased with altitude. On average 57% of S. plumosum seedlings were killed by fire, but fire had no significant (P > 0.05) influence on the mortality of mature shrubs. Fire significantly (P . 0.01) stimulated seedling emergence of S. plumosum, to such an extent that an average of 510 seedlings ha^-1 occurred on the foot slope, while only 9.14 seedlings ha^-1 emerged in the unburnt treatment. Seedling emergence showed greater association with protection from direct sunlight and seedlings emerged not closer than 281 mm from the nearest leaves (canopy) of a mature S. plumosum shrub. The aboveground phytomass production of the unburnt grass sward was nearly double that of the burnt areas over the first season following the fire. Fire as a control measure should be carefully handled because it can lead to increased encroachment of S. plumosum.

Keywords: bankrupt bush, mortality, seed germination, slangbos, Stoebe vulgaris

African Journal of Range & Forage Science 2011, 28(2): 65–77