In Mediterranean type ecosystems which are subjected to periodic fires, riparian zones must deal with flood, seasonal drought and fire. Despite the importance of riparian zones as habitat and transport for nutrients and propagules, little is understood about regeneration in this community, particularly in Mediterranean type ecosystems, such as the Western Cape of South Africa. This study examines mode of recruitment in relation to location within a stream cross section before and after fire in the Fynbos ecosystem. In 2009, a large wildfire burned through the Fynbos in the Jonkershoek Nature Reserve located in the Western Cape Province of South Africa. Most of the riparian vegetation along the Erste river was affected creating a perfect opportunity to study the post-fire recruitment strategies of dominant riparian woody species; Meterosideros angustifolia, Brabejum stellatifolium, Cunonia capensis, Brachylaena neriifolia, and Erica caffra. We compared pre- and post-fire recruitment at two reaches, and at one reach that did not burn before and after the fire. Pre-fire surveys were conducted in January 2008, and post-fire surveys were conducted in January 2010. Eight transects were laid out perpendicular to the stream channel, and 1 m2 plots were sampled from the thalweg to the end of the riparian zone where upland species became dominant; for each individual of the target species within the plot, we recorded recruitment mode (seedling, re-sprouting, new branching) and stem diameter. Data were analyzed using ANOVA with species, reach, location with respect to thalweg, and recruitment mode as factors determining density.
Results/Conclusions
Post fire seedling recruitment for all species was significantly reduced at the reaches where fire occurred. For example, M. angustifolia, a heavy seedling recruiter in 2008 with mean density of 2.1 (individuals/ meter²) had virtually no seedlings in 2010. Re-sprouting was found to be the greatest contributor to recruitment as all species, except E. caffra, had significantly more re-sprouts in burned reaches. Although post fire seedling densities decreased, overall post-fire density of stems increased in both burned and unburned reaches. Increased fire frequency as a result of human ignition coupled with increased fire intensity resulting from climate change has the potential to alter the structure and composition of these communities; understanding the interaction between fire, flood and seasonal drought may contribute to management strategies that will preserve these important habitats.
