Effects of simulated fire and browsing on the resprouting of subtropical dune thicket shrubs in the southeastern Cape Floristic Region

Abstract

Aim: The expansion of subtropical thicket vegetation at the expense of more species-rich, fire-prone fynbos, potentially due to lower frequency and severity of fire and browsing, is a concern in many coastal dune landscapes of the Cape Floristic Region (CFR) where these two vegetation types co-occur. We were interested in the effects of severe fire and browsing treatment on the vigour of post-fire resprouts of dune thicket shrubs. Location: Cape St Francis, CFR, South Africa. Methods: We used an in-situ experimental approach to compare the effects of simulated fire and browsing by herbivores on mortality, resprouting vigour and resprouting rate of ten canopy-forming dune thicket shrub species from different architectural guilds, five years after a previous severe wildfire. Results: Survival was significantly lower after fire (85%) than after browsing (95%), and was significantly positively related to pre-treatment shrub size. All measures of resprouting vigour were significantly lower after fire than after browsing, and were significantly positively related to pre-treatment size. Resprouting rate was significantly lower after fire than after browsing, and was significantly positively affected by pre-treatment size. Survival and measures of resprouting vigour were generally decoupled from architectural guild and species identity. Conclusion: Dune thicket shrubs showed high survival after both fire and browsing treatments, suggesting that these species are resilient to frequent, severe defoliation disturbances. Our results suggest that short interval fires (5-15 years) of high severity will merely maintain the co-occurrence of dune fynbos and thicket vegetation by setting back thicket growth rather than causing large-scale mortality of thicket shrubs.

Drivers of post‐fire resprouting success in restored Banksia woodlands

“…We found evidence of plant size increasing post-fire resprouting vigour in all species in this study, potentially due to increased resources in larger plants promoting quicker growth following fire. Similar evidence of vigour increasing with plant size has been found following fire and coppicing for resprouting individuals in intact ecosystems (Casals et al, 2018;Moreira et al, 2012;Strydom et al, 2023).…”

“…Conversely, we found that survival increased with plant size for three species (although not significantly for two species). In forest stands in Mediterranean Iberia (Casals et al., 2018) and thickets in South Africa (Strydom et al., 2023), post‐fire resprouting success was higher in larger plants, or resprouting success varied with plant size (Giddey et al., 2022).…”