Sandplain heathlands are home to a host of rare openland species and are threatened by commercial development and afforestation, due to the disruption of historical disturbance regimes. Restoration and management of this habitat is inhibited by gaps in scientific knowledge about the life history and growth requirements of many sandplain species. We conducted an experimental restoration for the endemic sandplain subshrub, Corema conradii (broom crowberry). The regeneration requirements for this species are unknown. We hypothesized that mechanical soil disturbance would increase germination and survivorship of Corema conradii (hereafter Corema), as compared to controls. We predicted that hot summer burns would have the highest levels of Corema germination, followed by spring burns, and unburned plots. Additionally, we expected to see the highest levels of germination and survivorship in plots that received both fire and mechanical disturbance treatments. We predicted that burned plots would have greater Corema germination and survivorship than mechanically disturbed plots. We used Poisson regressions to analyze seedling establishment in subplots that received seeding and control treatments. This allowed us to test for the main effects of both fire and mechanical disturbance as well as the interaction between the two.
Results/Conclusions
Seasonal burning, seeding, and mechanical disturbance treatments had the greatest effects on germination of Corema conradii. Plots burned in the spring had significantly greater numbers of Corema seedlings than those burned in the summer or control plots, contrary to our hypothesis that the hottest burns would result in the greatest numbers of seedlings. Seeded subplots had significantly greater numbers of Corema seedlings than controls. Undisturbed plots resulted in significantly greater numbers of Corema seedlings than those plots which experienced mechanical disturbance, contrary to our hypothesis that human disturbance would promote regeneration of this species. We found an interaction between season of burn and disturbance, with the spring burn, undisturbed plots having the greatest number of Corema seedlings in the subplots, as compared to the other fire season and mechanical disturbance treatment combinations. It is possible that mechanical disturbance inhibited successful burns, as the leaf litter and understory became fragmented, which might have inhibited fire movement and intensity. For this species, natural disturbance promoted successful regeneration and establishment, whereas leaving the heathlands alone or mechanically disturbing them did not. We suggest that heathland management and restoration efforts should focus on spring burns of habitat that has not experienced mechanical disturbance.