Regulation of seedling recruitment and survival in diverse ecotonal temperate forest understories

Abstract

Fire is an important factor driving the position and stability of ecotones between fire-prone and less flammable forest types. To better understand, the recruitment processes that mediate plant persistence in ecotonal systems, we used manipulative field experiments in Australian wet eucalypt forests to investigate factors that may be regulating seedling recruitment and survival in burnt and unburnt forest. We found no evidence that safe sites from predators or exposure regulated seedling recruitment in three of the four study species, but one species associated with less flammable rainforest systems had increased germination rates in response to soil scarification. Seedlings of all four study species experienced higher rates of mortality resulting from herbivory or water stress in the post-fire environment. We found that intact ground cover increased seedling survival by reducing exposure to dessicating conditions and providing refuge from vertebrate herbivores. Our results suggest that shrubs associated with mesic, low-flammability forests have fewer opportunities for recruitment with desiccation risks in post-fire environments limiting seedling survival. In contrast, shrubs associated with high-flammability forests were capable of recruiting and surviving in both burnt and unburnt forests. Post-fire recruitment is likely to be more abundant after fire than at other times, but we found that survival can be highly constrained by post-fire herbivory. The ability of these species to recruit in undisturbed conditions provides some insurance against recruitment failure under stochastic variation in herbivory and desiccating conditions. The capacity to spread risks could be important in maintaining boundary position and diversity in these ecotonal systems.