Regeneration failure threatens persistence of Persoonia elliptica (Proteaceae) in Western Australian jarrah forests

Abstract

The severe disruption of herbivore relationships can result in catastrophic, demographic consequences for plant populations. We investigated the potential roles of herbivory, fire and their interaction, in the observed long-term regeneration failure of Persoonia elliptica R.Br. (Proteaceae), an understory tree species of fire-prone jarrah (Eucalyptus marginata Sm.) forests in southwestern Australia. Seed production, storage and viability were assessed, as was seedling recruitment in both the presence and absence of fire (a potential germination cue), using experimental herbivore exclosure plots. We also sought to determine the ‘herbivory zone’ (height) within which P. elliptica was susceptible to browsing. Herbivores, primarily the western grey kangaroo, preferentially consumed leaves of P. elliptica up to a browsing height of 1.5 m. Viability of fresh seeds was low at ca. 39 % and rapid viability loss was observed in the soil seed bank, with only ca. 5 % of seeds remaining viable for >1 year. Germination was restricted almost solely to burned areas and survival of recruits to the confines of herbivore exclosures. We suggest that an increase in the primary herbivore, combined with low viable seed supply, is the likely cause of continuing regeneration failure in this species. The slow growth of the species suggests that without intervention, seedlings and juvenile plants will be unable to escape the herbivory zone. Management actions to facilitate recruitment might best focus on the combination of managed fires to break seed dormancy, followed by fencing to protect seedlings from large herbivores.