Seed ecology of the invasive woody plant African Olive (Olea europaea subsp. cuspidata): Implications for management and restoration

Knowledege of the seed ecology of invasive exotic species, including soil seedbank dynamics, is essential to understanding key factors in successful invasion and in identifying management opportunities. African Olive, Olea europaea L. subsp. cuspidata, is an exotic invasive woody plant in Hawaii, Norfolk Island and eastern Australia, and is now well established in the Cumberland Plain region of western Sydney, Australia. In the present study, the key aspects of the seed ecology of African Olive were determined for populations in western Sydney. Extracted seed germinated at a wide range of temperatures, consistent with tolerance of a wide range of climatic conditions. A seed-burial experiment indicated a slow decrease in viability down to 70.3% during the first year, followed by a rapid decline down to 14.7% in the second year. Probit analysis indicated that under field conditions, seed persistence in the soil was ∼29 months (2.4 years). In situ germination was low (3.3%) and did not occur until the mechanical constriction of the endocarp was released through decomposition. The woody seed endocarp was found to be permeable to water, indicating that physical dormancy was not imposed by providing a barrier to water uptake. Within its invasive range, African Olive produces abundant seed. However, the rapid loss of viability of soil-stored seed results in a narrow window of opportunity for germination. The short persistence of seed in the soil may provide an opportunity for managers to achieve control of African Olive once mature plants are removed.