Improving weed management by targeting the seed ecology of blackberry (Rubus anglocandicans) in a biodiversity hotspot

Context. Germination is a vulnerable life stage for plants, therefore understanding the dynamics of seed ecology is essential to guiding management recommendations for highly invasive weeds. Aim. We addressed the knowledge gap for how seeds contribute to the invasion process for European blackberry (Rubus anglocandicans), a threatening weed across the riparian ecosystems of south-western Australia. Methods. We performed mechanical, chemical and thermal treatments on seeds to test for changes in germination success and conducted seed-burial trials to monitor seed viability over time in the soil seedbank. Key results. In germination trials, freshly picked and frugivore egested seeds failed to germinate with the endocarp intact. With the endocarp removed, germination remained lower at 4-6 months compared with 10-28 months after collection, indicating a significant after-ripening period. Seeds in intact endocarps survived water immersion for more than 2 months, indicating an ability to survive winter flooding. Acid immersion did not improve germination. The germination success of seeds with endocarp removed increased linearly above 11 degrees C, was greatest at 30 degrees C and thereafter declined rapidly (no survival at 40 degrees C). In a 5-year seed-burial trial, germination varied from 7.6 to 48.4% and was significantly lower closer to a river, and in areas where "blackberry decline' syndrome was present. Conclusions. While germination of seed without its pyrene coat occurred over a range of controlled conditions, the natural processes needed to break the pyrene remain unknown. Implications. High germination success and the long-term survival of seeds in soil clarifies that the management of blackberry remains a difficult challenge in Australia.