Riparian zones are vulnerable to high levels of weed invasion by a wide diversity of species, due to their location in the landscape and the impacts of human activities. Restoring indigenous vegetation communities is challenging in riparian sites dominated by weed species. We asked whether intensive pre-sowing weed control was sufficient to protect establishing native seedlings from weed competition, and if not, what technique of post-sowing weed control was most effective. At several sites in south-eastern Australia we tested management techniques to promote direct seeding outcomes in riparian zones with high weed loads. Our study found that intensive pre-sowing weed control, involving multiple herbicide applications and physical removal of weeds, was insufficient to protect native seedlings from weed competition during establishment. At one site, native plant numbers were four times lower in plots receiving pre-sowing weed control only than in plots which received pre-sowing and post-sowing weed control. At two other sites, hand weeding in the months immediately after sowing was more effective than spraying a broad-spectrum herbicide at the same frequency, with twice as many native plants establishing in the hand weeded plots. Despite the high cost of manual labour, it may be more cost-effective to hand weed than to not hand weed after direct seeding, due to the higher rates of plant establishment. These results indicate that direct seeding in riparian zones with high weed loads can be successful, but only if effective post-sowing weed control is undertaken.
Audio/Video, Conference Presentation, SER2019
Society for Ecological Restoration