Weed management and woodland creation - an evidence review of herbicide alternatives and impacts on biodiversity.
1. Weed control is important for ensuring the rapid and successful establishment of trees in woodland creation projects. Over recent decades, herbicides have fulfilled this role across the forestry and conservation sectors because they are cost-effective, practical and have high efficacy. Glyphosate is currently widely used for this purpose. However, there are questions regarding the impact of herbicides on human and environmental health, prompting research into alternatives. 2. This evidence review assesses the effectiveness of a range of alternative weed control methods for woodland creation. The impact of weed control methods on the biodiversity value of created woodlands is also discussed. 3. Review findings: mulching can be as effective for promoting tree growth if the material used is sufficiently durable to last throughout the establishment period. Traditional black plastic is the most durable option but has clear environmental drawbacks. Biodegradable mulches, such as a straw and woodchips, show some promise but more research is needed to establish their utility. Mechanical weeding can have specific use on a site-by-site basis but cannot continue beyond the establishment phase. Mowing is ineffective in reducing root competition but has benefits when used in combination with other methods. Natural Herbicides (e.g. bilanafos) have a limited evidence base. Cover crops - particularly grass/wildflower mixes - have potential in former agricultural sites, especially in combination with soil inversion. Direct seeding also has significant weed control potential, producing a dense competitive canopy but also increasing establishment variability. The option of no weed aftercare increases the likelihood of competition and may enhance the sensitivity of seedlings to abiotic stress such as drought. 4. Recommendations for future research: Research gaps were identified on the efficacy of biodegradable mulches, soil inversion and direct seeding methods. The longer-term impact of glyphosate and other methods on biodiversity in newly created woodland is also an evidence gap.