Management of invasive alien plants in forests: A global perspective

Abstract

1. Forests are critical to the provision of goods and services. They experience many threats including the presence of invasive alien plants (IAPs) which can impact native biodiversity and ecosystem functioning. However, there is a lack of synthesis around outcomes and costs of managing IAPs in forests. 2. We conducted a systematic review to identify (i) where IAP management is reported globally, (ii) which IAP species are being managed, (iii) which methods are being used and (iv) which are the most effective, relative to a control or baseline condition, at managing IAPs in forests. 3. Studies assessing outcomes of IAP management in forests were conducted in 26 countries. The United States dominated the evidence base, accounting for 61% of included studies, covering the widest range of IAP species. This likely reflects a combination of extensive forest cover, high IAP prevalence, and research infrastructure and investment. 4. Across 192 studies, 623 combinations of species and management treatments were studied. Chemical application was most popular (41% of methods) and generally had a high success rate. Most methods had mixed outcomes, with the use of animals for grazing being the most varied. Low replication across treatments made it difficult to draw firm conclusions about management effectiveness. 5. Only 15% of included studies evaluated the effect of seasonal timing on management outcomes, despite evidence from these studies that seasonality can influence success. Furthermore, only 6% of studies reported management costs, and reporting was inconsistent among those that did. 6. Synthesis and applications. This review exposes urgent and critical knowledge gaps in forest IAP management, which need addressing to meet global targets for biodiversity and forest health. These gaps include highly uneven global research effort, narrow species focus, limited method replication, overlooked seasonal effects, and inconsistent cost reporting. A strong legacy of using chemical methods may also be deterring efforts to develop non-chemical approaches. Immediate action is needed to develop standardised methodologies and reporting channels to close these gaps and thus aid informed choice of management options by practitioners.