Experimental Evidence for Scalable, Cost-Effective Revegetation Interventions

Field-based evaluations regarding the cost-effectiveness of planting interventions are required to maximise the effcicacy of funding and resources allocated to revegetation efforts. Yet, costs and benefits are frequently reported in isolation or left undisclosed, leaving stakeholders with an incomplete picture of the resourcing required to support large-scale revegetation efforts. In particular, early evaluations of costs and benefits are important to consider to ensure that interventions are on track to achieve desired outcomes. We compare the cost-effectiveness of early plant establishment across three revegetation interventions (direct seeding, pelletised seeding, and tubestock seedlings) using theoretical and empirical, field-based methods to provide guidance on the costs and benefits of different interventions and inform evidence-based decision-making in native species revegetation. Theoretical estimates of cost-effectiveness were developed via Theories of Change, which map interventions to desired outcomes. Empirical estimates of cost-effectiveness were derived by combining implementation cost accounting with observed benefits from an experimental field trial that systematically compared each planting intervention. We show that the cost of establishing individual seedlings and the cost-effectiveness of revegetation as a whole significantly differed depending on intervention and planting scale. All revegetation interventions were cost-effective with scale; however, seed-based interventions provide the most cost-effective and scalable outcomes, with direct-seeded and pelleted plots exhibiting 1.8- and 1.6-times higher returns on investment compared to tubestock plantings. Tubestock, while more expensive to implement, yielded lower weed cover and more even establishment across the planted target species relative to either seed-based intervention, providing benefits that may be worth the added cost depending on the desired outcomes of a restoration project. Our methods and results provide evidence upon which practitioners and policymakers can base decision-making around the most cost-effective revegetation interventions for optimising ecological restoration outcomes.