Ecological restoration is a multibillion dollar industry critical for improving degraded habitat. However, most restoration is conducted without clearly defined success measures or analysis of costs. Outcomes are influenced by environmental conditions that vary across space and time, yet such variation is rarely considered in restoration planning. Here, we present a cost-effectiveness analysis of terrestrial restoration methods to determine how practitioners may restore the highest native plant cover per dollar spent. We recorded costs of 120 distinct methods and described success in terms of native versus non-native plant germination, growth, cover, and density. We assessed effectiveness using a basic, commonly used metric (% native plant cover) and developed an index of cost-effectiveness (% native cover per dollar spent on restoration). We then evaluated success of multiple methods, given environmental variation across topography and multiple years, and found that the most successful method for restoring high native plant cover is often different from the method that results in the largest area restored per dollar expended, given fixed mitigation budgets. Based on our results, we developed decision-making trees to guide practitioners through established phases of restoration-site preparation, seeding and planting, and maintenance. We also highlight where additional research could inform restoration practice, such as improved seasonal weather forecasts optimizing allocation of funds in time or valuation practices that include costs of specific outcomes in the collection of in lieu fees.

The limiting similarity hypothesis predicts that communities should be more resistant to invasion by non-natives when they include natives with a diversity of traits from more than one functional group. In restoration, planting natives with a diversity of traits may result in competition between natives of different functional groups and may influence the efficacy of different seeding and maintenance methods, potentially impacting native establishment. We compare initial establishment and first-year performance of natives and the effectiveness of maintenance techniques in uniform versus mixed functional group plantings. We seeded ruderal herbaceous natives, longer-lived shrubby natives, or a mixture of the two functional groups using drill-and hand-seeding methods. Non-natives were left undisturbed, removed by hand-weeding and mowing, or treated with herbicide to test maintenance methods in a factorial design. Native functional groups had highest establishment, growth, and reproduction when planted alone, and hand-seeding resulted in more natives as well as more of the most common invasive, Brassica nigra. Wick herbicide removed more non-natives and resulted in greater reproduction of natives, while hand-weeding and mowing increased native density. Our results point to the importance of considering competition among native functional groups as well as between natives and invasives in restoration. Interactions among functional groups, seeding methods, and maintenance techniques indicate restoration will be easier to implement when natives with different traits are planted separately.

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Ecological restoration is a global priority, with potential to reverse biodiversity declines and promote ecosystem functioning. Yet, successful restoration is challenged by lingering legacies of past land-use activities, which are pervasive on lands available for restoration. Although legacies can persist for centuries following cessation of human land uses such as agriculture, we currently lack understanding of how land-use legacies affect entire ecosystems, how they influence restoration outcomes, or whether restoration can mitigate legacy effects. Using a large-scale experiment, we evaluated how restoration by tree thinning and land-use legacies from prior cultivation and subsequent conversion to pine plantations affect fire-suppressed longleaf pine savannas. We evaluated 45 ecological properties across four categories: 1) abiotic attributes, 2) organism abundances, 3) species diversity, and 4) species interactions. The effects of restoration and land-use legacies were pervasive, shaping all categories of properties, with restoration effects roughly twice the magnitude of legacy effects. Restoration effects were of comparable magnitude in savannas with and without a history of intensive human land use; however, restoration did not mitigate numerous legacy effects present prior to restoration. As a result, savannas with a history of intensive human land use supported altered properties, especially related to soils, even after restoration. The signature of past human land-use activities can be remarkably persistent in the face of intensive restoration, influencing the outcome of restoration across diverse ecological properties. Understanding and mitigating land-use legacies will maximize the potential to restore degraded ecosystems.