Tree planting must be carefully planned and implemented to achieve desired outcomes

The selection of ecological indicators is an important step toward more effective restoration monitoring. The debate between Reid (2015) and Durigan and Suganuma (2015) regarding the usefulness of species composition for monitoring restoration trajectory is timely and salient, but it lacks a middle way proposal to balance ecological relevance and practical viability. We propose a way forward to resolving this debate, namely using easily measurable functional traits, a type of compositional measure, as an indicator. Assessing functional composition trajectory may help overcome some limitations with taxonomic identification and provide more meaningful outcomes to evaluate restoration success.

Transformative change is needed to align common small‐scale ecological restoration approaches with expectations to restore millions of hectares of degraded lands globally. Currently, most restoration projects target small areas using costly manual methods that cannot be scaled up to meet global commitments. We propose that a judicious integration of agricultural practices into ecological restoration offers an opportunity to address this issue. This transformative process relies on three sequential and interconnected steps: (1) ensure that sufficient land is truly available for restoration; (2) compensate for the loss of agricultural production, income, or land value to encourage landholders to opt for restoration; and (3) develop scalable, affordable, and effective methods for restoring native ecosystems across the pledged hundreds of millions of hectares to deliver benefits to both nature and people. Large‐scale terrestrial restoration will require incorporating agronomic practices into the restoration toolbox to go beyond vague, ambitious promises and wishful thinking.

Extensive evidence shows that regional (gamma) diversity is often lower across restored landscapes than in reference landscapes, in part due to common restoration practices that favor widespread species through selection of easily-grown species with high survival and propagation practices that reduce genetic diversity. We discuss approaches to counteract biotic homogenization, such as reintroducing species that are adapted to localized habitat conditions and are unlikely to colonize naturally; periodically reintroducing propagules from remnant populations to increase genetic diversity; and reintroducing higher trophic level fauna to restore interaction networks and processes that promote habitat heterogeneity. Several policy changes would also increase regional diversity; these include regional coordination amongst restoration groups, financial incentives to organizations producing conservation-valued species, and experimental designations for rare species introductions.

A growing number of initiatives at global, regional and national scales propose to plant millions, billions or even trillions of trees as a simple solution to resolve complex environmental problems. However, tree planting is much more complicated than it seems. We summarize the multifaceted decision‐making process needed and offer guidelines to increase the success of the proposed ambitious efforts to increase tree cover world‐wide. Given the varied definitions of and motivations for tree planting, it is critical that stakeholders work together to clearly define the biophysical and socioeconomic goals of each project. Then a series of questions must be addressed about where and how (e.g. planting trees vs. allowing for natural forest regrowth) to most effectively achieve these goals and minimize unintended negative consequences, as well as how, when and by whom success of efforts will be evaluated. Key guidelines to successfully increase tree cover include: (a) first addressing the underlying drivers of deforestation; (b) integrating decision‐making across scales from local to global; (c) tailoring tree planting strategies to clearly stated project goals and planning, adaptively managing and evaluating success over a sufficiently long timeframe; (d) focusing on the forest ecosystem as a whole, and not just the trees; (e) coordinating different land uses and (f) involving stakeholders at all stages of the planning process. Synthesis and applications. Tree planting, along with other strategies to increase tree cover in appropriate locations and contexts, can make a valuable contribution to ensuring the ecological and social well‐being of our planet in coming decades, but only if these efforts are considered as one component of multifaceted solutions to complex environmental problems and are carefully planned, implemented and monitored over a sufficiently long time‐scale with stakeholder engagement and broader consideration of socio‐ecological complexities.

Applied nucleation and other spatially patterned restoration methods are promising approaches for scaling up projects to meet ambitious international restoration commitments in an ecologically and economically sound manner. Much of the corresponding literature to date, however, has centered around theoretical discussions and small‐scale studies that are largely divorced from constraints faced by restoration practitioners. We briefly review recent academic literature about applied nucleation and other spatially patterned restoration methods and discuss practical challenges to their implementation. We offer several recommendations to move spatially patterned restoration from an academic conversation to scalable application, including: (1) comparing different planting designs and natural regeneration within the same system at an appropriate scale; (2) monitoring ecological outcomes throughout the restored area over sufficient time to evaluate recovery; (3) quantifying costs and documenting other logistical constraints to implementation; and (4) exploring methods for using unplanted areas to provide benefits to landholders until planted vegetation establishes.

Monitoring protocols are needed to evaluate the millions of hectares of land that are being proposed for forest restoration in the coming decades. Standardized proposals are critical to evaluate efficacy of restoration strategies, identify triggers for corrective actions, compare results across projects, and generally learn from past projects to inform future restoration efforts. We describe an iterative process, including over 200 stakeholders, to develop a protocol for monitoring Brazilian Atlantic Forest restoration. We give an overview of the ecological, socioeconomic, and management criteria, indicators, and metrics included in the protocol. Strengths of the protocol include the following: (a) testing and use across sites with a range of ages, forest types, past land uses, restoration techniques, and implementing institutions; (b) participation by a broad range of government, nongovernment, private, and academic institutions in the protocol development process; and (c) inclusion of socioeconomic and management criteria. Next steps for facilitating the broad adoption of the protocol in the Atlantic Forest region include providing in person and online training courses, establishing an online repository for storing and comparing monitoring data, and developing smartphone applications to facilitate data collection. Although the protocol was developed for the Atlantic Forest context and further refinements are needed, we think that the Atlantic Forest Pact monitoring protocol may serve as a model to inform the development of similar protocols in other regions, which ultimately could be integrated to produce a pantropical protocol for common use by several restoration forest programs worldwide.