Cunningham, S. C., Mac Nally, R., Baker, P. J., Cavagnaro, T. R., Beringer, J., Thomson, J. R., & Thompson, R. M. (2015). Balancing the environmental benefits of reforestation in agricultural regions. Perspectives in Plant Ecology, Evolution and Systematics, 17(4), 301-317.

Reforestation is an important tool for reducing or reversing biodiversity loss and mitigating climate change. However, there are many potential compromises between the structural (biodiversity) and functional (carbon sequestration and water yield) effects of reforestation, which can be affected by decisions on spatial design and establishment of plantings. We review the environmental responses to reforestation and show that manipulating the configuration of plantings (location, size, species mix and tree density) increases a range of environmental benefits. More extensive tree plantings (>10 ha) provide more habitat, and greater improvements to carbon and water cycling. Planting a mixture of native trees and shrubs is best for biodiversity, while traditional plantation species, generally non-native species, sequester C faster. Tree density can be manipulated at planting or during early development to accelerate structural maturity and to manage water yields. A diversity of habitats will be created by planting in a variety of landscape positions and by emulating the patchy distribution of forest types, which characterized many regions prior to extensive landscape transformation. Areas with shallow aquifers can be planted to reduce water pollution or avoided to maintain water yields. Reforestation should be used to build forest networks that are surrounded by low-intensity land use and that provide links within regions and between biomes. While there are adequate models for C sequestration and changes in water yields after reforestation, the quantitative understanding of changes in habitat resources and species composition is more limited. Development of spatial and temporal modelling platforms based on empirical models of structural and functional outcomes of reforestation is essential for deciding how to reconfigure agricultural regions. To build such platforms, we must quantify: (a) the influence of previous land uses, establishment methods, species mixes and interactions with adjacent land uses on environmental (particularly biodiversity) out- comes of reforestation and (b) the ways in which responses measured at the level of individual plantings scale up to watersheds and regions. Models based on this information will help widespread reforestation for carbon sequestration to improve native biodiversity, nutrient cycling and water balance at regional scales.

Suding, K. N. (2011). Toward an era of restoration in ecology: successes, failures, and opportunities ahead. Annual review of ecology, evolution, and systematics, 42.

As an inevitable consequence of increased environmental degradation and anticipated future environmental change, societal demand for ecosystem restoration is rapidly increasing. Here, I evaluate successes and failures in restoration, how science is informing these efforts, and ways to better address decision-making and policy needs. Despite the multitude of restoration projects and wide agreement that evaluation is a key to future progress, comprehensive evaluations are rare. Based on the limited available information, restoration outcomes vary widely. Cases of complete recovery are frequently characterized by the persistence of species and abiotic processes that permit natural regeneration. Incomplete recovery is often attributed to a mixture of local and landscape constraints, including shifts in species distributions and legacies of past land use. Lastly, strong species feedbacks and regional shifts in species pools and climate can result in little to no recovery. More forward-looking paradigms, such as enhancing ecosystem services and increasing resilience to future change, are exciting new directions that need more assessment. Increased evidence-based evaluation and cross-disciplinary knowledge transfer will better inform a wide range of critical restoration issues such as how to prioritize sites and interventions, include uncertainty in decision making, incorporate temporal and spatial dependencies, and standardize outcome assessments. As environmental policy increasingly embraces restoration, the opportunities have never been greater.

Meli, P., Martínez‐Ramos, M., Rey‐Benayas, J. M., & Carabias, J. (2014). Combining ecological, social and technical criteria to select species for forest restoration. Applied vegetation science, 17(4), 744-753.

Question: How to evaluate and integrate relevant ecological, social and technical criteria to select species to be introduced in restoration projects of highly diverse ecosystems such as tropical riparian forests.

Location: Riparian forest, Marques de Comillas municipality, southeast Mexico (16°54′N, 92°05′W).

Methods: We proposed a ‘species selection index’ (SSI) using five independent criteria related to ecological, social and technical information. SSI targeted species that (1) are important in the reference forest; (2) are less likely to establish following disturbance; (3) are not specific to a particular habitat; (4) are socially accepted; and (5) their propagation requires a reasonable time and financial investment. SSI may range between zero and 50, with higher values meaning higher potential for restoration purposes.

Results: Out of a local pool of 97 species, we identified 30 target tree species that together represented >60% of total importance value index in the reference riparian forests. SSI averaged 28.3  1.0 over the studied species, suggesting that species with high values are not frequent. For 20 species, reintroduction by means of active forest restoration was deemed necessary. Species that established through natural regeneration, following secondary regrowth, had lower social value among local farmers. Nearly half of the identified species showed technical constraints for easy propagation and seeding.

Conclusions: The proposed procedure is useful for selecting species to initiate forest restoration projects and of other woody ecosystems that harbour high biodiversity, and is suitable for several stakeholders interested in restoration.

Melo, F. P., Pinto, S. R., Brancalion, P. H., Castro, P. S., Rodrigues, R. R., Aronson, J., & Tabarelli, M. (2013). Priority setting for scaling-up tropical forest restoration projects: Early lessons from the Atlantic Forest Restoration Pact. Environmental Science & Policy, 33, 395-404.

Ongoing conversion of tropical forests makes it urgent to invest in ecological restoration on grand scales in order to promote biodiversity conservation and ecosystem services. The 4-year old Atlantic Forest Restoration Pact (AFRP) aims to restore 15,000,000 ha of tropical forest in 40 years. The approaches and lessons learned appear transferable, and could help achieve the global restoration targets. Fundamental prerequisites for success include: effective technology undergoing continuous improvement, ongoing teaching, outreach and capacity-building efforts, presence of local intelligentsia, maintaining a clear and transparent legal environment, and presence of effective economic instruments and incen- tives for landowners. These prerequisites can be achieved by expanding and strengthening the network of stakeholders both in public and private forums that must be aware of macro- economic and social/cultural shifts and trends which may provide opportunities and impose constraints to further restoration activities. Finally, environmental regulations imposing habitat protection and restoration are usually beyond individual land-owners’ possibilities and level of interest. Therefore, forest restoration, even in a biodiversity hotspot, must be approached as a potentially sustainable economic activity. Otherwise, private landowners, and most other stakeholders, will not persevere.

Lawson, S.S. and Michler, C.H., 2014. Afforestation, restoration and regeneration – Not all trees are created equal. Journal of Forestry Research, 25(1): 3−20 DOI 10.1007/s11676-014-0426-5.

Undulations in weather patterns have caused climate shifts of increased frequency and duration around the world. The need for additional research and model data on this pressing problem has resulted in a plethora of research groups examining a particular tree species or biome for negative effects of climate change. This review aims to (1) collect and merge recent research data on regeneration within old- and new-growth forests, (2) highlight and expand upon selected topics for additional discussion, and (3) report how shade tolerance, drought tolerance, and inherent plasticity affect tree growth and development. Although shade and drought tolerance have been well studied by a number of research groups, this review reveals that in-depth analysis of a single or a few species in a given area will not generate the data required to implement a successful regeneration plan. Studies using historical accounts of previous species composition, information regarding site seasonality, species competition, and individual responses to drought and shade are needed to (1) develop best management plans and (2) ensure future modeling experiments are focused on a greater variety of species using more innovative methods to evaluate climate change effects.

Holl, K. D. (2017). Restoring tropical forests from the bottom up. Science, 355(6324), 455-456.

Recent initiatives at regional, national, and global scales have called for unprecedented levels of forest restoration to counteract decades of rapid deforestation (1, 2). Thus far, 30 countries have committed to restore 91 million hectares (ha) of deforested landscapes, an area the size of Venezuela, by 2020; at the 2014 United Nations Climate Summit, a global target of 350 million ha was set for 2030 (1). These bold targets are motivated by diverse goals, including conserving biodiversity, sequestering carbon, improving the water supply, and sustaining human livelihoods (2, 3). How can these challenging targets be met, given competing land uses and limited funds for restoration?

Chazdon, R. L., Brancalion, P. H. S., Lamb, D., Laestadius, L., Calmon, M., & Kumar, C. (2017). A policy-driven knowledge agenda for global forest and landscape restoration. Conserv Lett 10: 125–132.

The global restoration movement is gaining momentum. International and national leaders are demonstrating unparalleled political will for achieving ambitious targets. However, the knowledge base for implementing large-scale forest and landscape restoration (FLR) needs further development. Besides application of scientific and local knowledge, a broad understanding of the social, economic, and environmental context in which this knowledge is being applied is also needed. To address knowledge gaps and guide implementation of FLR at local to global scales we propose a knowledge creation agenda that we derive from emerging policy goals. We present a holistic approach that addresses food security, ecosystem services, and livelihoods, and that supports implementation by a wide array of actors from farmers and municipalities to corporations and state agencies. Our knowledge creation agenda is based on six broad policy goals, with several associated knowledge gaps for each goal. We recognize that this agenda is simply a starting point and will surely evolve and become more locally focused as the concept of FLR gains ground and as multiple groups of stakeholders engage in the long-term process of restoring functionality and value to ecosystems and landscapes around the world.

Vadell, E., de-Miguel, S., & Pemán, J. (2016). Large-scale reforestation and afforestation policy in Spain: A historical review of its underlying ecological, socioeconomic and political dynamics. Land Use Policy, 55, 37-48.

Spain had not more than six million hectares of woodlands in the mid-19th century. Nowadays woodlands cover more than sixteen million hectares. During the last one hundred and fifty years, much effort was devoted to improving forest cover and, as a result, five million hectares were artificially regenerated, which represents ten percent of the whole country area. All this work required large nursery infrastructures, thousands of workers and high public investments. The outcome of these reforestation and afforestation efforts is nowadays obvious throughout the Spanish landscapes, and sometimes has given rise to controversy between supporters and opponents. Nevertheless, the process that led to the vast reforestation of Spain has not been yet studied in depth from a historical perspective. This study aims at reconstructing that historical process, by describing it through several features that help to understand the historical development of the artificial forest regeneration policy in Spain, together with its social, political and economic context. The study period comprises since 1879 to present, with special focus on the recent history, that is, since the mid-20th century. The lessons learnt from this analysis may contribute to improving the design of large-scale reforestation policies as well as their potential impacts in other parts of the world and, in the end, shed light on the debate about the possible solutions to deforestation and forest degradation.

Löf, M., Madsen, P., Metslaid, M., Witzell, J., & Jacobs, D. F. (2019). Restoring forests: regeneration and ecosystem function for the future. New Forests, 50(2), 139-151.

Conventions and policies for biodiversity conservation and climate change mitigation state the need for increased protection, restoration and climate change adaptation of forests. Much degraded land may be targeted for large-scale forest restoration, yet challenges include costs, a shortage of regeneration material and the need for restored forests to serve as a resource for communities. To ensure ecosystem function for the future, forest restoration programs must: (1) learn from the past; (2) integrate ecological knowledge; (3) advance regeneration techniques and systems; (4) overcome biotic and abiotic disturbances and (5) adapt for future forest landscapes. Historical forest conditions, while site-specific, may help to identify the processes that leave long-term legacies in current forests and to understand tree migration biology/population dynamics and their relationship with climate change. Ecological theory around plant–plant interactions has shown the importance of negative (competition) and positive (facilitation) interactions for restoration, which will become more relevant with increasing drought due to climate change. Selective animal browsing influences plant–plant interactions and challenges restoration efforts to establish species-rich forests; an integrated approach is needed to simultaneously manage ungulate populations, landscape carrying capacity and browse-tolerant regeneration. A deeper understanding of limiting factors that affect plant establishment will facilitate nursery and site preparation systems to overcome inherent restoration challenges. Severe anthropogenic disturbances connected to global change have created unprecedented pressure on forests, necessitating novel ecological engineering, genetic conservation of tree species and landscape-level approaches that focus on creating functional ecosystems in a cost-effective manner.

Strassburg, B. B., Iribarrem, A., Beyer, H. L., Cordeiro, C. L., Crouzeilles, R., Jakovac, C. C., … & Visconti, P. (2020). Global priority areas for ecosystem restoration. Nature, 586(7831), 724-729.

Extensive ecosystem restoration is increasingly seen as being central to conserving biodiversity and stabilizing the climate of the Earth. Although ambitious national and global targets have been set, global priority areas that account for spatial variation in benefits and costs have yet to be identified. Here we develop and apply a multicriteria optimization approach that identifies priority areas for restoration across all terrestrial biomes, and estimates their benefits and costs. We find that restoring 15% of converted lands in priority areas could avoid 60% of expected extinctions while sequestering 299 gigatonnes of CO2—30% of the total CO2 increase in the atmosphere since the Industrial Revolution. The inclusion of several biomes is key to achieving multiple benefits. Cost effectiveness can increase up to 13-fold when spatial allocation is optimized using our multicriteria approach, which highlights the importance of spatial planning. Our results confirm the vast potential contributions of restoration to addressing global challenges, while underscoring the necessity of pursuing these goals synergistically.