Dec. 2022 Science Corner | Diversity for Restoration (D4R): Guiding the selection of tree species and seed sources for climate resilient restoration of tropical forest landscapes

Authors: Tobias Fremout, Evert Thomas, Hermann Taedoumg, Siebe Briers, Claudia Elena Gutiérrez-Miranda, Carolina Alcázar-Caicedo, Antonia Lindau, Hubert Mounmemi Kpoumie, Barbara Vinceti, Chris Kettle, Marius Ekué, Rachel Atkinson, Riina Jalonen, Hannes Gaisberger, Stephen Elliott, Esther Brechbühler, Viviana Ceccarelli, Smitha Krishnan, Harald Vacik, Gabriela Wiederkehr-Guerra, Beatriz Salgado-Negret, Mailyn Adriana González, Wilson Ramírez, Luis Gonzalo Moscoso-Higuita, Álvaro Vásquez, Jessica Cerrón, Colin Maycock, Bart Muys

Interview and story by: Annapurna Holtzapple, Project Associate

Forests are critical ecosystems for habitat and biodiversity across the globe. They’re also deeply interconnected to human communities and provisioning benefits such as water storage, carbon sequestration, nutrition and food security, public health, and cultural and traditional resources. In the face of rapid deforestation due to harvest, grazing, and urban expansion, tree planting pledges have become widespread. In particular, tree planting and reforestation commitments are heavily emphasized as steps to reach the UN Decade of Ecosystem Restoration goals.

However, ecologically appropriate tree planting requires a deep understanding of the location and conditions of the parcel to be either reforested or conserved. Forests are complex, interconnected ecosystems, and decisions about tree planting designs require familiarity with the way different tree species perform over time, interspecies interactions in the ecosystem, and appreciation of the particular socio-ecological challenges that an area may face.

As discussed in this NYT article, reforestation initiatives must consider the right tree, in the right place, for the right reason, and the decision about what is “right” varies widely based on the intended objectives of a restoration project. Planting only for carbon sequestration outcomes does not consider biodiversity, long term resilience of the forest, or its various ecosystem benefits like habitat, public health, and water storage.

Informed and ecologically appropriate reforestation initiatives include considerations such as which tree species are native to a region, which provide specific co-benefits like erosion control or producing valued goods in agroforestry systems, and the needs of local communities who interact with and depend on the forest. In addition to these nuances, restoration practitioners now face the challenge of climate change and the emerging need to anticipate how long-lived species like trees will be impacted by changing water availability, heat patterns, and storm occurrences.

In particular, tropical forests are incredibly complex. These forests have extremely high biodiversity and can have hundreds of local tree species (compared to, for example, the yellow-pine mixed conifer system in the Sierra Nevada, which has five primary tree species). Given this biodiversity and species richness, reforestation commitments that rely primarily on planting new trees are especially challenging in tropical forests. To address this hurdle, researchers at the Alliance Bioversity International – CIAT and KU Leuven developed a scalable, free online tool called Diversity for Restoration (D4R) as discussed in this paper to the Applied Ecology journal.

At Blue Forest, work that was catalyzed to address the urgency of the wildfire crisis across the Western US is being expanded to riverscapes, coastal restoration, and international landscapes. D4R similarly addresses myriad needs and valuable outcomes of forest restoration, such as restoration for habitat and biodiversity goals, conservation and reforestation of degraded or converted forests, timber production, and agroforestry with a specific cultural understanding of the needs and nuances of various areas.

Tobias Fremout, an applied ecologist and lead author on this paper, emphasized the importance of thinking carefully about which species will be planted. Fremout highlighted the need for species diversity and appropriate seed selection in this work. “In restoration planning, it is important to think carefully about all of these steps, including the selection of the right species and seed sources, so they can be tailored to suit local conditions and objectives.”

Initially built for the tropical dry forests of Colombia, the D4R tool has been expanded to the forests of Burkina Faso, Cameroon, southern Ecuador, and northwestern Peru. D4R is also being developed for forested ecosystems of western Ethiopia, northern Thailand, the Sabah state of Malaysia, and the Western Ghats in India.

Restoration of these ecosystems is remarkably nuanced due to their diverse species composition, land use competition from grazing and promotion of crops for export, and various introduced and naturalized plants that have traveled from around the globe into tropical ecosystems. The place-based design of this tool is essential, as communities around the world interact with their forests in regionally specific and distinct ways, with various cultural and nutritional resources housed in these forests.

D4R is intended to support landscape scale restoration through unit-by-unit planning to create an overall biodiverse, functionally resilient forest mosaic. It can account for various target values, such as restoration for habitat and biodiversity goals, water supply protection, timber production, and agroforestry. In addition to catering to target values, regionally-specific concerns can also be accounted for in D4R, such as extreme drought, fire, pests, or disease. As D4R grows, new restoration objectives can be incorporated. Current additions are expanding to include goals related to nutrition and food security, and dynamic needs such as shade tree selection in cacao and coffee agroforestry systems. Fremout is also working on expanding the tool for agroforestry needs, particularly focused on cacao agroforestry throughout Ecuador, Peru, and Colombia.

D4R is freely available online in English, Spanish, and French. The tool is designed to support practitioners of all backgrounds, from scientists and restoration project managers to local governments, cooperatives, and NGOs. Fremout explained the value of D4R as an accessible way to gather and integrate fragmented knowledge from both academia and local communities.

“There is a lot of scientific knowledge on these species, but it often remains in scientific articles or in databases that are difficult to use, or even just in the heads of scientists. Then there is also local knowledge, held by the people living in those forests, who already know many of these things firsthand,” he said. “We found there is a need for a platform to put all of this information together and that’s what this tool does.”

D4R users will guide their restoration design through the input of various site conditions and information such as location, proximity to water, proximity to farmland, soil conditions, and threats like habitat fragmentation, fire, or steepness.

The tool is programmed with data about species that currently grow in the area and modeling to demonstrate and interpret how they will perform in future climate scenarios. This process considers and weighs a species’ adaptations that best fit the site’s specific conditions and tree species characteristics as they correspond to the desired restoration objectives. D4R then scores these potential species based on trait data, prevalent conditions like water and soil stress, and restoration objectives. Finally, functional and phylogenetic diversity are optimized as determined by the weighted goals and conditions at the site, to provide specific species recommendations. Fremout also emphasized that the design and planting process is only one component of these projects, “adaptive management, monitoring, and local communities feeling involved with a restoration project, are all important building blocks of a successful restoration process” where success is understood to be the long term survival of these planted trees and that the ecosystem meets particular goals and objectives of the community.

As we at Blue Forest know from exploring how conservation finance can support replanting and post-fire restoration, nursery and seed sourcing limitations are primary constraints for many reforestation operations. D4R anticipates and incorporates this challenge by laying out seed zones corresponding to the recommended species composition. The common replanting practice in ecology is to source locally, which is traditionally best for ensuring the persistence of condition-appropriate adaptations and protecting local population genetics. However, in many of the tropical dry forests this tool is intended for, the existing seed sources are fragmented and have low genetic diversity. This increases the risk of poor growth and mortality of seedlings. The seed zones provided by D4R identify geographic areas where planting material is dynamic (in anticipation of climate disturbances) and can be moved freely without reducing population fitness. Moreover, the D4R tool will include contact details of people or institutions who can provide specific seeds from appropriate sources. On the delicacy and nuance of sourcing seeds, Fremout emphasized that using seeds adapted to local conditions is critical to the success of the restoration project.

While many scientists and individuals in these restoration spaces have approved and support the methods and outputs of D4R, the author team indicates that the tool’s success will ultimately be determined by whether it is used and adopted into planning practices by on-the-ground restoration groups. Like most restoration initiatives, they also recommend that long-term monitoring be established for continued management needs, a primary goal of conservation finance and need that Blue Forest works to support.