Scientific Publications
The sounds of forest recovery: assessing the efficacy of Costa Rica's PES program through soundscapes
Can large-scale forest restoration bring biodiversity back? Using sound recordings from 119 sites across Costa Rica, we examined biodiversity recovery under the country's Payment for Ecosystem Services program. We found that restored forests had soundscapes increasingly resembling those of mature forests, suggesting substantial ecological recovery. Naturally regenerating forests showed stronger recovery than monoculture tree plantations, highlighting the importance of restoration approaches that encourage natural forest development. These findings provide compelling evidence that forest restoration can support biodiversity recovery across entire landscapes, demonstrating the potential of well-designed conservation incentives to address biodiversity loss and climate change at meaningful scales.
Delgado, G. L., J. van den Hoogen, D. H. Dent, et al. 2026. “ Large-Scale Forest Restoration Accompanied by Biodiversity Recovery in Costa Rica's Redistributive Payment for Ecosystem Service Program.” Global Change Biology 32, no. 2: e70730. https://doi.org/10.1111/gcb.70730
Spread of invasive ginger in native forests
Zingiber spectabile, a shade-tolerant ornamental ginger native to Southeast Asia, is invading tropical forest across Central America and South America, raising concerns about its impacts on native biodiversity and forest recovery. Our research found that Z. spectabile thrives in both old-growth and regenerating forests, but is three times more abundant in regenerating forests. Its prolific seed production and ability to resprout from cut stems enable rapid spread and make it particularly difficult to control. Chemical and mechanical control efforts increased native understory plant abundance within the first year, but had limited effect on ginger which reinvaded quickly. These findings highlight the growing threat of shade-tolerant invasive plants and the urgent need for more effective management strategies to protect tropical forests.
Cole et al. (2026). Spread of invasive ginger Zingiber spectabile in successional and old-growth tropical forest. Revista de Biología Tropical, 74. https://doi.org/10.15517/7jtv6t72
Contribution of biomass burning to black carbon deposition on Andean glaciers
Smoke from fires in the Amazon Basin can travel long distances and settle on glaciers high in the Andes. This study combined measurements of light-absorbing particles in snow and ice at four sites in Peru and one in Bolivia with computer models of atmospheric transport and snow reflectivity. Field measurements at Yanapaccha and Shallap glaciers in Peru’s Cordillera Blanca complemented ice-core and snow records from other high mountain sites. Led by Eimy Bonilla, the international collaboration included renowned glacier researcher Lonnie Thompson, Peruvian scientist Wilmer Sanchez Rodriguez, and researchers from several institutions. The study estimated that smoke from vegetation fires in the Amazon contributed approximately 20–70% of black carbon deposited at the study sites, depending on location. Black carbon darkens snow and increases its absorption of sunlight. The findings reveal a potentially important connection between regional fires, air pollution, and the continuing loss of tropical glaciers.
Bonilla, E. X., Mickley, L. J., Beaudon, E. G., Thompson, L. G., Rodriguez, W. E., Cruz Encarnación, R., Whicker, C. A., Flanner, M. G., Schmitt, C. G., & Ginot, P. (2023). Contribution of biomass burning to black carbon deposition on Andean glaciers: Consequences for radiative forcing. Environmental Research Letters, 18(2), 024031. https://doi.org/10.1088/1748-9326/acb371
Integrating belowground recovery into tropical forest restoration
Restoring tropical forests involves more than bringing back trees. Healthy soils, roots, and soil organisms are essential for carbon storage, biodiversity, and long-term ecosystem resilience, yet they are often overlooked in restoration monitoring. In this paper, we examine how belowground conditions influence forest recovery and whether aboveground vegetation can provide clues about soil health. We also propose a practical monitoring framework using affordable indicators of soil physical, chemical, and biological recovery. Our findings highlight the importance of looking beneath the surface to better understand restoration success and guide more effective, lasting tropical forest restoration efforts.
Laura Toro, Leland K Werden, et al. Integrating belowground recovery into tropical forest restoration design and monitoring, BioScience, Volume 75, Issue 11, November 2025, Pages 937–952, https://doi.org/10.1093/biosci/biaf097
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Innovations for upscaling forest landscape restoration
Restoring the world’s degraded forests is essential for addressing climate change and biodiversity loss, but high costs often limit restoration at scale. How can we accelerate forest recovery while making restoration more affordable? Drawing on 143 studies, we evaluated seven innovative restoration approaches that have demonstrated promising results in forests, woodlands, and mangroves. We found that these techniques can substantially improve vegetation recovery compared with conventional practices, although their effectiveness and costs depend on local conditions. Our findings highlight that many of the tools needed to accelerate global restoration already exist. The next challenge is implementing and evaluating them at scale.
Werden LK, Cole RJ, Schönhofer K, Holl KD, Zahawi RA, Averill C, Schweizer D, Calvo-Alvarado JC, Hamilton D, and Joyce FH (2024) Assessing innovations for upscaling forest landscape restoration. One Earth 7:1515–1528. DOI: 10.1016/j.oneear.2024.07.011
Forest restoration in practice across Latin America
Forest restoration offers a powerful opportunity to address climate change and biodiversity loss, but how is restoration being implemented on the ground? We surveyed 166 restoration practitioners across 14 Latin American countries to examine their goals, strategies, and costs. We found that practitioners combine multiple approaches, with tree planting remaining dominant despite its high costs. Larger projects increasingly rely on lower-cost natural regeneration. Importantly, restoration requires sustained investment well beyond initial planting, while monitoring often fails to adequately measure biodiversity recovery. Our findings highlight the need for cost-effective approaches, practical biodiversity monitoring, and long-term funding to achieve lasting restoration success.
Cole RJ, Werden LK, Arroyo FC, Quirós KM, Cedeno GQ, and Crowther TW (2024) Forest restoration in practice across Latin America. Biological Conservation 294:110608. DOI 10.1016/j.biocon.2024.110608
Assessment of smartphone apps for forest monitoring
As forest restoration expands worldwide, affordable and reliable tools are urgently needed to track recovery and measure success. We reviewed 42 smartphone applications and tested five promising tools against traditional field monitoring methods in Costa Rica, with additional evaluations by 15 partner organizations. Smartphone apps measured tree diameter accurately but were less reliable for assessing canopy openness and ground vegetation cover. Although they did not reduce fieldwork time, they eliminated the need for some specialized equipment. Our findings highlight the potential of smartphone-based monitoring while emphasizing the need for improved accuracy, coordinated app development, and standardized methods to evaluate restoration outcomes.
Schweizer, D., Cole, R.J., Werden, L.K., Cedeño, G.Q., Rodriguez, D., Navarro, K., Esquivel, J.M., Max, S., Chiriboga, F.E., Zahawi, R.A., Holl, K.D. and Crowther, T.W. (2024), Review and assessment of smartphone apps for forest restoration monitoring. Restor Ecol, 32: e14136. https://doi.org/10.1111/rec.14136
Active restoration accelerates tropical forest bird recovery
How can we restore tropical forests that support the rich diversity of birds found in natural ecosystems? We monitored bird communities over 12 years across 11 restoration sites in Costa Rica, comparing conventional tree plantations, planted tree islands, and natural regeneration. Both planting strategies accelerated the return of forest-associated birds, with tree islands performing as well as plantations despite requiring substantially less planting. Natural regeneration recovered more slowly but showed increasing benefits over time. Our findings highlight how strategic tree planting can accelerate biodiversity recovery while emphasizing the importance of long-term monitoring to track the return of forest specialists.
Joyce FH, Rosales JA, Holl KD, Zahawi RA, Bui A, and Reid JL (2024) Active restoration accelerates recovery of tropical forest bird assemblages over two decades. Biological Conservation 293:110593
How landscape structure influences tropical forest restoration success
Restoring tropical forests requires more than planting trees—it also depends on the surrounding landscape. How do forest cover, fragmentation, and connectivity influence recovery? We studied forest-dependent birds and naturally establishing tree seedlings at restoration sites in southern Costa Rica to understand how landscape structure shapes restoration success. Landscapes with more forest cover, less fragmentation, and better-connected forest corridors supported greater bird abundance and diversity. Similar, though weaker, patterns emerged for tree seedlings. Our findings highlight the importance of protecting forest remnants and connecting habitats, particularly through riverside forest corridors, to improve biodiversity recovery and the long-term success of tropical forest restoration.
San-José, M., Werden, L.K., Joyce, F.H. et al. Effects of landscape structure on restoration success in tropical premontane forest. Sci Rep 12, 13452 (2022). https://doi.org/10.1038/s41598-022-16542-3
Pollution and its impacts on the South American Cryosphere
Glaciers throughout the Andes are retreating, threatening water supplies for communities, agriculture, and hydropower. This review examines how air pollution, particularly black carbon (soot) from biomass burning, transportation, and urban emissions, may contribute to glacier loss. When deposited on snow and ice, these light-absorbing particles reduce surface reflectivity, increasing solar energy absorption and potentially accelerating melting. The publication brings together scientific observations, atmospheric modeling, and regional policy considerations to assess the impacts of pollution on South America's glaciers. Although existing measurements demonstrate that black carbon reaches high-elevation glaciers, insufficient observations make it difficult to determine how much pollution contributes to their retreat relative to other climate factors. The study highlights the urgent need for expanded monitoring, coordinated international research, and policies that reduce pollution while protecting vulnerable mountain water resources.
Molina, L.T., Gallardo, L., Andrade, M., Baumgardner, D., Borbor-Córdova, M., Bórquez, R., Casassa, G., Cereceda-Balic, F., Dawidowski, L., Garreaud, R., Huneeus, N., Lambert, F., McCarty, J.L., Mc Phee, J., Mena-Carrasco, M., Raga, G.B., Schmitt, C. and Schwarz, J.P. (2015), Pollution and its Impacts on the South American Cryosphere. Earth's Future, 3: 345-369. https://doi.org/10.1002/2015EF000311
Coffee pulp accelerates early tropical forest succession
Could agricultural waste help bring degraded tropical forests back to life? Restoring forests on abandoned agricultural lands is challenging, especially where depleted soils and invasive pasture grasses prevent trees from establishing. In southern Costa Rica, we tested whether discarded coffee pulp could jump-start natural forest recovery, with remarkable results. Within just two years, coffee pulp enriched soils, eliminated pasture grasses, and triggered rapid vegetation growth. Compared to untreated land, the amended area supported 20 times more woody stems, 30 times greater tree and shrub basal area, and four times taller vegetation. Our findings reveal an exciting opportunity to turn agricultural waste into a powerful tool for tropical forest restoration.
Cole RJ, Zahawi RA. Coffee pulp accelerates early tropical forest succession on old fields. Ecol Solut Evidence. 2021; 2:e12054. https://doi.org/10.1002/2688-8319.12054
Applied nucleation facilitates tropical forest recovery
Can we restore tropical forests by planting fewer trees and letting nature do more of the work? Applied nucleation is a restoration strategy that plants small islands of trees across degraded landscapes, creating habitats that attract seed-dispersing wildlife and encourage forests to regenerate naturally. In a 15-year experiment across 15 sites in southern Costa Rica, we found that tree islands were nearly as effective as conventional tree plantations in restoring biodiversity, forest structure, and ecosystem functions, but at lower cost. Our findings demonstrate how working with natural regeneration processes can make tropical forest restoration more affordable and scalable.
Holl KD, Reid JL, Cole RJ, Oviedo-Brenes F, Rosales JA, Zahawi RA. Applied nucleation facilitates tropical forest recovery: Lessons learned from a 15-year study. J Appl Ecol. 2020; 57: 2316–2328. https://doi.org/10.1111/1365-2664.13684
Light absorbing particles on the glaciers in the Cordillera Blanca, Peru
Glaciers in Peru’s Cordillera Blanca are shrinking, threatening an important source of water for nearby communities. This study investigated whether light-absorbing particles, such as soot from combustion and mineral dust, is a substantial contributor to glacier melting. During the 2011, 2012, and 2013 dry seasons, 240 snow samples were collected from 15 mountains at elevations between 4,800 and nearly 6,800 meters. Light absorbing particles were analyzed using a newly developed, low-cost technique that measures how strongly they absorb visible light. Results showed that snow from glaciers near the city of Huaraz contained substantially more light-absorbing material than snow from more remote glaciers. These measurements were the first of their kind in South America. These findings provided early evidence that local air pollution may contribute to glacier loss, with important implications for regional water resources.
Schmitt, C. G., All, J. D., Schwarz, J. P., Arnott, W. P., Cole, R. J., Lapham, E., and Celestian, A.: Measurements of light-absorbing particles on the glaciers in the Cordillera Blanca, Peru, The Cryosphere, 9, 331–340, https://doi.org/10.5194/tc-9-331-2015
The ephemerality of secondary forests in southern Costa Rica
Regenerating tropical forests can restore biodiversity and capture carbon, but these benefits take decades to develop. What happens when recovering forests are cleared again before reaching maturity? We analyzed aerial photographs spanning 67 years across a 320 km² landscape in southern Costa Rica to examine how long secondary forests persist. We found that half were cleared again within 20 years, and 85% within 54 years. Larger forest patches and those near rivers were more likely to persist. Our findings highlight a critical challenge for forest restoration: achieving lasting environmental benefits requires not only encouraging forest regeneration but also protecting recovering forests over the long term.
Reid JL, Fagan ME, Lucas J, Slaughter J, Zahawi RA. The ephemerality of secondary forests in southern Costa Rica. Conservation Letters. 2019; 12:e12607. https://doi.org/10.1111/conl.12607
Does ecosystem function or biodiversity recover first?
How quickly do tropical forests recover the ecological processes that sustain healthy ecosystems? Decomposing leaves recycle essential nutrients, with insects and other soil-dwelling invertebrates playing a critical role. We studied forests recovering from cattle pastures, comparing sites of different ages with old-growth forests to understand how nutrient cycling and decomposer communities recover. Within 15–30 years, leaf litter production and nutrient levels approached those of old-growth forests. Larger invertebrates accelerated decomposition and nutrient release, yet their communities remained distinct even in older regenerating forests. Our findings reveal that essential ecosystem functions can recover long before the biodiversity supporting them fully returns.
Cole RJ, Selmants P, Khan S, Chazdon R. Litter dynamics recover faster than arthropod biodiversity during tropical forest succession. Biotropica. 2020; 52: 22–33. https://doi.org/10.1111/btp.12740
Return of leaf litter arthropods during tropical forest restoration
How can we restore the extraordinary biodiversity of tropical forests, including the small creatures that sustain healthy ecosystems? We compared three forest restoration strategies in southern Costa Rica to examine how soil and leaf-litter arthropods, including insects and other invertebrates, recover on abandoned pastures. After eight years, planting small islands of trees supported greater arthropod abundance, diversity, and ecological functions than conventional tree plantations or natural regeneration. However, none of the approaches fully restored the communities found in mature forests. Our findings highlight the potential of cost-effective tree island restoration while emphasizing the irreplaceable value of conserving existing forests.
Cole, R.J., Holl, K.D., Zahawi, R.A., Wickey, P. and Townsend, A.R. (2016), Leaf litter arthropod responses to tropical forest restoration. Ecol Evol, 6: 5158-5168. https://doi.org/10.1002/ece3.2220
Emergent trees in tropical forests of the Osa Peninsula
The largest trees in tropical rainforests store enormous amounts of carbon, yet we know surprisingly little about what determines where these giants grow. Using airborne laser scanning and imaging technology, we mapped towering emergent trees across Costa Rica’s Osa Peninsula to investigate how landscape features influence their distribution. We found that these forest giants were far more abundant in valleys and on lower slopes than on ridges and upper slopes. Their leaves also contained less nitrogen than those of surrounding trees. Our findings reveal how local topography shapes tropical forest structure, with important implications for understanding forest carbon storage and biodiversity.
Balzotti, C.S., Asner, G.P., Taylor, P.G., Cole, R., Osborne, B.B., Cleveland, C.C., Porder, S. and Townsend, A.R. (2017), Topographic distributions of emergent trees in tropical forests of the Osa Peninsula, Costa Rica. Ecography, 40: 829-839. https://doi.org/10.1111/ecog.02062
Mapping carbon in tropical rainforests
Tropical forests store vast amounts of carbon, but why do some landscapes hold far more than others? Using airborne laser scanning (LiDAR) and field measurements, we mapped forest carbon stocks across Costa Rica’s Osa Peninsula, home to some of the most carbon-rich forests in the Neotropics. We found trees reaching 67 meters in height and exceptionally high carbon storage. Our results revealed that geology and topography help shape how carbon is distributed across the landscape, with important differences even over short distances. These findings demonstrate the power of remote sensing to map forest carbon and improve our understanding of tropical ecosystems.
Taylor P, Asner G, Dahlin K, Anderson C, Knapp D, et al. (2015) Landscape-Scale Controls on Aboveground Forest Carbon Stocks on the Osa Peninsula, Costa Rica. PLOS ONE 10(6): e0126748. https://doi.org/10.1371/journal.pone.0126748
Nitrogen across a remote rainforest transect
How will rising temperatures affect the nutrients that sustain tropical forests? Nitrogen is essential for forest growth, yet its cycling through tropical soils remains poorly understood, particularly under changing climate conditions. We studied soils at 40 rainforest sites spanning 1,800 meters in elevation across Central America to investigate how temperature and rainfall influence nitrogen dynamics. We found striking differences between cool, wet mountain forests and warmer lowland forests, with evidence suggesting substantially greater nitrogen losses to the atmosphere at lower elevations. Our findings reveal important links between climate and soil nutrient cycling, helping us better anticipate how tropical forests may respond to global warming.
Weintraub, S. R., R. J. Cole, C. G. Schmitt, and J. D. All. 2016. Climatic controls on the isotopic composition and availability of soil nitrogen across mountainous tropical forest. Ecosphere 7(8):e01412. 10.1002/ecs2.1412
Restoring forests by planting tree islands
Can we accelerate tropical forest recovery while planting far fewer trees? Conventional restoration relies on costly, large-scale tree planting, but smaller clusters of trees may offer an effective alternative. We tested applied nucleation—planting islands of trees to attract seed-dispersing wildlife and encourage natural regeneration—across eight former pasture sites in southern Costa Rica. After four years, tree islands attracted more than twice as many naturally establishing animal-dispersed trees as unplanted areas, matching conventional plantations despite planting only 20% of the area. Our findings highlight a promising, lower-cost strategy that works with natural processes to restore tropical forests.
Zahawi, R.A., Holl, K.D., Cole, R.J. and Reid, J.L. (2013), Testing applied nucleation as a strategy to facilitate tropical forest recovery. J Appl Ecol, 50: 88-96. https://doi.org/10.1111/1365-2664.12014
Scaling forest restoration by planting tree islands
Can planting trees in small islands offer a more affordable alternative to conventional forest plantations? We tested these two restoration strategies across 12 former agricultural sites in southern Costa Rica, monitoring the survival and growth of four native tree species over three years. Seedling survival was equally high in both approaches, although trees generally grew faster in plantations and experienced more maintenance-related damage in islands. Growth also varied considerably among species and sites, with nitrogen-fixing trees performing particularly well. Our findings highlight the potential of tree islands to reduce restoration costs while emphasizing the importance of species selection and site-specific management.
Holl, K.D., Zahawi, R.A., Cole, R.J., Ostertag, R. and Cordell, S. (2011), Planting Seedlings in Tree Islands Versus Plantations as a Large-Scale Tropical Forest Restoration Strategy. Restoration Ecology, 19: 470-479. https://doi.org/10.1111/j.1526-100X.2010.00674.x
Sowing the seeds of forest recovery
Restoring tropical forests requires bringing back native tree species that often struggle to regenerate naturally, particularly those with large seeds that are poorly dispersed across fragmented landscapes. Could planting seeds directly offer an affordable solution? We tested five native tree species across abandoned pastures, young secondary forests, and restoration plantations in southern Costa Rica. After two years, seedling survival was highest beneath planted trees, reaching 75%, compared to approximately 40% in other habitats. Direct seeding cost 10–30 times less than planting nursery-grown seedlings. Our findings highlight an affordable strategy for enriching recovering forests with native tree diversity.
Cole RJ, Holl KD, Keene CL, and Zahawi RA (2011) Direct seeding of late-successional trees to restore tropical montane forest. Forest Ecology and Management 261:1590–1597. 10.1016/j.foreco.2010.06.038
Paying farmers to grow trees: benefits for people and nature
Can Costa Rica’s pioneering Payments for Environmental Services (PES) program encourage small-scale farmers to plant more trees while improving their livelihoods? We evaluated the program’s agroforestry incentives in southern Costa Rica, interviewing participating and nonparticipating farmers alongside local organizations. Farmers receiving PES payments planted substantially more trees and a greater diversity of species, while reporting positive economic benefits during the first years. Financial incentives and support from local organizations helped overcome barriers to adopting agroforestry. Our findings demonstrate the potential of Costa Rica’s PES program to support sustainable farming and biodiversity, while highlighting the importance of continued technical assistance.
Cole, R. J. (2010). Social and environmental impacts of payments for environmental services for agroforestry on small-scale farms in southern Costa Rica. International Journal of Sustainable Development & World Ecology, 17(3), 208–216. https://doi.org/10.1080/13504501003729085