For over two decades, I have studied factors limiting recovery and strategies to restore tropical forests in former agricultural lands in the the neotropics. My own field work is in Costa Rica, but I have advised students and/or have collaborations studying tropical forest restoration in Mexico, Panama, Colombia, Brazil, and other countries in Latin America. In 2004, I started a long-term, large-scale tropical forest restoration study with collaborator Dr. Zak Zahawi (Director of University of Hawaii Lyon Arboretum) and funding from the National Science Foundation. We are studying the novel idea of planting small patches of trees (islands) as a low-cost method to encourage seed dispersal and shade out pasture grasses. We are also investigating the effect of the amount of surrounding forest cover on forest recovery in these sites. We and collaborators have been measuring seed rain, seedling establishment, litterfall, birds, bats, insects, lichens, and many other variables in these sites for over 15 years. Our results show that planting tree islands is an effective and comparatively cheaper approach to accelerate forest recovery that better simulates the natural recovery process than a traditional plantation-style restoration approach. In addition, results to date show that the amount of surrounding forest cover does not strongly influence animal-dispersed seed rain and native woody species establishment early in succession. For more information on our results and outreach see our summaries and publications listed below. As we are moving through the second decade of this study, the results continue to become more interesting given that we have one of the few well-replicated, long-term studies of tropical forest recovery. Check out our 7-min summary video on the project (Spanish version).
General Audience Publications
Holl, K.D. & Reid, J.L. 2020. Do we really need to plant a trillion trees? Trees islands are an ecologically and economically sound strategy for tropical forest recovery. The blog discusses our Journal Applied Ecology paper which summarizes 15 years of results from our long-term experiment in Costa Rica.
Holl, K. D. 2019. Rules of thumb for predicting tropical forest recovery. This blog provides a general summary of our 2018 Applied Vegetation Science paper.
Holl, K.D., J.L. Reid, and R. A. Zahawi. 2016. Tree islands for tropical forest restoration: the outlooks is rosy after 10 years. This blog provides a general summary of our 2017 Journal of Applied Ecology paper on tree recruitment in our study.
Holl K.D. 2014. The (Forest) Island Effect. This blog provides a general overview of our research.
Kimbrough, L. 2014. Tree islands a more effective way to replant the worlds forest. General overview of our research published on the Mongabay rainforest news website.
Holl, K.D. 2013 Restoring Tropical Forest. This short article published in "Nature Education Knowledge" an open source educational journal provides an introduction to tropical forest restoration for classes and a general audience. Click here for translations En Español. Em Português.
Holl, K.D. (2012) Tropical forest restoration. Restoration Ecology (eds J. Van Andel & J. Aronson), pp. 103-114. Blackwell Publishing, Malden, MA.
When and Where to Actively Restore Ecosystems? This short summary by Karen Holl and Mitch Aide suggests some criteria for determining how to allocate limited conservation resources most effectively in a restoration context. En Español. Em Português.
Selected Scientific Publications
Holl, K. D., et al. 2020. Applied nucleation facilitates tropical forest recovery: Lessons learned from a 15-year study. Journal of Applied Ecology 57, 2316-2328.
Brancalion, P.H.S., Amazonas, N.T., Chazdon, R.L., van Melis, J., Rodrigues, R.R., Silva, C.C., . . . Holl, K.D. 2020. Exotic eucalypts: From demonized trees to allies of tropical forest restoration? Journal of Applied Ecology 57, 55-66.
Calle, A. & K. D. Holl (2019) Riparian forest recovery following a decade of cattle exclusion in the Colombian Andes. Forest Ecology and Management 452, 117563.
Holl, K. D., J. L. Reid, F. Oviedo-Brenes, A. J. Kulikowski, and R. A. Zahawi. 2018. Rules of thumb for predicting tropical forest recovery. Applied Vegetation Science 21:669-677.
Lanuza, O., F. Casanoves, R. A. Zahawi, D. Celentano, D. Delgado, and K. D. Holl. 2018. Litterfall and nutrient dynamics shift in tropical forest restoration sites after a decade of recovery. Biotropica 50:491-498
Holl, K. D. 2017. Research directions in tropical forest restoration. Annals of the Missouri Botanical Garden 102:237-250.
Holl, K. D., J. L. Reid, J. M. Chaves-Fallas, F. Oviedo-Brenes & R. A. Zahawi. 2017. Local tropical forest restoration strategies affect tree recruitment more strongly than does landscape forest cover. Journal of Applied Ecology 54:1091-1099.
Cole, R. J., K. D. Holl, R. A. Zahawi, P. Wickey & A. R. Townsend. 2016. Leaf litter arthropod responses to tropical forest restoration. Ecology and Evolution 6:5158-5168.
Reid, J. L., J. M. Chaves-Fallas, K. D. Holl & R. A. Zahawi. 2016. Tropical forest restoration enriches vascular epiphyte recovery. Applied Vegetation Science 19: 508-517.
Reid, J. L., K. D. Holl, and R. A. Zahawi. 2015. Seed dispersal limitations shift over time in tropical forest restoration. Ecological Applications 25:1072-1082.
Zahawi, R.A., J.P. Dandois, K. D. Holl, D. Nadwodny, J. L. Reid, and E.C. Ellis. 2015. Using lightweight unmanned aerial vehicles to monitor tropical forest recovery. Biological Conservation 186:287-295.
Reid, J. L., C. D. Mendenhall, J. A. Rosales, R. A. Zahawi, and K. D. Holl. 2014. Landscape context mediates avian habitat choice in tropical forest restoration. Plos One 9:e90573.
Holl, K. D., and R. A. Zahawi 2014. Factors explaining variability in woody above-ground biomass accumulation in restored tropical forest. Forest Ecology and Management 319:36-43.
Holl, K. D., V. M. Stout, J. L. Reid & R. A. Zahawi. 2013. Testing heterogeneity-diversity relationships in tropical forest restoration. Oecologia 173:569–578.
Zahawi, R. A., K. D. Holl, R. J. Cole & J. L. Reid. 2013. Testing applied nucleation as a strategy to facilitate tropical forest recovery. Journal of Applied Ecology 50:88-96.
Reid, J. L. & K. D. Holl. 2013. Arrival ≠ Survival. Restoration Ecology 21:153-155.
Lindell, C. A., R. J. Cole, K. D. Holl, and R. A. Zahawi. 2012. Migratory bird species in young tropical forest restoration sites: effects of vegetation height, planting design, and season. Bird Conservation International 22:94-105.
Holl, K. D. R. A. Zahawi, R. J. Cole, R. Ostertag, and S. Cordell. 2011. Planting seedlings in tree islands versus plantations as a large-scale tropical forest restoration strategy. Restoration Ecology 19: 470-479.
Holl, K.D., Aide, T.M., 2011. When and where to actively restore ecosystems? Forest Ecology and Management 261: 1588-1563.
Cole, R.J., Keene, C., Zahawi, R.A., and Holl, K.D. 2011. Direct seeding of late successional trees to restore tropical montane forest. Forest Ecology and Management 261:1590-1597.
Bonilla-Moheno, M. and K. D. Holl. 2010. Direct seeding to restore tropical mature-forest species in areas of slash-and-burn agriculture. Restoration Ecology 18(S2):438-445.
Cole, R.J., Holl, K.D., Zahawi, R.A. 2010. Seed rain under tree islands planted to restore degraded lands in a tropical agricultural landscape. Ecological Applications 20: 1255-1269.
Vieira, D. L. M., K. D. Holl, and F. M. Peneireiro. 2009. Agro-successional restoration as a strategy to facilitate tropical forest recovery. Restoration Ecology: 17: 451–459.
Holl, K. D. 2002. Effect of shrubs on tree seedling establishment in abandoned tropical pasture. Journal of Ecology 90:179-187.
Holl, K. D., M. E. Loik, E. H. V. Lin, and I. A. Samuels. 2000. Restoration of tropical rain forest in abandoned pastures in Costa Rica: overcoming barriers to dispersal and establishment. Restoration Ecology 8:339-349.
Holl, K. D. 1999. Factors limiting tropical moist forest regeneration in agricultural land: seed rain, seed germination, microclimate and soil. Biotropica 31:229-242.
Collaboration and Data Sharing
We have had numerous collaborators to date and welcome additional collaborators on our research project. To request more information on collaborating send an introductory email with your background, interests, and request to Dr. Karen Holl (kholl at ucsc.edu) and Dr. Zak Zahawi (rakan.zahawi at gmail.com). Many data for this project are available at merritt.cdlib.org/m/ucsc_lib_hollzahawi. If you are going to use our data for synthetic analyses we ask that you email us to let us know how you are using the data. For queries about additional data sets please contact Dr. Holl.