Islas Project

  D Research Description
In 2004, Dr. Rakan (Zak) Zahawi (Director of the Charles Darwin Foundation) and Dr. Karen Holl (UC Santa Cruz) started a long-term, large-scale tropical forest restoration studying applied nucleation (planting small patches or "islands" of trees) 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 now been measuring seed rain, seedling establishment, litterfall, birds, bats, insects, lichens, and many other variables in these sites for over 17 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 in the first decade of succession. For more information on our results and outreach see our summaries and publications listed below. As we move 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). We are extremely appreciative of multiple grants from the U.S. National Science Foundation and our numerous collaborators in Costa Rica, the US, and other countries that have allowed us to continue this research.

Recent General Audience Publications 

Wilson, S. J., N. S. Alexandre, K. D. Holl, J. L. Reid, R. Zahawi, D. Celentano, S. Sprenkle-Hyppolite, and L. Werden. 2021. Applied nucleation guide for tropical forests. Conservation International.

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. 
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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.

Selected Scientific Publications and Data

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.

Kulikowski II, A. J. 2020. Ant–scale mutualism increases scale infestation, decreases folivory, and disrupts biological control in restored tropical forests. Biotropica 52:709-716. Data

Werden, L. K., K. D. Holl, J. A. Rosales, J. M. Sylvester, and R. A. Zahawi. 2020. Effects of dispersal- and niche-based factors on tree recruitment in tropical wet forest restoration. Ecological Applications 30:e02139. Data

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. Data

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. Data

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. Data

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. Data

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. Data

Holste, E. K., K. D. Holl, R. A. Zahawi, and R. K. Kobe. 2016. Reduced aboveground tree growth associated with higher arbuscular mycorrhizal fungal diversity in tropical forest restoration. Ecology and Evolution 6:7253-7262. Data​

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. Data

Reid, J. L., C. D. Mendenhall, R. A. Zahawi, and K. D. Holl. 2015. Scale-dependent effects of forest restoration on Neotropical fruit bats. Restoration Ecology 23:681-689.​ Data

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. Data

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. Data

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. Data

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.

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.

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 the links next to the paper above and on Dryad. We also have additional data on soil nutrients, reference forest vegetation data, site descriptions, surrounding forest cover, and other topics. 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 Drs. Holl or Zahawi.