Tropical dry forests (TDFs) are critically endangered, and their restoration is understudied. Large-scale passive restoration efforts in north-west (NW) Costa Rica have catalysed TDF regeneration but are not effective on degraded Vertisols, where active restoration is necessary due to high content of shrink–swell clays that impede regeneration following degradation. We established a large-scale restoration experiment in degraded former pastures in NW Costa Rica to determine (1) the restoration potential of native TDF tree species on Vertisols, (2) if plant functional traits elucidate mechanisms behind interspecific variability in species performance and (3) if affordable and readily available soil amendments increase seedling survivorship and growth. We planted 1,710 seedlings of 32 native species coupled with five amendments aimed at ameliorating root-zone microclimatic conditions: sand, rice hulls, rice hull ash, hydrogel and unamended controls. For each species, we quantified a suite of resource-acquisition and ecophysiological functional traits, and monitored survival and growth seasonally over 2 years. Interspecific survivorship after 2 years ranged widely (0%–92.5%). Functional traits including wood density, photosynthetic parameters and upregulation of integrated water-use efficiency, explained interspecific variation in survivorship and growth at distinct ontogenetic stages. Easily measured leaf traits, however, were not good predictors of restoration potential. Hydrogel and sand amendments increased initial seedling survival, but after 2 years no differences among treatments were found. Synthesis and applications. We have shown it is possible, albeit challenging, to restore tropical dry forest (TDF) on degraded Vertisols. Our results support the use of functional trait-based screenings to select tree species for restoration projects as tree species with high survivorship and growth in this stressful environment have overlapping ecophysiological functional traits. Furthermore, practitioners should consider water-use and phytosynthetic traits when designing initial species mixes for TDF restorations.
Bibliographical noteFunding Information:
?omments from Rakan A. Zahawi, Susan M. Galatowitsch, Adam Martin, and three anonymous reviewers greatly improved this manuscript. This experiment was supported by a NSF GRFP 11-582, G?A Restoration Fellowship, UMN ?arolyn ?rosby and Dayton grants (to L.K.W), and a NSF ?AREER DEB-1053237 (to J.S.P.). Thanks to Daniel Pérez-Avilés, Géraldine Derroire, Beatriz G. Exceed, ?hristina M. Smith, Ronald ?astro and many volunteers for excellent field help, to Roberto ?ordero (UNA ?osta Rica) for use of the AD? instrument, and to Roger Blanco (A?G) for facilitating this work.
NSF, Grant/Award Number: GRFP 11-582 and ?AREER DEB-1053237; G?ARestoration Fellowship; UMN ?arolyn ?rosby and Dayton grants
© 2017 The Authors. Journal of Applied Ecology © 2017 British Ecological Society
- Costa Rica
- active restoration
- native species
- plant functional traits
- seedling establishment
- soil amendments
- stable isotopes
- tropical dry forest
- water-use efficiency