Abstract:
1. 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.
2. 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.
3. 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.
4. Hydrogel and sand amendments increased initial seedling survival, but after 2 years
no differences among treatments were found.
5. 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.
