Guiding seed source selection for the production of tropical dry forest trees: Coulteria platyloba as study model

Abstract

A major obstacle faced by reforestation/restoration programs is an insufficient supply of high-quality seed. Seed collection is commonly based on opportunistic strategies that only consider availability and distance to seed sources, but not seed quality. Although for commercial timber species from temperate ecosystems the selection of individuals with above-average phenotypes often results in high-quality seeds and seedlings, the validity of this criterion has not been assessed in tropical dry forests (TDF). By using the abundant TDF tree Coulteria platyloba as study model and piecewise structural equation modelling (pSEM), we examined the associations between germination success and seedling growth, and various tree, fruit and seed characteristics, for seeds from two provenances (natural vs. managed populations), that were either scarified or not. Unexpectedly, phenotypic attributes of trees, fruits and seeds had no effect on germination success, as this response variable depended on scarification only. Also, fruit quality was unrelated to tree size, but it was related to provenance. According to pSEM, the best supported path resulting in high quality seedlings established a relationship between managed populations, high quality fruits and seedlings with better roots systems, but only for seeds that were scarified and did not germinate very rapidly. Overall, the assessed relationships were complex, weak, and sometimes difficult to interpret. Nonetheless, these results provide guidance to improve seed source selection efforts that consider operation costs of nurseries and the success of future plantations. In TDF, selecting trees with above-average phenotypes as seed sources does not necessarily favour the quality of seedlings used to restore degraded areas. In these ecosystems, we recommend a seed collection strategy that combines managed and natural populations as seed sources to maximize genetic variability in future plantations, while improving nursery operation efficacy.