Seed germination variability and its association with functional traits in submontane tropical forest species of Indonesia: recommendations for direct seeding

Seed germination is a crucial component of the reproductive cycle of plants, and thus, knowledge of germination strategies plays a vital role in species selection for seed-based forest restoration. Conducting germination testing for tropical species requires enormous resources. Therefore, a functional trait-based approach is needed to predict germination success based on seed traits. However, there is a lack of comprehensive information on germination and the correlation between functional traits and germination for tropical native species. In this study, we assessed seed traits and conducted germination assays for 31 woody plant species from the submontane tropical forest of West Java, Indonesia. Our results indicated that seed functional traits and germination varied among the species examined. Germination clustered into five categories: early-high, early-medium, early-low, late-low, and failed. Specific seed traits can be used to predict both germination percentage and mean germination time. Variability in seed coat ratio and seed dormancy explains differences in germination percentages, while mean germination time is primarily influenced by seed mass and seed coat thickness. This study presents valuable germination data for ten woody tropical native species that germinate readily without the need for special treatments, including Acer laurinum, Aphanamixis polystachya, Engelhardia serrata, Ficus fistulosa, F. ribes, Gaultheria leucocarpa, Maoutia diversifolia, Ormosia penangensis, Phyllanthus emblica, and Saurauia pendula. Incorporating a trait-based approach in species selection strategies may reduce the number of seeds required for direct seeding and enhance the germination success of direct seeding efforts.