EARLY TO RISE MAKES A PLANT HEALTHY, WEALTHY, AND WISE.

Abstract

Seedling emergence time is a crucial event in the life cycle of a plant, determining its fitness via different components including survival, growth, and fecundity. Precocious emergents usually survive, grow, and/or reproduce earlier in the life cycle, but for perennials it is unknown whether these benefits are maintained throughout the life of the plant. Here, we examine for the first time whether fitness benefits due to the early emergence of perennial plants are perpetuated or vanish with time. For nine years, in a Mediterranean gorse community, we followed the fate of 2118 seedlings belonging to the four dominant woody species. We estimated phenotypic selection gradients on emergence time for three fitness components (survival, growth, and fecundity), under two experimentally simulated scenarios (fire and fire + erosion), at two different times in the life of the plant (3 and 9 years). Fire and erosion represent two potential selective forces constraining the temporal window of seedling emergence in Mediterranean habitats. All the species exhibited selection for early emergence, but through different fitness components. Directional selection favoring early emergence via survival in both fire scenarios was detected in the two Cistaceae species (Helianthemum marifolium and Cistus albidus), in which precocious emergents had higher fitness values late in the life cycle (9 years). In contrast, Fabaceae species (Ononis fruticosa and Ulex parviflorus) were not selected for early emergence via survival. Early emergents of all species in both fire scenarios had higher fitness values through growth early in the life cycle; these benefits decreased slightly with time but remained statistically significant, except in H. marifolium. Finally, late fecundity was enhanced by early emergence in both fire scenarios in C. albidus and U. parviflorus but not in H. marifolium. In conclusion, benefits acquired by emerging early are perpetuated for at least nine years.