Professor University of Puerto Rico San Juan, Puerto Rico, United States
Mast seeding is described as the synchronous and highly variable production of seed crops by a population of perennial plants. Studies on the patterns and drivers of mast-seeding synchrony over time predominantly focus on single-species, however, plant species rarely exist as monocultures. Cross-species synchrony in seed production patterns may occur because the benefits of seed predator satiation promoted through reproductive synchrony may extend to the community level, similarities in attributes between species related to reproductive variability may influence synchrony, or similarities in climatic cues linked to the timing and magnitude of reproduction may result in cross-species synchrony. Conversely, reasons to expect low levels of cross-species synchrony include that the benefits of synchronous reproduction via the pollination-efficiency hypothesis is based on single-species and would not promote synchrony among species, a divergence in species attributes related to reproduction could result in low synchrony, or competition for environmental resources across species could even lead to asynchrony in seed production. Our objectives were to: test for relationships between cross-species synchrony in woody plant reproduction over time and similarities in species attributes, and investigate whether sites with more extreme climates exhibited more cross-species synchrony. We compiled and analyzed data on seed production from a total of 114 species in eight Long-Term Ecological Research (LTER) sites spanning a range of biomes from tropical forest in Puerto Rico (Luquillo LTER) to boreal forest in Alaska (Bonanza Creek LTER). We characterized 11 attributes for each species (e.g. pollination vector, seed development time, leaf longevity, seed mass, shade tolerance, dispersal syndrome) based on the TRY database and literature searches. We quantified cross-species synchrony using spearman correlations for species pairs that overlapped for at least 10 years (maximum: 58 years). Cross-species synchrony was assessed only for co-occurring species within an LTER site; this avoided comparisons between species at large distances and in different biomes. Multiple regression analyses showed that species pairs with the same pollination vectors, leaf longevity, and/or mycorrhizal associations had the highest levels of cross-species synchrony in reproduction. Across LTER sites, the level of cross-species synchrony increased as climate water deficit increased, such that areas with high climatic water deficits (i.e., more arid sites) had higher synchrony in reproduction. Mast seeding has cascading effects in ecosystems, and the level of convergence or divergence in synchrony of seed production across species has consequences for understanding the dynamics of plant regeneration and consumer-resource interactions.