Globally, tree fecundity exceeds productivity gradients

Abstract

Lack of tree fecundity data across climatic gradients precludes the analysis of how seed supply contributes to global variation in forest regeneration and biotic interactions responsible for biodiversity. A global synthesis of raw seedproduction data shows a 250‐fold increase in seed abundance from cold‐dry to warm‐wet climates, driven primarily by a 100‐fold increase in seed production for a given tree size. The modest (threefold) increase in forest productivity across the same climate gradient cannot explain the magnitudes of these trends. The increase in seeds per tree can arise from adaptive evolution driven by intense species interactions or from the direct effects of a warm, moist climate on tree fecundity. Either way, the massive differences in seed supply ramify through food webs potentially explaining a disproportionate role for species interactions in the wet tropics.

Gradients in the time seeds take to germinate could alter global patterns in predation strength

“…physical defences, chemical defences (Levin, 1976), camouflage (Porter, 2013)) or mechanisms to escape seed predation such as synchronized seed production (Bogdziewicz et al, 2021) or producing more seeds (Journe et al, 2022). While few such adaptations have been studied at large geographic and taxonomic scales, seed production is indeed higher in the tropics (Journé et al, 2022), potentially evolving to counter high losses to pre-and post-dispersal seed predation. Thus, while we have increasing evidence that seed predation increases toward the equator, we are only just beginning to build a comprehensive understanding of how plants have responded.…”

Linking seed size and number to trait syndromes in trees

“…The MASTIF model and data from the MASTIF network are summarized here and have been described extensively in recent papers (Clark et al, 2019(Clark et al, , 2021Journé et al, 2022;Qiu, Aravena, et al, 2021;Sharma et al, 2022). The tree-year observations of seed numbers in the network come from seed traps and from crop counts.…”

“…We estimated the investment of species into reproduction using two metrics, both scaled to the tree basal area: annual seed number , is the product of seed size (its mass, m s ) and seed number, scaled to tree basal area per year (Journé et al, 2022). We quantify ISP as the mass of a tree's seed production relative to its basal area to standardize for tree size [intermediate trees produce more seeds than smaller ones;…”

“…To control for variation within species and, thus, to sharpen our understanding of interspecific differences, we estimate seed numbers produced by trees within an analytical framework that includes the condition of trees (species, size and shading), habitat (soils) and climate (temperature and moisture deficit), while accommodating dependence between and within trees across years (Clark et al, 2019). This large sample size is important for the notoriously noisy seed production in trees (Kelly et al, 2021), whereby tree-to-tree and year-to-year variation in seed number spans several orders of magnitude (Clark et al, 2004;Journé et al, 2022). By combining seed number with seed size into species seed productivity [seed size × seed number (SSP), developed by Qiu et al (2022)], we show how reproductive traits relate to one another separately and in combination.…”

“…The masting inference and forecasting (MASTIF) network includes 12 million tree-year observations of the number of seeds produced by 775,991 trees from 784 species from a broad range of biomes (Journé et al, 2022;Qiu et al, 2022). To control for variation within species and, thus, to sharpen our understanding of interspecific differences, we estimate seed numbers produced by trees within an analytical framework that includes the condition of trees (species, size and shading), habitat (soils) and climate (temperature and moisture deficit), while accommodating dependence between and within trees across years (Clark et al, 2019).…”