Temporal change and determinants of maternal reproductive success in an expanding oak forest stand

Abstract

Summary1. Global change is generating widespread local-scale expansions of tree populations. During demographic expansions, even small differences in individual reproductive success can generate large differences in the genetic composition of the resulting population. Colonizing tree populations almost invariably show highly skewed distributions of seed production, but the evolution of this reproductive skew during plant recruitment remains understudied. 2. We examine how recruit mortality modifies initial patterns of acorn dispersal and maternal reproductive success in a recently established, expanding Pedunculate oak (Quercus robur) forest stand and test different predictors of successful recruit establishment. 3. We mapped and genotyped a cohort of seedlings (n = 809) emerging within and around the stand (n = 254 adult trees), identified their habitats and monitored their fate until an age of 3 years. Their mother trees were inferred by Bayesian parentage analysis, and the number of assigned descendants was used as a proxy for tree maternal fertility. We examined temporal trends in tree fertility and patterns of dispersal, and tested effects of seed number-quality trade-offs, dispersal failure, dispersal distance and habitat of propagule arrival on the probability of seedling establishment. 4. We observed marked inequality in maternal reproductive success at the time of seedling emergence. A positive relationship between tree fertility and the proportion of non-dispersed seedlings pointed to disperser satiation. An overall seedling mortality of 69% generated considerable reshuffling in the fertility ranking of individual trees. Non-dispersal more than doubled seedling mortality. The establishment success of actually dispersed seedlings was independent of mother fertility and dispersal distance but strongly related to the habitat of arrival. Recruit survival was markedly higher in pine plantations or non-forested areas than in broadleaved forest. 5. Synthesis. A few highly fertile trees dominated reproduction in the stand. Differential recruitment success tended to reduce their initial advantage, however, suggesting that reproductive inequality might rapidly decline as more trees start to reproduce along the expansion process. Our results also suggest that field estimates of size or seed production are unlikely to provide reliable estimates of lifetime reproductive success in trees.

Effective Seed Dispersal and Fecundity Variation in a Small and Marginal Population of Pinus pinaster Ait. Growing in a Harsh Environment: Implications for Conservation of Forest Genetic Resources

“…According to our results, the hypothesis that fecundity is greater for bigger individuals should be rejected (see also [8,36]). Models based on tree size (basal area and tree height) to estimate fecundity were rejected for their performance being smaller than the null model.…”

“…Fecundity variation among adults will determine the population´s effective size or the within-population spatial genetic structure [7,8]. In addition, depending on pollen flow dynamics, unequal fecundity across adults may likely lead to biparental inbreeding and to a higher risk of random allele fixation and genetic drift that will shape the within-population genetic diversity and its adaptive potential.…”

Insect herbivory and avian insectivory in novel native oak forests: divergent effects of stand size and connectivity

“…Such stands are largely exempt from forest management. Many are actively expanding (Gerzabek et al, 2017), favoured by a recent change in silvicultural management that tends to conserve broadleaved trees recruiting within adjacent pine plantations as a mean of conservation biological control (Castagneyrol et al, 2014;Dulaurent et al, 2011).…”

“…Novel native forest stands establish from a few founder trees that colonize an available habitat patch within an unsuitable matrix through long-distance dispersal and fill their neighbourhood with their offsprings (Gerzabek et al, 2017;Sezen et al, 2005). Such stands share certain characteristics that set them apart from those created by fragmentation: (i) they typically are quite small-sizedeven smaller than the smallest fragments of remnant forest; (ii) they are dominated by young trees, resulting in a reduced amount and range of habitats available to forest-dwelling species (Franklin, 1988;Fuller et al, 2018); and (iii) all their species necessarily originate from colonization events over a limited period of time, implying that these systems are triggered by immigration credit instead of extinction debt (Jackson and Sax, 2010).…”

Dispersal processes driving plant movement: challenges for understanding and predicting range shifts in a changing world

“…). In this SF, three contributions relate to this aspect by (i) considering pollen dispersal as a vector of gene flow that comes in addition to seed migration (Klein, Lagache‐Navarro & Petit ; Robledo‐Arnuncio & Gaggiotti ) and (ii) deciphering how the local dispersal patterns determine the variance of reproductive success and the effective population size with regard to genetic drift (Gerzabek, Oddou‐Muratorio & Hampe ). Robledo‐Arnuncio & Gaggiotti (2017) and Gerzabek, Oddou‐Muratorio & Hampe (2017) both use molecular marker data to reconstruct dispersal events and raise conclusions about contemporary migration rates and/or dispersal kernels.…”