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

Jesús Charco,Nikos Nanos,Martin Venturas,Luis Gil

doi:10.3390/f8090312

Abstract

Small-size, relict and marginal tree-species populations are a priority for conservation of forest genetic resources. In-situ conservation of these populations relies on adequate forest management planning based on knowledge and understanding of both ecological (i.e., recruitment or dispersal dynamics) and population-genetic processes (i.e., female reproductive success, gene flow or inbreeding). Here, we estimate the fecundity (or female reproductive success) of adult trees (i.e., the number of successfully established offspring/adult tree) and the effective dispersal distance distribution in the pine forest of Fuencaliente (southern Spain), a small-sized, marginal and relict population of maritime pine growing on a steep, craggy hill with just 312 reproductively active individuals. Previous studies have shown the population to present reduced allelic richness and suffer from genetic introgression from nearby exotic plantations of unknown origin. Between 2003 and 2004, we surveyed all adults and recruits and we measured several adult-specific covariates, including the number of cones of all adults. The population was found to be distributed into two nuclei with 268 (Stand 1) and 44 adults (Stand 2). We used inverse modeling to adjust several dispersal-and-fecundity models including a model with random variation in fecundity among adults (Unrestricted Fecundity or UF model). Results show that: (i) the average fecundity is 2.5–3.2 recruits/adult; (ii) the mean effective dispersal distance is restricted to 13–24 m and (iii) fecundity is most likely controlled by the spatial location of adult trees in Stand ,1 but it should be considered randomly distributed in Stand 2 (in this stand five adults mothered 80% of recruits). We conclude that the low fecundity in Stand 1 and the unequal fecundity in Stand 2 may decrease the population genetic diversity and lead to lower effective population size while the low average dispersal distance may reduce the probability of this population expanding to adjacent areas. In light of the results, we define the management priorities for in-situ conservation of this population.

Highlights

Small-sized and isolated populations of tree species located in the rear-edge of the range distribution are considered long-term stores of genetic diversity and their conservation is crucial for adaptation of tree species to climate change [1,2]
Fecundity is very low in the pine forest of Fuencaliente and managerial actions seem to be necessary for the conservation of its genetic resources
Unequal fecundity among adults in one of the stands suggests that further loss of genetic diversity may be expected from reproductive inactivity of the majority of adult trees in Stand 2

Summary

Introduction

Small-sized and isolated populations of tree species located in the rear-edge of the range distribution are considered long-term stores of genetic diversity and their conservation is crucial for adaptation of tree species to climate change [1,2]. In situ conservation of genetic resources in such populations relies greatly on adequate forest management aiming at maintaining ecological and population-genetic processes while simultaneously reducing the risk of random genetic drift and allele. The average fecundity and its variation across adults of a population are crucial parameters in population dynamics, especially in small-sized and isolated populations. 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

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