Fire favors sexual precocity in a Mediterranean pine

Abstract

Wildfires are a natural disturbance in many ecosystems. Consequently, plant species have acquired traits that allow them to resist and regenerate in an environment with recurrent fires. A key trait in fire‐prone ecosystems is the age at first reproduction (maturity age); populations of non‐resprouting species cannot persist when the fire interval is shorter than this age. Maturity age is variable among individuals, so we hypothesized that short fire intervals select for early seed production (precocity). We selected 13 plots with different fire regimes in eastern Spain, all dominated by Pinus halepensis (a non‐resprouting serotinous pine species). Then, we evaluated the age at first reproduction and the size of the canopy seed bank of each individual tree. Our results show a significant effect of fire regime on the onset of reproduction in this species, suggesting a selection towards higher precocity in populations subject to shorter fire intervals. Due to this higher precocity, pines stored more cones and therefore, increased their potential for reproduction post‐fire. We provide the first field evidence that fire can act as a driver of precocity. Being precocious in fire‐prone environments is adaptive because it increases the probability of having a significant seed bank when the next fire arrives.

Plant phenotypes as trajectories: 38-yr monitoring reveals that shape of lifetime fecundity schedule is under selection in a long-lived shrub

“…Keeping these caveats in mind, it is worth noting that results of this study are among the few instances to date of empirical support to some central tenets of life history evolution theory in a within-population context. Regarding landmark parameters, the strong negative directional selection on age at first reproduction found here agrees with the selective value consistently attached to reproductive precocity in models of life history evolution, particularly in the case of species with colonizing, expanding populations (Cole, 1954; Lewontin, 1965; Stearns, 1976, 1992; Harper, 1977) such as L. latifolia and, more generally, Mediterranean woody plants whose populations are exposed to recurrent wildfires (Guiote and Pausas, 2023). Positive directional selection on reproductive lifespan also agrees with some assumptions of life history theory (Stearns, 1992).…”

Assessment of Pinus halepensis Forests’ Vulnerability Using the Temporal Dynamics of Carbon Stocks and Fire Traits in Tunisia

“…Regarding the regeneration potential of seeds, we were able to quantify the increasing cone biomass with age, but this started at 25 years old, before which no cones were observed in our area. This maturity threshold is higher than that previously reported for this species which was around 15 years old [72], but fire frequency has been shown to stimulate earlier maturity [73,74] and more cone biomass [10]. A relationship between cone biomass and DBH was previously demonstrated [75], so that older forests have an increased ability to regenerate as a consequence of there being more cones to germinate [76], although seed number was also not always considered as a limiting factor once the trees had passed the maturity threshold [77].…”

Evolutionary fire ecology: An historical account and future directions

“… 2013 , Vandvik et al. 2014 , Guiote and Pausas 2023 , Keeley 2023 ). Fire, by opening vegetation gaps, provides opportunities for the evolution of many light-demanding shade-intolerant species (Bond 2019 , Pausas and Lamont 2022 ).…”

“… 2013 , Vandvik et al. 2014 , Guiote and Pausas 2023 , Keeley 2023 ). What are the limits of those evolutionary changes in the framework of our current fire regime changes?…”