Repeated Stand-Replacing Crown Fires Affect Seed Morphology and Germination in Aleppo pine

Abstract

Post-fire reproductive niche of Aleppo pine (Pinus halepensis) is deeply interlaced with fire products. Indeed, the high pH and low osmotic potentials of ash beds under burnt crowns constitute the main constraints to seed germination. In this study, we aim to investigate whether fire recurrence, through the physico-chemical constraints imposed by the ash beds, affects the reproduction ability of P. halepensis at the germination stage. To this aim, Aleppo pine seeds were collected in neighboring even-aged stands subjected to 0, 1, or 2 fires (namely fire cohorts), and seed morphology and germination performance, in terms of cumulative germination and germination kinetics, were studied under increasing osmotic potentials (from 0.0 to −1.2 MPa) and pH (from 6 to 11). Besides fire history, the role of ontogenetic age of mother plants on seed morphology and germination was also investigated. Differences in seed morphology among the three cohorts have been highlighted in a multivariate context, with anisotropic enlargement of the seeds produced by pine stands experiencing repeated fires. The patterns of seed germination varied primarily in relation to the fire cohort, with seeds from the pine stand experiencing repeated fires exhibiting enhanced tolerance to pH stress. Conversely, germination performances under osmotic constraints mainly depends on tree ontogenetic stage, with an involvement of fire history especially in the timing of seed germination. Our results suggest that, at least in the short term, fire recurrence does not constrain the reproduction ability of Aleppo pine. These results highlight the need for further research to elucidate the mechanisms behind these responses to recurrent fires.

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].…”

Fire and legume germination in a tropical savanna: ecological and historical factors

“…Some seed traits (e.g. seed mass, seed shape, dormancy class) are predictors of seed responses to fire temperatures (Ribeiro et al, 2015;Gómez-González et al, 2016;Ramos et al, 2016;Saracino et al, 2017). For instance, larger seeds tend to show higher heat tolerance (Gashaw and Michelsen, 2002;Ribeiro et al, 2015), while smaller ones are more easily stimulated to germinate following fires (Hanley et al, 2003).…”

Effects of geoclimatic factors on the variability in Pinus pinea cone, seed, and seedling traits in Turkey native habitats

“…These were placed in 11-cm-diameter glass Petri dishes that were lined with two layers of filter paper, moistened with deionized water. The germinations were assessed daily, with germinated seeds being removed from the Petri dishes when their radicles had protruded (Farelli et al 1997;Saracino et al 2017). At the end of the test, the ungerminated seeds were subjected to a cut test to determine the proportion of sound to empty seeds in each replication of each treatment.…”