Determination of bark production costs, a fireadaptive trait, in a Mediterranean pine species

Abstract

Bark thickness is a fire-adaptive trait in plants, influenced by environmental factors. In this study, we use Pinus halepensis to study the production costs of bark, because even though this species is an obligate seeder, recent studies showed that some populations could survive certain fire regimens. In dry continental climates, P. halepensis populations require more time and resources to develop the minimum basal bark thickness necessary for survival under moderately intense fires. However, these populations do not reach a critical bark thickness at breast height. This can increase the immaturity risk, dead by fire before establishing an aerial seed bank capable of ensuring recruitment. Understanding ecotypic patterns, phenotypic plasticity, and relative resource allocation to bark requires assessing the construction costs of bark and wood, which have not been previously studied in trees. To address this, we collected bark and wood samples at breast height and the tree base by a destructive analysis. The samples underwent carbon-nitrogen (C/N) ratio analysis and ash/nitrate determination, as carbon concentration is a reliable indicator of construction costs. Our results showed that, as expected, bark construction costs were higher than wood. The construction costs of bark were also significantly higher than wood at the tree base. Moreover, we observed significant differences among populations between the costs of wood and bark, and in some cases, between breast height and the tree base. These findings highlight the importance of studying resource allocation to key adaptive traits such as bark thickness. Furthermore, our results confirm the importance of bark thickness in P. halepensis so implementing silvicultural treatments to reduce immaturity risk under changing climatic conditions is essential for the conservation and management of its populations, ensuring their persistence.

Este trabajo fin de máster trata sobre la determinación de los costes de construcción de la corteza y de la madera del pino carrasco, y la comparativa entre ambos para poder conocer mejor los patrones ecotípicos de esta especie además de la asignación de recursos y la plasticidad fenotípica entre diferentes poblaciones de toda la distribución natural de la especie, estudiando un caracter de la corteza como es su grosor y la propia corteza como adaptación al fuego. La metodología empleada ha sido el análisis del ratio carbono nitrógeno por calcinación y la determinación de nitratos por colorimetría, ya que el carbono es un buen indicador de los costes de construcción.