Tree rings provide information about environmental change through recording stress events, such as fires, that can affect their growth. The aim of this study was to investigate wood growth reactions in Pinus halepensis Mill. trees subjected to wildfires, by analysing anatomical traits and carbon and oxygen isotope composition. The study area was Southern France where two sites were selected: one subjected to fires in the last 50 years, the other characterised by comparable environmental conditions although not affected by fire events (control site). We analysed whether wood growth depends on the tangential distance between developing xylem cells and the limit where the cambium was directly damaged by fire. In the burnt site, thick wood sections, including fire-scar, were taken from surviving plants. Digital photo-micrographs were analysed to measure early- and latewood width, wood density, and tracheid size. Anatomical and isotopic traits were analysed in two series of tree rings (5 rings before and 5 after the fire) selected at different positions along the circumference (close or far from the scar). Anatomical and isotopic traits were quantified also on tree rings of the same years from cored trees growing at the control site. Results showed different wood reaction tendencies depending on the distance from the scar. The comparison between plants from the two sites allowed to exclude possible climate interference.
Our results are discussed in terms of two kinds of growth reactions: the local need to promptly compartmentalise the scarred cambial zone and sapwood after fire, and the general growth perturbations due to tree reaction to crown scorch during fire. Anatomical results, combined with dendrochronological and isotopic analysis, could provide an efficient way to distinguish between direct growth reactions due to heat-related damage on cambium and indirect outcomes related to defoliation.