Dating lightning: Dendrochronological and magnetic analyses of lightning scars

Abstract

Lightning impacts on forests and trees are still understudied from a tree-ring perspective. Lighting causes direct and indirect damages on forests and trees. Trees struck by lightning can show a growth reduction and lightning storms also trigger wildfires in seasonally dry areas such as Mediterranean mountains. Here we combined dendroecological and magnetic analyses to reconstruct and assess the impact of lightning on radial growth and the magnetic properties of wood in Scots pine (Pinus sylvestris) and Black pine (Pinus nigra) in two sites with a high density of lightning impacts located in eastern Spain. We dated several lightning scars, particularly in Scots pine, formed during 1982, when a wildfire was initiated by lightning during a dry summer storm. Growth was reduced during the year when the scar was formed in both pine species, albeit this effect could be masked or amplified by other disturbances (drought, outbreaks). However, despite that short-term growth reduction scarred trees showed higher growth rates than non-scarred trees in the case of Scots pine. The intensity of magnetization did not significantly differ in wood produced before and after the lightning scar was formed. This could be due to multiple lightning hits in the same or nearby stands affecting the magnetization of wood. Wood magnetic properties should be further explored as proxies of lightning impacts in sites where scars are not formed and tree-ring information is limited such as tropical forests. Further cross-disciplinary research is required to assess the impacts of lightning on tree growth and magnetism.