Severe growth disturbances in an early Permian calamitalean – traces of a lightning strike?

Abstract

Woody trees are regarded as excellent natural data archives, even far back in geological time. In addition to regular growth patterns, destruction scars bear witness to various kinds of growth disturbances which are recorded as a result of environmental impact during the life time of a tree. Although stem injuries can provide significant insight into plant-environment interactions, only minor attention has been paid to this subject in the fossil record. Here, we present a fossil scar documented in a petrified, basal calamitalean stem ( Arthropitys bistriata ) found in growth position in the early Permian Chemnitz Fossil Forest (SE-Germany). Because this forest was buried under volcanic deposits in a geological instant (i.e., a T 0 assemblage), the fossil lagerstätte permits detailed investigations of anatomically preserved plants and their environment. The special injury of the calamitalean described herein extends to 40 % of the stem circumference, exhibits an elongated to triangular shape, a central furrow, a scar-associated event ring of collapsed to distorted tracheids, and was ultimately overgrown by callus parenchyma. We suggest that this scar most likely was caused by a lightning strike, as two first order roots, still attached to the stem, show injuries, whereas the neighbouring trees at the excavation site seem to be unaffected. In response to this severe injury, the tree completely recovered within a relatively short time of ca. 12 years, revealing stress-induced rapid growth rates indicated by wide tree rings and large, thin-walled tracheids, and probable basal sprouting. Several scars of various shapes have been recognised in other specimens in the Chemnitz collection and excavation material suggesting multifaceted plant-environment interactions within this early Permian forest ecosystem.