Palaeontographica, Abt. B: Palaeobotany – Palaeophytology Article Vol. 298, Issues 1–3: 1–22 E Stuttgart, September 2018 Severe growth disturbances in an early Permian calamitalean – traces of a lightning strike? by Ludwig Luthardt, Mathias Merbitz, and Ronny Rößler With 10 text-figures and 1 table 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 T0 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. Keywords: Chemnitz Fossil Forest; T0 assemblage; wood anatomy; tree damage; dendroecology Contents 1 Introduction ������������������������������������������������������������������������������� 2 4.5.1 The palaeosol – former substrate of the in situ 2 Geological setting ��������������������������������������������������������������������� 2 tree . 14 3 Material and methods . 5 4.5.2 Crown remains ������������������������������������������������������� 15 4 Results ����������������������������������������������������������������������������������������� 6 4.5.3 Neighbouring trees of KH0277 . 15 4.1 Anatomy of KH0277 ������������������������������������������������������� 6 5 Discussion . 15 4.2 Stem damage . 6 5.1 Reconstruction of KH0277 . 15 4.3 Root damage ��������������������������������������������������������������������� 13 5.2 Potential causes of damage . 16 4.4 Tree-ring record . 13 5.3 Plant recovery response ��������������������������������������������������� 19 4.5 Periphery of KH0277 . 13 6 Conclusions ������������������������������������������������������������������������������� 19 Acknowledgements ����������������������������������������������������������������������� 20 References ��������������������������������������������������������������������������������������� 20 Authors’ addresses: Ludwig Luthardt, Mathias Merbitz, Ronny Rößler, Museum für Naturkunde Chemnitz, Moritzstraße 20, 09111 Chemnitz, Germany. [email protected] (corresponding author) Ludwig Luthardt, Ronny Rößler, Geological Institute, Technische Universität Bergakademie Freiberg, Bernhard-von-Cotta-Straße 2, 09599 Freiberg, Germany © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/palb/2018/0061 2194-900X/18/0298/0061 $ 9.90 2 L. Luthardt, M. Merbitz, and R. Rößler 1 Introduction Falcon-Lang et al. 2015; Feng et al. 2017). Addi- tionally, fossil stem injuries may provide inferences on The Chemnitz Fossil Forest represents a diverse fossil wound-healing strategies of extinct plants, and the vi- assemblage, which allows detailed studies of ecolog- tality of tree populations in ancient forest ecosystems ical processes and relationships in an early Permian in general. forest ecosystem, both in space and time (Rößler et Trees in the Chemnitz Fossil Forest were buried al. 2012a). Investigation of biotic elements and under- simultaneously in their places of growth by a series of standing of their role in a web of intricate environmen- pyroclastic deposits during a volcanic event. There- tal interactions is the major focus of investigations in fore, they represent a true T0 assemblage (Gastaldo this palaeo-ecosystem. To date, diverse studies on var- et al. 1995; DiMichele & Falcon-Lang 2011). The ious groups of organisms reflect the great potential of tree-ring record obtained from the forest community this unique fossil lagerstätte (Rößler 2000; Rößler encompasses nearly 80 years, whereas single scars were & Noll 2006; Rößler & Noll 2010; Rößler et found in the stem sections at several instances within al. 2008; Rößler et al. 2009; Rößler et al. 2010; this time span (Luthardt et al. 2017). Among them Rößler et al. 2012a; Rößler et al. 2012b; Rößler et is a prominent stem injury in specimen KH0277, a tall al. 2014; Feng et al. 2012; Feng et al. 2014; Dunlop calamitalean tree identified as Arthropitys bistriata & Rößler 2013; Dunlop et al. 2016; Luthardt et (Cotta 1832) Rößler et al. 2012 and found in an al. 2016; Spindler et al. 2018). upright position at the Chemnitz-Hilbersdorf excava- The capability to assess palaeoecological and tion (Rößler et al. 2012a; Rößler et al. 2014; Lu- palaeoenvironmental processes even in their fourth thardt et al. 2016; Luthardt et al. 2017). dimension by dendrochronological and -ecological The first note about a scar in a petrified trunk methods has been recently demonstrated (Luthardt from the Chemnitz Fossil Forest was provided by & Rößler 2017a; Luthardt & Rößler 2017b; Lu- Goeppert (1881). Referring to an Agathoxylon sp. thardt et al. 2017). As a result, tree rings were inter- trunk of 2.24 m extent, he described an elongated, fis- preted to depict a high-resolution climate archive re- sure-shaped scar, which shows a bulbous to elongated vealing climatic oscillations most likely caused by the overgrowth of wounded wood, reminding him of frost 11-year solar cycle (Luthardt & Rößler 2017a). cracks (Goeppert 1881: plate III, fig. 8). Different types of tree rings were recorded by pycno- The scope of this contribution is to evaluate po- xylic gymnosperms, calamitaleans and medullosan tential causes of a major injury and resulting recovery seed ferns, and differentiated, based on their morpho- reactions in the calamitalean KH0277 by applying logical features (Luthardt et al. 2017). Among these palaeobotanical and dendroecological methods to a tree-ring types, so called event rings (Type 3 according volcaniclastic T0 assemblage. Results shed light on un- to Luthardt et al. 2017) appear among the most usual plant-environment interactions within a short conspicuous growth interruptions. They occur in time span of several decades in an early Permian forest transverse sections of all investigated plants as solitary ecosystem. zones of injured living wood and are overgrown by pa- renchymatous callus tissue (Luthardt et al. 2017). Subtypes 3b and 3c only occur in calamitaleans and 2 Geological setting medullosans, and are interpreted to record episodes of The study site is located in the Chemnitz Basin (Sax- exceptionally severe drought. ony, SE-Germany), which is part of the eastern Saxo- Subtype 3a, however, involves distinct scars, re- thuringian zone and is bordered by Variscan meta- sulting from stem injuries caused by catastrophic morphic units of the Erzgebirge to the South and the environmental events. As there are several potential Granulite Massif to the North (Text-fig. 1a). With interpretations, deciphering scar formation processes an extent of 70 × 30 km, it represents one of the small in fossil trees remains challenging. This may be one intramontane Rotliegend basins in Central Europe reason that only minor attention has been paid to (Schneider et al. 2010). The Chemnitz Basin devel- this field of research in the fossil record, although it oped during the post-orogenic phase of the Variscids may offer considerable potential for palaeoenviron- and is composed of a 1,550 m thick succession of pre- mental reconstructions. Some recent studies focus dominantly continental red bed sedimentary rocks of on comparable phenomena in fossil trees and reflect early to late Permian age (Asselian–Wuchiapingian, a rising interest in this field (e.g., Byers et al. 2014; Text-fig. 1c). Based on six sedimentary megacycles, the Severe growth disturbances in an early Permian calamitalean 3 Text-fig. 1. Geological setting of the Chemnitz Fossil Lagerstätte: a – Geographical and geological overview. b – Detailed geological map of the study area in Chemnitz showing the distribution of the entombing Zeisigwald Tuff pyroclastics and the position of the Chemnitz-Hilbersdorf excavation. c – Stratigraphy of the Leukersdorf Formation (Chemnitz Basin) and posi- tion of the Zeisigwald Tuff pyroclastics. d – Lithological profile of the widely distributed lithofacies association 2 (Luthardt et al. 2018) of the Zeisigwald Tuff pyroclastics. e – Chemnitz-Hilbersdorf excavation