Warfare dendrochronology: Trees witness the deployment of the German battleship Tirpitz in Norway

Abstract

War has an immediate and obvious effect on people and communities, but its impacts on local ecology can be more subtle. This paper shows how one military encounter in the Second World War has left a clear legacy in the northern forests of Norway, trackable more than seventy years later. We used annual growth rings of ∼180 pine and ∼30 birch trees as witnesses of the deployment of the German battleship Tirpitz at the Kåfjord. The Tirpitz was the target of several Allied air attacks, but the Kriegsmarine (German navy from 1935 to 1945) used artificial smoke, consisting of chlorosulfonic acid and zinc/hexachloroethane, to hide the ship. These smoke-screen actions throughout 1944 caused pine forests surrounding the Kåfjord to exhibit a strong and unusual growth decline during the following year. Severe defoliation and limited photosynthetic activity likely triggered this decline. The tree damage extended up to 4 km away from the Tirpitz. In the most extreme case, growth was interrupted for nine years. ‘Warfare dendrochronology’ could help to evaluate potential environmental impacts of the Second World War on forest health and composition elsewhere in the European theatre.

Introduction

Warfare is a central and unique feature of Homo sapiens L. and has been part of human cultures and civilizations for thousands of years (Machlis et al., 2011; Francis and Krishnamurthy, 2014). Obviously, war leads to tragedies for societies and human suffering, but also poses a great threat to the environment and most living organisms (Farina, 2011). The fact that war leads to undesirable environmental impacts, including the (un)intentional destruction and degradation of natural resources, such as forests, crops and water resources, has long been recognized (Hupy, 2008; Machlis and Hanson, 2008; Reuveny et al., 2010; Hanson, 2011; Francis and Krishnamurthy, 2014). Ecological consequences can be generated during all three stages of war — preparation of war, war (violent conflict), and post-war activities (Machlis and Hanson, 2008) — and environmental damage is generally accepted as unavoidable collateral damage (Marler, 2013).

War has affected forests for millennia (McNeill, 2004). Roman accounts describe massive forest fires set by Germanic barbarian tribes to confuse and frighten their enemies, but the Romans themselves also used fire as a weapon in what is now France and Germany (Hupy, 2008). The era of modern chemical weapons in World War I (WWI) and the associated effects on forests reached a new level beyond simple burning. The Battles of Verdun and Ypres at the Western Front devastated forests in France and Belgium through stationary combative activities (Freedman, 1995; McNeill, 2004; Hupy, 2008). Names for some regions as “place à gaz” (gas place), “Forêt de Guerre” (War Forest) or “Zones Rouge” (Red Zones) still bear witness to the heavy and persistent environmental destructions. Even though explosion of ordnance itself had likely destroyed the forest, chemical warfare agents additionally contaminated these battlefields. These agents includes chlorine, phosgene/diphosgene, arsenicals and lachrymator, mostly contained in artillery shells (Thieme, 1998; Bausinger and Preuß, 2005; Bausinger et al., 2007; Prestidge, 2013). During the Greek Civil War in the late 1940s, napalm was used to burn down the forests in the Pindus Mountains of northern Greece, which served as refuge for rebel forces (McNeill, 2003, 2004). More recently, the Second Indochina War represents one of the most prominent and obvious forest devastations ever conducted by humans. With the application of chemical anti-plant herbicide and defoliation chemicals, including Agent Orange, ∼22,000 km² of Vietnamese forests (23% of all forested area in the country) were intentionally destroyed (Orians and Pfeiffer, 1970; McNeill, 2004; Westing, 2012 and references therein).

Scientific studies on the environmental impact of warfare on forests are still scarce, however, especially for WWI and World War II (WWII). Historical writings provide some assessments, but these documents focus on the environmental factors influencing battles rather than the effects of war on the environment (Hupy, 2008). Photographs, paintings, or first-person accounts that allow an appreciation of the intensity of forest devastation also enable assessment of the ecological effects of warfare (e.g. Parsons, 1919, also see Freedman (1995) for other examples). Studies using proxy archives to evaluate military related forest devastation are rare, except a stalagmite from Northern Italy, which indicates deforestation coinciding with pre-WWI military activities (Borsato et al., 2007). An archive that scholars have not used yet to identify the impacts of military conflicts on forest ecosystems are tree rings. Only one study used dendrochronology to identify the wood supply for trenches at the above mentioned Western Front during WWI (Haneca et al., 2018). Trees record environmental changes and impacts in high temporal resolution (Fritts, 1976), offering tree-ring research the potential to steadily expand its application areas (Büntgen, 2019). Tree-ring width is a parameter representing the tree’s vitality (Dobbertin, 2005), thus it enables assessment of damage through environmental disturbance. This paper introduces the general approach of ‘warfare dendrochronology’, which should be defined, as a previously unrecognized tool to evaluate the effects of warfare on local environments and forests specifically.

In this case, the theatre of war is the Kåfjord in northern Norway. There, the Tirpitz, the largest battleship in the Kriegsmarine (German navy from 1935 to 1945), was moored for several months during the latter stages of WWII in 1943 and 1944 (Fig. 1). The ship loomed as a constant threat to Allied shipping and, as a consequence, was the target of several Soviet and British efforts to sink the giant battleship. In this article, we first provide detail on the ship and its history, as well as the strategy employed by the Kriegsmarine to use ‘artificial smoke’ to conceal the ship’s location. Then, we detail our study of more than 200 trees at the surroundings of the Kåfjord (Fig. 1b). We addressed the following research questions: (1) How did the Tirpitz battles affect local forests? (2) What was the spatial impact and duration of those effects? (3) Did they have different effects on the two main tree species pine and birch? We report how we applied dendrochronological techniques to assess biological damages due to this smoke, which is still visible in the trees 70 years later.