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| Claudia Hartl: "You don't normally see trees in this region without rings" |
The relentless campaign to find and sink Germany's WWII battleship, the Tirpitz, has left its mark on the landscape that is evident even today.
The largest vessel in Hitler's Kriegsmarine, it was stationed for much of the war along the Norwegian coast to deter an Allied invasion.
The German navy would hide the ship in fjords and screen it with chemical fog.
This "smoke" did enormous damage to the surrounding trees which is recorded in their growth rings.
Claudia Hartl, from the Johannes Gutenberg University in Mainz, Germany, stumbled across the impact while examining pines at Kåfjord near Alta.
The dendrochronologist was collecting wood cores to build up a picture of past climate in the area. Severe cold and even infestation from insects can severely stunt annual growth in a stand, but neither of these causes could explain the total absence of rings seen in some trees dated to 1945.
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| Some had a ring but you would hardly see it |
A colleague suggested it could have something to do with the Tirpitz, which was anchored the previous year at Kåfjord where it was attacked by Allied bombers.
Archive documents show the ship released chlorosulphuric acid to camouflage its position.
"We think this artificial smoke damaged the needles on the trees," Dr Hartl told BBC News.
"If trees don't have needles they can't photosynthesise and they can't produce biomass. In pine trees, needles usually last from three to seven years because they're evergreens. So, if the trees lose their needles, it can take a very long time for them to recover."
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| The Tirpitz pictured in Kåfjord with the smokescreen seen drifting across the water |
In one tree, there is no growth seen for nine years from 1945. "Afterwards, it recovered but it took 30 years to get back to normal growth. It's still there; it's still alive, and it's a very impressive tree," Dr Hartl said.
In other pines, rings are present but they are extremely thin - easy to miss. As expected, sampling shows the impacts falling off with distance. But it is only at 4km that trees start to display no effects.
The Tirpitz sustained some damage at Kåfjord. However, a continuous seek-and-destroy campaign eventually caught up with the battleship and it was sunk by RAF Lancasters in late 1944 in Tromso fjord further to the west.
Dr Hartl believes her "warfare dendrochronology" will find similar cases elsewhere.
"I think it's really interesting that the effects of one engagement are still evident in the forests of northern Norway more than 70 years later. In other places in Europe, they also used this artificial smoke and may be also other chemicals. So perhaps you can find similar patterns and effects from WWII."
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| Sampling shows the impacts falling off with distance |
