How Norwegian trees tell the story of a cloaked Nazi war ship

The story of the battleship Tirpitz is no secret.

It was the German navy's largest and heaviest of the Second World War — significantly heavier than its sister ship, the Bismarck. It was stationed in northern Norway during the war.

But even though the story of the Tirpitz has been well-preserved in documents and history books, scientist have recently discovered some missing links — or rather, missing rings — by reading trees. 

Winnipeg-born Scott St. George is one of the researchers of the study, presented this week at a conference in Vienna. 

St. George, a geography professor at the University of Minnesota, spoke with As it Happens host Carol Off from Innsbruck, Austria. Here is part of their conversation.

What did researchers notice was different about these trees in this area of Norway?

What we noticed was the trees closest to the Kafjord — closest to the water — had a very unusual ring in 1945.

The growth patterns that we saw in all the other years before 1945 and after 1945 were really the same as the other trees in the same area. But 1945 was really different.

How many trees did you find [with] something different about them?

About 60 per cent of the trees in the Kafjord in 1945.

And we know that happens when trees are under extreme environmental stress — for example, by drought or when they're attacked by insects or affected by a wildfire — they often compensate to that stress by shutting down wood production. As a result, they don't get a ring for that year.

So what were the theories as to why these trees didn't have a ring in 1945?

If we had seen this skipped year in other trees in other places, we would have assumed it was because of an insect attack. That's the most common cause of trees skipping a ring.

This time it turned out to be due to Hitler's navy.

In this area, the Kafjord — that specific bay in northern Norway — is historically famous because of its role in harbouring and protecting the Tirpitz, the largest ship of the German navy, during the Second World War.

So what did the Tirpitz being in this fjord have to do with the trees not having rings?

There's a famous memo from Winston Churchill — the shortest memo he wrote in the entire Second World War — that simply asked, "Where is Tirpitz?"

So for about a year-and-a-half, the British military were trying to find the Tirpitz, sink it, and end the threat that it posed to allied shipping.

And when bombers were spotted by the German navy, they would attempt to shield the ship by producing what they described as artificial smoke or artificial fog to prevent the ship from being spotted.

And what was in that smoke? 

It was pretty nasty stuff. According to intelligence reports that the U.S. military filed in 1943, it was primarily made up of chlorosulphuric acid and sulphur trioxide. 

First-person accounts described the chemical concoction as stripping the paint off the boats and taking the putty off the windows of the same boats.

And so what effect did that have on the trees?

The smoke eventually drifted into the nearby forest. And what we think happened was that it chemically damaged the needles, and essentially acted as a defoliator, stripping the needles off pine and birch trees growing nearby.

And because the trees were stripped of their needles, they had to completely re-grow a new crop of needles for the next year. And because of that, they made a trade-off. In order to expand their needle crop, they drew down resources dedicated to growing wood.

Most people who study trees don't think about long-ago military conflicts as one of the stories that might be preserved in those trees.- Scott St. George

As a result, many of the trees in the area formed an exceptionally narrow ring in 1945. And many of them just didn't form any wood at all. In the most extreme case, one tree didn't form wood for nine years after 1945. 

They often say, "If trees could talk, the stories they could tell." Have you had a tree tell you so much about history before? 

Never something like this. I think it's fair to say that most foresters and most people who study trees don't think about long-ago military conflicts as one of the stories that might be preserved in those trees.

I think that that's one of the important lessons of the study. Now that 70 years have gone by, we've really lost that direct memory of 1945 in most places.

But in the Kafjord, the trees still keep this very subtle clue that tells us a little bit about what happened at that time.

Written by Kevin Ball. Interview produced by Katie Geleff. Q&A edited for length and clarity. 

Correction: This article previously stated that the battleship Tirpitz was stationed in Norway during the First World War. In fact, it was stationed there during the Second World War.