Once again, let us talk about trees. Do not be fooled by their innocent appearance – that is exactly what they want! In reality, they can be just as problematic as any animal species. This week Tanja Petersen takes a closer look at the Sitka spruce (Picea sitchensis).
Where did it come from?
It originates along the west coast of North America, and it was first introduced to Europe for timber production – the main route for invasive tree species. The first recorded appearances in Norway are from around 1890. In Canada and Alaska the distribution of Sitka spruce overlaps that of the White spruce (Picea glauca), producing the (fertile) hybrid Picea × lutzii, which has also been introduced in Norway. In Norwegian nature institute Artsdatabanken’s new assessment of alien species, this new hybrid and the Sitka spruce have been combined as one species, as plantations of what was assumed to be one, turned out to be the other, and vice versa. To make matters worse, the hybrid is capable of back-reproducing with both parent species. A family tree that would make even the Lannisters from Game of Thrones frown!
If you want to tell the Sitka spruce apart from other spruce species, the most characteristic traits are flat needles, which are green on the topside, and a whitish blue underside – and that the needles are extraordinarily pointy! A characteristic that has earned the species quite a few uncharismatic nicknames in Danish: the “hedgehog spruce”, “stabbing spruce”, and my personal favorite: the “shit-that-really-hurts spruce” (these were some more-or-less creative translations from the Danish Environmental Protection Agency’s fact sheet).
Where did it go?
The Sitka spruce is the most commonly introduced tree in Atlantic Europe, having reached even as remote areas as Iceland. In Norway, the area covered by planted Sitka spruce is estimated to be around 50 km2. At the same time, it is present in most of the country – the most likely estimated area of occurrence is 48,000 km! It was introduced here due to its high wind- and salt tolerance – which is definitely something you want in a tree destined for production in coastal Norway!
What does it do here?
So why is it a problem? One more conifer species in Norway does not seem like a bit issue at first glance, does it? Well, just as in the human world, things are not always merry when you bring in an extra relative. The Sitka spruce can cause problems when it starts moving outside of its intended plantations (just as when your small cousins etc. move outside of the designated “play-area”).
It matures quite early, occasionally producing cones already at 6 years old – almost a teenage pregnancy in the conifer world. Luckily, most Sitkas are more responsible, and wait with reproduction until they reach 20-40 years. It produces more seeds than other spruce species – so both early and massive reproduction. Traits definitely desirable in timber, not so desirable in a potential invader. These factors together is what makes it a potential problem: simulations from Artsdatabanken gives Sitka spruce a potential range expansion speed of 600 m/year – that may not sound fast to animals like us, but it’s borderline Usain Bolt speed for a tree!
However, as you probably know by now, it is not just the ability to move fast and far that makes a species invasive – it should also have a negative effect. In this case, it has an annoying tendency to move into nature types which are on the Norwegian Redlist. Here, it outcompetes the native vegetation by “stealing the spotlight” – and doing it very quickly. And if there is one thing we can’t stand, it is an obnoxious, bratty little cousin who steals the seat of a beloved grandmother, to complete the family metaphor.
So can’t we just… cut it down?
So we’ve established that the spruce is reducing biodiversity in Norway, and that it’s spreading quickly. But it’s a tree, right? What’s the issue? Get some of those deforesters up here STAT! But the spruce is a favourite among foresters and timber merchants in Norway. This is a case of economic priorities coming first, at least for the moment. And as long as the spruce benefits the timber industry, there’s the constant threat of it being able to escape from planted areas and wreak havoc.
For more information on the spruce, we invite you to read the following studies.
The Sikta Spruce – Artsdatabanken profile (Norwegian only)