UPDATE: See note at bottom.

Invasive species are non-native plants, bugs and beasts that for various reasons, usually lack of predators, spread so quickly after being introduced that they overwhelm native species. They’re a huge problem all over the world because they disrupt ecosystems, causing harm to other species that have evolved to depend on the natives that are being killed off.

But not always. An interesting study reported by the USDA Forest Service (details here) says that Norway spruce which were planted by foresters in western Massachusetts a century ago seem to do as good a job as native hemlocks in supporting birdsong populations: “Norway spruce share characteristics with eastern hemlocks, such as short needles and dense canopy cover, and could possibly serve as surrogate habitat for native wildlife.” This is important because hemlocks, as you probably know, are threatened by the hemlock wooly adelgid, an invasive insect that is slowly killing them off; the Norway spruce might provide an ecosystem replacement.

I love hemlock forests in the winter; they hold the snow better than any other conifer creating the perfect Currier & Ives effect. New Hampshire is on the edge of wooly adelgid territory because of our cold winters – but, of course, winters are getting less cold, so the sap-sucking monsters are going to become established here, too.

Readers more knowledgeable about forestry than I say that Norway spruce isn’t “invasive.” It’s non-native, yes, but it doesn’t spread fast enough to overwhelm native species, which is what makes invasive species so bad for the ecosystem. This is a good thing, because my wife pointed out that the two gorgeous conifers along our driveway that we planted years ago (partly to my regret – I blew out my back planting one of them with their big root ball and my back has never been the same since) are Norway spruce. They are loaded with songbirds when we put out the bird-feeder on the opposite side of the driveway; they do seem to like hiding among the thick foliage, perhaps because there’s a resident red hawk in our woods.