Northern Woodlands is an excellent quarterly magazine from the Center for Northern Woodlands Education in Vermont. It’s a terrific mix of touchy-feely outdoorsy stuff, science reporting on environmental, outdoors, wildlife and other issues, and information about the forest-products industry, including an explanation of the way that chainsaw teeth work which let me understand that tool for the first time. I heartily recommend it.
The current issue isn’t online because they want you to buy the darn thing, and I don’t blame them. Among several cool articles, including one about a study estimating how much biomass disappears per year as trees rot, was a piece about attempts to control the helmock wooly adelgid, a nasty invasive predator, by importing two species of silver fly from the Pacific Northwest, where they act as a natural predator on other adelgids.
Biological control of pests sounds great but it’s hard – partly because you have to be sure that the control won’t be worse than the pest (*cough* cane toad *cough*), and partly because of biology. Predators can’t wipe out a problem species because when the prey population gets too small, the predators die out themselves. To wipe out a pest, you need chemicals.
The hemlock woolly adelgid is a big problem in 18 states, from Vermont to Georgia. Hemlocks are scorned by foresters because their wood isn’t good for much, but their thick evergreen foliage makes them important as a woodlands ecological control. For example, streamside hemlocks can control water temperature and keep trout alive even as the climate warms.
I happen to know something about the adelgid-predator program because my daughter is helping one of two studies. She goes around and whacks sick hemlocks with a stick, gathering up the insects that fall onto tarps and so collecting predator species for study. She mostly deals with stressed trees that are on the edge of parking lots or in cemeteries, because stressed trees draw more insects – apparently people look at you oddly when you start whacking trees in the middle of a cemetery.