The Carlisle Mosquito Online

Friday, December 22, 2006


Black Spruce

I wanted a bright and cheery topic for the Christmas season and the Black Spruce — from its name at least — seems more suited for reminding us that today is the Winter Solstice, the deepest, darkest day of the year when we must light fires and candles and Yule logs to chase away the gloom.

But there's more to the Black Spruce story. Along with all its evergreen relatives it continues to show life when deciduous trees are bare and for this reason evergreens have traditionally served as symbols of hope. This use of evergreens at the solstice seems to have had its origin in early Pagan celebrations but is now firmly entrenched in secular Christmas traditions.

The Black Spruce has another connection to Christmas; its scientific name is Picea mariana where Picea means "pitch" (not very Christmas-like) but mariana means "from Mary, the mother of Jesus." The pitch is a reference to the resin that exudes from cuts in spruce bark and was once used as chewing gum. The mariana name was given because the species was first described, in the 1700s, as the Maryland spruce — even though it doesn't grow there. I haven't been able to find a single source telling why this spruce is called "black." Its other common names are bog spruce and swamp spruce.

When and where seen. There are two groves of this spruce along the Tophet trail in Great Brook Farm State Park.The trees are only two to three feet tall. One of the groves is swamp-side in the typical habitat for the species, and the other is on slightly higher drier ground. The "miracle on the Tophet trail" is that these trees are there at all. There is no sign of any parent trees.

Identification — it takes a village. I had help from John Bakewell, Tom Brownrigg and Tony Mariano to arrive at an identification, and I still wouldn't bet the farm on it. First, the easy part. You can tell a spruce by the four-sided needles. Fir trees, by comparison, have flattened needles. You can rule out white spruce because its crushed needles have a skunky smell.

Also, white spruce and Norway spruce have smooth hairless twigs. These trees have hairy twigs which gets you to red or Black Spruce but then, in the absence of cones, it gets tricky. (None of the trees in Great Brook have cones.) John Bakewell worked with me and together we consulted 13 books and built a comparison table of 10 key features. In the end a preponderance of the evidence pointed to the Black Spruce. The main differentiators were habitat, needles shorter than a half inch, and the angle of the needles to the twig.

Also, Tom Brownrigg and I found that one of the Tophet trees was a result of "layering," a documented phenomenon of black spruce in which a lower branch gets weighted down by snow and eventually takes root in the damp, mossy substrate and starts growing vertically like a new tree.

A closer look. Tony Mariano saw the trouble I was having with the spruce ID and arranged to get some scanning electron microscope (SEM) pictures in the hope that the added detail would be telling. Many thanks are due to Ernest Dobi of Aerotek P&K in North Billerica who prepared the specimen by immersing it in liquid nitrogen, mounting it on conducting tape on a pedestal, sputter-coating it with gold-palladium film, and then capturing secondary electron images.

The pictures are beautiful and show exquisite detail, but I have not yet found reference material for comparison. If anyone wants to see more of these photos than we could print in the paper, let me know.

A scanning electron microscope (SEM) photo depicts a four-sided Black Spruce needle. A characteristic stub peg to the right once supported a needle. Fine hairs are visible around the stem. (Photo by Ernest Dobi of Aerotech P & K)

This SEM photo shows a cross-section of the Black Spruce twig.

References (some of the 13). Forest Trees of the Northeast, Cornell Cooperative Extension; Native and Naturalized Trees of Massachusetts, UMass. Extension; Audubon Guide to North American Trees, Elbert L. Little; Manual of Woody Landscape Plants, Michael A. Dirr.

2006 The Carlisle Mosquito