Need to spruce up on identification skills?

Black spruce between Glennallen and Anchorage, by John Van Atta, via Flickr. Aug. 11, 2008.

This summer, I hiked around black spruce forests looking for lichen for my thesis. The mosquitoes in that wet terrain swarmed around us, leaving us begging for clouds of tiny black flies to drive them away. I forgot my gardening gloves and mosquito repellent once, and had about 25 bites… on one arm.

I also went to open white-spruce forests. Until late summer, I paid attention only to size and location to tell the difference between spruce trees.

My roommate corrected me when I told her this. We were setting up in a new stand of tall trees off the Parks Highway. “White spruce,” I said. No, she said, look at the cones on the ground. Black spruce.

Until then, I figured these spruce trees were similar enough. No one needed to know about my embarrassing inability to pick up on what people meant by “little hairs.”

Covered in snow, Fairbanks forests seem so simple now, a sharp line dividing trees that keep their leaves and trees that don’t. These trees will refresh us with hints of green throughout winter. Now is the perfect time to get to know how they differ.

Black spruce cone, July 5, 2003. You may be able to see some red hairs on the stem here. Photo by Mel Green, username yksin, via Flickr.

Red hairs – If you ever get the chance to hold branches of black and white spruce side-by-side, look at the youngest branch tips. Grab a hand lens if you have one, to magnify things. If the branch underneath the needles is a pale yellow – completely naked – you’re looking at white spruce. If it’s covered in red hairs, black spruce.

Cones – Black spruce cones approach a circular, acorn shape. White spruce cones are stretched out, like tapered ovals.

Needles – Black spruce has stubbier needles than white spruce. For biologists or the most adventurous of readers who have a razor handy, the resin ducts inside needles are also good indicators (link goes to a journal .pdf). Cross-sections of the needle reveal either two continuous ducts to either side of the larger vascular bundle (black spruce) or three to four patchy ducts (white spruce).

Ecology – This is all I was going on before – identification by habitat. Don’t rely on this, but it tells you a little about where each species is comfortable. White spruce likes to grow tall in sunny, dry areas. This might be a south-facing slope, or it might be a levy between a creek and its backswamp. Most trees can’t grow in swampy areas, or permafrost-laden north slopes with thick Sphagnum moss. Black spruce grows well here because very little else can tolerate the shade and acidic, cold soils. Black spruce is usually pretty scraggly, but trees can get to be quite big.

Unfortunately, these characteristics aren’t always cut-and-dry. If you use a combination of the above, though, you’ll most likely have the right tree.

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