Picea engelmannii / Engelmann spruce

Adjectives: drought tolerant, exposed, highly visible, interesting bits, native, tree, widespread, winter botany

Also known as: white spruce, mountain spruce, silver spruce
See also: Pine trees, conifers and evergreens; Picea pungens / Colorado blue spruce

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Engelmann spruce is the most common spruce in the Rockies; it is very well adapted to environments with harsh winds, extreme cold and deep snows. In the Valley, it is very seldom found in pure stands, but rather cohabits with all the other Pinaceae (except limber pine). If the soil is rich and moist as in lower, north-facing parts of a canyon, Engelmann’s neighboring conifers are likely to be subalpine firs, Douglas fir and blue spruce. On south facing slopes where the habitat is dry, it is more likely found with lodgepole pine.

The crown of this species forms a narrow spire when the tree is young, albeit not nearly so acute as subalpine fir. This changes to more cylindrical in older trees. The branches spread horizontally to somewhat drooping. The twigs are not pendant or drooping, however; they are rather stout and sometimes finely pubescent. I have found this latter characteristic highly unreliable.

The Engelmann spruce bark is thin and scaly, flaking off in small circular plates 2 to 4 inches across. I also find this difficult as a diagnostic difference with Colorado blue spruce but probably depends a lot on age and tree size.

The needles of Engelmann spruce are shiny (glaucous) blue-green above with several thin lines of stomata, and blue-white below with two, more distinct, bands of stomata. Indeed, the needle color is often described as dark blue green and quite variable. Overall, needle color in our two spruces is a very poor indicator of species.

The needles of this and all spruces are pointy and sharp, and are attached to the twigs with woody sterigmata (pegs) that remain after the needles drop. In this species, they tend to sweep toward the tip of the twigs rather than straight out, and while pointy, they are also sort of soft and non-threatening. In cross section, they are square (or rhomboid), and will roll between your fingers. The buds on the twigs are rounded, not pointy like Douglas fir.

Englemann spruce cones hang down. They are ovoid and oblong (see the photos in the gallery), and less than 2.5 inches long. As such, they are smaller than blue spruce cones. When dry, they open revealing appressed seeds about 1/8-inch long (including the wing). The cone scales are thin, somewhat flexible and with a wavy margin. It takes cones up to 7 months to mature after pollination. However, they only really produce a large seed crop every 3-6 years.

Interesting bits – First, Engelmann spruce wood has a very resonant quality making it sought after for pianos, violins, guitars and other stringed instruments. It is, of course, also harvested for lumber and pulp.

Second, although most trees grow better with more light, the ability to survive under a canopy may be just as important in the long run. In this case, the saplings can survive under a forest canopy for 50-100 years, growing rapidly once the overstory is thinned or lost.

This has some interesting practical ramifications. For example, if you go to the Forest Service District Ranger Station for a Christmas tree cutting permit, you may notice that you are requested, if possible, to select a tree under an aspen canopy. The “fear” is that, left alone, the spruce will replace the aspens. While that might seem “natural” and all that, it turns out that if a fire moves through, it will stop when it reaches an aspen grove, which, from a management and homeowners insurance standpoint, is a Good Thing.