Picea engelmannii

Engelmann spruce

Pinaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Pinaceae (pine). Genus - Picea L. Species - Picea engelmannii Parry ex Engelm.

Ecology: In the Rocky Mountains north and south of Montana and Idaho, Engelmann spruce and subalpine fir often codominate at climax to form extensive Engelmann spruce-subalpine fir forests. These spruce-fir forests are usually classified as subalpine fir climax series habitat types. In the understory of these stands, subalpine fir seedlings usually outnumber Engelmann spruce seedlings because they are more shade tolerant and readily establish on duff seedbeds. It may also occur in pure or nearly pure stands. Although spruce-fir forests form climax or near climax vegetation associations, they differ from most climax forests in that many stands are not truly all-aged. Some stands are clearly single-storied, indicating that desirable spruce forests can be grown under even-aged management. Other stands are two- or three-storied, and multi-storied stands are not uncommon. These may be the result of either past disturbances, such as fire, insect epidemics, or cutting, or the gradual deterioration of old-growth stands due to normal mortality from wind, insects, and disease.

In the Utah Forest Dynamics Plot (UFDP), Picea engelmannii is the third most abundant species with 86.8 live stems per ha.

Identification

Trees to 60m; trunk to 2m diam.; crown narrowly conic. Bark gray to reddish brown. Branches spreading horizontally to somewhat drooping; twigs not pendent, rather stout, yellow-brown, finely pubescent, occasionally glabrous. Buds orange-brown, 3--6mm, apex rounded. Leaves 1.6--3(--3.5)cm, 4-angled in cross section, rigid, blue-green, bearing stomates on all surfaces, apex sharp-pointed. Seed cones 3--7(--8)cm; scales diamond-shaped to elliptic, widest above middle, 13--20 9--16mm, flexuous, margin at apex irregularly toothed to erose, apex extending 3--8mm beyond seed-wing impression.

Threats

Fire effects: Engelmann spruce is very fire sensitive and is generally killed even by low-intensity fires. Postfire reestablishment is via wind-dispersed seeds which readily germinate on fire-prepared seedbeds. The occasional mature tree which surives fire, those escaping fire in small, unburned pockets, and trees adjacent to burned areas provide seeds to colonize burned sites. Large trees occasionally survive light fires.

Pests and pathogens: The most common diseases of Engelmann spruce are caused by wood-rotting fungi that result in loss of volume and predispose trees to windthrow and windbreak. The spruce beetle (Dendroctonus rufipennis) is the most important insect pest of Engelmann spruce. A severe spruce beetle outbreak occured in southwestern Utah in the 1990s, mortality rates were found to be as high as 98%. Mature trees are most susceptible to spruce beetle, but young trees may be attacked it beetle populations are large enough. Damaging attacks have been largely associated with extensive windthrow, where downed trees have provided an ample food supply for a rapid buildup of beetle populations. The beetle progeny then emerge to attack living trees, sometimes seriously damaging the residual stand. Dwarf mistletoe (Arceuthobium microcarpum) causes heavy mortality in spruce in Arizona and New Mexico, but it has a limited range in the Southwest and is not found elsewhere.

Other: Engelmann spruce is susceptible to windthrow, especially after any initial cutting in old-growth forests. Engelmann spruce has a shallow root system. The weak taproot of seedlings does not persist beyond the juvenile stage, and when trees grow where the water table is near the surface or on soils underlain by impervious rock or clay hardpans, the weak, superficial lateral root system common to the seedling stage may persist to old age. Under these conditions, most roots are in the first 30 to 46 cm of soil.

Reproduction

Flowering and Fruiting - Engelmann spruce is monoecious; male and female strobili are formed in the axils of needles of the previous year's shoots after dormancy is broken, usually in late April to early May. Ovulate strobili (new conelets) are usually borne near ends of the shoots in the upper crown and staminate strobili on branchlets in the lower crown. Separation of male and female strobili within the crown reduces self-fertilization. Pollen is wind disseminated.

Seed Production and Dissemination - Although open-grown Engelmann spruces begin bearing cones when they are 1.2 to 1.5 m tall and 15 to 40 years old, seed production does not become significant until trees are larger and older.

Seedling Development - Engelmann spruce will germinate in all light intensities found in nature, but 40 to 60 percent of full shade is most favorable for seedling establishment at high elevations. Light intensity and solar radiation are high at elevations and latitudes where spruce grows in the central and southern Rocky Mountains, and seedlings do not establish readily in the open. Because of its slow initial root penetration and extreme sensitivity to heat in the succulent stage, drought and heat girdling kill many first-year spruce seedlings.

Vegetative Reproduction - Engelmann spruce can reproduce by layering. It most often layers near timberline, where the species assumes a dwarfed or prostrate form. Layering can also occur when only a few trees survive fires or other catastrophes. Once these survivors have increased to the point where their numbers alter the microenvironment enough to improve germination and establishment, layering diminishes.

Species Distribution

Citation

USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

Silvics of North America
Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers, Volume 2: Hardwoods). USDA Forest Service Agricultural Handbook 654.

The Jepson Herbarium
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA.

USGS Plant Species Range Maps
Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97. Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.