Picea pungens

Blue 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 A. Dietr. Species - Picea pungens Engelm.

Ecology: Blue spruce is a native evergreen tree with a dense, pyramidal to spire-shaped crown. The oldest blue spruce was 600 years. The shallow roots of blue spruce restrict it to moist sites where water is close to the surface. Blue spruce occurs on montane streambanks; well-drained floodplains or cobble flats; first-level terraces; ravines; intermittent streams; or subirrigated, gentle slopes. Blue spruce occurs in various seral stages from pioneer to climax. Its successional status depends on location and associated species. Blue spruce is a pioneer species in riparian communities that are subject to periodic disturbances, such as scouring and flooding. It is present in all size classes along the riparian systems and on the lower slopes in the southwestern United States, where it may be a topoedaphic climax species. Blue spruce is an intermediate to late, long-lived seral or climax species in montane or subalpine zones. Blue spruce is intermediate in shade tolerance. It may be seral to or climax with any of the conifer species in the mixed-conifer forests. Quaking aspen and lodgepole pine (Pinus contorta) can be seral to blue spruce.

Picea pungens is the 5th most abundant species in the Utah Forest Dynamics Plot (UFDP) by number of stems, and the 5th most abundant species by basal area. Most Picea pungens in the UFDP are found growing in association with Pinus longaeva on a gently sloping part of the plot with geology characterized as old landslide deposits of Claron formation parent material.

Identification

Trees to 50m; trunk to 1.5m diam.; crown broadly conic. Bark gray-brown. Branches slightly to strongly drooping; twigs not pendent, stout, yellow-brown, usually glabrous. Buds dark orange-brown, 6--12mm, apex rounded to acute. Leaves 1.6--3cm, 4-angled in cross section, rigid, blue-green, bearing stomates on all surfaces, apex spine-tipped. Seed cones (5--)6--11(--12)cm; scales elliptic to diamond-shaped, widest below middle, 15--22 10--15mm, rather stiff, margin at apex erose, apex extending 8--10mm beyond seed-wing impression.

Threats

Fire effects: Low severity fires will kill saplings and seedlings. Slow burning of fine fuels will kill the shallow roots of blue spruce. Blue spruce is easily killed by fire. It has thin bark and shallow roots which make it susceptible to hot surface fires. Blue spruce is slow to self-prune lower branches; therefore, surface fires can crown. Blue spruce foliage has moderately volatile oils. Crowns are dense and highly flammable. However, surviving blue spruce remain windfirm in stands opened by fire. Blue spruce does not sprout after fire. Rates of establishment will vary depending on proximity of seed trees and moisture. Seed must be transported from off-site. Blue spruce will establish by wind-dispersed seed that readily germinates on the mineral soil exposed by fire. Small mammals and birds may also carry cones or seeds into a recent burn.

Pests and pathogens: Blue spruce is a host of western spruce budworm (Choristoneura occidentalis). While blue spruce is an infrequent host of mountain pine beetle (Dendroctonus ponderosae) and spruce beetle (D. rufipennis), it is generally not highly susceptible. Blue spruce is the principal host of western spruce dwarf mistletoe (Arceuthobium microcarpum) and minor host of other dwarf mistletoe species. Infected blue spruce seedling mortality under a heavily infested canopy was twice that of the control. Despite its shallow roots, blue spruce is windfirm.

Reproduction

Seed production - Seed production begins at about 20 years and peaks at 50 to 150 years. Blue spruce is a good to prolific seed producer, producing full cone crops every 2 to 3 years. Cones mature in August of the first year and have 85 to 195 seeds per cone. Seeds are wind disseminated, falling within 90 m of the upwind timber edge. Most germination occurs on exposed mineral soil; however, seeds germinate on a variety of substrates. Natural germination rates usually are low; however, one study reported 80 percent germination. Seeds germinate without stratification under a wide range of temperature and light conditions. Blue spruce seedlings will establish beneath parent or other conifer canopies if understory vegetation is lacking or sparse. Overall tree growth is slow. Seedlings are susceptible to frost heaving and may be susceptible to drought due to shallow roots.

Vegetative regeneration: Natural vegetative reproduction does not occur, although epicormic shoots sometimes sprout on the trunks.

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.

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.