Picea Brewerana - Brewer Spruce

Brewer Spruce 1

Abstract

Brewer spruce (Picea breweriana), named for its first collector, is often considered "mysterious" because this attractive conifer is found on seldom-visited high mountain ridges and steep north slopes. Its other common name, weeping spruce, is derived from the distinctive feature of many rope-like branchlets that hang in a fringe from all but the topmost slender horizontal limbs. This branching habit results in many knots in the wood, which has little commercial importance.

Habitat

Native Range

Brewer spruce is found only in the mountains of northwestern California and southwestern Oregon near the Pacific coast. The best-developed stands are on the high ridges of the western Siskiyou Mountains in California and Oregon. Other concentrations are found on high ridges and in upper valleys of the Marble, Salmon, and Trinity Mountains of California (7). Throughout the rest of the range, Brewer spruce grows as a single tree and as scattered small populations in valleys and on ridgetops (9,12,16).

Climate

The range of Brewer spruce is primarily influenced by the maritime climate of the Pacific Ocean: cool, wet winters and warm, relatively dry summers. The climate changes drastically, however, from west to east across the range of Brewer spruce, which is 70 mi. On the most westerly ridge occupied by Brewer spruce, average annual precipitation is more than 110 in; farther east, it is less than 39 in. Most of the precipitation falls as winter rain or snow; less than 5 percent occurs in the summer. The amount of -snowfall and accumulated snowpack varies greatly from year to year and geographically across the range.

Brewer Spruce 2

A few stands of Brewer spruce in valleys receive no snow some years, whereas other stands accumulate up to 13 to 16 ft (5). Humidity is high in the western part of the range and relatively low in the eastern part. Summer fog is common along the western-most ridges and valleys. Summer thunderstorms are common in the eastern portion of the range. Temperatures also vary widely. In the western portion, the mean temperature in January is 41o F; in July, 52o F. On the eastern edge of the range, the mean temperature is 30o F in January and 68o F in July.

The varied climate indicates that Brewer spruce has an ecological amplitude that should enable it to obtain a wider and more contiguous distribution. Its sensitivity to fire seems to have restricted its range (13).

Soils and Topography

Brewer spruce grows on a wide variety of geologic parent materials and soils. It is found on soils developed from sedimentary, granitic, serpentine, and metavolcanic rocks. Most of the large stands of Brewer spruce are found on shallow, rocky, undeveloped soils of the order Entisols; a few stands are on deeper, well-developed soils. Throughout its range, Brewer spruce is never found in areas where the soils are saturated during the growing season. It appears to be generally restricted from the more fertile soils by competition from true firs (Abies spp.). Brewer spruce is more abundant on less fertile soils.

Brewer spruce is found on most topographic locations-ridgetops, north- and south-facing slopes, benches, and valley bottoms. The only habitat restriction is boggy or wet areas. The apparently preferred location is the steep, north-facing slopes where the largest stands are located. In the western Siskiyou Mountains, these locations are north slopes near the tops of the ridges, but in the eastern Salmon Mountains, the largest stands are on middle, north-facing slopes. Brewer

Brewer Spruce 3

spruce is found from elevations of 2,300 to 6,900 ft in the western Siskiyou Mountains and from 4,500 to 7,500 ft in the eastern Klamath region.

Life History

Reproduction and Early Growth

Flowering and Fruiting

Brewer spruce is monoecious. Strobilus buds form in early summer and develop in the fall. The dark purple male strobili are borne the following spring in axils of needles of the previous year's shoots, on branches throughout the tree. The pollen-bearing strobili are from 0.75 to 1.25 in long and about 0.5 in, in diameter. Pollen is shed in early summer; the male strobili dry and fall soon after pollen is shed. Female strobili are borne at the tips of primary branches in the upper two-thirds of the crown. They develop into erect, dark green, cylindrical conelets that are 1.5 in long and 0.5 in thick when receptive. The female conelets are apparently receptive at the time pollen is shed. The location of female and male flowers throughout the tree, concurrent with timing of strobilus development, apparently encourages selfing of Brewer spruce located singly or in small, isolated stands. After pollination, the conelets turn down and mature the same season into dark brown cones 3 to 6 in long. The fruit matures from September to October; dissemination immediately follows.

Seed Production and Dissemination

Seed production starts when the trees are from 20 to 30 years old. Actual production has not been determined. Observations indicate that mature Brewer spruce trees are fair seed producers; crops occur at 2-year intervals, and some trees produce cones each year.

Brewer Spruce 4

The seeds are 0.1 to 0.2 in long; the wing is four times as long as the seed. The seeds are the largest of the North American spruces: 61,000/lb, with a range of 51,000 to 74,000/lb. The relatively large wing aids dissemination of the seed by the wind. Cones and seeds do not appear to be a preferred food for rodents. Seeds may be stored for 5 to 17 years in sealed containers at low temperatures, 33o to 38o F, at a moisture content of 4 to 8 percent. A cold, moist stratification of 30 days increases germination. Germination of sound seed ranges from 50 to 96 percent; the reported average is 88 percent (15).

Seedling Development

The germination of Brewer spruce is epigeal, seedlings becoming established on all types of natural seedbeds: decaying logs, forest humus, loose soil from upturned roots, and leaf litter under brush fields. Throughout the range of Brewer spruce, natural regeneration is abundant under dense Brewer spruce-white fir stands. These stands contain an average of 1,360 Brewer spruce and 3,460 white fir seedlings per 550 and 1,400/acre less than 6 in, in height. Brewer spruce seedlings

...