Abies amabilis

Pacific silver fir

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 -Abies Mill. Species - Abies amabilis Dougl. ex J. Forbes

Ecology: Pacific silver fir commonly occurs in late seral or climax mixed-conifer stands. Throughout its range the most commonly associated conifer is western hemlock (Tsuga heterophylla). Pacific silver fir also reportedly grows in extensive pure stands in parts of the southern Washington Cascade Range. The climate throughout the range of Pacific silver fir is maritime to submaritime. Pacific silver fir is usually submontane to subalpine. It thrives in areas that receive a great deal of precipitation.

Identification

Pacific silver fir (Abies amabilis), also known as silver fir and Cascades fir, has a gray trunk, a rigid, symmetrical crown, and lateral branches perpendicular to the stem. Trees to 75m; trunk to 2.6m diam.; crown spirelike, with age becoming flat topped, cylindric. Bark gray, thin, smooth, with age breaking into scaly plates. Branches diverging from trunk at right angles, short, stiff; twigs mostly opposite, darker brown abaxially, light brown adaxially, pubescence tan. Buds hidden by leaves or exposed, brown, globose, small, resinous (at least apically), apex rounded; basal scales short, broad, triangular, densely pubescent, usually not resinous, margins entire, apex sharp-pointed. Leaves (0.7--)1--2.5cm ´ 1--3mm, mostly 2-ranked, flexible, ± concealing the adaxial surface of the twigs (especially in mid to upper crown), some leaves forwardly directed, others usually longer and spreading horizontally, proximal portion ± straight; cross section flat, prominently grooved adaxially; odor pungent; abaxial surface with 5--6 stomatal rows on each side of midrib; adaxial surface dark, lustrous green, lacking stomates; apex prominently notched; resin canals small, near margins and abaxial epidermal layer. Pollen cones at pollination red, becoming reddish yellow. Seed cones cylindric, 8--10(--13) ´ 3.5--5cm, purple, sessile, apex round to nipple-shaped; scales ca. 2 ´ 2cm, pubescent; bracts included. Seeds 10--12 ´ 4mm, body tan; wing about as long as body, rose to tan; cotyledons 4--7.

Threats

In the WFDP: The primary pathogens affecting Pacific silver fir in the WFDP are: Armillaria root rot (aka Honey fungus; Armillaria spp.), laminated root rot (Phellinus weirii), and fir engraver beetle (Scolytus ventralis). While Pacific silver fir is not subject to herbivory in the WFDP, elk often scrape against the bole of Pacific silver fir to a fatal extent. Mortality of Pacific silver fir in WFDP is also largely caused by suppression and, to a lesser extent, wind-throw.

Fire effects: Pacific silver fir has a low fire tolerance and is usually killed by any forest fire. Pacific silver fir is easily killed by fire because of its shallow rooting habit and thin bark.

Pests and pathogens: Pacific silver fir is a secondary host for hemlock dwarf mistletoe (Arceuthobium tsugense) and can be infected in mixed stands containing western or mountain hemlock. The silver fir beetle (Pseudohylesinus sericeus) and fir root bark beetle (P. granulatus) can be very destructive together and in combination with the root rotting fungi Armillaria mellea, Heterobasidion annosum, Phellinus weirii, and Poria subacida. The last major outbreak of silver fir beetles lasted from 1947 to 1955; it killed 2.5 million cubic meters of timber in Washington.

Reproduction

Flowering and Fruiting - Pacific silver fir is monoecious; self-fertilization is possible because times of pollen dispersal and seed cone receptivity overlap on the same tree. When receptive to pollination, the seed cones appear purple, erect, and 8 to 16 cm tall on the upper surfaces of 1-year-old branches in the upper parts of tree crowns. Just before pollination, the pollen cones appear red, pendent, and usually abundant on the lower surfaces of the branches somewhat lower on the crowns than the seed cones. Seeds are fully mature in late August, and dissemination begins in mid-September- one of the earliest dispersal times for Pacific Northwest conifers.

Seed Production and Dissemination - Cone production begins at years 20 to 30. Good seed years vary from region to region; a good seed crop generally occurs every 3 years. Pacific silver fir is not considered a good seed producer; this condition is attributed to frequent years of low pollen, the extended period between pollination and fertilization, and archegonial abortion producing empty seeds. Seeds each contain a single wing but often fall from the upright cone axis by pairs on ovuliferous scales, as the bracts contort and tear themselves from the cone-a process that does not require wind. When the seeds are dispersed by the wind, they do not carry far; unsound seeds are carried farther than sound seeds.

Seedling Development - Pacific silver fir germinates in the spring after overwintering under snow. Cool, moist habitats are best for germination, but full sunlight produces maximum subsequent growth. Seedlings can also grow under dense shade; seedlings 8 to 12 years old and about 10 cm tall can frequently be found beneath older, closed forest canopies. Seedlings that survive continue to grow very slowly, existing as advance regeneration that can be 65 to 110 years old and only 45 to 200 cm tall. When existing as advance regeneration, Pacific silver fir has flat-topped crowns caused by slow height growth relative to lateral branch growth.

Vegetative Reproduction - Although Pacific silver fir can produce epicormic or adventitious sprouts, it does not regenerate by stump sprouting. Upturning of lower branches after tops of young trees are cut may resemble sprouting.

Species Distribution

Citation

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.

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.

Burke Museum of Natural History and Culture
Burke Museum. 2016. Abies amabilis [Online]. University of Washington.