Populus tremuloides

Quaking aspen

Salicaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (flowering plants). Class - Magnoliopsida (dicotyledons). Subclass - Dilleniidae. Order - Salicales. Family - Salicaceae (willow). Genus - Populus L. Species - Populus tremuloides Michx.

Ecology: Populus tremuloides is a native deciduous tree; it is the most widely distributed tree in North America. Populus tremuloides forms clones connected by a common parent root system. It is typically dioecious, with a given clone being either male or female. Some clones produce both stamens and pistils, however. Populus tremuloides stands may consist of a single clone or aggregates of clones. Clones can be distinguished by differences in phenology, leaf size and shape, branching habit, bark character, and by electrophoresis. In the West, Populus tremuloides stands are often even-aged, originating after a single top-killing event. Populus tremuloides is shade intolerant and generally does not regenerate well beneath its own canopy. Beyond that, there is no single, generalized pattern of succession in Populus tremuloides. Populus tremuloides is seral to conifers in most of its range in the West, and in some portions of its eastern range. Populus tremuloides readily colonizes after fire, clearcutting, or other disturbance. The names refer to the leaves, which in the slightest breeze tremble on their flattened leafstalks. The soft smooth bark is sometimes marked by bear claws. A pioneer tree after fires and logging and on abandoned fields, it is short-lived and replaced by conifers. Sometimes planted as an ornamental. Principal uses of the wood include pulpwood, boxes, furniture parts, matches, excelsior, and particle-board. The twigs and foliage are browsed by deer, elk, and moose, also by sheep and goats. Beavers, rabbits, and other mammals eat the bark, foliage, and buds, and grouse and quail feed on the winter buds.

Identification

Plants to 35 m, 10 dm diam.; moderately heterophyllous. Bark dark gray, shallowly furrowed only basally on large trees, (greenish or yellowish white to gray and smooth otherwise). Branchlets reddish brown, becoming grayish yellow by third year, round, 1.2-3.5(-5) mm diam., coarse or not, glabrous. Winter buds reddish brown, glabrous, (shiny), slightly resinous; terminal buds (2.5-) 4-6(-9) mm, (glabrous); flowering buds separated on branchlets or clustered distally, (4.5-)6-10(-11) mm. Leaves: petiole distally flattened at right angle to plane of blade, (0.7-)1-6 cm, about equaling blade length; blade somewhat circular to ovate, (1-)3-7(-12) (0.5-) 3-7(-10.5) cm, w/l = ca. 1, base shallowly cuneate to subcordate, shouldered, basilaminar glands (0 or) 1 or 2, round, margins not translucent, not ciliate, apex acuminate to acute, abaxial surface whitish green, resin stains not obvious, (slightly glaucous), glabrous, adaxial dark green, glabrous; preformed blade margins subentire to finely crenate-serrate throughout, teeth (12-)18-30(-42) on each side, sinuses 0.1-1 mm deep, (surfaces glabrous or sparsely sericeous); neoformed blade margins finely crenate-serrate throughout, teeth (20-)25-40(-50) on each side, sinuses 0.1-1.3 mm deep. Catkins densely (20-)50-65(-130)-flowered, (1.7-)4-7(-12.5 in fruit) cm; floral bract apex deeply cut, ciliate. Pedicels 0.5-1.5(-2 in fruit) mm. Flowers: discs narrowly cup-shaped, obviously oblique, entire, 1.3-1.8(-3 in fruit) mm diam.; stamens 6-12; anthers truncate; ovary 2-carpelled; stigmas 2, filiform, basal lobes expanded, erect. Capsules narrowly ovoid, (2-) 2.5-4.5(-7) mm, glabrous, 2-valved. Seeds (3-)5-7(-9) per placenta.

Threats

Fire effects: The thin bark has little heat resistance, and Populus tremuloides is easily top-killed by fire. Root systems of top-killed stems send up a profusion of sprouts for several years after fire. Moderate-severity fire does not damage quaking aspen roots insulated by soil. Severe fire may kill roots near the soil surface or damage meristematic tissue on shallow roots so that they cannot sprout. Deeper roots are not damaged by severe fire and retain the ability to sucker.

Reproduction

Sexual reproduction - The staminate-pistillate ratio of adult clones is 1:1 in most localities, although it may be as high as 3:1 or more. Some clones alternate between staminate and pistillate forms in different years, or produce various combinations of perfect, staminate, and pistillate flowers. Populus tremuloides first flowers at 2 to 3 years. Populus tremuloides seedlings can easily be misidentified as cottonwood (Populus spp.) or willow (Salix spp.) seedlings because Populus tremuloides seedlings bear only a slight resemblance to the adult form.

Vegetative regeneration - Root sprouting is the most common method of regeneration. Root suckers originate from meristems in the root's cork cambium and can develop anytime during secondary growth. Saplings may begin producing root sprouts at 1 year of age. There are thousands of suppressed shoot primoridia on the roots of most mature Populus tremuloides clones. Recently initiated meristems or primordia usually sprout and elongate more vigorously than older primorida or suppressed root buds. Root suckering is affected by depth and diameter of parent roots. Sprouts grow rapidly by extracting water, nutrients, and photosynthate from an extant root system, and may outcompete other woody vegetation. In contrast to most trees, Populus tremuloides is self-thinning. Without intervention, a mature forest of healthy trees can develop from dense sprouts.

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.