tremuloides – resembling the trembling poplar (P. tremula, or European aspen)

Native range: Western & Northern North America

Leaves:

• alternate
• simple
• cordate to orbicular 1–3” long
• serrulate (finely toothed)
• margins hairy
• dark green above
• pale green below
• long, laterally-flattened petiole (at right angle to plane of leaf) result in leaves fluttering even in slight breezes (hence the name)
• shorter than P. trichocarpa

Flowers:

• dioecious
• male and female catkins drooping, 1–3” (2.5–10 cm) long
• female – pistillate catkins at maturity 4–10 cm long, with numerous fruits

Fruit:

• capsules lanceolate
• 4–6 mm long
• on pedicles 1–2 mm long

Other characteristics:

• smaller tree (to 25 m.)
• slender trunk
• white/grey bark with obvious branch scars (does not peel like paper birch)
• leaves flutter in the slightest wind
• yellow autumn color

Relevant info:

• wood is used for particleboard and pulp
• widest geographical distribution of any North American tree
• found throughout cold and cool-temperate regions from coast to coast and from within the Arctic Circle to the north rim of the Valley of Mexico
• from sea level in the north and east to north slopes of high elevations in the south
• southerly locations, like Mt. Livermore, Texas, the most southerly stand in the flora area, may be Pleistocene (Ice Age) relicts
• largest and oldest known aspen clone is the “Pando” clone on the Fishlake National Forest in southern Utah
  • over 100 acres in size and weighs more than 14 million pounds
  • aged at 80,000 years old, although 5–10,000 year-old clones are more common
• soft whispering rustle of a quaking aspen is unlike the sound of any other tree in the forest

Ecology & Adaptations:

• Alaska to California, east to Labrador and New Jersey
• in Washington, broadly distributed, but chiefly east of the Cascades
• found in dry to wet, open to closed woodlands and forests, edges of meadows and prairies, dry mountainsides, avalanche chutes, talus-slopes and canyon-heads, sites of human disturbance, timber cuts, mine tailings, gravel pits, quarries, roadsides, gentle slopes near valley bottoms, alluvial terraces, and along watercourses
• sea level on both coasts to 11,500 ft. (3,505 m.) in northern Colorado
• pollinated by wind
• seed dispersal & germination:
  • seeds with tufts of hairs are dispersed by wind for distances of 1,600 ft. to several miles with heavy winds
  • also disperse by water, and can germinate while floating or submerged
  • few aspen seedlings survive in nature due to the short time a seed is viable, lack of moisture during seed dispersal, fungi, adverse day/night temperature changes, and unfavorable soil conditions
• vegetative reproduction:
  • forms clonal stands connected by a common root system
  • groves often occupied by single clones and show no sexual reproduction but persist and spread by root suckers
  • when stems are killed (e.g., by fire) and apical dominance is removed, cytokinins (hormones) in the roots initiate root sprouting
  • clones share traits such as leaf shape and size, bark character, branching habit, resistance to disease and air pollution, sex, time of flushing, and autumn leaf color
• fire adapted:
  • thin bark has little heat resistance, and all but larger diameter trees are easily top-killed by fire
  • root systems of top-killed stems send up a profusion of sprouts for several years after fire
  • they grow rapidly by extracting water, nutrients, and photosynthate from an extant root system, and may outcompete other woody vegetation
  • following a fire, a new, even-aged quaking aspen stand can develop within a decade
  • also establishes from off-site, wind-blown seed after fire
  • in contrast to most trees, quaking aspen is self-thinning and, without intervention, a mature forest of healthy trees can develop from dense sprouts
  • before fire-suppression practices began in 1900, low-intensity fire-return intervals were ~7–10 years in the intermountain west, including those used by Native Americans to manage the landscape
• succession – quintessential “foundation species” in early-successional forest ecosystems
• herbivore & microbial defense:
  • phenolic glycosides (salicinoids) and condensed tannins
  • phenolic glycosides reduce feeding, growth and survival of insect herbivores and deter feeding by mammalian herbivores
  • tannins bind with plant proteins, making them more difficult to digest
• low-nutrient conditions – association with mycorrhizae facilitates water and nutrient uptake
• wildlife:
  • provides important breeding, foraging, and resting habitat for a variety of birds and mammals
  • elk, moose, and mule and white-tailed deer consume the leaves, buds, twigs, bark, and sprouts
  • black and grizzly bears feed on forbs and berry-producing shrubs in quaking aspen understories, which also provide excellent denning and foraging sites for black bear
  • rabbits, hares and pikas eat plant, as do squirrels, pocket gophers, mice and porcupines
  • beaver consume the leaves, bark, and twigs, and use quaking aspen stems within 400 feet of waterways for constructing dams and lodges
  • provide important feeding and nesting sites for a diverse array of birds, such as sandhill crane, western wood pewee, six species of ducks, blue, ruffed, and sharp-tailed grouse, band-tailed pigeon, mourning dove, wild turkey, red-breasted nuthatch, and pine siskin