Home Salicaceae Populus Populus trichocarpa (black cottonwood)

synonym – P. balsamifera ssp. trichocarpa (subspecies of eastern balsam poplar)

trichocarpa – hairy fruited

  • thrix – hair (Greek)
  • karps – fruit (Greek)

Native range: Western North America

Populus trichocarpa 05897.JPG

Leaves:

  • alternate
  • simple
  • broadly ovate (highly variable & young different than adult
  • paler below
  • round petioles (genera trait is flat petioles)

Populus-trichocarpa.JPG

Flowers:

  • dioecious
  • male and female flowers are catkins
  • male w/ 40–60 stamens
  • female w/ 3 stigmas

Populus trichocarpa male flowers near the Columbia River in East Wenatchee, Douglas County Washington

Fruit:

  • pubescent capsule
  • seeds released in spring and may look like snow in spring

Populus trichocarpa mature female catkins bursting open

Other characteristics:

  • tree to 90 ft.
  • “Q-tip” shape
  • tallest, fastest-growing hardwood in the western US
  • lives 100–200 years
  • deciduous
  • ~brown pubescent branchlets
  • leaves have reddish resinous buds with a strong cinnamon scent
    • when leaves push through they pick up some of the resin and the leaf underside may appear to have orange blotches, especially in spring and early summer

Black cottonwood buds - Flickr - brewbooks

Ecology & Adaptations:

  • native to southern Alaska to southern California, east to the Rocky Mtns in Alberta and Wyoming
  • occurring throughout Washington
  • found in streambanks and moist woods, moist to wet sites, sea level to mid- elevations in the mountains (up to 5,000 ft in the Cascades)
  • forms extensive stands on islands and floodplains along major rivers and disturbed upland sites
  • vegetative regeneration:
    • re-sprouts from stumps following felling by beavers
    • following beaver activity or flood disturbance, branches of a fallen tree may establish new shoots that become trunks
    • cuttings of young branches (live stakes) can be used in restoration to plant this species in moist ground
    • regeneration in established forests is by root suckers or coppice sprouts
  • pollinated by wind
  • seed dispersal – cottony hairs attached to seeds aid rapid disseminated by wind and water in late spring
  • Adapted to disturbance:
    • when moist mineral soil in floodplains is exposed, germination rates are high, particularly when moist conditions persist for a month after seed deposition
    • shade-intolerant seedlings rarely establish under parent trees
    • suitable conditions for seedling establishment sometimes occur (erratically) in approximately 5 to 10 year intervals
  • tolerant of winter flooding (while dormant)
    • but requires some aeration of soils during the growing season
    • shallow root system facilitates access to oxygen
  • tolerant of seasonal hotter, drier conditions – resin covering leaves reduces water loss through transpiration
  • fire tolerance:
    • mature trees with thick bark may survive low- to moderate-severity fire without top-kill
    • younger trees have relatively thin barks that make them more vulnerable to fire damage
    • fire creates disturbed areas that may be colonized by wind- or water-dispersed seedlings
  • herbivory/microbial defense:
    • high terpene and phenolic resin content in buds reduces cellulose digestion, rendering the tissue less palatable to herbivores and less inviting to fungi and bacteria
    • resin transferred to leaves as they emerge from the buds provides extended protection
    • resin later produced by glands at leaf edges