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Description
General Appearance
- Has an open, spreading crown.
- Bark is smooth and yellowish-grey in colour; as the tree matures, the bark gets rougher and more furrowed.
Size
- Is a medium-sized to large tree, attaining heights up to 30 metres (98.4 feet).
Flowers
- Male and female catkins produced on separate trees, form before leaves develop in spring.
- Staminate (male) catkins, reddish – purple in colour, 8 to 10 centimetres (3.14 to 3.94 inches) long with 40 to 60 stamens.
- Pistillate (female) catkins, green in colour, 9 to 15 centimetres (3.54 to 5.91 inches) long.
Fruit
- Found on mature pistillate catkins, small, egg-shaped, green in colour, 15 to 25 centimetres (5.91 to 11.81 inches) long.
Leaves
- Simple, triangular or heart shaped, 5 to 10 centimetres (1.97 to 3.94 inches) long and 4 to 11 centimetres (1.57 to 4.33 inches) wide.
- Rounded teeth with a short tip without teeth.
- Glossy, bright green above, slightly paler on underside.
Distribution
- Distributed within Southern Alberta along riparian valleys of the Oldman River and its tributaries.
Natural History
Habitat
- Commonly found along riparian areas with adequate moisture and soil rich from periodic flooding of the river.
When Active
- Is perennial, lifespan can range from 100 to 150 years.
- Catkins produced in early spring before leaves appear.
- Pistillate (female) catkins mature and release seed for up to three weeks in early summer.
Reproduction and Growth
- Able to reproduce sexually and asexually.
- Reproduces asexually by sprouting new shoots from roots, stems or branches that have broken off.
- Sexual reproduction through staminate and pistillate catkins.
- Staminate (male) catkins release their pollen in the early spring.
- Pistillate (female) catkins, once pollinated, develop small, green fruits 15 to 30 centimetres (5.91 to 11.81 inches) long.
- Fruit opens up in early summer, when river flows are at their highest, to release an abundant supply of seeds attached to cotton-like strands.
- High river flows form moist sand bars or silt beds that are necessary for germination because cottonwood seeds are unable to out-compete weeds and other plants. These locations also provide ideal sites for asexual reproduction from plant parts.
- Germination sites must remain moist and receive lots of sunlight in order for germination to occur.
- Seeds remain viable for two to four weeks and must germinate during this time.
- Seeds, together with cotton-like strands are continuously released for up to three weeks, thus resulting in the common name of "Cottonwood".
Conservation and Management
Status
Issues
- Cottonwoods are heavily dependent upon the natural cycle of flooding in order to grow and thrive.
- Altering river flows for dams, drought conditions within Southern Alberta and growing city populations are all factors that can limit the success of Cottonwoods.
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