Aspen, Cottonwood, Balsam... what's the difference?
Article by: Heather Pyra & Shelley Heidinger
In fact, Trembling Aspen, Plains Cottonwood,and Balsam Poplar are all types of Poplar. Because of the use of different common names, confusion often results. Hybrid Poplars also add to this confusing mix.
Let’s take a closer look.
Trembling Aspen (Populus tremuloides)
This tree is also commonly known as White Poplar. The Trembling Aspen is the most common tree in Saskatchewan and is identifiable by its characteristic heartshaped, toothed leaves that tend to flutter in the wind. This flutter is due to the flattened stalks on the leaves. The bark is white to greenish and tends to get gray to black streaks as it gets older. There is a white powder that rubs off when you touch it. Trembling Aspen can grow up to 20-25 metres in height. These trees are very shade intolerant and grow best on moist, well-drained, sandy or gravelly loams.
Plains Cottonwood (Populus deltoides)
Cottonwood leaves are more triangular, with a rounded base, and rounded teeth. The tops of the leaf are shiny whereas the leaves of the Aspen are dull. The bark is smooth and yellowish-gray. It tends to turn darker gray and become furrowed with age.
Plains Cottonwood grows up to about 30m and is one of the fastest growing native trees in the province. The Cottonwood is also a source for those cottony bundles of seed that are released into the air in the spring. These trees prefer rich, moist soils.
Balsam Poplar (Populus balsamifera)
Balsam Poplar is native to Canada and can stand from 30-60 metres high. It has yellow-grey bark which is thick and furrowed. The leaf petiole or stalk is round and the leaves are rounded at the base and quite pointed at the tip. The leaves have a waxy whitish coating on the undersides which helps to distinguish them from other poplars. They also produce white cotton like fluff in the spring. This trees’ name was derived from the pleasant balsam smell when the buds and leaves are opening in the spring.
Poplar Hybrids and Clones
Hybrid poplar is created by cross-breeding closely related species of poplar. This can either occur spontaneously or artificially. Hybrid poplar is not a genetically modified organism (GMO). The new Okanese Poplar is an example of an artificially bred hybrid.
Since poplars (both hybrids and non-hybrids) can easily be propagated through vegetative means from stem cuttings, an infinite number of genetically identical trees from one (hybrid) poplar with exactly the same properties can be created. We refer to genetically identical trees simply as a ‘clone’. For instance the clone ‘Walker’ is a well-known hybrid poplar clone used for farm shelterbelts.
AESB Agroforestry Development Centre, formerly known as PFRA Shelterbelt Centre, is continuing to devote large amounts of resources into developing Poplar Hybrids. The 6 hybrids they are currently distributing are “Assiniboine”, “Katepwa”, “Walker”, “Okanese”, “Hill” and “CanAm”. The goal is to develop species that are more drought tolerant, cold hardy, pest resistant, fastgrowing, and of acceptable wood quality. Walker and Hill are female clones and the remaining hybrids are all male clones.
No matter what the type, because of the rapid growth of Poplars they make very good carbon sinks and have a future in carbon sequestration programs.