Western Producer Calgary reporter Barbara Duckworth attended an invasive plants conference in Calgary and filed these reports.
Two problem trees are threatening the cottonwoods lining the streams and rivers of the western plains.
Already under threat because of livestock and wildlife overgrazing, these native trees are being pushed out by Russian olives and saltwater cedars, said Derald Smith, a University of Calgary environmental design professor. He spoke at an invasive plants conference in Calgary Oct. 2-3.
Saltwater cedars have been planted as ornamentals because they are showy, bushy trees with soft, feathery fronds and long lasting purple flowers.
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They were originally planted in the midwestern United States to prevent erosion along irrigation canals. They are now found in great abundance along the Yellowstone River in Montana and Wyoming, along irrigation return flow channels and reservoir banks.
“If they are not in Alberta and Saskatchewan, they will be here shortly,” said Smith.
A mature tree can produce one million seeds spread by wind, water and waterfowl. They grow a tap root as big as a normal tree trunk that is almost impossible to remove.
In some areas of dried out reservoirs in Montana, the cedar has started to grow as thickly as kochia weeds in a slough. They have choked out willow and cottonwoods. The plant also takes up considerable amounts of salt and when it sheds branches or fronds, the salt is released into the soil, sterilizing it.
It grows back even more densely after a fire but it can be drowned. Some environmental managers are looking at flooding reservoirs to defeat the trees.
Another threat is the Russian olive with its dark coloured bark and showy silver-green leaves.
It grows well anywhere but prefers floodplains where it can outcompete cottonwoods. It has been planted as a shelterbelt but has managed to spread beyond its usefulness. Birds eat its small green berries and then spread the seeds in their droppings.
