INTERNATIONAL PEACE GARDEN, Manitoba-North Dakota border — The death of some trees can be predicted as soon as they are planted.
Experts might not be able to say exactly what will kill the trees, but they know that some are more susceptible to disease and pests than others. That can destroy entire shelter belts and windbreaks.
It depends on which trees are planted.
“I can’t tell you what’s coming, but I can tell you if you’re planting a genus with lots and lots and lots of members, there’s lots and lots of potential for a future problem to come in and finish them all,” said John Ball, a forest health specialist at South Dakota State University.
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He told a Canadian-American windbreak conference this summer that the potential for pest and disease issues is high when trees are planted with close family members.
He said there was a single large forest on the Earth before it settled into the continents and oceans that exist today.
As a result, there are tree species that are similar no matter where they are found on Earth.
Some trees, such as oak, have hundreds of different species. Others, such as the coffee tree, have only two.
However, Ball said trees also developed their own insect and disease problems as they settled into separate forests.
Examples of what could happen include blight devastating American chestnuts in the early 20th century, Dutch elm disease wiping out millions of urban and rural trees and the more recent case of the emerald ash borer.
“What do all three have in common?” he said. “The pest became a deadly threat when they were introduced to a new continent.”
None of the three problems occurs in China, but the pests hitched a ride and recognized North American trees as hosts with no natural resistance as goods and people began to move back and forth.
“I have job security,” he joked with the conference participants. “New pests are coming in all the time. We have lots of problems yet to come. The problem that we have, of course, in North America is the Chinese ship us all these goods that little things can come in and we ship them money and nothing will go with money.”
North Americans have also made a mistake by replacing one problem with another.
Millions of dead elm trees were largely replaced with ash, which are now affected by the emerald ash borer. Planting maples to replace dead ash won’t work because there are more than 120 species of them.
“It doesn’t mean we should stop planting maples, but it does mean we should have diversity on the landscape,” Ball said.
He spends time in China each year collecting seeds from different sources to try to outsmart disease and pest.
The trees have to be climatically suitable for the North American northern Plains.
He also doesn’t want to introduce species that will become like weeds, such as the Norway maple, which became invasive and Siberian elms, which grow everywhere.
Ball said Siberian elms can actually be nice trees, but the seeds that were first brought to North America were not the best varieties.
A lot of careful selection has to go into bringing new species across the ocean.
“This is a very long process,” he said.
There are few pests that threaten all trees, Ball added.
“Most of our lethal threats tend to be fairly genus specific.”
