di·ver·si·ty (noun) : The state of having different forms and types.
There is good reason for diversity in the trees we plant in our yards, boulevards, and public areas in Bozeman. If one variety is planted exclusively and then an insect or disease afflicts that particular variety of tree, our yards and boulevards could end up with no trees at all.
Already, diseases and insects have done just that. Dutch elm disease wiped out most of the elms, the common boulevard tree in the Midwest, in the 1970’s. A few years ago, mountain pine beetle decimated lodgepole pines in the forests of Western Montana and other states. Then, this beetle infiltrated our city forests and killed Scotch and other pines in our yards and parks. Now, emerald ash borer threatens our ash trees, particularly green ash, Bozeman’s most commonly planted boulevard tree. Emerald ash borer was accidently introduced to the Eastern US from Europe in 1990’s. So far this insect, decimating to all species of ash trees, has advanced as far west as Minnesota and Colorado. It may reach Montana someday and then we will know that planting so many green ash in Bozeman was too much of a good thing. That would be unfortunate since green ash has proven to be a one of our best shade trees–winter hardy and adaptable to our soils.
The chart shows eight trees that are not so commonly planted but do well here and could provide some diversity in our landscapes. Some, like Ivory Silk Lilac, are newer cultivars that are improved over the original species.
I am hesitant to list American elm, native to Eastern Montana, as a tree that should be planted more here, even though it is a great shade tree for our climate. Dutch elm disease has been found as close as Helena, and there is a report of one case in Bozeman several years ago. Researchers are trying to develop an elm that is resistant to the Dutch elm disease with the same good characteristics of the native American elm. So far, none of the newly developed elms have proven to be quite as good as the native American elm.
Swiss mountain pine is a tree seldom seen in our home landscapes, but according to my husband Jerry, is a beautiful evergreen that should be planted more. Its needles seldom winterburn; it grows in a perfect conical shape to about 30’.
Commonly planted green ash, quaking aspen, and Canada red cherry all have a place in our landscapes, but look beyond these common trees and try planting one of these–be different!