Scarcity of white birch trees

Have you noticed the increasing scarcity of White Birch trees over the past few years?

The snow-white bark of these trees makes them stand out among all other trees.
Not only that, but their bark is very attractive, making them popular for planting
around houses.

For years I've regularly driven between my home in Nashua to my in-laws home in Portland, Maine.
It was easy to pick out the numerous white birch trees along the way.
But I've been noticing fewer and fewer of these trees over the past few years.
When I look more carefully, it seems like over half of the remaining white birch trees
are either dead or dying.

At first I thought the scarcity might be due to white canker. But although bark splits are a chief
indicator of white canker, white birch trees rarely show these characteristic splits.

I changed my mind when the gray birch in my yard started to die in mid-summer.
Like other birches, the leaves all started turning yellow, and then began dropping.
Luckily I happened to spray with fungicide Mancozeb as the yellowing started.
This stopped the yellowing and the leaves reverted to a healthy green.

Later, when I examined tissue of this birch under a microscope, I saw definite signs of
a white canker infection, tending to confirm my suspicion.

My sense is that white birch is more sensitive to white canker infection that other
trees are, and this is why they are dying off faster than other trees.

Have others noticed this dieoff?