I have two Rowan or Mountain Ash trees growing in an uncultivated part of my property, so I'm guessing they grew from seeds dropped by birds. One tree has orange fruits, the other has bright red fruits. How can I tell if they are native, non-native, or hybrid trees?

They sure are pretty trees and you might have two different types of Sorbus. I think S. americana has orange fruit and S. decora has red but I'm not certain about that. I googled and found a few Sorbus listed for Canada, one says it is introduced. Scroll all the way to the bottom of this page:

http://en.wikipedia.org/wiki/L...

Thanks, Lin. I will need to take a closer look at the trees' bark and buds, to see what matches up with the descriptions. I think the trees aren't likely to be Sorbus decora as I live to the south of its distribution area, but anything is possible!

I've taken another, closer look at both trees. The undersides of their leaves have hairs on them, and the leaf buds are densely hairy, and so I think they are Sorbus aucuparia, the European Mountain Ash.

We are lucky it is fall. The buds are an easy diagnostic for the European species.