Walnut vs Tree of Heaven vs. Sumac Backyard Identification - June 2020

That's a look *up* from the ground through a young, skinny tree limb as well as a larger, more mature (and confirmed) Black Walnut tree.  The leaves, from a distance look similar.  Back last year, I mentioned that I wanted to try to identify if a couple of young trees were worth keeping or if I should remove them.  And, knowing that I wanted to hold myself accountable, I included it as #15 on my to-do list for the yard this year.

After poking around on the web in various places, I think I've settled on this clear cut detail that I found on r/WhatIsThisPlant on Reddit:  Walnut tree leaves have no notches.  Tree of Heaven (an invasive tree), do.  From u/blacksheep998:

Ailanthus has a small notch at the base of it's leaflets.
Black walnut leaflets, while slightly toothed, lacked that distinctive nub.

So, that's first thing to check:  Does the little tree leaves have those 'thumbs' or notches?
 

*Looks closer*...

Sure, enough.   Thumbs are present.  See below.  That means this is a Tree of Heaven

So, what does that mean?  The Nature Conservancy puts it this way:

Tree of heaven (Ailanthus altissima) is known by a number of names: stinking sumac, Chinese sumac, varnish tree and stink tree. No matter what you call it, it's an invasive species.

That means I have to take it out.  What are we dealing with?  Here's the caliper measurement on the trunk below.  1.20" diameter.  Not tiny. 

I got out the saw and cut it off at about five inches from the ground.  That's not enough, but it at least is a start.  Have to think about yanking the root/stump out later this Summer.

There is another tree back there that I need to identify that is very weed-like in shape with big growth coming out of an inherited stump.  It has heavy serrated leaves that you can see below:

In my original tree-identification post, I mentioned that there were three (or four) potential options for some of these trees:

Black Walnut

Tree of Heaven

Smooth Sumac

Black Ash

Or...perhaps an Elm - as it has serrated leaves?

Due to the Emerald Ash Borer, I know it isn't an Ash.  They're all gone.  

The photo shows opposite leaves - not alternate.  The Elm tree that the University of Illinois identified for us in 2018 has alternate branching.  So, this is NOT an Elm. 

As for the rest of the list...They're all similar, but it seems that just one of them is technically invasive:  Tree of Heaven.  

This serrated one is, I'm pretty sure:  a Smooth Sumac.  I mentioned that this new growth is coming out of a stump.  This NDSU pdf talks about how the Smooth Sumac grows:

Usually grows in masses and suckers profusely.

I think we can confirm that behavior.  The question now becomes:  should I leave it?  Or take it out?  I'm thinking that it should go.  

As for "keeping score" on my 2020 to-do list, I think I can cross off #15 on the list.