River Birch Going Yellow in Early August - 2020

Just a few days ago, I posted a photo of our three-trunk River Birch in our backyard that we inherited with our lot.  If you look close enough at the photo in that post, you'll see a few yellow leaves on the tips of the tree.  I didn't notice the yellow at the time, but when I was out in the yard this week, I saw something that surprised me:  the yellow leaves covering this thing.  And...seeing a bunch of leaves drop to the ground.  Here's what the patch of grass underneath this River Birch looks like (photo below).  In the top right corner of the photo, you can see the three-trunks of the tree.

Seeing all those leaves on the ground is, ummm, concerning.  I mean...it is early August.  Not early October.  And, it has happened really fast.  Like, from green a week ago to yellow and dropping now.

I went poking around and found some (potential) answers.

Miller Nursery says it is one of two things:  Stress.  Or something called chlorosis - which sounds like it is lacking iron.


The folks at Davey have a post about the issue and point to water being the most likely suspect, but they call it 'seasonal leaf loss' and they don't seem to make it out to be a concern.  They talk about the color of leaves and talk about the big issue is if you have green veining with yellow leaves.

Mine are almost ALL yellow. 

Here's a closeup of one of the leaves on the ground:

I haven't documented this tree loosing leaves over the years, but now it is on my radar and I'll try to keep an eye on it each season.