I'll bet $50 that it has absolutely NOTHING to do with the roots using water (where would they send the water, anyway?). But I believe what you're seeing. Here's what I believe is happening: The soil microbes are in overdrive as the roots actually begin decaying. Instead of working to release Nitrogen, they actually get so busy that they TIE UP the Nitrogen in the soil. I've seen the equivalent when people put too much Molasses into a Molasses treatment. The difference is that the Molasses (the fuel source) burns out in 3-4 weeks and things return to normal. That won't happen with 25 trees worth of roots. It could go on for years. There isn't much you can do - the roots will probably dissolve into stuff like wet sawdust if you use a stump grinder. I'm betting you'll see mushrooms everywhere too at some point. The only thing that I can say "might" work is to put a cup of household ammonia into a hose-end sprayer and spread that over 1000 sq ft every two weeks - that may get enough extra Nitrogen to the grass to keep it from yellowing or fading out. I know it sounds weird, but it has worked before.

I see many knees seemly cut off at ground level. I've actually wondered myself if someone cut them off or was it just the mower. Some are so big that if a mower hit them it wouldn't be pretty. They seem to have healed over with new tissue and don't look like there has been any new growth. I would just mow over them as long as there's no damage to the mower of course but that's just me. I do think that there will be others popping periodically, forever I'm sure.

@lou_midlothian_tx: I took a casual look into the work you introduced that SFA is doing with Cypress hybrids. A theory mentioned on at least one of the related websites is that the differences between central Texas Bald Cypress and those further east (alkaline tolerance, fewer knees, etc) can be explained by natural (and ancient) cross-breeding in the Bald/Montezuma border region... Texas BC have more MC-like characteristics. Interesting stuff - thanks for mentioning it. Webworms/bagworms show up in the local fruitless mulberry and pecans every few years. Imagine they'd be in the BC too if there were any planted nearby. Fortunately we seem to have predators (birds, wasps, fire ants,...?) that take care of them if the bags are torn open with a pole saw early enough. What I've learned is that I'm looking for Texas BC or BC/MC hybrid with a mature crown spread of ~25ft or less... in other words, a cultivar that does not yet exist. Though photos of a mature Nanjing Beauty hybrid in China show a pretty narrow spread that MBG specs at 20-30ft. The space is tight, but may be able to adjust location if I can remove a large stump to get an additional 5ft or so - besides, any eventual crowding is unlikely to become an issue during my lifetime :-) Losing the early fall color seems like a fair trade for better alkaline tolerance, no risk of knees in the lawn, and faster growth rate. Thanks again for all the advice on this. Here is a link that might be useful: Taxodium 'Zhongshansa' NANJING BEAUTY

are they a bunch of seedlings ...or are they sprouts from a prior tree??? here's how i forecast size: https://duckduckgo.com/?q=Taxodium&t=ffcm&ia=images&iax=images from the pix.. id say its 15 to 20 feet too close to the house ... there are dwarfish cultivars ... but they probably arent from seed ... and if there was a prior dwarf that died .. odds were it was grafted.. and the root stock was not dwarf ... you would move it in dormancy .... ken