And here is the close up of the fungus

@salicaceae - I'm hoping you are still using Houzz. You had such great advice years ago on posts similar to this, I would love to hear your opinion.

"Would planting that new tree disrupt the roots and accelerate the death of the big oak?"

No. But its days seem numbered.

Thank you Embothrium. We did, the ISA certified arborist came just four months ago. He said it was not possible to tell if the tree had damage that could really kill it. He recommended getting another tree planted closer to it in case that one had to be removed in the future.
Following his advice, we were going to get a smaller nutall oak planted in a couple of weeks. But now that I see the fungi (probably armillaria and inonotus) I’m re-thinking the plan.

Some fungus at the base isn't necessarily a death sentence. Foliage looks OK...

Foliage looks great. We just had a big storm last night and lots of trees lost branches. This one is looking great. See picture from street level this morning (tree is 8ft down from the st) where we can see the whole canopy. But, on the other hand, a little more fungi are showing up!

New trees planted near existing trees that are likely to be cut down or fall on their own are in danger of being crushed when that happens. At the very least they are likely to be in the way during removal and cleanup.

That’s so true! As we look around we keep thinking - what space do the tree guys have to remove this giant when it’s cut down? There’s our house, the neighbors guest house, other smaller trees.
Maybe we just need to suck it up and cut it now before we plant another tree (the “insurance tree” the arborist recommended). We are just AGONIZING about getting rid of this tree while we’re not sure it’s really about to die. I wish there was a way to know...

its going to die.. in tree time.. usually counted in decades ... the risk of it falling the wrong way on its own is the issue ... and that is the risk that would bother me ... whether it would fall on me or my neighbors ..... it has to go ...

but when ... thats your decision based on blood pressure and your ability to handle risk aversion ...

tree guys can get it out of there .. the only issue is cost ... i recall once on this old house.. they renting a crane that could reach from the other side of the house ... yikes ... they have all sorts of methods that you have no idea.. so dont worry about that part ... get 3 estimates.. and demand current insurance documents ... just in case ... this type of work can be done almost all winter long .. and you can often get reduced prices in the off season ...

if you have a fireplace... there would be a lot of good firewood there .. have it properly cut and sectioned.. and get a splitter or hire that out ...

as to a new tree.. understand.. there is little instant gratification with trees ... larger specimens take longer to establish a root mass.. to start growing to expectation ... whereas smaller ones get that job done faster ... [though we are still talking years..] ... and often outgrow the larger transplant ... so keep that in mind ..

life is too short .. and im sure you have enough other things to worry about.. just take care of this and be done with it .,..

over the years.. you would probably be surprised now many posts we have had like this.. where some BUILDER tries to insert a house in a woodland ... with no real concept of what ends up being done to the tree roots .. and a few years down the road.. the homeowner is not happy all the trees are suffering ... or failing .... [and dont get me started on BUILDERS and the landscaping they throw in ... lol]

good luck

ken

"That’s so true! As we look around we keep thinking - what space do the tree guys have to remove this giant when it’s cut down?"

You'd be amazed what a good tree crew can do. A few months ago (had more youtube binges than usual since COVID started) I saw an amazing video from some guys in the PNW who have their tree trimming company on youtube. They can get giant douglas firs - bigger than your oak - out of tiny Seattle yards.

I'm a little more skeptical about assuming it will be there "for good". The bark damage looks to me like there is some serious rot going...but I'm not a "professional", obviously. If nothing else, if it's taller than other trees around it, and it looks like it might be...in the southeast, especially, you are talking about a lightning magnet. I had a probably bigger white oak on the corner of my 3 acre property, fortunately far away from the house. On an old US government aerial photo from the 1940s that I found in some digital mapping archive, I could see it was the only tree in the farmland this subdivision used to be. The others were trash trees (maples) that grew in after the land was developed in the early 60s. So it towered 20-30' above the canopy around it for a half mile or so either way.

Lightning struck it in 2011 I think. Luckily it fell into the woods, not my yard! Thing is, I was shocked to see that, when I examined the exploded trunk fragments, they were more than 1/2 empty from decay anyhow. Clearly it was going to fall unexpectedly, sooner rather than later. Trees decay from the inside out. The lightning had actually done me a favor.

So, if it does stick up above everything else...maybe think about getting a lightning arrestor installed!

this was the video I found: https://www.youtube.com/watch?v=lRnFXVVBL3s

Wow, these guys are amazing! Incredible. Thanks for sharing, David. This is making me want to keep the tree even more :) We plant another tree a little south of the big oak, and if the oak really starts dying, a skilled crew can still get this giant out of there. The only thing is that we’ll probably find a species that is more resistant to these fungi we have. Not another oak, unfortunately.

Fungus needs moisture. If there's any loose bark/wood at the base (or anywhere else for that matter), use no more than your hands to see if any can be pulled off/out. That might help by allowing air to dry those areas out. I've done this in many instances.

One of the things you must considered is the loss, if the tree is removed. Is this tree in a place where it provides significant shade. Or is it one of several that shades your house from the summer heat.

If it is the only tree providing shade on that side of your yard, I would leave it for as long (tree time) as possible and get a replacement planted. (Remember it is going to be decades before it provides the shade of this one.) If it could be removed without affecting your heating bill, ie have other shade trees, then I may Consider taking it our now.

Have you discussed the situation with your neighbor? While he does not have voting privileges, it may help with your decision knowing what he thinks.

Brother's very large white oak infected with terminal oak-wilt taken down in steps w/a "cherry-picker" a few months ago: