Raised bed garden - Want to use old fallen tree bottom layer

I am fascinated by hugel.  I had already built most of the raised bed when I learned of it.  My raised bed walls are 33 inches tall and are made from cedar fence posts.  We are in Houston, TX.  That area gets at least 5 hours direct Sun.

My plan was to try to put wood under the soil kind of like a hugel.  First two layers with this tree that fell at least 4 years ago.  Its very soft and looks like termites have finished with it.  Was going to put tree discs and then smaller logs and RCW and then compost and soil.

Is this a decent plan?  Would any termites or bugs in tree on bottom be a problem?  Its kind of close to my house But we have concrete perimeter and flashing under the wood.  

Is the wood in the picture too old?  Does it still have anything to offer the soil?

Not only is that wood not too old, it's ideal. Most of us have a couple of years before we start seeing the strongest benefit from our hugels because we have to wait for fresher logs to break down to that spongy and absorbant texture. I think using wood like that will actually put you well ahead of most of us in this process.

Will be awesome, maybe not the first year but by the second with that rotten wood should be luxurious. I would also tell you the mycorrhizal culture may suffer with thin walls, but will do better than dirt. If there is any way of channeling water into the buried wood, it is thirsty!

I use wood in all my raised beds,and that looks perfect.
I would wet it down and then pee on it,and/or add manure,then leaves or grass, all before adding a particle p "soil" .
A watering pipe can be inserted to add water deep into the bed were the wood can suck it up.

I've used very rotten wood like that pictured and it works quite well. As others mentioned, urine works well to get plants goings with wood like that. The rotten wood should act like a huge sponge. I wouldn't hesitate to use that wood in one of my hugels.

Good wood!  I wouldn't think twice about using that stuff, you could mix in some fresher wood too if you have access to it to prolong the benefits of your hugel beds.  I made beds just like this in my greenhouse and it works fantastic!  You will likely have to add more dirt and organic matter to keep the beds filled every year (I know I do!) but they work great for annuals.  

One thing to think of is maybe not using cedar next time to build your beds.  The same stuff that keeps it from rotting fast can also have detrimental effects on your plants and you will loose some of the hugel benefits as far as microryza fungi establishment etc.  I used douglas fir to make mine and they are holding up really well after 4 years, but I know I'll be working them over soon....