The author notes how there are advantages to having the bed raised, like less irrigation required, but why can't you get the same effect by burying the logs instead?
You could, but it's more work as it takes a lot of digging. You could also have flat raised beds setup the same way, with logs and branches and hay - it's a lot more common thing actually. However small slopes and mounds on their own have a number of advantages: catching more heat when Sun is low on the horizon, and less in the summer/midday, and better drainage of any excess water - soil will never turn into mud, so less chances of roots rotting when there's too much rain - and there's also more air circulation around plants. However for smaller plants to get enough of the sun it takes more planning how to position them, as one side is always in shade. Slopes catch less rain, so in dry areas you need densely planted small plants or grass to catch it, and water that runs down needs to be channeled to accumulate on the bottom of the slope. Also, when planting and doing composting at the same time one needs to be careful that decomposition doesn't go too fast because the heat released in the process can hurt the roots, too.
Also, either way, what kinds of plants can you grow without irrigation or rain for a full summer? I'm guessing only ones whose roots go deep enough into the pile?
Exactly. The apex of the hugel is fruit trees and perennials. with annuals filling in as they can. Zepp Holzer, the originator of the word, scatters seed mixes with great numbers of different species while at the same time planting out many fruit, nut, and other trees.
And what's interesting is that the roots of short and mid height vegetation join together, creating a dense mat of roots and fibers, that contain a surprising amount of mostuire. When you combine that with spongy soils, buried wood, and shade they provide localized cycles of fluids and humidity. Overall it makes for much more resilient and productive food systems. Though you have to pay more attention to what you are doing.
If you plant one by one, neatly spaced apart, you won't have this type of nutrient cycling and moisture uptake.
Depends on context but burring wood works just as well. I've done both but it's easier for me to build up the land then dig down because the contractors who built my house 20 year ago, ruined the natural forest and buried gravel and stone underground as fill ...
I do dig swales on contour and fill with wood chips to make garden paths. I harvest stone at that time to build garden walls and depending how deep the path is before filling I toss in some old logs before covering with woodchips for walking.
The end result is the walking paths become resavoirs for holding water and my feet stay dry and I'm left with topsoil to further raise up my garden beds and rocks to build with.
Basically rearranging the material that already exist on site to build a self renewing system!
You can do this below ground level, but it loses some other useful properties (catching more sunlight, improved drainage, ergonomics). Depending on where you live, one approach may work better than the other.
