Burying logs, branche, leaves and other organic debris and growing on top of it is called Hugelkultur. Your raised beds look great. I use raised beds I made on the cheap out of 55 gallon barrels and IBC totes. I fill them most of the way with raw manure, of all sorts and use composted manure and soil for the last 12 inches or so to grow in. I top the raised beds off during the Winter with rabbit manure. I rob them out for soil for the plants I sell and refill them too.
You can get free arborist chips from Chip Drop and the power companies. I got 30 some loads since early this year. Once composted, the chips make excellent soil. They make good mulch too. Burying the entire area in 8" or more of wood chips is often called the Back to Eden method based on the books and films of the same name.
Keith
I have tried using chip drop for 2 years. No takers yet. I imagine its cause of location and lack of arborist work in a more rural area.
I have access to lots of wood and I make some of my own wood chips from woodworking along with the fact I have a pto driven
Woodchipper. I could use ALOT more tho. But no access to animal manure.
All this to say not all materials are easily available.
Myself I made raised beds from 2 x 12,s. I wuldn't use wood again. It seems to wick alot of moisture out of the ground in the beds. The beds dry out much faster than surrounding ground. I'd use metal or plastic. Keith's idea of using 55 gallon drums or plastic totes is a very good one.