No these aren't three graves they are hugelkultur beds sometimes known as woody beds. The concept was made famous by Sepp Holtzer in Austria.
Paul Wheaton of permies.com is a big proponent of hugelkultur. The essence of hugelkultur is this: Wood is stacked up into a pile. Traditionally the pile should be about six feet in height. The piled up wood can be logs, sticks, branches etc. The pile is then mulched over. This is then planted into with whatever you like. There is a ton of video and material on the internet about hugelkultur.
These beds are about knee high and around eight feet long. I arranged them where they are and like they are for a couple of reasons. First, they are in an area that receives an okay amount of sun. Going to the left of the photo it gets shadier. Secondly, this part of the yard contains the septic tank drain field and digging down to plant anything isn't something I want to do. So I needed to go up instead of down. They are situated pretty much on contour. The elevation being higher on the right of the photo sloping downward toward the upper left of the picture. The one on the far left is the lowest in the landscape.
Since this area is fairly shady during the summer months I've chosen to go with shade tolerant plants. There is elderberry, currant, gooseberry and a juneberry as well.
The premise of the system is that the woody material when stacked up and mulched forms a zone of moist decaying material that needs little to no water even during the hottest periods. The principle simulates a forest floor, where a tree falls and debris is blown and washed up against it. This becomes an area of high fertility. "A forest grows on a fallen forest" or so the saying goes.
These beds are roughly a year old. The leaf litter that just fell, mainly poplar and maple leaves and some pine straw, is really the first abundant matter that we've been able to mulch over them with. The fertility should really escalate come spring. Fungi has gotten a good toe-hold on the logs and the system seems to be beginning to really "turn on" so to speak.
Quite a lot of interesting things happened after we piled this wood up. When we bought this property it had been sitting unoccupied for about a year at least, I think. The yard became the default territory of chipmunks. They were here en mass.
They took up residence in the wood piles nearly as soon as we had them constructed. Something else showed up as well. This copperhead pit viper on the left was nearly under my bare foot one day this past summer. This is probably near the limit of how large they grow. He was at least two feet long. I've never seen one longer than a foot before.
I figure that if a snake has lived long enough to get this big then it's been around here for a while, I just never saw it before. They're there just the same. I've seen probably four more little copperheads since then. I just leave them alone. Between them and my cats the chipmunk population has decreased substantially.
They are actually really beautiful and perform a useful function. They decimate rodents. So if you've got them, you've probably got rodents. They are working for you. He stands out well against the green in the picture, however he is virtually the exact same color as the clay soil that the yard consists of.
Besides copperheads, I've also seen garter snakes in the yard. I don't know what they eat. Maybe insects. Another predator that preys on the chipmunks is the hawk. Around here they are Red Tail hawks and I've seen them take quite a number of chipmunks right out of the backyard. I've also seen them take squirrels.
It's odd to me that people are so fearful of snakes. I doubt 999 people out of one thousand know anyone who's ever been bitten by a poisonous snake and yet people tend to kill any snake they come across. I can't remember having ever killed one personally. I rather like them.