Hugelkultur is an old German concept/word meaning “hill-culture”. Wood is buried under topsoil (either in a hole or right on the ground) and as it breaks down, it holds lots of moisture and provides sustained nutrients for plant growth. Some more awesome benefits of Hugelkultur is that it greatly increases the available organic matter in the soil over time and for those of us with alkaline soils, which are mainly found in the more arid areas (which coincidentally is where water retention is greatly needed) the hugelkultur bed will release negative ions as it decomposes which will increase soil acidity.
Many people are using these beds for vegetables, but they are great for Fruit trees and windbreaks since the decomposition leans towards the fungal side and not as much the bacterial side as in compost. This is more natural for trees and bushes, whereas compost is more natural for grains, grasses and vegetables.
The basic concept involves digging a trench and putting logs covered with branches and then covering that with smaller stuff such as straw, weeds, compost etc. that will provide an initial nitrogen source. The mound is covered with the soil that you dug out. You can dig a pit, trench or just start at ground level with your mound. This is a great way to turn an old stump into a benefit. Water will be retained by the wood acting as a sponge for roots to tap into while also releasing nitrogen and other nutrients to feed the trees. The soil is loose because of voids left by the decaying wood and gives great aeration for your newly planted trees and bushes. Because of this your trees and bushes will send down deeper roots, quicker and be much less susceptible to drought. Once established the amount of irrigation water required is substantially less than normal. Combining this method with swales to capture our scare rainwater and snowfall and you have a win-win for your trees.
There are lots of good resources on the internet and several great videos to show and explain better the concepts and actual application. Below I have listed a few:
Here is a Youtube that is a good and simple introduction https://www.youtube.com/watch?v=DbFGK_kFt00&feature=youtu.be
This one explains more how it saves water https://www.youtube.com/watch?v=mibKS_Bdolg
This page is tremendous! It show tons of good photos and different methods in action and also tells best and worst types of wood to use. http://www.inspirationgreen.com/hugelkultur.html