Snags are dead trees left standing. They can be cut or broken several feet from the ground if they pose a falling hazard, but if you are lucky enough to have one in your yard that can be left alone, it will soon be teeming with life. In the forest these snags will often be covered with moss or ferns and are visually appealing. It seems that snags are nature's way of telling us that nothing should be wasted. Every kind of woodpecker will be attracted to your snag, as well as bark-climbing birds from the tiny bushtit to the brown creeper. A snag is a good centerpiece for your brush pile. Often, people like to keep their yards and gardens free of debris, dead branches, leaves, weeds, etc., and that is fine up to a point. It is, however, advantageous to allow a small corner of the yard to "return to nature" as this will become a sanctuary for small ground-dwelling birds such as spotted towhees and juncos and the young of every variety of bird as it is often weeks before they have mastered the art of flying. During this time, they are particularly vulnerable to predators. Your place of refuge will also become home to daddy long-leg spiders, bumblebees, and other valuable ground dwellers that would not survive in an immaculate yard simply because they have nowhere to hide from bigger bugs, birds, cats, and dogs.
My brush pile consists of a snag (and I realize not everyone is lucky enough to have an intact dead tree in their yard!), surrounded by various weeds, a low pile of cut branches and bushes, and a few old pieces of lumber. I supplement this with low dishes, usually just discarded jar lids or cracked saucers, which I keep filled with water during the summer months. A water supply is invaluable to the small critters that will take up residence in your snag/brush pile.
In addition to the small containers of water placed around my garden, I always have some kind of water feature. I enjoy building these from scratch. They do not have to be expensive or time consuming to make. It can be something as simple as a large bowl turned into a birdbath or a whiskey barrel turned into something more elaborate.
Here is a temporary "fountain" I made one year while I built a more permanent one. As you can see, it is just a bowl, about two feet across with some shells and rocks and a very small pump to keep the water circulating. circulating water will not freeze and will provide a place for birds and bugs to drink through a long cold winter. This tiny fountain was visited by hummingbirds, robins, finches, bluejays, and an occasional raccoon, and by the time I finished a bigger water feature, I had already attracted a wide variety of creatures to my yard.
In the lower right you can see a fountain I built for a friend. It is a 3-foot tall piece of stone with a hole drilled through it vertically that allows water to be pumped up and over the lip. There is a small depression in the top of the stone that creates a pool. Hummingbirds visit this very tiny pool almost nonstop all summer long to bathe and drink water. It was really a complete surprise to have them take over the fountain this way, a surprise and an absolute delight!
And here is my current fountain. This is simply a barrel liner buried in a hole. It takes some work, but eventually it does get done. This fountain is a focal point for every kind of wildlife and provides very nice water sounds besides. The small pump was less than $30 and has been running continuously for five years, even through 10 degree winters.
All of this can be part of what helps maintain an organic garden by attracting beneficial insects, frogs, toads and lots of birds, and eliminating the poisons that have a devastating effect on not only "bad" bugs, but all life and Mother Earth herself.