A brush pile or wood pile can be constructed as an ordered criss-crossed stack of logs or as a messy pile of sticks of various sizes. In either case, or with something in between these two extremes, the pile should be big enough to retain some permanence through the winter season. Something around four or five feet high and 7 feet wide will do, but if you have the space and time, a larger brush pile will support more diversity. Larger logs will create larger spaces, so place the larger stuff at the bottom. Even if your brush pile is supposed to look natural, criss-cross the larger logs at the bottom to get some decent size spaces. You can also add some rocks for the same purpose. Smaller sticks are piled on top to protect the spaces underneath. Then piles of leaves should be added on top of the sticks to stop rain and snow falling straight through. If you think a brush pile is not sightly, you might consider planting a native vine around the base.
Position the brush pile away from your home to avoid bringing wild animals too close. Place the pile in a somewhat shaded area or at the edge of a more open area. Ecotones are excellent places to site these piles because they will provide services for a greater diversity of animals and will help animals transition between two ecosystems. For example, a pile placed close to a water source may prove invaluable to amphibians. If you have a large amount of space, then you can place brush piles about 150 feet apart or have a few in each acre of land. Some vines can be added to green it up and provide even more protection.
A brush pile must be completed by the end of the summer so that overwintering insects are not disturbed. Several nymphalid butterflies such as the Morning Cloak require somewhere dry to overwinter. Once it freezes, they will become torpid and will not be able to move about in response to a disturbance. They are extremely well camouflaged against the bark of trees and are hard to see. The brush pile protects them from bad weather and potential predators. This is also true for many other animals that use brush piles.
The brush pile also provides security for birds and small mammals, and will serve as a launching point for them to enter your garden. Dark eyed juncos and chipmunks will especially appreciate even a small brush pile.
The rotting wood will attract insects that will become a food source for birds and other small insectivorous animals. The rate at which wood rots depends on tree species and different woods will attract different animals. If you are pruning trees and shrubs, consider saving the wood and making a brush pile for wildlife. It will really improve the biodiversity of your garden.