Plantings Rule No. 1: Plant variety. Diversity provides greater options for food, shelter and nest space. Diversity allows that if something dies, it'll only be one or two and not everything you planted. I have one shrub spruce that cannot be rid of a moth whose larvae decimate new growth each year. I'm glad there's only one bush.
Rule No. 2: Plant for change. In our cultured and cultivated world we expect our properties to look like the pictures in landscape design books. Sameness is exactly what to avoid. Plant slow-growing species for long life. Plant fast-growing species to fill in until slower-growing species can catch up and replace them. Then plant shrub replacements for the fast-growing species (such as poplar) you remove because they no longer grow well (or they die) under the shade of matured slower-growing species. For example, as trees mature and shade the ground around them, light-loving plants will no longer grow but ferns and many perennial wildflowers will.
Rule No. 3: Plant trees that grow naturally in your area; stay away from exotic species. I live in northern SE Pennsylvania so I planted pines (red, white, Scots); maples (silver and one Norway); oaks (pin and white); spruces (Norway, Serbian, blue and one or two others); two firs and a hawthorne. The oaks were for acorns (some day), the maples for their many fine nest spots and winged seeds, the conifers for windbreaks, winter hiding places for birds, and cone-borne seeds; the hawthorne for its berries, which attract migrating evening grosbeaks. If you find "volunteers" (seedlings) of value in the right spot, encourage them because they're part of natural succession.
Rule No. 4: Pay attention to what the books say about the mature diameter of trees. When the books says a tree's base will reach 25 feet across, you had better plant it half that distance from the nearest object you don't want it to touch. If you think young trees look lonesome (the space between them is bare), plant something between them that you are willing to sacrifice when the trees fill in.
Rule No. 5: Plant to create "edge." One purpose of all my planting was to simulate a "woodlot" (my simulated woodlot is only about about 30 feet wide) and its companion--"edge." Edge is naturally what is along the outside of a woodlot. Birds love "edge" because they can hunt for weed seeds along it but duck back in for protection when a predator appears. Birds also can seek shelter from wind, rain, snow and sun in the woods, build nests along the edge, find nesting material, and enjoy an abundance of insects.
