Summarize the following:
Gardeners should keep in mind that most conifer species, with the exception of yew, cannot survive a severe pruning. Although the green foliage can be trimmed, the brown areas of old growth should be left alone because these places will not regenerate if cut. Some conifers have an area in the center where no foliage grows, but this is normal and not indicative of any problems.  In trees where this is the case, gardeners should avoid pruning into this area because doing so will result in a lopsided tree. The plants will not grow back to cover up the hole.  Therefore, tree trimmers should check the foliage areas before making decisions about which branches to lop off Although wanting to remove the lower branches of a tree is understandable, gardeners who do so may end up with an unsightly specimen when the tree gets taller. Therefore, tree trimmers should exercise restraint and only remove the bottom branches when it becomes absolutely necessary. Evergreens should not be topped, or cut off at a certain height, because this will produce trees that are anything but attractive. Trees that are topped are also at a greater risk for disease and other ailments. Conifers should not be pruned later in the summer or in the fall. Late season pruning can result in new, lush growth that will not have a chance to mature before the cold, damaging winter weather.

Summary:
Be aware that most conifer species will not survive a severe pruning. Refrain from pruning into the empty, central area of the tree. Only remove the bottom branches of trees when absolutely necessary. Avoid topping evergreen trees. Do not prune conifer trees too late in the year.