Sometimes the need for tree removal is obvious, such as if a tree is suffering a disease or pest infestation that is impossible to combat or if there is unrecoverable damage to the tree. There are two common situations, though, where you may be able to save the tree rather than remove it, depending on the specifics of the situation.
1. Near-Building Trees
Trees growing near buildings can be problematic due to the roots putting pressure on the foundation walls, but the branches can also be a problem if they scrape against the roof or siding.
Near-building trees can sometimes be saved with careful trimming. Your tree service will need to prune annually to remove any long branches that touch the house, otherwise, they can scrape off shingles or puncture siding. The service may also recommend installing a root barrier between your house and the tree so the roots don't put pressure on the foundation.
Trees that are growing right up against the house instead of just close to it are more problematic, especially if it is a large tree or expected to grow much larger. In this case, removal is often the safer choice. Leave the job to a professional, though, as removal of near-building trees requires skill so that the tree doesn't damage your home.
2. Leaning and Instability
Trees can lean for a variety of reasons. Some trees lean due to poor pruning or over-shading when they were saplings, while others develop a lean later due to unbalanced weight in the crown, damage, or soil instability.
A full assessment is needed to see if a leaning tree can be saved. If the tree appears to be otherwise healthy with a deep and well-anchored root system, then you may be able to save the tree. Your tree professional will trim to the crown to both reduce and evenly distribute the weight to help combat the lean. They may also install anchors to prevent the lean from worsening.
Trees that have poorly developed root systems or other health problems are often removed as they simply pose too much of a fall danger. It's also better to remove a leaning tree if it is in an especially hazardous place, such as one that is leaning over your home or over a road. Climate may also impact your decision. Leaning trees are more likely to come down in high winds, so it may be safer to simply remove the tree in windy climes.
Contact a tree service in your area for more assistance.