If you're looking at buying a home with large, older trees in the yard, you need to take a very close look at those trees. The older and bigger a tree gets, the more opportunities fungi and other pathogens have to harm the tree, to the point of killing it. Trees like this need to be removed, which means you would either have to spend extra money on the tree removal or negotiate the removal as a covenant if you go ahead and buy the home. While you should get an official inspection from an arborist, there are a few signs you can look for quickly that will let you know if that property has some problems on its hands.
Mushrooms on the Tree
If you see mushrooms growing on the tree (mushrooms growing in the soil under the tree can also be a warning sign, but it's not as clear-cut as mushrooms growing on the tree itself), chances are the interior of the tree is either rotten or in the process of rotting. A rotted interior makes for a weak tree that can fall over in strong winds or drop dead branches on unsuspecting people below.
Half of the Tree Looks Dead
Trees can look sick and stressed from things like drought without actually being dead or about to fall over. But if, when you stand back and look at the tree, one side of it appears weakened or dead, that is a danger sign. It indicates that even if the tree is alive, it's not going to be very steady -- there's the potential for the roots on that weak side to be weak as well. Trees like that can fall over easily.
Animals Linving in the Trunk
When looking at the tree, did you see an animal scamper into the trunk? Animals like raccoons and squirrels can make their homes inside hollows, and small hollows aren't necessarily bad. But because trees aren't see-through, the knowledge that a hollow exists is grounds for suspicion. Many times these hollows, which are remnants of fungal damage, are extensive enough to make the structure of the tree fragile. These are trees that need to be inspected immediately to ensure the hollow isn't large. Of course, then you also have the issue of a nearby animal family and its potential to get into the house.
If you have any other questions about the health of the trees on the property you're looking at, talk to arborists as well as the seller to ensure he or she is disclosing everything. Problems with the trees can indicate further problems with the landscaping or house, so these are details you don't want to ignore.
For more information, consider websites like http://www.kctreecaresiteks.com/home.html.