Question
QUESTION: I live in Los Angeles and I have a beautiful 400 year old Ca Live Oak in my front yard. The tree has always had a slight lean to it. Two years ago when we had record rainfall, the tree started to lean a little more -- about 18 inches when measured ten feet up on the trunk.   I'm concerned that the roots may have cracked or been compromised when the tree moved. Is there any way to tell by looking at the tree if the roots have been compromised or weakened? The tree appears very healthy with thick foliage and no dead spots or discoloration. If the tree were to fall, it could damage my house. However, I am extremely reluctant to cut it down as it is so beautiful and it's the only large tree on my property. I've also set up a system by which I can measure the lean of the tree against a fixed spot. In the last year and a half the tree seems to have leaned an additional quarter of an inch. I suspect the additional lean is due to several periods of very high wind. Is this something to be worried about? Thank you.
ANSWER: a tree that old unless you see signs of the ground being pulled up by the root ball on the opposite side of the lean then the tree is ok. As long as the foliage is healthy looking I would not worry about it. Leaning or lopsided trees present more of a hazard than those growing vertically, but if a tree has always grown off center, it generally is not an undue risk. However, any sudden lean indicates breakage or weakening of support roots and should be cause for alarm and immediate action. It also depends on the crown and how it has developed --if the tree has leaned by many years the tree has compensated for the lean by balancing the crown foliage and also growing compression wood along the side of the trunk to give it greater support. IF the lean has just started you should see the ground being up lifted if so then this is a hazard since the toot system may have been damaged. Sounds like this is an old tree and is in good shape--remember this tree has with stood many many weather events and survived and made itself stronger.
Here is an article that will describes the calculations for determining lean in trees.

http://www.urbanforestrysouth.org/Resources/Library/Citation.2005-12-07.5903/at_

---------- FOLLOW-UP ----------

QUESTION: Thanks for the reply. I have a follow up. There are some signs of the ground being raised on the opposite side of the lean. This occurred a couple of years ago during an extended period of extremely heavy record rainfall. The ground has not raised any more since then. However if the root system was damaged or broken, would there be some outward sign of that on the tree such as limb die off or thin canopy? Is it possible that the roots have been damaged but yet there is no visible sign on the tree above ground? Thanks.

Answer
The root damage can show up as foliage die back but if the root system was just loosened then the roots would still be productive and show no signs in the crown. I would watch for any other ground movement especially after a wind storm. The root system is normally twice width of the crown so it will have plenty of roots to hold it up. If you see any further ground movement then I would get an arborist to look at possibly prune part of the crown to take the load off the leaning side. Do not get just any "tree person" but find an arborist that can advice you on the ground about your tree. But for now I would enjoy the tree. Here is the web site for the California Arborists Association if you want to find one near you.

 http://www.cal-arb-association.com/