It's really up to you if you want to replace it. If it looks good with one oak I would just keep one. My live oak in my yard is dropping a lot of leaves this time of year which is somewhat of a pain to deal with. Good luck.

Live oaks have leaves, and should be green, year round. They do go through cycles of leaf drop, and new growth. Many other oaks, and the list goes on, loose their leaves and will be 100% barren of leaves at some point during the year. Almost always during the cooler months (although intensity of sunlight is the trigger).

If the tree is dead it should be removed, it can become a liability. Determining if the tree is dead is the issue. If you have a narrow, less than .5", drill bit that is at least as long as 1/2 half the diameter of the trunk of the tree (breast height or so) you can drill into the tree. The center will be dead, but not rotten or soft. It should look like you drilled through a hardwood 2x4. The outer layers should be alive and moist, and when the weather warms up have a thin green layer beneath the bark that feels slimy (this is the cambium where the tree cells divide and the tree grows). If you pull out rotten tissue the tree may be dead. This process may not be something you are comfortable with, but if the tree is dead or dying and you are thinking of removing it, what do you have to lose by playing tree doctor.

I grew up SE of Houston in Galveston County and the major soil profile around your area, and a large part of the gulf coast, is high in clay. Holds too much water and is poor structure. The home builder brings in sand. Sand doesn't hold water and has better structure. When it rains the clay and the sand become a fluid solution. The microscopic clay particles remain suspended while the sand sinks. After a few good rain showers you end up with a 'hard pan' beneath the clay and the problem is exacerbated. Foundation repair companies owe a huge portion of their success to this clay phenomenon, compounded by the fact that ours is âÂÂshrinking/swellingâ type.

I am not certain this is your problem, obviously.

Good point, are you sure they are the same kind of trees? The 'dead' one may just be deciduous, dormant for winter. Are there still bare trees around the area?