I looked up my new zone and it changed from 8 to 7 so all my plants should be safe.

I don't know about this change, don't understand it in the lease cause our weather has always been unpredictable. I myself see no change in North Texas weather.
Watching the news tonight record date in 1934 it was 84 degree on that day.
I've seen many a winters were the trees lose their leaves and then it warms up long enough for them to think it's spring and start budding out just to get hit by a hard freeze with ice. They lose the buds but come back once spring does get here.
My point is: I don't think our weather is changing as much as they say.

What is very scary is that many states are going through a drought, some so bad that the whole town has no water at all. Even though there small towns some are not so small and the people are in much need of water, they've been hauling it in on trucks.

As for your question if a decidious tree can become an evergreen I think it would go against it's nature. I would think it would need it's dormant time out.

No doubt some weather changes are coming, but it will be years and years down the road before it will be totally tropical in San Antonio, if ever. So you'll have your decidious trees for quite some time. Like Barb said we have some wild weather swings in Texas where trees bloom and leaf out of season so just enjoy it. Mature trees can take it.

I remember once years ago when the web worms COMPLETELY defoliated live oak trees in my neighborhood THREE TIMES -- one after the other!!! The trees would put out fresh leaves and BAM -- the web worms hit them again. I thought surely they couldn't survive, but they did.

Life goes on -- weather changes or not.

Be happy gardening!

Thanks for the encouragement.

Many of our decidious trees such as hybrid pecans, eastern redbud, bur oaks, etc are from northern parts of Texas and grow in much colder areas of the country, so they need some cold dormancy. So, that's why I'm worried.

Although the pecan is our state tree and grows as far south as Corpus, many of the hybrids are probably best suited for places like Georgia.

And Barb is right, they can't change from decidious to evergreen.

But, it is encouraging to know that mature trees can grow sporadically in the winter and they won't die from it.

I did find out that one of our decidious trees is probably a semi-evergreen: The cedar elm. I read that it's evergreen in the valley. It grows native all over San Antonio, so it doesn't surprise me.

The decidious chinkapin oak seems to have a fairly far southern native range.

(I got my tree info from Sally Wasowski's Texas Native Plant book.)

The drought in the Southeast is very scary. I think we are heading for a dry spell down here. I'm glad the aquifier is full, so we won't have watering restrictions for awhile.

Rainwater catchment is becoming popular, but the technology needs to be improved and affordable so that it can sustain a landscape, or even more, if it is to provide household water.

South Florida trees survival, is more about the water table than the heat. You can hit salt water as little as 6 ft. down, in the oolitic limestone.

Thanks Rick:

The University of Florida keeps a vast database of trees and shrubs. Although these publications are produced in conjunction with the National Forestry Service, I wonder if part of their hardiness recommendations could be due to salinity problems in South Florida. These publications include the upper level of hardiness limits of trees as well as the traditional lower limit.

Here is a link that might be useful: Florida Tree Data Base

I've seen crape myrtles in Hawaii and in Belize. My pecan tree never sheds its leaves in summer, and Galveston is plenty hot and humid all summer.

Doesn't matter much, if they are right you'll be treading water anyway & the trees will drown.

I know several people that have water collection system, they provide enough water for not only the household use but one has a HUGE truck garden that is watered from the collection system. They don't even have a well or water lines on the property.

I'm more worried about the LNG operation they want to put on Pelican Island, if it blew up people in HOUSTON would die too. Then there is that nice biohazard lab I can see from the window where I work, the worlds most deadly organisms on a barrier island that was the site of the worst natural disaster in US history. And don't forget the Tx City explosion-worst manmade disaster in US history, just over the causeway, damaged homes on the island.
Just think of all the pipelines, plants, etc. etc. that surround us all.
Now you have something to worry about!
Tally HO! What? Me worry?

Tally:

Oh my!!!!! How awful!!!

Disaster is surrounding all of us!!! If the Gulf decides to throw a huge tsunami before Galveston blows up, then you will be saved. You can ride the waves up to San Antonio on a surfboard and warn us of the impending doom.

You made me ROFL!!
Gotta have a sense of humor about this....What is it???