Mature Trees and Drought

I am quite the newbie, sobplease excuse my lack of understanding:
I was told the other day that it takes differing amounts of time for trees to become established, based on the water table depth--that once roots get to the water table, the tree has plenty of access to water, and this is why older trees survive droughts. Is this a decent explanation?

That is only part of the reason trees can survive draught conditions, for trees to have enough roots reach a deep water table the tree would most likely need to survive for at least ten years.
Most trees will have a root structure that is equal to the height of the tree or more, depending on the rain fall average for that area.

Other factors are; if the tree is a tap root type or a spreading root type, type of soil, soil condition/friability (texture) and depth of both top soil and subsoil, then there is the type of subsoil, Location and type of terrain is yet another factor.
Trees that are growing in a valley will probably have deeper soil to live in than trees growing on the top of a hill or mountain.
Valley trees are also going to have a higher water table than hill or mountain top/side trees, making the valley trees less likely to be stricken by lack of water than the same species up or on top of a hill or mountain.

Humus (organic material) content of the soil affects how much water that soil can retain and clay content determines how long that water can be retained.
Microorganism counts also have a part to play in how effectively water can be moved through the roots, this is one of the functions of mycorrhizae both endo and exo varieties.

So, while what you are told is viable information, it is far from complete information but now you have the rest of the story.

Redhawk

I'll add to the conversation a little, based on a number of drought years I lived through in my region.

Yes, speaking of trees planted by the gardener or homesteader, an older tree that has grown & set its roots deeper has more stability in drought periods.  As you're suggesting, Dennis, the roots have gotten themselves into the water table at normal summer levels.

I'll add to that that this year in spring we started out with a lot of surface water (due to a great accumulation of snow) which melted and seeped into the ground.  However, our summer was hot with little rainfall, and a lot of the homesteads in my area do not include much (or any) bottom land down near the river, plus tend to have sandy soils.  I was talking with a neighbor who is part of an organic-farming family who have homesteaded in their acreage for about 40 years.  She was pointing out the reddish discoloration in many branches of the natural cedars on her property (due to these tough old trees having less water than they'd like).  In response, I said that the Red Cedars are survivors and will grow more green foliage in wetter years.  But she said that, in her observation, the affected cedars on their homestead have never returned to the glorious thick green coniferous foliage they had decades ago when they first moved onto the property.  (Of course, there are way too many of these native-species conifers on their land to try to assist them with human-controlled irrigation.)

Also, I was talking with a friend who has a permaculture homestead about the weather this year, and he said that he has so many berry bushes, and fruit and nut trees, that he has been irrigating like crazy, using many devices in many locations, to keep his food-forest plantings alive in reasonably good health. And in many cases these are plantings he put into the ground with tender-loving-care 15-20 years ago.

With droughtish conditions recurring every so many years in our region, it's a crap shoot which individual established trees and shrubs will survive & thrive and which will not.  So we use our knowledge & experience and best efforts and hope for the best.  And accept some losses.

I've realized that making posts like this, based on my own experience & observation, and info from other skilled local homesteaders, usually doesn't encourage a reader to click the "Like" button — but I feel contributing another reference point may still be worthwhile.

The UK this summer has been unusually hot for an unusual length of time. Many trees have died but I think it is mostly betula ~pioneer trees. I wonder if the trees could not get the water to where it was needed faster than the evaporation, irrespective of how much water they had access to. It was certainly the case for smaller plants. Pots standing in water still went past the wilt point.
I had a 20yrold prunus that totally split at every branch once the weather changed and we had slightly cooler days with a bit of rain. It looked like it gorged itself and bust a gut!

Trees have "memory" and so a mature tree will react better and faster than a less mature tree to drought conditions.

And yes I do have to agree that the deeper rooted tree will have access to more water.
And that the tree isn't surviving in a vacuum, instead it is working with the soil microbes to grow

Also when you see that one or two mature tree that is still standing, you are looking at survival of the fittest.
There was probably dozens of seedling that competed for that space and all the weaker ones got culled by drought, microbes, animals, insects, etc.

When you plant dozens of "seedling" you might have to lets nature select which ones can survive the local environment.
Except that might be an expensive experiment.  

Now for some possible help.
Plant seed and then graft your own named cultivars on the ones that survive the drought.
Inoculate the bare-roots or seeds and the hole and the area in general with beneficial soil life.
Plant drought tolerant species (and cultivars too if you just dont want to do your self-selection+grafting)
To encourage deep rooting growth pattern, try to water as infrequent as possible at most once a week for trees.
Hardening off the plant for a drought just like winter, be reducing nitrogen inputs or just inducing leave drop (manually pick off the leaves).
Most of the time what plants want is not water, but the dissolved minerals in the water. So the more nutrient dense the "soil-water" is the better it is for the plant. Keep in mind we are talking about bio-available nutrients not gross mineral levels.

It is important to plant trees suitable for your climate zone.  If your area is prone to drought, then it is better to plant trees that can handle a drought better.  

Cedars in it's natural environment grows where the water table is quite high or near streams or high moisture environments.  It would not be surprising that their leaves turn red during droughts.  But cedars are still tough trees.  

Some trees will lose much of it's leaves during severe drought but the leaves will grow back when the rains come back.  If the tree struggles year after year, it might be time to replace it with a drought tolerant tree.  

You should not have to keep watering a mature tree.  That being said, if it is a fruit tree, the fruit will be smaller in drought years and maybe less of them.

Of course young trees will struggle to survive in a drought unless they are watered.

Thanks all!

"Trees that are growing in a valley will probably have deeper soil to live in than trees growing on the top of a hill or mountain.
Valley trees are also going to have a higher water table than hill or mountain top/side trees, making the valley trees less likely to be stricken by lack of water than the same species up or on top of a hill or mountain."
I am probably missing something, but if the water table is higher in a valley, how can the soil be deeper?

Dennis Hamilton wrote:
"Trees that are growing in a valley will probably have deeper soil to live in than trees growing on the top of a hill or mountain.
Valley trees are also going to have a higher water table than hill or mountain top/side trees, making the valley trees less likely to be stricken by lack of water than the same species up or on top of a hill or mountain."
I am probably missing something, but if the water table is higher in a valley, how can the soil be deeper?

Again, I'll report more from my many years of observation, as I'm not a geologist or soil scientist.

As I go upslope in my valley, the "soil" tends generally to be composed more and more of sand and gravels of various degrees of coarseness.  This type of soil is called a spodosol. There is less and less what might be called "topsoil" as I hike up from the river bank, through the "bottom land", and up the slopes.  Whereas, in the valley bottom, the mineral portion of the soil is more a balance of clay, silt and sand particles — plus, there is much greater natural content of humus.  The mixtures of humus with a good balance of clay, silt and sand is what's generally referred to as "topsoil".  In some regions (but not in my own home area) it's said that top soil can be three, five, ten feet deep.

Also, down close to the river the water table comes up in spring to cover the flood-plane area... for a period of weeks, the water table is right at the surface.  It's never anywhere remotely near that level on my upslope property.

I'll veer off slightly from the OP topic to say that the fact that I'm upslope on a natural sand bench means that the agrarians on my property before me, and well as my wife and myself, have built a lot of humus into what is now our topsoil on this acreage.  Before this happened, there was a conifer-forest natural spodosol here.