One thing I have noticed about apple trees that puzzles me: I know thaT Apple trees age just like human do-after about 35 years, the apple trees planted by my granfather were showing signs of old age. The new branches were deformed and shriveled, and the trees bore less and less fruit. However, when we cut the trees down, new shoots (coppices) spang up from the old stumps. These shoots are now 5-6 feet tall, and appear to be youthful trees. So, has the DNA somehow “reset” itself? I would have thought that the DNA of the tree, having degraded through constant cell regeneration, would be old and defective now-why are these new shoots so young looking?
I think our DNA has some sort of division limitation device in them - it will only divide so many times - then that’s it. Plants don’t have these. I think the aging has more to do with constantly rebuilding pathways to transport neutients, after a while the paths arn’t as straight and some may dead end or short circuit.
It’s extremely likely that what actually happened was that your grandpa’s apple trees were grafted onto other, different rootstocks, and that what’s sprouting is actually coming up from the rootstock. The DNA hasn’t “reset” itself–the top part of the tree, that you cut down, is now basically gone, and you’re seeing the rootstock tree. Rootstock trees don’t usually make very good apples, BTW. You’ll need to go down to the nursery and get some more trees if you still want nice apples.
http://www.ces.ncsu.edu/depts/hort/hil/hil-8301.html
Apple trees require careful pruning every year in order to keep producing good apples. Did Grandpa ever go out there and prune them? If not, then it’s not “the DNA aging” that caused them to put out less and less fruit, it’s just that apples grow best with annual pruning. You encourage them to put out vigorous new growth every year, because the vigorous new growth commands the most resources from the tree and gives you better apples.
In effect, you rejuvenate the tree every year by pruning it.
And, yeah, you’ve probably figured out by now that you could have just pruned Grandpa’s apple trees this winter and had some nice apples next summer. Sorry. 
http://www.ces.ncsu.edu/depts/hort/hil/hil-8301.html
Dang.
IMNAPD (that’s “plant doctor”), but the OP got me a’thinkin. Which hurts. So, at the risk of hijacking the thread, I’d like to ask a question and conjucture an answer, which includes something about the DNA, and hopfully makes it relavent to the OP.
Does anyone know why pruning works?
I googled and found plenty of sites singing its praises, instructions of how to do it, etc… But noone got down to the nitty gritty and explained what’s actually going on (other than to talk about removing diseased branches, which must be important, but can’t account for everything).
So I was wondering if it’s got something to do with the tree, or any plant, needing to distribute a relatively constant amount of water and nutrients to an increasing amount of tree.
As the tree grows, the number of branches increases. The supply of nutrients must then be distributed to a larger amount of tree, so each part gets less. Thus, each part doesn’t develop quite right, and looks a bit scraggly, doesn’t produce as good of fruit, etc…
Combine this with the “old road and pot hole” effect mentioned by k2dave, and the tree as a whole looks old and decrepit.
Maybe pruning, by keeping growth in check, helps prevent the tree from out-growing its supply of nutrients. Sort of like culling some animal populations.
Of course, the root system would grow also, increasing the amount of nutrients delivered. But maybe it has something to do with differential proportions. Here agian, maybe pruning is helping to keep the growth of the branches and root system more in balance.
So, in the case of your grandfather’s tree, I would be less inclined to think the DNA changed. Rather, maybe what happened is the old tree had outgrown its nutrients. Then the new sprouts, tapped into the pre-existing extensive root system, could gorge themselves and grow, well, like weeds. Typical young whipper-snappers, living easy off the products of their elders’ sweat and toil.
Thanks for thought-provoking question. Sorry if I hijacked it.
Oly, he cut off the top grafted part, and left the tree to grow back from the rootstock. It doesn’t have anything to do with DNA. That’s what happened, unless he comes back and says they were heirloom apples growing on their own roots. If so, then he’s not S.O.L. after all and he can look forward to nice apples next year without having to plant more trees. 
If they were heirloom apples growing on their own roots, then what happened was that cutting off the major portion of the tree told it, “You’re going to die soon”, and so it responded by frantically sending up new growth with the carbohydrate reserves that are normally stored in its root system, one last shot at getting some seeds produced, because to a tree, that’s all that counts–reproducing itself. Once the sprouts get up and growing, they start producing more carbohydrates themselves (via photosynthesis), which get transported to the roots and stored, so there’s a limit to the amount of time the sprouts are living off the tree’s stored energy reserves.
Some trees can come back three or four times like this, in their desperate desire to make seeds. And some trees won’t come back at all. If you cut them down, that’s it, they’re dead.
But I think that if Grandpa’s apples were “heirloom apples”, somebody in the family would have known about them.
But if they were standard nursery-variety grafted apple trees, each tree when it was planted in its burlap ball was actually two different trees, originally. The top of the tree came from an apple variety that makes nice apples but has a weak root system. A sprig of this kind of apple tree was grafted (spliced) onto the bottom part, the rootstock, which came from a variety of apple tree that makes wonderful vigorous roots but terrible tiny sour apples. So the top part would draw nutrients from the strong roots and make nice apples.
Trees don’t partition their root systems, “this part over here is available for old branches, and this part over here available for young sprouts” etc. All the root system is available for all the tree’s needs. This would be like saying that your circulatory system made blood available to your body parts on a contingency basis, and that as you grew up, your arms and legs (the older parts) would get less blood than your permanent teeth (the newer parts), which is not true, and also that the amount of blood you were born with would be the same amount all your life, which is also not true. Your body makes more blood as your growing body needs it, so an adult has more blood in his body than an infant. Trees are the same way–they just make more of the nutrient fluid (“sap”).
The reason pruning makes an apple tree put out new vigorous growth is the same reason that cutting down the whole tree in some species makes it grow back from the roots–because cutting off a piece of the tree tells it, “You may die”, so it responds by trying twice as hard to send out lots of seeds. For an apple tree, this means “apples”. Read the gardening link, you’ll see that after you prune apples, you have to go out there in the late spring, after they’ve started making teeny apples, and actually thin them out by hand, because otherwise you’ll get lots of too-small, not-very-good apples. The apple tree has responded to your pruning by stepping up its seed production to a truly astonishing level, horticulture-wise.
Pruning a tree doesn’t cut back on the amount of nutrients it needs–it actually increases them. The tree needs even more energy to put out all that new growth, and those prodigious quantities of seed-bearing fruit. If you don’t fertilize as well as prune, you’re just wasting your time out in the garden and you might as well buy your apples at Kroger.
Thanks for the explanation (although I don’t think I quite made some of the assertions you “correct,” like trees partitioning their root systems 
).
To paraphrase your explanation, so I can be sure I’ve got it: Would I be right to think that the tree stores up carbos in the roots for hard times? Pruning, to the tree, seems like hard times, so it mobilizes its reserves. This results in new growth and seed/fruit production. In the case of tree in the OP, this is in the form of new sprouts from the old trunk.
This seems like a good explanation of why pruning works (which, BTW, is not in the gardening link). Thanks for that.
Would you be able to explain why the tree gets scraggly in the first place?
Right, you got it.
I didn’t say the gardening link explained why pruning works–I said it explained about how you have to go out there and thin the apples by hand after the pruning has done its work and spooked the apple tree into putting out far more apples than it normally would have.
As for why the trees get scraggly, well, trees do age and die–they have “average life spans” the same way that animals do. They spend a certain amount of DNA-encoded years growing to a DNA-encoded maximum size, and then they stop growing much bigger, although they do continue to put out new leaves every spring, to replace the leaves they dropped the previous winter. But they put out fewer and fewer new branches (twigs), so eventually the tree is at its maximum size. And then it starts to get old.
As for “why organisms age” in the first place, I have no idea (have to ask God that one, next time I see Him ). I do know that plants have hormones the same way that animals do, so whatever biological time clock that’s in DNA that tells an organism, “Now you are getting old”, trees have it, too.
And some old trees start getting scraggly, like apples, and some old trees, like oaks, don’t get particularly scraggly, but they get rot in their hearts and get hollow and eventually fall over in windstorms.
But it seems more than just “aging” is making the tree look scraggly.
Based on what’s been said about pruning, seems you could have two trees, one that’s been regularly pruned, the other not. They could be the same age, but while the first tree would look young and vigorous, the second would look old and scraggly, yes?
Now, we know the wonders of pruning–that regular mutilation and freaking out of the tree to keep its stress levels up and metabolic machinery cranking–is working in the first tree. What’s going on with the second?
Maybe it’s like other living things: Unless you regularly stress the system, every thing sludges up, gets flabby, and degerates, huh?
So, pruning for trees = aqua aerobic for humans?
One more question: Does pruning influence the life span of a tree, or just make it more productive per unit time alive?