I have two huge oak trees in the front yard about 40’ apart. Nothing is taller than they are so they get the same amount of sun. Each year tree A is completely free of leaves by the second week in Oct. However tree B still has most of its leaves sometimes as late as the the first week in Dec.
What would cause this to happen?
differences in shade? (does one shade the other?)
differences in nutrients?
differences in soil quality?
a difference in gene expression on which natural selection may or may not act?
Assuming they are the same species one may end up being more successful due to this difference and so end up creating more offspring. Evolution in action (but very slowly!)
I have two hickory trees in my backyard that do the same thing. Right now, one looks like it will have shed all it’s leaves within the next week, while the other one has just started turning color. It will drop it’s leaves in December, if past history proves out.
No difference in shade or soil quality that I can imagine. Has to be some genetic fluke.
Ah. At first they appear to be in identical conditions; however A the fast dropper is very near the road and gets salt from the snow plow during Winter. Tree B is nearer the house and nearer to the leech field/septic system so possibly it gets more water.
It did not occur to me the trees would be that sensitive.
We have one huge pin-oak that holds it’s leaves forever, continuously dropping just enough to make us clean them up weekly until snow falls.
I call that tree, “that fucking tree”. But it’s a pretty cool tree otherwise.
how close is one to a water or sewer line, with a tiny leak in it?
Not knowing where you live makes it harder to answer more specifically than this:
Oaks require dormancy (for the most part) and this is brought on by temperature and sunlight-length changes. Dropping temps/shorter days trigger phsiological changes within the trees’ chemistry balance that affects growth and the transferral of certain chemicals that seasons affect. Root mass has lot to do with this and is strongly affected by temperature of soil.
If one tree has a shallower root system than the other (maybe atop a rockier-type subsoil and/or slab of shallower bedrock, etc) it will tend to go into dormancy sooner than one with a deeper/warmer/longer-to-cool-off root mass. Or maybe one tree gets more sun-time on average on soil beneath the canopy than the other keeping the roots non-dormant longer (?).
This is just semi-wild guessing based on limited info, of course. It is not uncommon, IME, for trees to go into dormancy (or break dormancy in Spring) at varying times based on location in relation to possible shading from other trees nearby and/or amount of sun able to warm ground beneath them, etc. It is also possible that the trees have a slight genetic difference/physiology, of which is fairly common in oaks nowadays that are pollinated ‘in the wild’, so to speak.
Sorry can’t get more ‘factual’, being GQ and all. And on ‘preview’ I see most of this haws already been mentioned, but will post anyways 
It does seem like a really simple thing but it does throw up so many fascinating little differences and confounding factors. Salt from the road never occurred to me and I bet that given closer scrutiny there’ll be many more minor differences that could contribute.
Dollars to doughnuts there’s a thesis or two out there on precisely this subject
I live in Eastern CT in growing zone 6A
Our town does not have sewers
The septic system is approx 50’ from tree B, the late shedder and approx 90’ from tree A.
Tree A bark is exfoliating a bit
Another difference: since tree B sheds so late it stays all Winter with a thick layer of leaves as mulch; tree A, the one very close to the road, has no cover but snow, sand and salt.
Maybe you have two different species of oak trees. There are many different types of oaks.
It just occurred to me that the road de-icer might contain magnesium chloride, a somewhat common part of deicers. MgCl is also a plant nutrient/supplement, but in largish amounts can lead to defoliation, etc. I always added some to my bonsai fertilizer, but in smallish amounts in relation to what your earlier-defoliating tree might be getting from run-off of the ice/snow.
A possibility is that higher amounts of the Mg and Cl ions makes the leaves defoliate sooner - but just a hunch, and partially supported by thewiki on MgCl in the ‘toxicology’ portion of the linked article
Basically, overdosing a tree with MgCl will cause the leaves to die/fall off from excess concentration of the two elements, if not outright kill the tree from defoliaing all the leaves.
From the article:
*Plant Toxicity: Chloride (Cl−) and magnesium (Mg2+) are both essential nutrients important for normal plant growth. Too much of either nutrient may harm a plant, although foliar chloride concentrations are more strongly related with foliar damage than magnesium. High concentrations of MgCl2 ions in the soil may be toxic or change water relationships such that the plant cannot easily accumulate water and nutrients. Once inside the plant, chloride moves through the water-conducting system and accumulates at the margins of leaves or needles, where dieback occurs first. Leaves are weakened or killed, which can lead to the death of the tree
*Like I already said, just a hunch, though, and thought worth mentioning. Roadside tree may be ‘weaker’ physiologically speaking if MgCl is used near part of its root mass, IOW. And, as a rule of thumb, the root system width (on average, but not always) is about the same diameter of the the tree’s unpruned/natural canopy. Not exactly sure of oaks, but I think (IIRC) they somewhat follow this generalization of root-system diameter-v-canopy spread.
There could be a variety of issues affecting the trees that you don’t know about.
Eight years ago I planted virtually identical bald cypress saplings from the same source near each other in the front yard. Sun, soil and distance from the road are about the same for both trees. One of them always leafs out about ten days before the other in spring, and has grown maybe a foot and half taller over the years. Otherwise they both look healthy and have thrived. Does one have slightly better DNA? Is there a sizable rock down there that one tree had to send roots around? Who knows?
There are three dawn redwoods, also from the same source, planted a decade ago as virtually identical saplings in the same general location in the back yard. The largest is about 40 feet tall; the smallest maybe 25 feet. Again, conditions are much the same for all of them. Why the difference?
Trees is weird.
I want that (bolded) on a t shirt to wear while I remove the fallen leaves from my lawn:D