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bwrussell4 years ago
Just spit-balling but I'm guessing that sap and water flow might be responsible.
It may be able to detect temp by sap viscosity which it can measure by flow rates. Plants can also determine sun exposure and are sensitive to sun intensity. Evergreens can probably measure sun exposure via photosynthesis rates since they are green year round. Besides temp though I'm not sure how deciduous trees sense the return of the sun in spring.

As far as knowing it's been cut, I'm not sure it does know. It would be creating new shoots at the top and on sun exposed branches if it hadn't been cut so it may just be creating shoots as high up as possible which now is the stump. It is possible that it does know it's been cut due to a big drop in sap and water draw from the roots.
rickharris (author)  bwrussell4 years ago
Sound reasonable hypothesis but I am still looking for the internal mechanism. the shoots look quite different to the normal twig growth you get high up.

This is connected in a way to a holly tree only grows spines on the lower leaves - How does it know when it is high enough to stop growing them is it just age or is there some more subtle mechanism.
rickharris (author) 4 years ago
Ok Ok! :-) I have posted the following question 3 times but it refused to appear! Don't know why unless it's the mention of Biology.

Question:

My neighbour chopped down a tree year before last - In the spring the cut trunk sprouted shoots again.

1. how does the tree know it has been cut off - By what physical means does it sense that.

2. Connected by what means does the tree know it's time to shoot, I know practically it is connected with day length and temperature but HOW does the tree senses those things?

I have seen this happen myself. the tree trunk will sprout and attempt to grow as long as it is supplied with water. When the water in the trunk is used up the sprout dies.
The growth is obviously not being cause by the roots which are no longer there. Since the trunk also no longer has branches and other leaves it also cannot be a response to daylight. That leaves temperature as the only variable left. When you consider that trees will sprout and bloom early in years with a warm spring then it appears to support the idea that the process is temperature related. Seed germination is determined by temperature as well as moisture so the idea that plants call tell what the temperature is appears to be valid.
The need to sprout appears to be related more to the lack of other branches more than anything else. Almost any plant that is pinched back will sprout from other areas.
rickharris (author)  Vyger4 years ago
This tree has its roots in place so the shoots flourished - but this doesn't explain the mechanism
rickharris (author)  rickharris4 years ago
On the good new side one of the 3 did publish 48 hours later!

however the question remains.

There seems to be little on line about the mechanisms just a lot from gardeners saying this happens.
Vyger4 years ago
Must have something to do with your reputation.
onrust4 years ago
Is this not posted?
iceng onrust4 years ago

Yes very questionable of you !