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.