Why do the leaves fall off in the autumn? Part III

For all leaf-bearing trees and bushes, it is therefore better to let these cells shrivel up and put energy on creating new leaf rudiments and empty as much water as possible to prevent frostbite and cell burst. In areas on earth where there is no risk of frost, the leaf-bearing plants are green year round. They even manage a few nights of frost and a total loss of foliage, but would the cold period hold for longer cells would burst and kill the plant

Why do the leaves fall off in the autumn? Part II

Despite all the rain- and snowfall, the winter is a relatively dry season with cold dry air. It actually works to dry laundry outdoors cold, clear winter days. The water freezes in the garment and then evaporates without passing through the liquid state. We have, in other words, a fairly high vapor pressure on the garment surface and the same would apply to the leaves. The tree would have a hard time trying to retain moisture and at the same time not able to take up new liquid (the ground's frozen) with dehydration as a result.

Who do the leaves fall off in the autumn? Part I

OK it is summer on the norhern hemisphere and one should maybe not think so much about autumn and winter, but newertheless her comes some thoughts:

With water-filled leaves left on the tree, would first of all the cells burst as the water expands when it freezes. The trees could protect themselves by producing/store lots of sugar in the leaves during the early fall to get a high sugar content in the cells.

This would work like glycol in the coolant/antifreeze and provide some protection. To produce this sugar is obviously more dangerous and energy consuming than to simply turn off all cell functions in the leaves and let them fall off.