A year or so ago I planted a pair of year-old deciduous trees in my yard. It being winter now the pair have naturally dropped their leaves and are literally just two groups of wooden sticks about three feet high. These two trees lost their leaves in late November and probably won’t have any again until mid-March. This got me to thinking how they survive. Not in the cold, but without the ability to photosynthesize. I was taught that plants survive by turning those little photons from the sun into food via photosynthesis. Okay. But plants need leaves for photosynthesis. Or do they? What say ye, O Wise and All Knowing Bio-Dopers out there.
Trees store energy in the form of carbohydrates prior to winter, and this sustains them during winter (when they have low energy requirements), and allows them to regrow in spring. This is why maple syrup is a thing, by the way: The maple tree stores starches in its roots prior to winter, then in spring when it’s time to grow new leaves, it turns those starches to sugars and sends them up the tree. Put a tap in at the right time, and you can divert some of that sugary sap, process it, and sell it to folks who put it on their pancakes or whatnot.
Another factor in this is that the tree is consuming less energy in this state - Obviously, the processes of respiration in the leaves are not happening, because the leaves are gone - and respiration in the other plant tissues is reduced to a lower level - a little like hibernation in animals.
Same reason bears survive in the winter without having to find prey.