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When a leafless deciduous tree 'comes to life' in the spring and puts forth new leaves, where does the mass for these leaves come from? The tree has no leaves to make use of photosynthesis to get the carbon it needs to grow these leaves, so where does the carbon come from: has it been stored in the root system over winter just for this purpose? And if so, has enough been stored for the tree to produce most if not all of its new leaf growth for this season, or only enough to get a few leaves out that will 'take over' the task of providing carbon fixation (making sugars) via photosynthesis to grow the remaining new leaves?

It has been suggested in the comments that the new leaf buds were grown at the end of the previous season. It would seem to me that this strategy for new growth in the spring would be fraught with all sort of dangers from 'winter kill', so these buds would not remain viable come the next spring. So, are the sugars needed for new spring growth coming from the roots or last seasons leaf buds?

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    $\begingroup$ Possible duplicate: biology.stackexchange.com/questions/1041/… The first answer might be a bit unclear that it is not only talking about seedlings but everything written there applies to wintering trees as well. Though there still may be an additional question here to be answered as far as the precise storage mechanism. $\endgroup$ – Bryan Krause♦ Jul 16 at 19:31
  • $\begingroup$ @BryanKrause Thanks for the link. The first answer seems to say that the carbon for new growth comes from stored sugars. Was this sugar supply 'stored' in the plant's roots? Was it stored there to be ready for its new spring growth? How much mass are we talking about, i.e., enough to grow all new leaves for that season, or just enough to get a few leaves out that will take over through photosynthesis? $\endgroup$ – OneMug Jul 16 at 19:43
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    $\begingroup$ Leaf buds are usually prepared the preceding summer/autumn. $\endgroup$ – fileunderwater Jul 16 at 19:49
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    $\begingroup$ I think you could edit your question to add what you've learned and clarify what you'd still like to know. I'm not a plant guy so I'm uncertain if some of your questions are too broad across the diversity of deciduous trees. SE questions are supposed to be individual questions rather than multiple but think yours are probably related enough to be part of one question. $\endgroup$ – Bryan Krause♦ Jul 16 at 19:50
  • $\begingroup$ @user1136 Answers are not supposed to be posted in comments. $\endgroup$ – Bryan Krause♦ Jul 16 at 21:26
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While I can't provide references to actual studies, simple observation suggests that it must be stored in the roots, at least in part. That observation is the existence of maple syrup (and other tree syrups, such as birch: https://practicalselfreliance.com/trees-species-tap-syrup/ In the spring, before leaves start to grow, sugar-rich sap rises from the roots, and can be collected by tapping the tree.

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