The tree and its nutrients
Resource allocation
All parts of the tree need the sugars produced by the leaves through photosynthesis. Demand can vary greatly depending on the season. In spring, the trunk and branches may be in full growth. If flowers or fruit are present, they will use up lots of resources. Before shedding its leaves, the tree will extract as much as possible from them and store it in its wood. All this nutrient movement, in a dissolved form, are made through phloem, (Conductive tissue for nutrients or sap.) from the foliage to the deepest roots.
The Building Code
The tree follows strict delivery rules – they're kind of like a building code in its genes, telling it that about 90% of the sugars produced by the leaves must be sent down the tree, to feed the branches, trunk and roots. This is known as Pressler's Law. After all, if you take a leaf at random and look at where it is growing, there are sure to be more cells to be fed below it than above it, since the branches, trunk and roots are all lower down. Disobeying these rules would put the whole structure at risk.
