Liquid gold

The last few days have been devoid of prime photographic opportunity. We drove all the way to Hyner yesterday morning only to find the access road to the scenic overlook covered in snow. Joanna was game but I was not – she says I have no sense of adventure (true). When we arrived back at the farm it was time for chores and the horses announced, in no uncertain terms, that their hay and grain were overdue and that was unacceptable. Rain and freezing rain were forecast for overnight to be followed by more rain during the day on Monday. In a last valiant attempt to capture a bit of blogging material we took an hour in the afternoon to drive our usual route through the Nippenose Valley to the top of what we call the 44 Hill. On our way back through Collomsville a small sugar bush caught my eye and we stopped. A number of pails were out by the main road and I noticed that there were more around the corner. Nestled within this beautiful group of Sugar Maples was a small cemetery. After a low of 8°F the night-before-last and an afternoon high of  35° the following afternoon it was no wonder that the sap was running nicely and the drip-drip-drip reminded me that the sugaring season was near. Most folks know that the Syrup that goes so well with pancakes is concentrated Maple Tree sap and that tree sap is a fluid which is associated with tree nutrition. But perhaps you do not know why it is that sap flows and why, in particular, the sugaring season is limited to a brief period of time in the very early spring. The simple explanation goes like this. Fluids move beneath the protective bark of a tree. These fluids are called xylem sap and phloem sap and both move through the part of the trunk called the sapwood. Xylem sap (water) flows in one direction (from the bottom of the tree to the top) in the xylem tubes and phloem sap (water and nutrients) flows in two directions (from bottom to top and from top to bottom) in the phloem tubes. When discussing maple syrup we’re talking about the movement of phloem sap in particular. Sapwood is made up of living cells and these produce carbon dioxide when they respire, in much the same way you do. When this gas is released by the cells the pressure in the sapwood, and on the sap, goes up. If you should drill a hole into the side of a tree, and into the sapwood, sap will escape because of this positive pressure. The other, and somewhat more complicated, explanation involves something called osmotic pressure. Nutrient sugars are stored in the roots of all trees, having been produced during the summer months and then transported down to the roots. When there is a lot of sugar dissolved in a root cell, water will tend to move into that cell and generate pressure. That pressure will force sap away from the source of the pressure (the root cells) and up the tree. Eventually this becomes important when the rapid growth of newly developing leaves needs to be supplied with nutrient sap. So both of these forces, that created by the formation of gas and that created by what we’ll call sugar pressure, push sap up the tree. And the way to harvest this sap is to simply drill a hole into the side of  tree; doing so interrupts the integrity of the sapwood and redirects the flow of the phloem sap into your waiting bucket. But what about the seasonality of Sugaring and why is it limited to early spring? It turns out that sap flows in the highest volume when night time temperatures fall below freezing and when day time temperatures rise above the same. This fluctuation is critical. During the day positive pressures develop in the sapwood and sap is pushed up the tree. During the night the carbon dioxide, generated by the cells of the sapwood, contracts and this results in a negative pressure (or suction) inside the tree which draws water into the roots to replenish the sap supply. Do not fear for it has been estimated that tapping may remove just 10% of a tree’s nutrient stores which cannot, under normal circumstances, hurt an otherwise healthy tree.



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