Why does sap rise

When a branch breaks or is cut, the pressure causes the sap to flow out. When starch is converted to sucrose, water flows into the cell. In maple syrup production, a metal spile is driven into the stem and connected to plastic tubing, allowing the sap to flow from the tree to the sugar shack. Maple syrup production is only commercially practical in places with the right weather — cold soil, cool nights and warm days. The cool nights promote the conversion of starch to sugar, while warm, sunny days allow water to flow from the soil into the stem.

In Kentucky, where I live, commercial maple production is not practical. The spring tends to warm up rapidly and there is usually little snow to insulate the soil, making the sap flow season too short to make any money. A year like , though, could be a good sap year. I have already seen bleeding sap in a number of maple trees. The positive pressure inside the stem lasts for only a few days to weeks. These cells act as pipes, which transport sap through the living sapwood much like pipes, transport water through a house.

In most hardwoods, the dead wood fibers that surround the vessel elements are filled with water. In maple trees however, these dead wood fiber cells are filled with gas. When the cells start to freeze, frost forms on the inside of the cells. After long periods of freezing weather re-charge the tree with sap, the tree will yield this sap when the weather turns warm enough to thaw out the frost in the cells.

The sap can then flow down the tree via gravity and out a tap hole, or can be forced out the hole by increasing internal pressure.

In this case the positive pressure inside the maple tree is a result of pressure from warming, released gasses, osmotic pressure caused by sugar and other substances in the sap, as well as gravity on the sap higher up in the tree. It must be understood that usually different parts of the tree respond at different times. After a cold night, when the sun rises and warms the southeast exposure, that portion of the tree will start to flow. Tapholes on other exposures may still be under negative pressure.

As the sun moves around the tree these other tapholes will start to flow. Sap flow will continue as long as the pressure inside the tree is greater than the atmospheric pressure outside the tree. Vacuum pumps on tubing systems show their greatest gain over gravity flow systems when tree pressures are low.

This is because there is a small pressure differential between the internal tree pressure and the atmospheric pressure outside the tree. The tree responds by continuing to flow at a rate usually associated with higher tree pressures. The period of sap flow can vary from just a few hours to a few days on end. Many environmental factors and tree metabolic factors affect the length of sap flow period and the amount of sap produced.

For strong sap flows to be repeated, a suitable temperature cycle above and below freezing must occur to allow strong positive sap pressure to develop.

The sap flow ceases entirely when these temperature cycles cease to exist. Bumper sap years also depend on the growing season of the previous summer to store as much carbohydrates as possible in the form of starch. These stored starch reserves convert to sucrose and are dissolved in the sap as spring approaches.

The amount of sugar sucrose in the springtime sap depends on many factors including tree genetics, leaf mass, site conditions, amount of sun the previous growing season and overall tree health. Wounds on conifers tend to release a sticky resin rather than sap. This is a defence mechanism by the tree to seal the wound from fungi and insects.

Resin is much stickier than sap and tends to be a dark colour. It contains chemicals manufactured by the tree to seal the wound and kill pathogens. In Europe much of the amber we see is Baltic amber, and this comes from trees that oozed resin million years ago! Primordial landscapes, tangled branches, breathtaking wildlife and miles of woodland trails. From the countryside to cities, we care for thousands of woods throughout the UK, all free to visit.

Why does sap rise in spring? Public enquiries officer. What is sap? Deciduous trees in winter In early winter, deciduous trees enter a dormant phase. Spring — a flurry of activity When air temperatures rise, the tree is primed and ready to go.

Should I try to seal a wound? What about evergreen trees?