Collecting maple and birch sap and its effect on trees
In Estonian climate maple sap flow typically occurs during the first half of March. Birch sap flow begins two or three weeks later – in April. Maple sap flow can even begin before the snow melts, when the daytime air temperature rises to +4 … +5 degrees, but by night falls to zero and below. Duration of the sap flow period is 1.5 months. Maple sap flow stops when the temperature continuously stays above zero. Birch sap flow usually coincides with beginning of flowering of the liverworts – when the night temperature no longer falls below zero. The movement of the birch sap stops with the onset of flowering of the wood anemone. Approximately two weeks out of the entire period of sap movement are ideal for sap collecting.
Both birch and maple sap contain not only sugar, but also numerous useful substances. Tree saps are great for quenching thirst in the spring. Maple sap contains 2-3% of sugar on average, while sugar content in birch sap is even lower – only 1-1.5%.
In order to collect tree sap, drill a hole in the southern side of the tree trunk, at a height of 40 cm or above. Sufficient depth of the hole is 5 cm. It is recommended to use a hose – thus you will avoid getting annoying debris into your sap container. If during the day you do not have an opportunity to regularly check the container, use one of larger capacity, since on a warm day a tree can produce ca. 15 liters of sap. The higher the daily temperature, the more intensive the flow. The sap stops dripping in the evening when the temperature drops below zero.
Is collection of sap harmful to trees? While you should not choose a young tree to collect sap, adult trees with a trunk diameter of 20-40 cm are perfectly suitable for this. In fact, a tree with a thick trunk can produce even too much sap for an entire family – there is almost a year’s supply of nutrients in the trunk, branches and roots of a tree. Nutrients, which the tree loses during collection of sap, account for only a small fraction of the entire stock, so the process has little effect on the growth of an adult tree. In spring, the tree can easily refill any moisture lost during sap collection, as the soil has moisture in abundance. Let us look at the summer daily moisture demand of a leafed tree: per day such a tree requires 60-70 liters of water for transpiration, and on a hot day, the moisture demand can exceed 400 liters. It turns out that the amount of moisture that a tree loses during the entire sap collection period is incomparable with the evaporation of moisture on a single summer day.
Do you need to clog the hole left after collecting the sap? After removing the hose or the tap, the flow from the drilled hole will naturally cease within a couple of weeks, while in the meantime, ants and other living creatures will be pleased to taste the flowing sap. Nevertheless, after you have finished collecting sap, it is recommended to clog the remaining hole with a wooden stopper to reduce the flow.
P.S. The picture shows a great spotted woodpecker tasting juice flowing out of the holes it made in the bark of a Norway maple (Acer platanoides).
Text: Olev Abner, dendrologist