I have a friend who produces maple syrup on his woodlot, and he has invited me to help out in the production process over the past few years. This has been a lot of fun and hard work, and always worth it for the syrup he gives out in the end. He has a great deal invested in his operation, and is very interested in protecting it. That is why he came to me with a couple of questions regarding the management of his maples.
His first question was about maximizing the production sap from each tree he tapped. I responded with 1) picking the right trees and 2) giving them the best conditions to grow. Besides species and the size of trees, here are the characteristics to look for when picking the right trees to tap: healthy, vigorously growing trees with deep, wide crowns.
Healthy trees will be free from fungi and have few if any wounds including broken off branches, large seams in the bark, and bark sloughing off. The crowns of healthy trees will be full and most, if not all, the leaves will be green during the growing season. Evaluate the trees you tap every summer and switch to other trees if you find unhealthy conditions.
Vigorously growing trees are those that are mature, but not too old and are growing at a good pace. Very old trees will grow much slower than younger trees and will produce less sap. Growth rates can slow when trees become too crowded, so it is a good idea to give your tap trees plenty of room to grow by occasionally removing surrounding trees. Don’t remove all of the surrounding trees, and instead remove trees on three sides of the tap tree. Evaluate the space around tap trees every summer, and think about removing a surrounding tree or two every 5-10 years.
Finally, you will get a deep and wide crown by creating space around your tap tree to grow into. You are looking to create trees with branches on all sides that are not just located at the top but instead extend some ways down the tree as well. The more branches and leaves, the more sap/sugar the tree will produce and store.
His second question was about the health of the trees and the impacts of removing sap will have. By tapping trees you are taking some of the sugar that the tree would use to produce new leaves and branches. It may seem like you are harvesting a lot of sap, but in fact you are taking only about 1-3% of the total the tree is transporting to its branches.
Trees can usually easily handle this amount of loss of sugar under normal conditions. It is when there are abnormal conditions or an extreme event has taken place that you need to think about the impact tapping will have on your trees. Some abnormal conditions include drought, flooding, and insect or disease infestations that kill leaves.
Several successive years of abnormal conditions can have a big impact on the sugar reserves of your trees. If you have experienced this, then it may be wise to forego tapping your trees, especially those that are the least vigorously growing and have the smallest crowns. Trees can usually handle a year or two of abnormal conditions.
Extreme events include things like windstorms or ice storms that have damaged branches and bark and may have partially dislodged trees. After events like these you need to evaluate the condition of your trees to see if they are no longer healthy trees and decide if they should be removed to make way for other trees.
My friend and I walked his sugar bush and I identified a number of trees for him to remove and showed him the signs to look for in unhealthy trees. If you are not sure you can evaluate your stand in this way, then I encourage you to contact a forester that works in your area to help you with that. Foresters that work for the state or your county may be able to help you or can point you to reputable private consulting foresters.