Mad About Science

Maple trees

By Brenden Bobby
Reader Staff

Maple trees are one of the most striking additions to any outdoor vista, providing striking color, cooling shade and in some cases delicious syrup.

Maple trees are famous for two reasons: Canada’s flag and maple syrup. You can’t just go around jamming a tap into any old maple tree to flavor your flapjacks, though. You need a specific type of maple tree, which we’ll examine later.

Maples are of the genus Acer, which is in the Sapindaceae family, including soapberries such as lychee. Maples are closely related to Dipteronia, which is another genus of tree native to China that has similar winged fruit for aerial transmission of seeds.

Aside from how their seeds are grown and delivered, maples and Dipteronia also share a similar evolutionary timeline, with the fossil record showing the emergence of both trees during the Paleocene epoch, which began around the time the Chicxulub asteroid impact triggered the extinction of the dinosaurs.

Maples have a wide range of lifespans that vary from tree to tree. Sugar maples are the longest-lived with a lifespan that can reach up to four centuries, while red maples will live up to 150 years. External factors in the environment can drastically alter this longevity, such as the availability of water or presence of pests and other stressors.

Sugar maples are the tree from which we extract maple syrup. Maple syrup begins as maple sap, which is a sticky liquid substance extracted from the tree in winter and early spring via a metal tap. The sap is collected in containers and boiled to remove the water and condense the sugar that provides its famous flavor.

Tree sap serves similar functions to blood in animals. In animals, blood circulates through the body and carries with it oxygen, nutrients, hormones and heat to regulate biological functions. This is accomplished by the heart acting as a fluid pump to push blood through the veins and arteries. Trees don’t have a heart to do this, and they don’t need one.

Trees have a vascular system that differs substantially from animals. During the growing season, transpiration is the primary method of moving water through plant structures. Water evaporates from the stoma in the leaves, creating negative pressure and suction that draws water up from the roots. It’s effectively the same thing as sucking on a straw to pull water from a lower area to a higher one.

Maple trees take this a step further during the winter months. The tree will go dormant and shed its leaves as temperatures drop, but it isn’t just idly hibernating for spring — its internal structures are working mechanically. Air freezing at night causes air to contract, most notably affecting the xylem, which are like the tree’s veins. This contraction causes suction that pulls in water. As the air warms and expands, it pushes nutrients through the tree using its sap.

Sap has the added benefit of acting as a resinous seal in the event the tree is damaged. Our blood functions similarly by sealing a wound and coagulating to create a barrier from external bacteria while the wound heals. In a sense, maple tapping is kind of like donating blood. It’s done with the tree’s health in mind so that it isn’t sucked dry and left to die.

A sugar maple isn’t able to produce syrup for the first 30 to 40 years of its life. This is why the tree needs to be carefully tended and not drained immediately. Imagine waiting 30 years to put syrup on your pancakes.

A collection of maple trees for tapping is called a sugar bush and it is organized similarly to other plantations. A sugar bush takes up a tremendous amount of space, with one of the largest in the world currently being Sweet Tree Holdings in Island Pond, Vt. The company operates more than 24,000 acres and can produce in excess of 35,000 gallons of maple syrup annually. At an average of $75 per gallon, that means this company alone produces at least $2.6 million worth of delicious tree blood per year.

One of the most interesting things a maple tree is capable of is hydraulic lift. Maple trees move an immense amount of water using the methods described above. A single sugar maple can draw upward of 150 liters of water from its deepest roots to the shallow lateral roots at its base. It seems to do this for two reasons. The primary reason is to give the tree extra reserves of water during times of drought or potential drought. The tree doesn’t know when water may dry up, so it builds itself to maintain moisture in the soil just in case the weather may take a turn for the worse for an extended period of time.

The second is to promote growth of symbiotic organisms in its own environment. This includes grasses, fungi and low-lying shrubbery that serve multiple ecological roles. These other organisms provide food and shelter for insects and other animals that will use the tree for shelter and protect it from pests that would aggressively feed on it. It also provides more shade around the tree’s roots, which helps hold that water at the ground level while equalizing the tree’s overall ability to regulate its ability to transport water and nutrients.

Stay curious, 7B.